2/10/2016 Modeling and Simulation of D­STATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra ­ Academia.edu

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Modeling and Simulation of D­STATCOM for Voltage

Regulation Imparting VariousControl Strategies

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 National conference on Trends & Challenges in Applied Science and Engineering

21-22 Jan 2014 SATI Vidisha (M.P)

Abstract  —   This paper describes the modeling, controlling and

simulation of Distributed static synchronous compensator

(DSTATCOM). It is important for a distribution system to have

controllability, voltage stability and good power transfer

capability. Here, voltage source converter based d-statcom

achieves voltage regulation in the system by absorbing or

supplying the required reactive power. The system is modeled

using various control strategies like direct and indirect control

which includes D-Q transform. The comparative analysis of the

control strategies has been done. The results of simulation are

demonstrated and analyzed using MATLAB.

I ndex Terms  —   reactive power compensation, DSTATCOM,

dq-model, phase shift, voltage control, VSC.

I.  INTRODUCTION

He rapidly developing power electronics technology providesan opportunity for developing new power equipment for

improving the performance of the power system. Flexible AC

Transmission system technology (FACTS) uses the latest powerelectronic devices and methods to control electronically the high-voltage side of the network. FACTS devices can be used for

 power flow control, voltage regulation, transient stability

improvement, and damping of power oscillations. FACTS devicescan be of shunt or series or combination of shunt and series types.The shunt devices can be used for voltage regulations, while seriesdevices can be used for regulation of line impedance and series -

 parallel combination can be used for real and reactive powercompensation in addition to regulation of voltage and regulation ofline impedance [1]

The f a m i l y of e m e r g i n g power electronic devices

 being offered to achieve these custom power objectives is: (i)

Distribution Static Compensator (DSTATCOM) that protects the

distribution system from the effects of fluctuating voltage, voltage

sags and swells and non-linear loads, (ii) DVR that protects a

critical load from disturbances like sags, swells, transients and

harmonics originating on the interconnected distribution system,

(iii) Unified Power Quality Conditioner (UPQC), a combination of

series and shunt controller, which compensates supply voltage

and load current imperfections in the distribution system.

The DSTATCOM is a versatile device for providing reactive

 power compensation in ac networks. The control of reactive

 power is achieved via the regulation of a controlled voltage

source behind the leakage impedance of a transformer [2]. It is

similar to a conventional synchronous compensator, which is

essentially a synchronous generator where the field current is used

to adjust the regulated voltage. The DSTATCOM uses voltage

source converter (VSC) to achieve the regulation task. When used in

low or medium voltage distribution systems the STATCOM is

normally identified as Distribution STATCOM (D-STATCOM). It

operates in a similar manner as t h e STATCOM (FACTS

controller), with the active power flow controlled by the angle

 between the AC system and VSC voltages and the reactive

flow controlled by the difference between the magnitudes of these

voltages. As with the STATCOM, the capacitor acts as the energy

storage device and its size is chosen based on power ratings, control

and harmonics considerations. The D-STATCOM controller

continuously monitors the load voltages and currents

determines the amount of compensation required by the AC system

for a variety of disturbances.

The DSTATCOM is a shunt device. It should therefore be ableto regulate the voltage of a bus to which it is connected. The operating

 principle of a DSTATCOM in this mode has been termed DSTATCOM in voltage control mode. This report shows that even

though the structure of DSTATCOM used in both current control andvoltage control modes is the same, its operating principle is different.In the current control mode it is required to follow a set of reference

currents while in the voltage control mode it is required set of reference voltages. This paper discusses the reference voltage

generation scheme and the control of DSTATCOM in the voltagecontrol mode. 

II.  BASIC CONFIGURATION OF D-STATCOM

The D-STATCOM system comprises of a VSC, a set of

coupling reactors (leakage reactances of the transformer) and a

controller. The D-STATCOM generates a controllable ac voltage

from the voltage source inverter (VSI) connected to a dc capacitor

(energy storage device). The ac voltage appears behind the

transformer leakage reactance.

Fig.1 Basic Block Diagram of D-STATCOM

The active and reactive power transfer between the power system

and the D-STATCOM is caused by the voltage difference across

this reactance. The D-STATCOM is connected to the power network

at the point of common coupling (PCC), where the voltage-quality

 problem is a concern. All required voltages and currents

measured and are fed into the controller to be compared with the

reference. The controller then performs feedback control and

Modeling and Simulation of D-STATCOM for Voltage

Regulation Imparting Various Control Strategies

Dhananjay Kumar, Nupur Jejurikar and Pradyumn Chaturvedi

Electrical Engineering Department, SATI, Vidisha (MP), India-464001

djaydelhi@gmail.com, pc220774@gmail.com , n28388@yahoo.co.in 

T

 

 National conference on Trends & Challenges in Applied Science and Engineering

outputs a set of switching signals to drive the main semiconductor

switches (IGBTs) of the power converter accordingly [3]. The basic

IV.  MODELING OF DSTATCOM

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2/10/2016 Modeling and Simulation of D­STATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra ­ Academia.edu

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21-22 Jan 2014 SATI Vidisha (M.P)

switches (IGBTs) of the power converter accordingly [3]. The basic

diagram of the D-STATCOM is illustrated in figure 1.

III.  PRINCIPLE OF DSTATCOM

D-STATCOM is to suppress voltage variation and control reactive

 power in phase with system voltage. It can compensate for inductive

and capacitive currents linearly and continuously. Figure 2 shows

the vector diagram at the fundamental frequency for capacitive and

inductive modes and for the transition states from capacitive to

inductive and vice versa. The terminal voltage () is equal to the

sum of the inverter voltage () and the voltage across the

coupling transformer reactive VL in both capacitive and

inductive modes. I mean that if output voltage of

DSTATCOM () is in phase with bus terminal voltage () and

()  is greater than   D-STATCOM provides reactive power to

system.And if   is smaller than , D-STATCOM absorbs reactive

 power from power system.    and   have the same phase, butactually they have a little phase difference to component the loss oftransformer winding and inverter switching, so absorbs some real

 power from system.

Figure 2 is DSTATCOM vector diagrams, which show inverteroutput voltage VI, system voltage VT, reactive voltage VL and line

current I in correlation with magnitude and phase δ. Figure 2.a and bexplain how VI  and VT  produce capacitive or inductive power bycontrolling the magnitude for inverter output voltage VI in phase with

each other.

Figure 2: Vector diagram of DSTATCOM(a) Capacitive mode, (b) inductive mode

Fig.3 Simplified single line diagram of D-STATCOM

Rf ia + Lf dia/dt = Vsa-Vca (1)

Rf ib + Lf dib/dt = Vsb – Vcb (2)

Rf ic + Lf dic/dt = Vsc – Vcc (3)

Here,Vsa, Vsb, Vsc : Voltage at the PCCVca, Vcb ,Vcc : Inverter output voltage

Lf : Filter inductanceRf : Equivalent filter resistanceC : DC Link capacitor

*Designing a)  Qstat= √3 V Ic

 b) Vdc= 2√2 V /√3mac) Lac= (√3ma Vdc)/ 12a fs I(statp-p)

d) Capacitor designingCdc= 3Vs ΔIL T/(Vdc^2 –  Vdc1^2)

Here,Ic =dstatcom line current

V= line voltageMa= modulation indexVdc = dc link voltageQstat= power rating

V= line voltageLac = ac inductor

a= over current factor (1.2)

*Park’s transformation:-

This block performs the abc to dq0 transformation on a set of three-

 phase signals. It computes the direct axis Vd, quadratic axis zero sequence V0 quantities in a two axis rotating reference frameaccording to the following transformation:The following transformation is used:

Vd=2/3*[Va*sin(wt)+Vb*sin(wt-2pi/3)+ Vc*sin(wt+2pi/3)]Vq=2/3*[Va*cos(wt)+Vb*cos(wt-2pi/3)+Vc*cos(wt+2pi/3)]V0 = 1/3*[Va + Vb + Vc]

Where w= rotation speed (rad/s) of the rotating frame.

This transforms three quantities (direct axis, quadature axis and zero-sequence components) expressed in a two axis reference frame back

 phase quantities.

 

 National conference on Trends & Challenges in Applied Science and Engineering

The following transformation is used:

Va = [Vd*sin(wt) + Vq*cos(wt) + Vo ]

Vb = [Vd*sin(wt-2pi/3) + Vq*cos(wt-2pi/3) + Vo)Vc = [Vd*sin(wt+2pi/3) + Vq*cos(wt+2pi/3) + Vo)where w= rotation speed (rad/s) of the rotating frame.

V.  CONTROL STRATEGIES 

Satisfactory performance, fast response, flexible and easy

implementation are the main objectives of any compensationStrategy .the control strategy of DSTATCOM are mainly implementedin the following steps[4],[5]:*Measurements of system variables and signal conditioning.*Extraction of reference compensating signals.

*Generation of firing angles for switching devices.

  Phase shift control

In this control algorithm the voltage regulation is achieved in a D-STATCOM by the measurement of the rms voltage at the load

 point and no reactive power measurements are required. Fig.4shows the block diagram of the implemented scheme (4)

Since vq=0, id and iq completely describe the instantaneous value ofreal and reactive powers produced by the DSTATCOM when thesystem voltage remains constant. Therefore the instantaneous three

 phase current measured is transformed by abc to dqo transformation.The decoupled d- axis component id and q axis component iq areregulated by two separate PI regulators. The instantaneous idreference and the instantaneous iq reference are obtained by thecontrol of the dc voltage and the ac terminal voltage measured.Thus, instantaneous current tracking control is achieved using foPI regulators. A Phase Locked Loop (PLL) is used to the control loop to the ac supply so as to operate in the adqo reference frame.

2/10/2016 Modeling and Simulation of D­STATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra ­ Academia.edu

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21-22 Jan 2014 SATI Vidisha (M.P)

shows the block diagram of the implemented scheme (4)

Fig.4. Block diagram of phase shift control

Sinusoidal PWM technique is used which is simple andgives a good response. The error signal obtained by comparing themeasured system rms voltage and the reference voltage, is fed to a

PI controller which generates the angle which decides thenecessary phase shift between the output voltage of the VSC and theAC terminal voltage. This angle is summed with the phase angle ofthe balanced supply voltages, assumed to be equally spaced at 120

degrees, to produce the desired synchronizing signal requiredto operate the PWM generator. In this algorithm the D.C. voltage ismaintained constant using a separate dc source.

  Decoupled current control p-q theory

This algorithm requires the measurement of instantaneous

values of three phase voltage and current. Fig.5. shows the blockdiagram representation of the control scheme. The compensation isachieved by the control of id and iq. Using the definition of theinstantaneous reactive power theory for a balanced three phase three

wire system, the quadrature component of the voltage is always zero,the real (p) and the reactive power (q) injected into the system bythe DSTATCOM can be expressed under the dq referenceframe as:

P = Vd Id + Vq Iqq = Vq Id - Vd Iq

Fig.5. block diagram of decoupled theory based control ofD-STATCOM

VI.  SIMULATION RESULTS

In this work, the performance of VSC based power devices

acting as a voltage controller is investigated.

  Phase shift control

It does not have a self supporting dc bus and requires aseparate dc source to pre-charge the dc side capacitor & maintain

its voltage during the operation of D-STATCOM .It assumes the supply side voltage is balanced and without harmonics, sincefundamental wave form is used to obtain the phase angles supply wave form.  There is no provision for harmonic suppression

in case the load connected to PCC is nonlinear. This method results

in generation of active power by the VSC along with the var.

Fig.6. Simulink model for phase shift control

 

 National conference on Trends & Challenges in Applied Science and Engineering

.

Source voltage

DC voltage

Inverter voltage

Compensated output voltage and current

Fig.6 Simulink model for decoupled current control

Source voltage

Load current

0 1000 2000 3000 4000 5000 6000 7000 8000 9000-400

-300

-200

-100

0

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TIME(SEC)

  s  o  u  r  c  e  v  o   l   t  a  g  e

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0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-800

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   V   d  s   t  a   t  c  o  m

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-400

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time(sec)

   l  o  a   d  v  o   l   t  a  g  e ,

   l  o  a   d  c  u  r  r  e  n   t

  IL

VL

0 500 1000 1500 2000 2500 3000 3500 4000 -400

-300

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time(sec)

   s   o   u   c   e 

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1000 2000 3000 4000 5000 6000 7000 8000 -100

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time(sec)

   l   o   a   d 

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   d  c 

   l   i  n   k 

  v  o   l   t  a  g  e   (  v   )

Modeling and Simulation of D­STATCOM for Voltage Regulation Imparting Various Contro… DOWNLOAD

2/10/2016 Modeling and Simulation of D­STATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra ­ Academia.edu

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21-22 Jan 2014 SATI Vidisha (M.P)

  Decoupled current control

The advantageous features of this scheme are:

It incorporates a self supporting dc bus. The active and reactive power control achieved through id and iq control are decoupled from

each other. The dc bus control/ regulation are decoupled from the

ac bus control like voltage regulation or power factor correctionand load  balancing. 

Switching of devices of VSC is done at fixed frequency. Thus

switching losses can be limited within the rating of the devices.

  This type of control is inherently linear & robust and uses PI or

PID controls.

DC voltage

SPWM technique

0 5000 10000 0

100

200

time(sec)

5000 5020 5040 5060 5080 5100 5120 -3

-2

-1

0

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2

3

time(sec)

  v  o   l   t  a  g  e

 

 National conference on Trends & Challenges in Applied Science and Engineering

VII.  CONCLUSION

Detailed modeling is presented and results are discussed withdifferent control studies. These Power devices provide solutions

to power quality at the medium and low voltage distributionnetwork level. This project presents the detailed modeling of one ofthe custom power products, DSTATCOM is presented usinginstantaneous P-Q theory and phase shift theory used for the

control of DSTATCOM are discussed. These control algorithmsare described with the help of simulation results under linear loadsand nonlinear loads. It was observed that undersized capacitordegrades all three aspects. On the other hand, an oversizedcapacitor may also lead to a PWM control with a sluggish

response but it will reduce D- STATCOM harmonic generationand transient overshooting. It is concluded that a DSTATCOMthough is conceptually similar to a STATCOM at the transmissionlevel; its control scheme should be such that in addition to complete

reactive power compensation, power factor correction and voltageregulation the harmonics are also checked, and for achievingimproved power quality levels at the distribution end.

S.no.

PARAMETERS

PHASE

SHIFT

CONTROL

DECOUPLED

CURRENT

CONTROL

1. Reactive powercompensation

Average Partial

2. Performance undernonlinear loads

Containsundesiredharmonics

 Not Satisfactory

3. Applicable for single phase systems

Yes No

4. Harmonic

compensation

less average

5. PWM switchingfrequency

fixed Fixed

6. Self supporting DC bus

 No Yes

7. Generation of firing

 pulses

Sine PWM Sine PWM

8. Power factor .8 to.97(linear)

.8 to .94(linear)

.8 to

.92(nonlinear)

.8 to

.95(nonlinear)

9. Response time less More

10. Control scheme easy complex

VIII.  FUTURE WORK

  This project presents a detailed modeling and analysis ofone of the custom power device DSTATCOM.Instantaneous Decoupled Current Control or instantaneous

 p-q theory and phase shift control is discussed and verifiedthrough detailed simulations by developing the models inMATLAB simulink using the sim power system control tool

 boxes. Now we are posing a challenge to complete If the

remaining control strategies which includes the synchronousframe theory, regulation of Bus and DC link voltage, andANN based Adaline theory .these control strategies are

implemented and studied in detail through varioussimulations then it would be of immense help for the realtime implementation of the DSTATCOM across all over the

globe.  If thrown light on other custom power devices like the

Dynamic voltage Regulator (DVR), and Unified powerquality conditioner (UPQC), applying different strategies

then we can bring a revolution in the control of power in thedistribution systems.

REFERENCES

[1] N. Hingorani, “FACTS — Flexible ac transmission systems

 IEE 5th Int. Conf. AC DC Transmission, London, U.K., 1991, Conf. Pub.

345, pp. 1 – 7.

[2] P. Lehn and M. Iravani, “Experimental evaluation of STATCOM

closed loop dynamics,”   IEEE Trans. Power Delivery, vol. 13, pp.

1378 – 1384, Oct. 1998.

[3] “Introducing custom power,”  IEEE Spectrum, vol. 32, pp. 41

1995.

[4] “Control Algorithms for Distribution Static Compensator 

Masand, Shailendra Jain and Gayatri Agnihotri and Maulana AzRad

Dept. Of Electrical Engineering National Insti tute of Technology, Bho

(MP), India.

[5] “A comparative study of Control algorithms

DSTATCOM for load compensation”  by Bhim Singh, Department

of Electrical Engineering, Indian Institute of Technology ,Hauz Khas ,

 New Delhi .

[6] Pierre Giroux, Gilbert Sybille and Hoang Le-Huy,

and Simulation of a Distribution STATCOM using

Power System Block set,” IECON’01: the 27th Annual Conference of the

IEEE Industrial Electronics Society, 2001.

[7] D.Masand, S.Jain and G.Agnihotri, “Distribution Static

Compensator Performance under Linear and Nonlinear Current

Regulation Methods” J. Electrical System 4-1 (2008): pp.91-105.

2/10/2016 Modeling and Simulation of D­STATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra ­ Academia.edu

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