1 power up gradation

8/6/2019 1 Power Up Gradation

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Possibility of Power Tapping From

Composite ACDC Power Transmission

Lines

ABSTRACT

Large power (steam, hydro, nuclear) stations are usually located far from load

centers. The wheeling of this available electric energy from these remotely located

stations to load centers is achieved either with extra high voltage (EHV) ac or HVDC

transmission lines. These EHV ac/HVDC transmission lines often pass over relatively

small communities/rural areas that do not have access to a major power transmission

network. It is most desirable to find methods for connecting these communities to the

main transmission system to supply cheap and abundant electrical energy. However, the

HVDC transmission system does suffer a significant disadvantage compared to EHV ac

transmission, in regards to the tapping of power from a transmission system. Techno-

economical reasons prevent the tapping of a small amount of power from HVDC

transmission lines. This is considered a major drawback due to the fact that in many

instances, HVDC transmission lines pass over many rural communities that have little orno access to electricity.

A recently proposed concept of simultaneous acdc power transmission

enables the long extra high-voltage ac lines to be loaded close to their thermal limits. The

conductors are allowed to carry a certain amount of dc current superimposed on usual ac.

This paper presents the feasibility of small power tapping from composite acdc power

transmission lines which would pass over relatively small communities/rural areas having

no access to a major power transmission network. The proposed scheme is digitally

simulated with the help of a PSCAD/EMTDC software package. Simulation results

clearly indicate that the tapping of a small amount of ac power from the composite acdc

transmission line has a negligible impact on the normal functioning of the composite ac

dc power transmission system.

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CHAPTER 1

INTRODUCTION

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INTRODUCTION

1.1 INTRODUCTION ABOUT HVDC

High Voltage Direct Current (HVDC) transmission is widely recognized as

being advantageous for long-distance, bulk power delivery, asynchronous

interconnections and long submarine cable crossings. HVDC lines and cables are less

expensive and have lower losses than those for three-phase ac transmission.

Typical HVDC lines utilize a bipolar configuration with two independent poles and are

comparable to a double circuit ac line. Because of their controllability HVDC links offer

firm capacity without limitation due to network congestion or loop flow on parallel paths.

Higher power transfers are possible over longer distances with fewer lines with HVDC

transmission than with ac transmission. Higher power transfers are possible without

distance limitation on HVDC cables systems using fewer cables than with ac cable

systems due to their charging current.

HVDC systems became practical and commercially viable with the advent of high

voltage mercury-arc valves in the 1950s. Solid-state thyristor valves were introduced in

the late 1960s leading to simpler converter designs with lower operation and

maintenance expenses and improved availability. In the late 1990s a number of newer

converter technologies were introduced permitting wider use of HVDC transmission in

applications which might not otherwise be considered.

1.2 NEED FOR HVDC

High Voltage Direct Current (HVDC) transmission is widely recognized as beingadvantageous for long-distance, bulk power delivery, asynchronous interconnections and

long submarine cable crossings. HVDC lines and cables are less expensive and have

lower losses than those for three-phase ac transmission

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HVDC links offer firm capacity without limitation due to network congestion or

loop flow on parallel paths. Higher power transfers are possible over longer distances

with fewer lines with HVDC transmission than with ac transmission. Higher power

transfers are possible without distance limitation on HVDC cables systems using fewer

cables than with ac cable systems due to their charging current.

The main advantages of HVDC transmission systems are

1. Greater power per conductor

2. Simpler line construction

3. Ground return can be used hence each conductor can be operated as an independent

circuit.

4. No charging current

5. No skin effect

6. Cables can be worked at a higher voltage gradient

7. Line power factor is always unity; line does not require reactive compensation

8. Less corona loss.

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power upgrading has already been demonstrated by converting the EHV ac line into a

composite ac-dc transmission line without any alteration. The transmission angle can be

increased up to 80 in a composite ac-dc line without losing transient stability, which is

impossible in a pure EHV ac line.

From this composite acdc line, small power tapping is also possible

despite the presence of a dc component in it. This paper proposes a simple scheme of

small power tapping from the composite acdc power transmission line along its route. In

this study, the tapping stations are assumed to draw power up to 10% of the total power

transfer capability of the composite line. However, more power tapping is also possible

subject to the condition that it is always less than the ac power component.

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CHAPTER 2

INTRODUCTION

SIMULTANEOUS ACDC

POWER TRANSMISSION

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CHAPTER 2 INTRODUCTION

SIMULTANEOUS ACDC POWER TRANSMISSION

Fig. 1.1 depicts the basic scheme for simultaneous acdc power flow through

a double circuit ac transmission line. The dc power is obtained through line commutated12-pulse rectifier bridge used in conventional HVDC and injected to the neutral point of

the zigzag connected secondary of sending end transformer and is reconverted to ac again

by the conventional line commutated 12-pulse bridge inverter at the receiving end. The

inverter bridge is again connected to the neutral of zig-zag connected winding of the

receiving end transformer.

The double circuit ac transmission line carriers both three-phase ac and dc

power. Each conductor of each line carries one third of the total dc current along with ac

current. Resistance being equal in all the three phases of secondary winding of zigzag

transformer as well as the three conductors of the line, the dc current is equally divided

among all the three phases.

Fig. 1.1 Basic scheme for composite acdc transmission.

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Fig 1.2

2.1SYSTEM UNDER STUDY:

The network depicted in Fig.1.1 has been taken up for the feasibility of a small power tapfor remote communities from the composite acdc power transmission system. The

details of power tap substations are shown in Fig.1.2 A synchronous machine is

delivering power to an infinite bus via a double-circuit three-phase, 400-kV, 50-Hz, 450-

km ac transmission line. The minimum value of ac phase voltage and maximum value of

dc voltage with respect to ground of the converted composite acdc line, respectively, are

1/2 and times that of per phase voltage before conversion of the conventional pure

EHV ac line. The line considered is converted to a composite acdc transmission line

with an ac rated voltage of 220 kV and a dc voltage of 320 kV. In a composite acdc

transmission line, the dc component is obtained by converting a part of the ac through a

line-commutated 12-pulse rectifier bridge similar to that used in a conventional HVDC.

The dc current thus obtained is injected into the neutral point of the zig-zag-connected

secondary windings of sending end transformer. The injected current is distributed

equally among the three windings of the transformer. The same is reconverted to ac by

the conventional line commutated inverter at the receiving end. The inverter bridge is

connected to the neutral of zig-zag-connected winding of the receiving end transformer.

The transmission line is connected between the terminals of the zig-zag windings at both

ends. The double-circuit transmission line carries both three-phase ac as well as dc power

after conversion to a composite acdc line. The zig-zag connection of secondary

windings of the transformer is used at both ends to avoid saturation of the core due to the

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flow of the dc component of current. The replacement of a Y-connected transformer from

a conventional EHV ac line with a zig-zag transformer in composite acdc power

transmission is accomplished along with the reduction of ac voltage in such a way that

the insulation-level requirements remain unaltered. However, the neutral point of this

transformer needs insulation to withstand the dc voltage. Moreover, the zig-zag

transformer transfers only 25% of the total power by transformer action. To tap ac power

from the line, the transformer can be directly connected to the conductors of the line

without breaking them.

In this study of a composite ac-dc transmission line, the ac-line voltage component has

been selected as 220 kV. Each tapping station transformer (rated as 120 MVA, 220/66

kV, is connected to the local ac load via a circuit breaker (CB) as depicted in

Fig. 1(b). These CBs are provided for local protection, to clear the fault within the local

ac network. The nature of the local load considered here is that of a summer time

residential class with the following characteristics.

The three conductors of the second line provide return path for the dc current.

Zig-zag connected winding is used at both ends to avoid saturation of transformer due to

dc current. Two fluxes produced by the dc current Id /3 flowing through each of a winding

in each limb of the core of a zig-zag transformer are equal in magnitude and opposite in

direction. So the net dc flux at any instant of time becomes zero in each limb of the core.

Thus, the dc saturation of the core is avoided. A high value of reactor Xd is used to reduce

harmonics in dc current. In the absence of zero sequence and third harmonics or its

multiple harmonic voltages, under normal operating conditions, the ac current flow

through each transmission line will be restricted between the zigzag connected windings

and the three conductors of the transmission line. Even the presence of these components

of voltages may only be able to produce negligible current through the ground due to

high value of Xd. Assuming the usual constant current control of rectifier and constant

extinction angle control of inverter, the equivalent circuit of the scheme under normal

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steady-state operating condition is given in Fig. 2. The dotted lines in the figure show the

path of ac return current only. The second transmission line carries the return dc current,

and each conductor of the line carries Id/3 along with the ac current per phase and are the

maximum values of rectifier and inverter side dc voltages and are equal totimes converter ac input line-to-line voltage. R, L, and C are the line parameters per

phase of each line. , are commutating resistances, and, are firing and

extinction angles of rectifier and inverter, respectively. Neglecting the resistive drops in

the line conductors and transformer windings due to dc current, expressions for ac

voltage and current, and for active and reactive powers in terms of A, B, C, and D

parameters of each line may be written as

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Fig 2.1

Neglecting ac resistive drop in the line and transformer, the dc power Pdr and Pdi of each

rectifier and inverter may be expressed as

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The net current I in any conductor is offseted from zero. In case of a fault in the

transmission system, gate signals to all the SCRs are blocked and that to the bypass SCRs

are released to protect rectifier and inverter bridges. The current in any conductor is no

more offseted. Circuit breakers (CBs) are then tripped at both ends to isolate the faulty

line. CBs connected at the two ends of transmission line interrupt current at natural

current zeroes, and no special dc CB is required. Now, allowing the net current through

the conductor equal to its thermal limit (Ith)

Let Vph be per-phase rms voltage of original ac line. Let also V a be the per-phase voltage

of ac component of composite acdc line with dc voltage Vd superimposed on it. As

insulators remain unchanged, the peak voltage in both cases should be equal

Electric field produced by any conductor possesses a dc component superimpose on it a

sinusoidally varying ac component. However, the instantaneous electric field polarity

changes its sign twice in a cycle if is insured. Therefore, higher

creepage distance requirement for insulator discs used for HVDC lines are not required.

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Each conductor is to be insulated for, Vmax but the line-to-line voltage has no dc

component and. Therefore, conductor-to-conductor separation

distance of each line is determined only by rated ac voltage of the line. Allowing

maximum permissible voltage offset such that the composite voltage wave just toucheszero in each every cycle;

The total power transfer through the double circuit line before conversion is as follows:

Where X the transfer reactance per phase of the double is circuit line, and is the

power angle between the voltages at the two ends. To keep sufficient stability margin,

is generally kept low for long lines and seldom exceeds 30. With the increasing

length of line, the loadability of the line is decreased. An approximate value of may

be computed from the loadability curve by knowing the values of surge impedance

loading (SIL) and transfer reactance of the line

Where M is the multiplying factor, and its magnitude decreases with the length of line.

The value of M can be obtained from the loadability curve. The total power transfer

through the composite line

The power angle between the ac voltages at the two ends of the composite line may

be increased to a high value due to fast controllability of dc component of power. For a

constant value of total power, may be modulated by fast control of the current

controller of dc power converters. Approximate value of ac current per phase per circuit

of the double circuit line may be computed as

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The rectifier dc current order is adjusted online as

Preliminary qualitative analysis suggests that commonly used techniques in HVDC/AC

system may be adopted for the purpose of the design of protective scheme, filter, and

instrumentation network to be used with the composite line for simultaneous acdc power

flow. In case of a fault in the transmission system, gate signals to all the SCRs are

blocked and that to the bypass SCRs are released to protect rectifier and inverter bridges.

CBs are then tripped at both ends to isolate the complete system. A surge diverter

connected between the zig-zag neutral and the ground protects the converter bridge

against any over voltage.

2.2 SMALL POWER TAPPING STATION

REQUIREMENTS:The main requirements of a small power tapping stations are as follows.

The per unit cost of the tap must be strongly constrained (i.e., the fixed cost must be

kept as low as possible).

The tap must have a negligible impact on the reliability of the acdc system. This

implies that any fault in the tap must not be able to shutdown the whole system.

The tap controls should not interfere with the main system (i.e., the tap control system

has to be strictly local). Failure to achieve this leads to a complex control system

requirement and, thus, higher cost of hardware.

Small tap stations having a total rating less than 10% of the main terminal rating have

potential applications where small, remote communities or industries require economic

electric power.

The tapping stations considered in this study are of fairly small power rating, up to 10%

of the total transfer capacity of the composite ac-dc power transmission line. Short

interruption of the power supplies should be tolerable at the occurrence of temporary

earth faults on the main simultaneous acdc power transmission system. Further, any

fault occurring within tapping station and its local ac network is to be cleared by local

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CHAPTER 3

DESCRIPTION OF THE SYSTEM MODEL:

A synchronous machine is feeding power to infinite bus via a double circuit, three-phase,

400-KV, 50-Hz, 450-Km ac transmission line. The 2750-MVA (5 * 550), 240-KV

synchronous machine is dynamically modeled, a field coil on d-axis and a damper coil on

q-axis, by Parks equations with the frame of reference based in rotor. It is equipped with

an IEEE type

Fig 3.1

Fig 3.2

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AC4A excitation system of which block diagram is shown in Fig. 3. Transmission lines

are represented as the Bergeron model. It is based on a distributed LC parameter

travelling wave line model, with lumped resistance. It represents the L and C elements of

a PI section in a distributed manner (i.e., it does not use lumped parameters).

It is roughly equivalent to using an infinite number of PI sections, except that the

resistance is lumped (1/2 in the middle of the line, 1/4 at each end). Like PI sections,

the Bergeron model accurately represents the fundamental frequency only. It also

represents impedances at other frequencies, except that the losses do not change. This

model is suitable for studies where the fundamental frequency load flow is most

important. The converters on each end of dc link are modeled as line commutated two

six- pulse bridge (12-pulse), Their control system consist of constant current (CC) and

constant extinction angle (CEA) and voltage dependent current order limiters (VDCOL)

control. The converters are connected to ac buses via Y-Y and Y- converter transformers.

Each bridge is a compact power system computer-aided design (SIMULINK)

representation of a dc converter, which includes a built in six-pulse Graetz converter

bridge (can be inverter or rectifier), an internal phase locked oscillator (PLO), firing and

valve blocking controls, and firing angle /extinction angle measurements. It also

includes built in RC snubber circuits for each thyristor. The controls used in dc system

are those of CIGRE Benchmark , modified to suit at desired dc voltage. AC filters at each

end on ac sides of converter transformers are connected to filter out 11th and 13th

harmonics. These filters and shunt capacitor supply reactive power requirements of

converters.

A master current controller (MCC), shown in Fig. 3.2, is used to control the current order

for converters. It measures the conductor ac current, computes the permissible dc current,

and produces dc current order for inverters and rectifiers.

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CHAPTER 4

HVDC

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CHAPTER 4

4.1HVDC

Over long distances bulk power transfer can be carried out by a high

voltage direct current (HVDC) connection cheaper than by a long distance AC

transmission line. HVDC transmission can also be used where an AC transmission

scheme could not (e.g. through very long cables or across borders where the two AC

systems are not synchronized or operating at the same frequency). However, in order to

achieve these long distance transmission links, power convertor equipment is required,

which is a possible point of failure and any interruption in delivered power can be costly.

It is therefore of critical importance to design a HVDC scheme for a given availability.

The HVDC technology is a high power electronics technology used in

electric power systems. It is an efficient and flexible method to transmit large amounts of

electric power over long distances by overhead transmission lines or

underground/submarine cables. It can also be used to interconnect asynchronous power

systems

The fundamental process that occurs in an HVDC system is the conversion of

electrical current from AC to DC (rectifier) at the transmitting end and from DC to AC

(inverter) at the receiving end.

There are three ways of achieving conversion

1. Natural commutated converters.

2. Capacitor Commutated Converters.

3. Forced Commutated Converters.

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4.1.1Natural commutated converters (NCC):

NCC is most used in the HVDC systems as of today. The component

that enables this conversion process is the thyristor, which is a controllable

semiconductor that can carry very high currents (4000 A) and is able to block very high

voltages (up to 10 kV). By means of connecting the thyristors in series it is possible to

build up a thyristor valve, which is able to operate at very high voltages (several

hundred of kV).The thyristor valve is operated at net frequency (50 Hz or 60 Hz) and by

means of a control angle it is possible to change the DC voltage level of the bridge..

4.1.2Capacitor Commutated Converters (CCC):

An improvement in the thyristor-based Commutation, the CCC

concept is characterized by the use of commutation capacitors inserted in series between

the converter transformers and the thyristor valves. The commutation capacitors improve

the commutation failure performance of the converters when connected to weak

networks.

4.1.3Forced Commutated Converters(FCC).

This type of converters introduces a spectrum of advantages, e.g. feed

of passive networks (without generation), independent control of active and reactive

power, power quality. The valves of these converters are built up with semiconductors

with the ability not only toturn-on but also to turn-off. They are known as VSC (Voltage

Source Converters). a new type of HVDC has become available. It makes use of the more

advancedsemiconductor technology instead of thyristors for power conversion between

AC and DC. The semiconductors used are insulated gate bipolar transistors (IGBTs), and

theconverters are voltage source converters (VSCs) which operate with high switching

frequencies (1-2 kHz) utilizing pulse width modulation (PWM).

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4.2Configurations of HVDC

There are different types of HVDC systems which are

4.2.1Mono-polar HVDC system:

In the mono-polar configuration, two converters are connected by a single

pole line and a positive or a negative DC voltage is used. In Fig 4.1. There is only one

Insulated transmission conductor installed and the ground or sea provides the path for the

return current.

Fig 4.1

4.2.2Bipolar HVDC system:

This is the most commonly used configuration of HVDC transmission

systems. The bipolar configuration, shown in Fig. 4.2 Uses two insulated conductors as

Positive and negative poles. The two poles can be operated independently if both

Neutrals are grounded. The bipolar configuration increases the power transfer capacity.

Under normal operation, the currents flowing in both poles are identical and there is no

ground current. In case of failure of one pole power transmission can continue in the

other pole which increases the reliability. Most overhead line HVDC transmission

systems use the bipolar configuration.

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Fig 4.4

4.3 VOLTAGE-SOURCE CONVERTER:

A voltage-source converter is connected on its ac-voltage side to a

three-phase electric power network via a transformer and on its dc-voltage side to

capacitor equipment. The transformer has on its secondary side a first, a second, and a

third phase winding, each one with a first and a second winding terminal. Resistor

equipment is arranged at the transformer for limiting the current through the converter

when connecting the transformer to the power network. The resistor equipment includes a

first resistor, connected to the first winding terminal of the second phase winding, and

switching equipment is adapted, in an initial position, to block current through the phase

windings, in a transition position to form a current path which includes at least the first

and the second phase windings and, in series therewith, the first resistor, which current

path, when the converter is connected to the transformer, closes through the converter

and the capacitor equipment, and, in an operating position, to interconnect all the first

winding terminals for forming the common neutral point.

In VSC HVDC, Pulse Width Modulation (PWM) is used for generation of

the fundamental voltage. Using PWM, the magnitude and phase of the voltage can be

controlled freely and almost instantaneously within certain limits. This allows

independent and very fast control of active and reactive power flows. PWM VSC is

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therefore a close to ideal component in the transmission network. From a system point of

view, it acts as a zero inertia motor or generator that can control active and reactive

power almost instantaneously. Furthermore, it does not contribute to the short-circuit

power, as the AC current can be controlled.

4.4Voltage Source Converter based on IGBT technology

The modular low voltage power electronic platform is called

PowerPak. It is a power electronics building block (PEBB) with three integrated

Insulated Gate Bipolar Transistor (IGBT) modules. Each IGBT module consists of six

switches forming three phase legs. Various configurations are possible. For example

three individual three-phase bridges on one PEBB, one three phase bridge plus

chopper(s) etc. The PowerPak is easily adaptable for different applications.

The IGBT modules used are one Power Pak as it is used for the SVR. It

consists of one three-phase bridge (the three terminals at the right hand side), which

provides the input to the DC link (one IGBT module is used for it) and one output in form

of one single phase H-bridge (the two terminals to the left) acting as the booster

converter. For the latter two IGBT modules are used with three paralleled phase legs per

output terminal. By paralleling such PEBBs adaptation to various ratings is possible.

4.5GTO/IGBT (Thyristor based HVDC):

Normal thyristors (silicon controlled rectifiers) are not fully controllable

switches (a "fully controllable switch" can be turned on and off at will.) Thyristors can

only be turned ON and cannot be turned OFF. Thyristors are switched ON by a gate

signal, but even after the gate signal is de-asserted (removed), the thyristor remains in the

ON-state until any turn-off condition occurs (which can be the application of a reverse

voltage to the terminals, or when the current flowing through (forward current) falls

below a certain threshold value known as the holding current.) Thus, a thyristor behaves

like a normal semiconductor diode after it is turned on or "fired".

The GTO can be turned-on by a gate signal, and can also be turned-off

by a gate signal of negative polarity.

Turn on is accomplished by a positive current pulse between the gate and cathode

terminals. As the gate-cathode behaves like PN junction, there will be some relatively

small voltage between the terminals. The turn on phenomenon in GTO is however, not as

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reliable as an SCR (thyristor) and small positive gate current must be maintained even

after turn on to improve relieabilty.

Turn off is accomplished by a negative voltage pulse between the gate and cathode

terminals. Some of the forward current (about one third to one fifth) is "stolen" and used

to induce a cathode-gate voltage which in turn induces the forward current to fall and the

GTO will switch off (transitioning to the 'blocking' state.)

GTO thyristors suffer from long switch off times, whereby after the

forward current falls, there is a long tail time where residual current continues to flow

until all remaining charge from the device is taken away. This restricts the maximum

switching frequency to approx 1 kHz.

It may however be noted that the turn off time of a comparable SCR is

ten times that of a GTO.Thus switching frequency of GTO is much better than SCR.

Gate turn-off (GTO) thyristors are able to not only turn on the main

current but also turn it off, provided with a gate drive circuit. Unlike conventional

thyristors, they have no commutation circuit, downsizing application systems while

improving efficiency. They are the most suitable for high-current, high speed switching

applications, such as inverters and chopper circuits.

Bipolar devices made with SiC offer 20-50X lower switching losses as

compared to conventional semiconductors. A rough estimate of the switching power

losses as a function of switching frequency is shown in Figure 4. Another very significant

property of SiC bipolar devices is their lower differential on-state voltage drop than

similarly rated Si bipolar device, even with order of magnitude smaller carrier lifetimes in

the drift region.

This property allows high voltage (>20 kV) to be far more reliable and

thermally stable as compared to those made with Silicon. The switching losses and the

temperature stability of bipolar power devices depends on the physics of operation of the

device. The two major categories of bipolar power devices are: (a) single injecting

junction devices (for example BJT and IGBT); and (b) double injecting junction devices

(like Thyristor-based GTO/MTO/JCT/FCT and PIN diodes). In a power BJT, most of the

minority carrier charge resides in the low doped collector layer, and hence its operation

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has been approximated as an IGBT. The limited gain of a BJT will make the following

analysis less relevant for lower voltage devices.

Silicon carbide has been projected to have tremendous potential for high voltage

solid-state power devices with very high voltage and current ratings because of its

electrical and physical properties. The rapid development of the technology for producing

high quality single crystal SiC wafers and thin films presents the opportunity to fabricate

solid- state devices with power-temperature capability far greater than devices currently

available. This capability is ideally suited to the applications of power conditioning in

new more- electric or all-electric military and commercial vehicles.

These applications require switches and amplifiers capable of large currents with

relatively low voltage drops. One of the most pervasive power devices in silicon is the

Insulated Gate Bipolar Transistor (IGBT). However, these devices are limited in their

operating temperature and their achievable power ratings compared to that possible with

SiC. Because of the nearly ideal combination of characteristics of these devices, we

propose to demonstrate the first 4H-SiC Insulated Gate Bipolar Transistor in this Phase I

effort. Both n-channel and p-channel SiC IGBT devices will be investigated. The targeted

current and voltage rating for the Phase I IGBT will be a >200 Volt, 200 mA device, that

can operate at 350 C.

4.6 12-pulse converters:The basic design for practically all HVDC converters is the 12-pulse double

bridge converter which is shown in Figure below. The converter consists of two 6-pulse

bridge converters connected in series on the DC side. One of them is connected to the AC

side by a YY-transformer, the other by a YD transformer. The AC currents from each 6-

pulse converter will then be phase shifted 30. This will reduce the harmonic content in

the total current drawn from the grid, and leave only the characteristic harmonics of order

12 m1, m=1,2,3..., or the 11th, 13th, 23th, 25th etc. harmonic. The non-characteristic

harmonics will still be present, but considerably reduced. Thus the need for filtering is

substantially reduced, compared to 6-pulse converters. The 12-pulse converter is usually

built up of 12 thyristor valves. Each valve consists of the necessary number of thyristors

in series to withstand the required blocking voltage with sufficient margin. Normally

there is only one string of thyristors in each valve, no parallel connection. Four valves are

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built together in series to form a quadruple valve and three quadruple valves, together

with converter transformer, controls and protection

Figure:4.5 -12-pulse converter.

Fig 4.6 Main elements of a HVDC converter station with one bipole consisting

of two 12-pulse converter unit.

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equipment, constitute a converter. The converter transformers are usually three winding

transformers with thewindings in Yy d N-connection. There can be one three-phase or

three single phase transformers, according to local circumstances. In order to optimize the

relationship between AC- and DC voltage the converter transformers are equipped with

tap changers.

4.7 HVDC converter stations:

An HVDC converter station is normally built up of one or two 12-pulse converters

as described above, depending on the system being mono- or bipolar. In some cases each

pole of a bipolar system consists of two converters in series to increase the voltage and

power rating of the transmission. It is not common to connect converters directly in

parallel in one pole. The poles are normally as independent as possible to improve the

reliability of the system, and each pole is equipped with a DC reactor and DC filters.

Additionally the converter station consists of some jointly used equipment.

This can be the connection to the earth electrode, which normally is situated some

distance away from the converter station area, AC filters and equipment for supply of the

necessary reactive power.

Fig 4.7 Mono-polar HVDC transmission Voltage in station B according to reversed

polarity convention.

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CHAPTER 5

BASIC CONTROL PRINCIPLES

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CHAPTER 5

BASIC CONTROL PRINCIPLES

5.1Control System Model:

The control model mainly consists of measurements and generation of firing signals for

both the rectifier and inverter. The PLO is used to build the firing signals. The output

signal of the PLO is a ramp, synchronized to the phase-A commutating bus line-to-

ground voltage, which is used to generate the firing signal for Valve 1. The ramps for

other valves are generated by adding 60 to the Valve 1 ramp. As a result, an equidistant

pulse is realized. The actual firing time is calculated by comparing the order to the value

of the ramp and using interpolation technique. At the same time, if the valve is pulsed but

its voltage is still less than the forward voltage drop, this model has logic to delay firing

until the voltage is exactly equal to the forward voltage drop. The firing pulse is

maintained across each valve for 120.

The and measurement circuits use zero-crossing information from commutating bus

voltages and valve switching times and then convert this time difference to an angle

(using measured PLO frequency). Firing angle (in seconds) is the time when valve turns

on minus the zero crossing time for valve.

Extinction angle (in seconds) for valve is the time at which the commutation bus voltage

for valve crosses zero (negative to positive) minus the time valve turns off.

Following are the controllers used in the control schemes:

Extinction Angle Controller;

DC Current Controller;

Voltage Dependent Current Limiter (VDCOL).

5.1.1 Rectifier Control: The rectifier control system uses Constant Current Control

(CCC) technique. The reference for current limit is obtained from the inverter side.

This is done to ensure the protection of the converter in situations when inverter side does

not have sufficient dc voltage support (due to a fault) or does not have sufficient load

requirement (load rejection). The reference current used in rectifier control depends on

the dc voltage available at the inverter side. Dc current on the rectifier side is measured

using proper transducers and passed through necessary filters before they are compared to

produce the error signal. The error signal is then passed through a PI controller, which

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produces the necessary firing angle order. The firing circuit uses this information to

generate the equidistant pulses for the valves using the technique described earlier.

5.1.2 Inverter Control:The Extinction Angle Control or control and current control

have been implemented on the inverter side. The CCC with Voltage Dependent Current

Order Limiter (VDCOL) has been used here through PI controllers. The reference limit

for the current control is obtained through a comparison of the external reference

(selected by the operator or load requirement) and VDCOL (implemented through lookup

table) output. The measured current is then subtracted from the reference limit to produce

an error signal that is sent to the PI controller to produce the required angle order.

The control uses another PI controller to produce gamma angle order for the inverter.

The two angle orders are compared, and the minimum of the two is used to calculate the

firing instant.

5.2 Control System Model:

The control blocks available in SIMULINK have been used to emulate the control

algorithm described above Section, and enough care has been taken. Some control

parameters required conversion to their proper values due to differences in units. The

rectifier side uses current control with a reference obtained from the inverter VDCOL

output (implemented through a lookup table), and the inverter control has both current

control and control operating in parallel, and the lower output of the two is used to

generate the firing pulses. The angle is not provided directly from the converter valve

data. It needed to be implemented through measurements taken from valve data. The

control block diagrams are shown in following figures.

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fig 5.1

fig 5.2

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Fig 5.3

5.3DC transmission controlThe current flowing in the DC transmission line shown in Figure below is determined by

the DC voltage difference between station A and station B. Using the notation shown in

the figure, where rdrepresents the total resistance of the line, we get for the DC current

and the power transmitted into station B is

2In rectifier operation the firing angle should not be decreased below a certain

minimum value min, normally 3-5 in order to make sure that there really is a positive

voltage across the valve at the firing instant. In inverter operation the extinction angle

should never decrease below a certain minimum value min, normally 17-19 otherwise

the risk of commutation failures becomes too high. On the other hand, both and

should be as low as possible to keep the necessary nominal rating of the equipment to a

minimum. Low values of and also decrease the consumption of reactive power and

the harmonic distortion in the AC networks.

To achieve this, most HVDC systems are controlled to maintain = min in normal

operation. The DC voltage level is controlled by the transformer tap changer in inverter

station B. The DC current is controlled by varying the DC voltage in rectifier station A,

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The current/voltage characteristics expressed in above are shown for normal values ofid

and dxN. In order to create a characteristic diagram for the complete transmission, it is

usual to define positive voltage in inverter operation in the opposite direction compared

to rectifier operation.

It is clear that to operate both converters on a constant firing/extinction angle principle is

like leaving them without control. This will not give a stable point of operation, as both

characteristics have approximately the same slope. Small differences appear due to

variations in transformer data and voltage drop along the line. To gain the best possible

control the characteristics should cross at as close to a right angle as possible. This means

that one of the characteristics should preferably be constant current. This can only be

achieved by a current controller.

If the current/voltage diagram of the rectifier is combined with a constant current

controller characteristic we get the steady state diagram in Figure below for converter

station A. A similar diagram can be drawn for converter station B. If we apply the

reversed polarity convention for the inverter and combine the diagrams for station A and

station B we get the diagram in Figure below In normal operation, the rectifier will be

operating in current control mode with the firing angle

Fig 5.4 Steady state ud/id diagram for converter station A Steady state ud/id diagram

for converter station A.&B

The inverter has a slightly lower current command than the rectifier and tries to decrease

the current by increasing the counter voltage, but cannot decrease beyond min. Thus

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we get the operating point A. We assume that the characteristic for station B is referred to

station A that is it is corrected for the voltage drop along the transmission line. This

voltage drop is in the magnitude of 1-5 % of the rated DC voltage. If the AC voltage at

the rectifier station drops, due to some external disturbance, the voltage difference is

reduced and the DC current starts to sink. The current controller in the rectifier station

starts to reduce the firing angle , but soon meets the limit min, so the current cannot be

upheld. When the current sinks below the current command of the inverter, the inverter

control reduces the counter voltage to keep the current at the inverter current command,

until a new stable operating point B is reached. If the current command at station A is

decreased below that of station B, station A will see a current that is to high and start to

increase the firing angle , to reduce the voltage. Station B will see a diminishing current

and try to keep it up by increasing the extinction angle to reduce the counter voltage.

Finally station A meets the min limit and cannot reduce the voltage any further and the

new operating point will be at point C. Here the voltage has been reversed to negative

while the current is still positive, that is the power flow has been reversed. Station A is

operating as inverter and station B as rectifier. The difference between the current

commands of the rectifier and the inverter is called the current margin. It is possible to

change the power flow in the transmission simply by changing the sign of the current

margin, but in practice it is desirable to do this in more controllable ways. Therefore the

inverter is normally equipped with a min limitation in the range of 95-105. To avoid

current fluctuations between operating points A and B at small voltage variations the

corner of the inverter characteristic is often cut off. Finally, it is not desirable to operate

the transmission with high currents at low voltages, and most HVDC controls are

equipped with voltage dependent current command limitation.

CHAPTER 6

Master control system:

The controls described above are basic and fairly standardized and similar for all HVDC

converter stations. The master control, however, is usually system specific and

individually designed. Depending on the requirements of the transmission, the control

can be designed for constant current or constant power transmitted, or it can be designed

to help stabilizing the frequency in one of the AC networks by varying the amount of

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active power transmitted. The control systems are normally identical in both converter

systems in a transmission, but the master control is only active in the station selected to

act as the master station, which controls the current command. The calculated current

command is transmitted by a communication system to the slave converter station, where

the pre-designed current margin is added if the slave is to act as rectifier, subtracted if it

is to act as inverter. In order to synchronize the two converters and assure that they

operate with same current command (apart from the current margin), a

telecommunications channel is required.

Should the telecommunications system fail for any reason, the current commands to both

converters are frozen, thus allowing the transmission to stay in operation. Special fail-

safe techniques are applied to ensure that the telecommunications system is fault-free.

The requirements for the telecommunications system are especially high if the

transmission is required to have a fast control of the transmitted power, and the time

delay in processing and transmitting these signals will influence the dynamics of the total

control system.

CHAPTER 7

7.1Comparison of Different HVAC-HVDC

In order to examine the behavior of the losses in combined transmission and not in order

to provide the best economical solutions for real case projects. Thus, most of the

configurations are overrated, increasing the initial investment cost and consequently the

energy transmission cost. The small number of different configurations analyzed provides

a limited set of results, from which specific conclusions can be drawn regarding the

energy transmission cost. Nevertheless, the same approach, as for the individual

HVACHVDC systems, is followed in order to evaluate the energy availability and the

energy transmission cost.

7.2 Presentation of Selected Configurations and Calculation of theEnergy Transmission Cost

For the combined HVAC-HVDC transmission systems only 500 MW and 1000 MW

windfarm were considered.

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The choices for the transmission distance were limited to 50, 100 and 200 km. The three

following, general combinations were compared:

1. HVAC + HVDC VSC

2. HVAC + HVDC LCC

3. HVDC LCC + HVDC VSC

The specific configurations for each solution, based on the transmission distance and the

size of the wind farm, are presented in Tables.

500MW Wind Farm, 50Km Transmission DistanceHVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC

Case 1 Case 2 Case 1 Case2 Case 1 Case 2

Rated Power 280MW(

400KV )AC+

230MV

VSC

150MW(2

30KV)Ac+

350MW

VSC

200MW(2

20KV)AC+

300MW

LCC

60MW(220K

v) AC+400MW

LCC

300MW

LCC+220MW

VSC

250MW

LCC+350MW

VSC

CableNumbers

1 (AC)+

2 VSC

1 (AC)+

2 VSC

1 (AC)+

1 LCC

1 (AC)+

1 LCC

1 (LCC)+

2 VSC

1 (LCC)+

2 VSC


Case 1 Case 2 Case 1 Case 2 Case 1 Case 2

Rated Power 280MW

(400KV)

AC +230MV

VSC

150MW

(230KV)

AC +350MW

VSC

370MW

(400KV)A

C +130MW

LCC

250MW

(400KV)AC

+ 250MWLCC

300MW

LCC +

220MWVSC

250MW

LCC +

350MWVSC

Cable

Numbers

1 (AC)+

2 VSC

1 (AC)+

2 VSC

1 (AC)+

1 LCC

1 (AC)+

1 LCC

1 (LCC)+

2 VSC

1 (LCC)+

2 VSC

500MW Wind Farm, 200Km Transmission Distance

HVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC

Case 1 Case 2 Case 1 Case 2 Case 1 Case 2

Rated Power 280MW

(220KV)Ac +

220MV

VSC

150MW

(230KV)AC +

350MW

VSC

370MW

(400KV)AC +

130MW

LCC

250MW

(400KV)AC+ 250MW

LCC

300MW

LCC +220MW

VSC

250MW

LCC +350Mw

VSC

Cable

Numbers

1 (AC)+

2 VSC

1 (AC)+

2 VSC

1 (AC)+

1 LCC

1 (AC)+

1 LCC

1 (LCC)+

2 VSC

1 (LCC)+

2 VSC

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Table 1:Configurations for the study of combined transmission systems. Windfarm

rated at 500 MW


Case 1 Case2 Case 1 Case 2

Rated Power 200MW(220Kv)AC+ (2x350+220)MW

VSC

200MW(400KV)

AC+(600+2

50)MW

LCC

330MW(400KV)AC

+(600+130)

MW LCC

600MWLCC+

(350+220)

MWVSC

250MWLCC+

(2x350+

220) VSC

Cable

Numbers

1 (Ac)+ 4 (VSC) 1 (AC)+

2 LCC

1 (AC)+

2 LCC

1 (LCC)+

24 VSC

1 (LCC)+

6 VSC


Case 1 Case 2 Case 1 Case 2

Rated Power 500MW(400KV)

AC+ (350+220)MW VSC

800MW

(400KV)AC

+ 250MW

LCC

900MW

(400KV)AC+ 130MW

LCC

600MW

LCC+(350+220)

MW

VSC

250MW

LCC+(2x350+220) VSC

Cable

Numbers

1 (AC)+ 4(VSC) 2 (AC)+

1 LCC

2 (AC)+

1 LCC

1 (LCC)+

4 VSC

1 (LCC)+

6 VSC1000MW Wind Farm, 200Km Transmission Distance

HVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC

Case 1 Case 2 Case 1 Case 2

Rated Power 500MW(220KV)A

C+ (350+220)MWVSC

800MW

(220KV)AC +

250MW

LCC

9000MW

(220KV)AC+ 130MW

LCC

600MW

LCC+(350+22

0)MW

VSC

250MW LCC

+(2x350+220)

VSC

CableNumbers

2(AC)+ 24(VSC) 3 (AC)+1 LCC

4(AC)+1 LCC

1 (LCC)+4 VSC

1 (LCC)+6 VSC

Tab 2 Configurations for the study of combined transmission systems. Wind farm

rated at 1000

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Only the rated power of each transmission technology changes every time while the

distance to shore and the condition of the onshore grid remain the same.

1. The HVAC system has a voltage level of 220 kV and it connected to a weak

grid 50 km from the offshore substation.

2. The HVDC VSC system is connected to a grid of medium strength at a distance

of 100 km from the offshore substation.

3. The HVDC LCC system is connected to a strong grid 200 km from the offshore

substation. The average losses for the cases described above were calculated by

Barberis table-1 and Todorovic table-2. The losses and the results concerning

the energy unavailability and the energy transmission cost are presented in

Table -3.

1000 MW Windfarm with Multiple Connection Points to Shore

Besides the combinations of the transmission technologies presented above, three cases

of transmission solutions from a 1000 MW windfarm are analyzed. In these cases the

windfarm is connected to three different onshore grids, utilizing all three transmission

technologies studied so far.

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Tab 3

Average power losses, energy unavailability and energy transmission cost for

transmission solutions from a 1000 MW windfarm with multiple connection points

to shore.

CHAPTER 8

Simulink circuit:

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Fig 8.1

Zig zag transformer

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Fig 8.2

Controlling circuit

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fig 8.3

fig8.4

CHAPTER 9

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Blocks functionalities :

9.1Three-Phase Source:

The Three-Phase Source block implements a balanced three-phase voltage source with

internal R-L impedance. The three voltage sources are connected in Y with a neutral

connection that can be internally grounded or made accessible. You can specify the

source internal resistance and inductance either directly by entering R and L values or

indirectly by specifying the source inductive short-circuit level and X/R ratio.

9.2Three-Phase Parallel RLC Branch:

The Three-Phase Parallel RLC Branch block implements three balanced branches

consisting each of a resistor, an inductor, a capacitor, or a parallel combination of these.

To eliminate either the resistance, inductance, or capacitance of each branch, the R, L,and C values must be set respectively to infinity (inf), infinity (inf), and 0. Only existing

elements are displayed in the block icon. Negative values are allowed for resistance,

inductance, and capacitance

9.3Three-Phase Transformer (Three Windings):

This block implements a three-phase transformer by using three single-phase

transformers with three windings. You can simulate the saturable core or not simply by

setting the appropriate check box in the parameter menu of the block. See the Linear

Transformer and Saturable Transformer block sections for a detailed description of the

electrical model of a single-phase transformer.

The three windings of the transformer can be connected in the following manner: Y Y

with accessible neutral (for windings 1 and 3 only) Grounded Y Delta (D1), delta lagging

Y by 30 degrees Delta (D11), delta leading Y by 30 degrees.

9.4Universal Bridge:

The Universal Bridge block implements a universal three-phase power converter that

consists of up to six power switches connected in a bridge configuration. The types of

power switch and converter configuration are selectable from the dialog box.

The Universal Bridge block allows simulation of converters using both naturally

commutated (and line-commutated) power electronic devices (diodes or thyristors) and

forced-commutated devices (GTO, IGBT, and MOSFET).

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The Universal Bridge block is the basic block for building two-level voltage-sourced

converters (VSC).

9.5Connection Port:

The Connection Port block, placed inside a subsystem composed of SimPowerSystems

blocks, creates a Physical Modeling open round connector port on the boundary of the

subsystem. Once connected to a connection line, the port becomes solid. Once you begin

the simulation, the solid port becomes an electrical terminal port, an open square.

You connect individual SimPowerSystems blocks and subsystems made of sim Power

Systems blocks to one another with Sim Power Systems connection lines, instead of

normal Simulink signal lines. These are anchored at the open, round connector ports.

Subsystems constructed of SimPowerSystems blocks automatically have such open round

connector ports. You can add additional connector ports by adding Connection Port

blocks to your subsystem

9.6Breaker

The Breaker block implements a circuit breaker where the opening and closing times can

be controlled either from an external Simulink signal (external control mode), or from an

internal control timer (internal control mode).

The arc extinction process is simulated by opening the breaker device when the current

passes through 0 (first current zero crossing following the transition of the Simulink

control input from 1 to 0).

When the breaker is closed it behaves as a resistive circuit. It is represented by a

resistance Ron. The Ron value can be set as small as necessary in order to be negligible

compared with external components (typical value is 10 m). When the breaker is open it

has an infinite resistance.

If the Breaker block is set in external control mode, a Simulink input appears on the

block icon. The control signal connected to the Simulink input must be either 0 or 1: 0 to

open the breaker, 1 to close it. If the Breaker block is set in internal control mode, the

switching times are specified in the dialog box of the block.

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If the breaker initial state is set to 1 (closed), SimPowerSystems automatically initializes

all the states of the linear circuit and the Breaker block initial current so that the

simulation starts in steady state.

A series Rs-Cs snubber circuit is included in the model. It can be connected to the circuit

breaker. If the Breaker block happens to be in series with an inductive circuit, an open

circuit or a current source, you must use a snubber.

9.7 Distributed Parameter Line:

Implement an N-phase distributed parameter transmission line model with lumped losses.

The Distributed Parameter Line block implements an N-phase distributed parameter line

model with lumped losses. The model is based on the Bergeron's traveling wave method

used by the Electromagnetic Transient Program (EMTP).In this model, the lossless

distributed LC line is characterized by two values (for a single-phase line) For multiphase

line models, modal transformation is used to convert line quantities from phase values

(line currents and voltages) into modal values independent of each other. The previous

calculations are made in the modal domain before being converted back to phase values.

In comparison to the PI section line model, the distributed line represents wave

propagation phenomena and line end reflections with much better accuracy.

CHAPTER 10

Description of the Control and Protection Systems:

The control systems of the rectifier and of the inverter use the same Discrete HVDC

Controller block from the Discrete Control Blocks library of the SimPowerSystems

Extras library. The block can operate in either rectifier or inverter mode. At the inverter,

the Gamma Measurement block is used and it is found in the same library. The Master

Control system generates the current reference for both converters and initiates the

starting and stopping of the DC power transmission.

The protection systems can be switched on and off. At the rectifier, the DC fault

protection detects a fault on the line and takes the necessary action to clear the fault. The

Low AC Voltage Detection subsystem at the rectifier and inverter serves to discriminate

between an AC fault and a DC fault. At the inverter, the Commutation Failure Prevention

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Control subsystem [2] mitigates commutation failures due to AC voltage dips. A more

detailed description is given in each of these protection blocks.

10.1HVDC Controller Block Inputs and Outputs

Inputs 1and 2 are the DC line voltage (VdL) and current (Id). Note that the measured DC

currents (Id_R and Id_I in A) and DC voltages (VdL_R and VdL_I in V) are scaled to

p.u. (1 p.u. current = 2 kA; 1 p.u. voltage = 500 kV) before they are used in the

controllers. The VdL and Id inputs are filtered before being processed by the regulators.

A first-order filter is used on the Id input and a second-order filter is used on the VdL

input.

Inputs 3 and 4 (Id_ref and Vd_ref) are the Vd and Id reference values in p.u.

Input 5 (Block) accepts a logical signal (0 or 1) used to block the converter when Block =

1.

Input 6 (Forced-alpha) is also a logical signal that can be used for protection purposes. If

this signal is high (1), the firing angle is forced at the value defined in the block dialog

box.

Input 7 (gamma_meas) is the measured minimum extinction angle of the converter 12

valves. It is obtained by combining the outputs of two 6-pulse Gamma Measurement

blocks. Input 8 (gamma_ref) is the extinction angle reference in degrees. To minimize the

reactive power absorption, the reference is set to a minimum acceptable angle (e.g., 18deg).

Finally, input 9 (D_alpha) is a value that is subtracted from the delay angle maximum

limit to increase the commutation margin during transients.

The first output (alpha_ord) is the firing delay angle in degrees ordered by the regulator.

The second output (Id_ref_lim) is the actual reference current value (value of Id_ref

limited by the VDCOL function as explained below). The third output (Mode) is an

indication of the actual state of the converter control mode. The state is given by a

number (from 0 to 6) as follows:

0 Blocked pulses

1. Current control

2. Voltage control

3. Alpha minimum limitations

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CHAPTER 11

RESULTS:

Fig 12.1

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Fig 12.2

Fig 12.3

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Fig 12.4

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Fig 12.5

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Fig 12.6

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Fig 12.7

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Fig 12.8

CHAPTER 12

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CONCLUSION:

The feasibility of tapping a small amount of power to feed remotely located communities

in the same simple way as tapping in the case of an EHV ac line is demonstrated for the

composite acdc transmission system. It is also economical compared to complicated

methods of tapping from the HVDC line. The results clearly demonstrate that the tapping

of a small amount of ac component of power from the composite acdc transmission line

has a negligible impact on the dc power transfer.

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APPENDIX

SOFTWARE

MATLAB - SIMULINK

What is MATLAB?

MATLAB (Matrix Laboratory) is a tool for numerical

computation and visualization. The basic data element is a matrix, so if you need a

program that manipulates array-based data it is generally fast to write and run in

MATLAB (unless you have very large arrays or lots of computations, in which case

youre better off using C or Fortran).

MATLAB is a numerical computing environment andfourth-

generation programming language. Developed by Math Works, MATLAB allowsmatrix

manipulations, plotting offunctions and data, implementation ofalgorithms, creation of

user interfaces, and interfacing with programs written in other languages, including C,C+

+, and Fortran.

HISTORY:

MATLAB was created in the late 1970s by Cleve Molar, then chairman of the

computer science department at the University of New Mexico.[4] He designed it to give

his students access to LINPACKand EISPACKwithout having to learn Fortran. It soon

spread to other universities and found a strong audience within the applied mathematics

community. Jack little, an engineer, was exposed to it during a visit Molar made to

Stanford University in 1983. Recognizing its commercial potential, he joined with Moler

and Steve Bangert. They rewrote MATLAB in C and founded Math Works in 1984 to

continue its development. These rewritten libraries were known as JACKPAC. In 2000,

MATLAB was rewritten to use a newer set of libraries for matrix manipulation,

LAPACK. MATLAB was first adopted by control design engineers, Little's specialty, but

quickly spread to many other domains. It is now also used in education, in particular the

teaching oflinear algebra and numerical analysis, and is popular amongst scientists

involved with image processing.

59
http://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Fourth-generation_programming_languagehttp://en.wikipedia.org/wiki/Fourth-generation_programming_languagehttp://en.wikipedia.org/wiki/Fourth-generation_programming_languagehttp://en.wikipedia.org/wiki/MathWorkshttp://en.wikipedia.org/wiki/Matrix_(mathematics)http://en.wikipedia.org/wiki/Matrix_(mathematics)http://en.wikipedia.org/wiki/Function_(mathematics)http://en.wikipedia.org/wiki/Function_(mathematics)http://en.wikipedia.org/wiki/Algorithmhttp://en.wikipedia.org/wiki/Algorithmhttp://en.wikipedia.org/wiki/User_interfacehttp://en.wikipedia.org/wiki/C_(programming_language)http://en.wikipedia.org/wiki/C_(programming_language)http://en.wikipedia.org/wiki/C%2B%2Bhttp://en.wikipedia.org/wiki/C%2B%2Bhttp://en.wikipedia.org/wiki/Fortranhttp://en.wikipedia.org/wiki/Cleve_Molerhttp://en.wikipedia.org/wiki/Computer_sciencehttp://en.wikipedia.org/wiki/University_of_New_Mexicohttp://en.wikipedia.org/wiki/MATLAB#cite_note-origins-3http://en.wikipedia.org/wiki/MATLAB#cite_note-origins-3http://en.wikipedia.org/wiki/LINPACKhttp://en.wikipedia.org/wiki/LINPACKhttp://en.wikipedia.org/wiki/EISPACKhttp://en.wikipedia.org/wiki/Fortranhttp://en.wikipedia.org/wiki/Applied_mathematicshttp://en.wikipedia.org/wiki/John_N._Littlehttp://en.wikipedia.org/wiki/Stanford_Universityhttp://en.wikipedia.org/wiki/C_(programming_language)http://en.wikipedia.org/wiki/MathWorkshttp://en.wikipedia.org/wiki/MathWorkshttp://en.wikipedia.org/wiki/MathWorkshttp://en.wikipedia.org/wiki/LAPACKhttp://en.wikipedia.org/wiki/Control_engineeringhttp://en.wikipedia.org/wiki/Linear_algebrahttp://en.wikipedia.org/wiki/Linear_algebrahttp://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Image_processinghttp://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Fourth-generation_programming_languagehttp://en.wikipedia.org/wiki/Fourth-generation_programming_languagehttp://en.wikipedia.org/wiki/MathWorkshttp://en.wikipedia.org/wiki/Matrix_(mathematics)http://en.wikipedia.org/wiki/Function_(mathematics)http://en.wikipedia.org/wiki/Algorithmhttp://en.wikipedia.org/wiki/User_interfacehttp://en.wikipedia.org/wiki/C_(programming_language)http://en.wikipedia.org/wiki/C%2B%2Bhttp://en.wikipedia.org/wiki/C%2B%2Bhttp://en.wikipedia.org/wiki/Fortranhttp://en.wikipedia.org/wiki/Cleve_Molerhttp://en.wikipedia.org/wiki/Computer_sciencehttp://en.wikipedia.org/wiki/University_of_New_Mexicohttp://en.wikipedia.org/wiki/MATLAB#cite_note-origins-3http://en.wikipedia.org/wiki/LINPACKhttp://en.wikipedia.org/wiki/EISPACKhttp://en.wikipedia.org/wiki/Fortranhttp://en.wikipedia.org/wiki/Applied_mathematicshttp://en.wikipedia.org/wiki/John_N._Littlehttp://en.wikipedia.org/wiki/Stanford_Universityhttp://en.wikipedia.org/wiki/C_(programming_language)http://en.wikipedia.org/wiki/MathWorkshttp://en.wikipedia.org/wiki/LAPACKhttp://en.wikipedia.org/wiki/Control_engineeringhttp://en.wikipedia.org/wiki/Linear_algebrahttp://en.wikipedia.org/wiki/Numerical_analysishttp://en.wikipedia.org/wiki/Image_processing


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MATLAB ADVANTAGES:

1. Matlab is an interpreted language for numerical computation.

2. It allows one to perform numerical calculations, and visualize the results without

the need for complicated and time consuming programming.

3. Matlab allows its users to accurately solve problems.

4. Which produce graphics easily and produce code efficiently.

SOME FEATURES OF MATLAB:

1. Matlab help facilities.

2. Matlab matrices and vectors.

3. Matlab arithmetic operations.

4. Matlab software.

5. Matlab graphics.

6. Matlab data handling.

WHAT IS SIMULINK:

INTRODUCTION:

Simulink is an environment for multidomain simulation and

Model-Based Design for dynamic and embedded systems. It provides an interactive

graphical environment and a customizable set of block libraries that let you design,

simulate, implement, and test a variety of time-varying systems, including

communications, controls, signal processing, video processing, and image processing.

Simulink is integrated with MATLAB, providing

immediate access to an extensive range of tools that let you develop algorithms, analyze

and visualize simulations, create batch processing scripts, customize the modeling

environment, and define signal, parameter, and test data.

Key Features

Extensive and expandable libraries of predefined blocks

Interactive graphical editor for assembling and managing intuitive block diagrams

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Ability to manage complex designs by segmenting models into hierarchies of

design components

Model Explorer to navigate, create, configure, and search all signals, parameters,

properties, and generated code associated with your model

Application programming interfaces (APIs) that let you connect with other

simulation programs and incorporate hand-written code

Embedded MATLAB Function blocks for bringing MATLAB algorithms into

Simulink and embedded system implementations

simulations interpretively or at compiled C-code speeds using fixed- or variable-

step solvers

Graphical debugger and profiler to examine simulation results and then diagnose

performance and unexpected behavior in your design

Full access to MATLAB for analyzing and visualizing results, customizing the

modeling environment, and defining signal, parameter, and test data

Model analysis and diagnostics tools to ensure model consistency and identify

modeling errors Simulation modes (Normal, Accelerator, and Rapid Accelerator)

for running

TOOL BOXES of MATLAB

SIGNAL PROCESSING:

The Signal Processing Blockset extends Simulink with efficient

frame-based processing and blocks for designing, implementing, and verifying signal

processing systems. The blockset enables you to model streaming data and multirate

systems in communications, audio/video, digital control, radar/sonar, consumer and

medical electronics, and other numerically intensive application areas.

Embedded Target for Motorola MPC555:

The Embedded Target for Motorola MPC555 lets you deploy

production code generated from Real-Time Workshop Embedded Coder directly onto

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MPC5xx microcontrollers. You can use the Embedded Target for Motorola MPC555 to

execute code in real time on the Motorola MPC5xx for on-target rapid prototyping,

production deployment of embedded applications, or validation and performance

analysis.

Real-Time Windows Target:

Real-Time Windows Target enables you to run Simulink and

State flow models in real time on your desktop or laptop PC. You can create and control a

real-time execution entirely through Simulink. Using Real-Time Workshop, you generate

C code, compile it, and start real-time execution on Microsoft Windows while interfacing

to real hardware using PC I/O boards. Other Windows applications continue to run during

operation and can use all CPU cycles not needed by the real-time task.

Real-Time Workshop:

Real-Time Workshop generates and executes stand-alone C code for

developing and testing algorithms modeled in Simulink. The resulting code can be used

for many real-time and non-real-time applications, including simulation acceleration,

rapid prototyping, and hardware-in-the-loop testing. You can interactively tune and

monitor the generated code using Simulink blocks and built-in analysis capabilities, or

run and interact with the code outside the MATLAB and Simulink environment.

Real-Time Workshop Embedded:

Real-Time Workshop Embedded Coder generates C code from

Simulink and State flow models that has the clarity and efficiency of professional

handwritten code. The generated code is exceptionally compact and fastessential

requirements for embedded systems, on-target rapid prototyping boards, microprocessors

used in mass production, and real-time simulators. You can use Real-Time Workshop

Embedded Coder to specify, deploy, and verify production-quality software. To let you

make a side-by-side comparison between the capabilities and characteristics of the codegenerated by Real-Time Workshop and Real-Time Workshop Embedded Coder, the

demos for both products have been placed together on the Real-Time Workshop.

SimDriveline:

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SimDriveline extends Simulink with tools for modeling and simulating the

mechanics of driveline (drivetrain) systems. These tools include components such as

gears, rotating shafts, and clutches; standard transmission templates; and engine and tire

models. SimDriveline is optimized for ease of use and speed of calculation for driveline

mechanics. It is integrated with Math Works control design and code generation products,

enabling you to design controllers and test them in real time with the model of the

mechanical system.

SimEvents:

SimEvents extends Simulink with tools for modeling and simulating discrete-

event systems using queues and servers. With SimEvents you can create a discrete-event

simulation model in Simulink to model the passing of entities through a network of

queues, servers, gates, and switches based on events. You can configure entities with

user-defined attributes to model networks in packet-based communications,

manufacturing, logistics, mission planning, supervisory control, service scheduling, and

other applications. SimEvents lets you model systems that are not time-driven but are

based on discrete events, such as the creation or movement of an entity, the opening of a

gate, or the change in value of a signal.

SimMechanics:

SimMechanics extends Simulink with tools for modeling and simulating

mechanical systems. It is integrated with Math Works control design and code generation

products, enabling you to design controllers and test them in real time with the model of

the mechanical system.

Simulink Accelerator:

The Simulink Accelerator increases the simulation speed of your model by

accelerating model execution and using model profiling to help you identify performance

bottlenecks.

Simulink Control Design:

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Simulink Control Design provides advanced functionality for

performing linear analysis of nonlinear models. You can extract linear approximations of

a model to analyze characteristics such as time and frequency responses and pole-zero

dynamics. A graphical user interface (GUI) and programming capabilities reduce the

complexity and time required to develop the linearized models.

Simulink Fixed Point:

Simulink Fixed Point enables the intrinsic fixed-point capabilities of

the Simulink product family, letting you design control and signal processing systems

that will be implemented using fixed-point arithmetic.

Simulink Parameter Estimation:

Simulink Parameter Estimation is a tool that helps you calibrate the

response of your Simulink model to the outputs of a physical system, eliminating the

need to tune model parameters by trial and error or develop your own optimization

routines. You can use time-domain test data and optimization methods to estimate model

parameters and initial conditions and generate adaptive lookup tables in Simulink.

Simulink Report Generator:

The Simulink Report Generator automatically creates documentation

from Simulink and State flow models. You can document software requirements and

design specifications and produce reports from your models, all in a standard format. You

can use the pre built templates or create a template that incorporates your own styles and

standards.

Simulink Response Optimization:

Simulink Response Optimization is a tool that helps you tune design

parameters in Simulink models by optimizing time-based signals to meet user-defined

constraints. It optimizes scalar, vector, and matrix-type variables and constrains multiple

signals at any level in the model. Simulink Response Optimization supports continuous,

discrete, and multirate models and enables you to account for model uncertainty by

conducting Monte Carlo simulations.

Simulink Verification and Validation:

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KEY FEATURES:

Modeling environment for building electrical power system models for AC, DC,

and mixed AC/DC systems

Libraries of application-specific models, including models of common AC and

DC electric drives, Flexible AC Transmission Systems (FACTS), and wind-power

generation

Discretization and phasor simulation modes for faster model execution

Ideal switching algorithm, enabling fast and accurate simulation of power

electronic devices

Analysis methods for obtaining state-space representations of circuits and

computing load flow for machines

Demonstration models of key electrical technologies

MODELING ELECTRICAL POWER STSTEMS:

With SimPowerSystems, you build a model of a system just as you

would assemble a physical system. The components in your model are connected by

physical connections that represent ideal conduction paths. This approach lets you

describe the physical structure of the system rather than deriving and implementing the

equations for the system. From your model, which closely resembles a schematic,

SimPowerSystems automatically constructs the differential algebraic equations (DAEs)

that characterize the behavior of the system. These equations are integrated with the rest

of the Simulink model.

You can use the sensor blocks in SimPowerSystems to measure

current and voltage in your power network, and you can then pass these signals intostandard Simulink blocks. Source blocks enable Simulink signals to assign values to the

electrical variables current and voltage. Sensor and source blocks let you connect a

control algorithm developed in Simulink to a SimPowerSystems network.

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REFERENCES:

[1] L. Chetty, N. M. Ijumba, and A. C. Britten, Parallel-cascaded tapping station, in

Proc. IEEE Int. Conf. Power System Technology, 2004, pp. 16741878.

[2] H. Rahman and B. H. Khan, Power upgrading of transmission line by combining ac-dc transmission,IEEE Trans. Power Syst., vol. 22, no.1, pp. 459466, Feb. 2007.

[3] A. Ekstrom and P. Lamell, HVDC tapping station: Power tapping from a dctransmission line to a local ac network, inProc. AC-DCConf., London, U.K., 1991, pp.

126131.

[4] Task force on SmallHVDCTaps,Working Group, Integration of small taps into

(existing) HVDC links,IEEE Trans. Power Del., vol. 10, no. 3, pp. 16991706, Jul.

1995.

[5] M. R. Aghaebrahimi and R. W. Menzies, Small power tapping from HVDCtransmission system: A novel approach,IEEE Trans. PowerDel., vol. 12, no. 4, pp.16981703, Oct. 1997.

[6] PSCAD/EMTDC, Users Guide Manitoba-HVDC Research Centre. Winnipeg, MB,Canada, Jan. 2003.

[7] P. S. Kundur, Power System Stability and Control. New York: Mc-

Graw-Hill, 1994.

1 power up gradation

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