combined inverter and oltc control in pv parks

of y 04.12.2018 Combined Inverter and OLTC control in PV parks CTC Mr Nilakantan I I I

COMBINED INVERTER AND OLTC

CONTROL IN PV PARKS An enhancement in capacity and efficiency

04.12.2018, CTC Mr Nilakantan


Yesterday‘s grids Tomorrow‘s grids

I Transmission grid: Frequency stability and thermal capacitance

I Distribution grid: Voltage control Challenges

CHALLENGES ARISE FROM MORE VARYING POWER FLOWS IN

OUR GRIDS


+10 %

+5 %

0 %

-5 %

-10 %

Dev

iati

on

fro

m r

ated

vo

ltag

e (i

n %

)

Medium voltage grid

Secondary

substation Low voltage grid

Maximum

feed-in case

Maximum

load case

Regulation

„downwards“

Regulation

„upwards“

1. VOLTAGE REGULATED DISTRIBUTION TRANSFORMERS

ALLOW INTEGRATION OF MORE RENEWABLES AND LOADS

20 kV 0.4 kV 0.4 kV 20 kV

Outside of allowed voltage band

Outside of allowed voltage band


APPLICATION SHOWCASES OF VRDT IN THE GRID

Selective use of VRDTs with a focus on the

LV grid Feeder-based use of VRDTs with a

focus on the MV grid

Use in all parts of the grid of VRDTs with a focus on the MV grid


FINANCIAL IMPACT OF THE TECHNOLOGY FOR THE

INTEGRATION OF RENEWABLES IS ENORMOUS

Source: Moderne Verteilernetze für Deutschland“(Verteilernetzstudie), Study for the Federal Ministry of Economics and Technology (BMWi), September 2014


VOLTAGE REGULATED DISTRIBUTION TRANSFORMER

IITM SHOWCASE SIMULATION

PV

=3~

PV

=3~

PV

=3~

PV

=3~

PV

=3~

CP1 CP2 CP3 CP4 CP5

PV

=3~

PV

=3~

PV

=3~

PV

=3~

PV

=3~

CP1 CP2 CP3 CP4 CP5

Schematic sketch of reference grid Load parameters of grid connection points

Increase in headroom in % for additional in-feed of renewable energy due to the effect of

utilization of VRDT

Technical paper presented at the ISGF Utility week 2017

This World-proven and validated technology would be utilized for a showcase implementation

during the field trial project of Islanded microgrids under IGCS research programme (applied for

UAY funding)


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 1000 2000 3000 4000 5000 6000 7000 8000

P [nominal power solar inverter]

annualy hours of operation

Annually load duration curve solar park

Leistung Park unterdimensioniert

P_PV_über (Park) [W]

P_PV_1zu1 (Park) [W]

DIMENSIONING OF THE COMPONENTS:

SOLAR GENERATOR IN RELATION TO SOLAR INVERTER

≈

<

>

Limitation to the nominal power delivered by the solar inverter enhanced by the use of OLTC

I The dotted line is not

reachable, since the Solar

inverter capacity is not

sufficient


INFLUENCE OF THE OLTC TO SOLAR INVERTER

DIMENSIONING

IAC [A]

UAC [V]

Example for operational range of an inverter

UAC variation

I max inverter

I Voltage axis limited by the

dielectric strength of the inverter

components

As the solar inverter unit is connected to the grid, the

grid voltage is allowed to vary +/- 10% at the inverter

I Current axis limited by the

current carrying capacity

of the inverter components



DIMENSIONING

IAC [A]

UAC [V]

Example for operational range of an inverter

UAC min

without OLTC: P max = UAC min x I max inverter

P max ̴ red area

I max inverter

I For the dimensioning of the solar

park the worst voltage situation

has to be considered



DIMENSIONING

I The application of an OLTC

increases the power transfer

capability of the same inverter

hardware

(from red area to blue area)


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 1000 2000 3000 4000 5000 6000 7000 8000

P [nominal power solar inverter]

Hours

Load duration curve of the park during a year

BENEFIT OF INNOVATIVE CONTROL APPROACH

a

b

+7% energy yield

with OLTC control

concept

a

b

energy yield

without OLTC

control

concept

>


COSTS OF INVERTER

I Cost savings occur in inverter manufacturing if the AC side of the inverter could be designed for

a lower output current by using OLTC control

I In our case study, the current carrying capacity of the AC side of the inverters could be reduced

by about 13 %.

I AC Side contributes approx. 75% of inverter costs.

I This leads to 13% * 75% = 9.75% reduction of the total cost of the inverter.

I Result: The Levelized Costs of Energy (LCOE) are reduced significantly. (about 10%)


STANDARDS PROVIDED BY VDE/FNN

F02125:00

I 160 kVA to 2,250 kVA (10 kV with delta

connection on high-voltage side), to 4,500 kVA

(20 kV with delta connection on high-voltage

side)

I Short circuit voltage – 4%,6%

I No. of tap change operations – 700,000

I No. of taps – 5,7 or 9 taps with up to 3% per tap

I Step voltage: 600V / step

I Communication protocols IEC 60870-5-104 and

MODBUS TCP

I Type tests: Transformer type-tested to IEC 60076

, On-load tap-changer type tested to IEC 60214

Technical Specifications


BENEFITS OF USING VACUUM TYPE OLTC TO DIFFERENT

STAKEHOLDERS

Transformer manufacturer Utility / solar park operator

I No maintenance

I Enhanced transformer availability

I The dynamic nature of distributed

generation needs more switching

operations. This flexibility of not changing

the OLTC frequently is provided by

Vacuum type

I Increases the transmitting capability of

the inverters

I High economic benefits due to lack of

need for maintenance as well as more

power flow

I Influential in sizing of new solar parks

I Caters to future requirements

Benefits of

Vacuum OLTC

Vacuum type OLTC needs to be mentioned as a requirement in the specifications

considering the advantages and this, being a pilot showcase for other projects to follow.

combined inverter and oltc control in pv parks

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