in the clustered PV condition system.pdfProblems in the clustered PV condition 1166 p Overvoltage beyond the limit of PEA regulation due to clustered PV may occur in the following

Establishing solutions to technical problems on grid connection in the clustered PV condition

Aug 17, 2006 The Kansai Electric Power Co., Inc. , Fuji Electric Systems Co., Ltd. and

Photovoltaic Power Generation Technology Research Association

Challenges for the Project (1)

1. Possibility of islanding prevention 1. Possibility of islanding prevention malfunction could be increasing malfunction could be increasing in clustered PV system. in clustered PV system.

2. Over voltage due to reverse power flow 2. Over voltage due to reverse power flow by a large number of PV could limit PV output. by a large number of PV could limit PV output.

Technical problems on grid connection Technical problems on grid connection

We develop new methods solving these We develop new methods solving these subjects on both islanding prevention and subjects on both islanding prevention and voltage control. voltage control.

2 2

What is the clustered PV condition?

……

Customer connecting to the utility grid at higher voltage (eg.22kV)

Customer connecting to the utility grid at lower voltage (eg.400V)

The power utility’s substation

Distribution line

3 3






4 4

What is the islanding condition?

breaker

Open

Private generator

Customer Generator PEA system

“Islanding” : The condition in which a portion of the utility network including both loads and generations is isolated from the remainder of the network and keeps functioning solely.

5 5

Islanding have to be prevented.

breaker

Open

Generator PEA system

M3~

Electrocution Electrocution of the public !! of the public !!

Voltage and frequency Voltage and frequency not controlled properly not controlled properly

Damage on the Damage on the distributed resource distributed resource equipment equipment because of because of out out of phase re of phase re closure closure

Private generator

Customer

6 6

AntiIslanding is required for grid interconnection of VSPP

Thailand Japan Islanding condition Not Allowed Not Allowed

Islanding prevention method

IEEE929 IEC1727

Japan standard . . . . . .

JET

Inverter must be antiislanding type as per IEEE 929 or equivalent

7 7

An Example of Conventional Active Methods for Islanding Detection

ID

PV

Main Grid

V Q

ｔ

▼Island Formed

Cease power conversion

Continuous reactive power variation

No voltage fluctuation because reactive power from inverters are absorbed into the main grid

Reactive Power Variation method Reactive Power Variation method

Q

1

2

3

5

4 Voltage fluctuation in islanding grid

8 8

The Conventional Methods have possibilities of detection failure

ID

PV

Q ID

PV Q

t

Q

t

V In clustered PV system

t

Main Grid

▼Island Formed

▼Island Formed

▼Island Formed

Signals (reactive power fluctuation) from the multiple islanding detector (ID) could act to cancel each other , resulting detection failure.

9 9

CH8

-2

0

2

4

6

-1 0 1 2 3 4 5

CH2

-1

0

1

2

3

4

5

-1 0 1 2 3 4 5

CH8

-2

0

2

4

6

-1 0 1 2 3 4 5

FREQUENCY

49 49.2 49.4 49.6 49.8

50 50.2 50.4 50.6 50.8

51

-1 0 1 2 3 4 5

We succeeded to catch interference phenomena in clustered PV condition using the actual PV system.

Phase signal of PCA

Phase signal of PCB

System Frequency

Detection signal of Active ID

Reverse phase.

Frequency fluctuation is little.

No detection.

Islanding is formed.

10 10 1. Possibility of islanding prevention malfunction in clustered 1. Possibility of islanding prevention malfunction in clustered PV system. PV system.

We have developed new islanding detector without possibility of malfunction even in the clustered PV condition.

Load

[Hz]

utility’s grid

Islanding grid

Substation

ID

Customer

Load

Islanding Grid

Frequency

Ｇｅｎ

Ｔｉｍｅ

Adm

ittance

Islanding formed

Adm

ittance


[sec]

islanding formed

Our ID could definitely detect islanding condition at 0.10 second by 7 th admittance variation.

Time（ｍｓ）

<5 th >

Admittance

Detection Detection

<7 th >

Admittance variation

Activation signal

islanding formed

Time（ｍｓ）

Threshold 0.3

And We have verified that the newly developed ID can detect islanding condition even in the clustered PV.







13 13

Overvoltage is said to occur at the end of distribution line in the clustered PV network.

14 14

……

The power utility’s substation

Voltage at the end of distribution line becomes higher and may cause equipment damage

Voltage at the end of distribution line becomes higher and may cause equipment damage

We have confirmed that overvoltage may occur at the end of distribution line under the condition where a large amount of PV installed on the very long distribution line.

15 15

O A B C D E F G 1.00pu

1.02pu

1.04pu

1.06pu

1.08pu

1.10pu

Voltage profiles of distribution network, which have distribution line of L L between 2 PVs and have 7 PVs whose outputs are about 0.35pu(7kW).

I

II

III

PEA regulation for 400V

L L

2. Over voltage in clustered PV could limit PV output. 2. Over voltage in clustered PV could limit PV output.

L=100m, P=7kW

O A B C D E F G

PC1 PC2 PC3 PC4 PC5 PC6 PC7

L=60m, P=7kW

L=40m, P=7kW

L L L L L L L L L L L L

P P P P P P P P P P P P P P

Problems in the clustered PV condition 16 16

p Overvoltage beyond the limit of PEA regulation due to clustered PV may occur in the following situation

1) In case there are total about 50kW (7*7kW) PV on the distribution line of total 700m (7*100m) in 400V system.

It is necessary to develop the voltage controller.

The overvoltage may give influences to the electric devices of electric customers.

As countermeasures of the overvoltage, both of OVR and voltage mitigation function are equipped in the

present power conditioner.

17 17

2) Trip (Stop generation) by Over Voltage Relay

1) Power cut by voltage mitigation function

Time

Output (voltage)

Time

Output (voltage)

Loss of energy

Loss of energy

If voltage mitigation function can not work properly.

Problems of the conventional voltage control by the voltage mitigation function of PC.

18 18

Upper limit voltage

Power cut Power cut (=power generation loss). (=power generation loss).

V A V B V F V G

O A B F G

PC1 PC2 PC6 PC7

….

….

Problem1. Output power cutting results in loss of the solar energy.

Problem2. The quantities of power cuttings are different by the connecting points of PVs. That means that the PV connecting to the end of distribution line has less chance of full generation than the others.

Output power of the PV inverter restrained by voltage mitigation function

Power generation capacity of the PV inverter

Connecting point to the utility’s grid

We have suggested two types of voltage control system as countermeasures against the problems.

19 19


Problem2. The quantities of power cuttings are different by the connecting points of PVs.

Development of the new voltage control using battery.

Development of the voltage control system by integrated monitoring and control

We have developed new voltage control system using Battery.

20 20

Time

Output (voltage)

Loss of energy

P output from PV using the conventional voltage mitigation function.

Time

Output (voltage)

Charge to the battery

Expected P output from PV + Battery system which is newly developed.

Discharge from the battery No loss of energy!! No loss of energy!!

Check voltage

Output control

Charge / discharge control

PV PV Battery

System Voltage

380

390

400

410

420

430

440

12:00:00 15:00:00 18:00:00 Time

Sys

tem

Voltag

e(V

) We have developed new voltage control system using battery and found that it can increase the system output energy by 10kWh.

21 21

P output

0

5000

10000

15000

12:00:00 15:00:00 18:00:00 Time

PC

outp

ut

(W)

PV generation capability

Restrained power output by conventional control

PV + Battery system output

Charged by Battery

Discharged from Battery

System voltage is high.

System voltage is low.

System voltage can keep under its cap over almost all duration,

2. Over voltage in clustered PV could limit PV output. 2. Over voltage in clustered PV could limit PV output.

We have suggested two types of voltage control system as countermeasures against the problems.

22 22

Development of the new voltage control using battery.

Development of the voltage control system by integrated monitoring and control


Problem2. The quantities of power cuttings are different by the connecting points of PVs.

O A B F G

PC1 PC2 PC6 PC7

….

Development of the new voltage control method by integrated monitoring and control of PV system ICS shall calculate the optimal active and reactive power output value for each PVPC, using system voltage profile and/or power flow profile which are measured at various points in the grid and are collected via communication infrastructure, and control the output of each PVPC. Targets:

(1) Mitigation of overvoltage. (2) The equalization of the power generation efficiency.

Integrated control system (ICS).

Communication

PV output suppression PV output suppression (=power generation loss). (=power generation loss).

V A V B V F ….

Output power of the PV inverter restrained by voltage mitigation function

Power generation capacity of the PV inverter

Connecting point to the utility’s grid

V G

23 23

Simulation results when the PV inverters control grid voltage individually.

24 24

①Irradiance[kW/m 2 ]

②Grid voltage(V)[pu]

③PV inverter active power output(P)[pu]

④PV inverter reactive power output(Q)[pu]

⑤Power factor(Pf)

Upper limit voltage:1.05pu (=420V)

PV3 PV3 PV6 PV6 PV7 PV7

The PV inverter makes each terminal voltage proper with the “P+Q control”.

Power cut

In the daytime, PV7 can’t generate electric power.

6:00 19:00 12:00 6:00 19:00 12:00 6:00 19:00 12:00

Leading power factor operation. (Pf≧0.85)

2006.05.23

Demonstration results of the function of the voltage control system which we have developed.

25 25

PV3 PV3 PV6 PV6 PV7 PV7

Each grid voltage is properly maintained by “ICS”. Each grid voltage is properly maintained by “ICS”.

①Irradiance[kW/m 2 ]

②Grid voltage(V)[pu]

③PV inverter active power output(P)[pu]

④PV inverter reactive power output(Q)[pu]

⑤Power factor(Pf)

System maintenance.


PV Power cut

System maintenance.


PV Power cut PV Power cut

6:00 19:00 12:00 6:00 19:00 12:00 6:00 19:00 12:00

ICS execution.

2006.05.23

Upper limit voltage:1.05pu (=420V)

Unfairness, which we can see in case of individual control, has been dissolved by adopting integrated control system.

26 26

Integrated control systems(ICS). (Experimental result)

Individual control by each PV inverter. (Simulation result)

The power generation efficiency is unequal. The power generation efficiency is equal.

The customer connecting to the end side of the distribution line

are unprofitable .

Eliminated PV output. (=power generation loss.)

27 27 Conclusion Conclusion

> We have obtained significant results which will contribute to introduction of further PV systems in both of Thailand and Japan.

The End

Thank you!

Documents

in the clustered PV condition system.pdfProblems in the clustered PV condition 1166 p Overvoltage beyond the limit of PEA regulation due to clustered PV may occur in the following