Control system in a converter and a method of operating a converter

Patent metadata

Field	Value
Publication number	US-10677219-B2
Application number	US-201815944225-A
Country	US
Kind code	B2
Filing date	Apr 3, 2018
Priority date	Apr 4, 2017
Publication date	Jun 9, 2020
Grant date	Jun 9, 2020

Abstract

A method and a control system adapted to control a power conversion system connected to an AC power grid, wherein the control system is adapted to receive an externally provided reactive power reference and the control system includes a controller adapted to control the reactive power fed to the AC grid by the power conversion system and to produce a reactive current reference, an active current reference, a total current limiter for producing limited active and reactive current references. The total current limiter operates in reactive current priority limiting the active current reference. Further including means adapted to produce a capacity signal indicating the current capacity of the power conversion system. The control system further includes a minimum reactive power reference tracker adapted to generate an internally generated reactive power reference which is adapted to be fed to the controller adapted to control the reactive power fed by the power conversion system to the AC grid, where the minimum reactive power reference tracker is adapted to control the internally generated reactive power reference to a value with which the active current reference is not limited.

First claim

The invention claimed is:

1. A control system adapted to control a power conversion system connected to an AC power grid, wherein said control system is adapted to receive an externally provided reactive power reference and the control system comprises
a controller adapted to control the reactive power fed to the AC grid by said power conversion system and to produce a reactive current reference (Ir_ref), an active current reference (Ia_ref), and a total current limiter for producing limited active and reactive current references (Ia_ref_lim, Ir_ref_lim),
wherein the total current limiter is adapted to operate in reactive current priority limiting the active current reference when the total current composed of reactive current reference and active current reference exceeds a set limit and means adapted to produce a capacity signal (CS) indicating the current capacity of the power conversion system, the capacity signal having a limit value (CS_L),
a minimum reactive power reference tracker adapted to receive the externally provided reactive power reference and the capacity signal, and further adapted to generate an internally generated reactive power reference (Uref 2 ) based on the externally provided reactive power reference, the capacity signal and the limit value set for the capacity signal, which internally generated reactive power reference (Uref 2 ) is adapted to be fed to the controller adapted to control the reactive power fed by the power conversion system to the AC grid,
wherein the minimum reactive power reference tracker is adapted to control the internally generated reactive power reference (Uref 2 ) to a value with which the active current reference is not limited.

2. The control system according to claim 1 , wherein the capacity signal is the total current composed from reactive current reference and active current reference and the limit value (CS_L) set for the capacity signal is the current capacity of the converter.

3. The control system according to claim 1 , wherein the capacity signal is obtained from the amount by which the active current reference is limited and the limit value set for the capacity signal is zero.

4. The control system according to claim 2 , wherein the capacity signal (CS) is obtained from the total current limiter.

5. The control system according to claim 1 , wherein the capacity signal is composed from a I 2 t integral value maintained by a short term current overload controller, wherein said short term current overload controller provides a converter current limit to the total current limiter.

6. The control system according to claim 1 , wherein the capacity signal is a signal indicating the temperature of the converter, estimated current of the converter, measured current of the converter or current reference of the converter, and the limit value set for the capacity signal is such that it prevents over currents of the converter.

7. The control system according to claim 1 , wherein the externally provided reactive power reference is implemented as AC voltage reference (Uref 1 ) and the controller adapted to control the reactive power is implemented as an AC voltage controller adapted to control the grid side AC voltage.

8. The control system according to claim 1 , wherein the minimum reactive power reference tracker is adapted to increase the value of internally generated reactive power reference (Uref 2 ) from the value of the externally provided reactive power reference (Uref 1 ) when the capacity signal exceeds its set limit.

9. The control system according to claim 1 , wherein the minimum reactive power reference tracker is adapted to set the value of the internally generated reactive power reference (Uref 2 ) equal to externally provided reactive power reference if the externally provided reactive power reference is higher than the internally generated reactive power reference.

10. The control system according to claim 1 , wherein the minimum reactive power reference tracker is adapted to increase the value of internally generated reactive power reference (Uref 2 ) in response to the amount of the capacity signal exceeding its set limit.

11. The control system according to claim 1 , wherein the minimum reactive power reference tracker composes an error signal from the capacity signal and its limit value and which is further adapted to feed said error signal into a controller adapted to generate the internally generated reactive power reference (Uref 2 ).

12. A control converter system comprising:
a converter according to claim 1 , wherein the converter system comprises an upper level controller and the internally generated reactive power reference is transmitted to the upper level controller which provides the externally provided reactive power reference.

13. The converter system according to claim 12 , wherein the upper level controller is adapted to modify power reference given to the converter system until the externally provided reactive power reference equals to the internally generated reactive power reference.

14. A method of operating a converter comprising a DC link for receiving power to the converter, wherein the method comprises
receiving an external reactive power reference in the converter,
controlling the reactive power fed to the AC grid and producing a reactive current reference,
obtaining an active current reference,
limiting the active current reference (Ia_ref) when the total current composed of reactive current reference and active current reference exceeds a set limit,
producing a signal indicating converter capacity,
generating an internally generated reactive power reference based on the externally provided reactive power reference, said capacity signal, and
setting the internally generated reactive power reference to a value with which the active current reference is not limited.

15. The control system according to claim 3 , wherein the capacity signal (CS) is obtained from the total current limiter.

16. The control system according to claim 2 , wherein the externally provided reactive power reference is implemented as AC voltage reference (Uref 1 ) and the controller adapted to control the reactive power is implemented as an AC voltage controller adapted to control the grid side AC voltage.

17. The control system according to claim 1 , wherein the minimum reactive power reference tracker is adapted to increase the value of internally generated reactive power reference (Uref 2 ) from the value of the externally provided reactive power reference (Uref 1 ) when the capacity signal exceeds its set limit.

18. The control system according to claim 2 , wherein the minimum reactive power reference tracker is adapted to set the value of the internally generated reactive power reference (Uref 2 ) equal to externally provided reactive power reference if the externally provided reactive power reference is higher than the internally generated reactive power reference.

19. The control system according to claim 2 , wherein the minimum reactive power reference tracker is adapted to increase the value of internally generated reactive power reference (Uref 2 ) in response to the amount of the capacity signal exceeding its set limit.

20. The control system according to claim 2 , wherein the minimum reactive power reference tracker composes an error signal from the capacity signal and its limit value and which is further adapted to feed said error signal into a controller adapted to generate the internally generated reactive power reference (Uref 2 ).

Assignees

• Abb Technology Oy
• Abb Schweiz Ag

Inventors

• Muszynski Peter
• Huju Kalle
• Tamminen Jussi
• Vilhunen Antti
• Virta Antti

Classifications

• Y02E10/723

  Cross-Sectional Technologies · mapped topic

• Y02E10/563

  Cross-Sectional Technologies · mapped topic

• F03D7/048

  controlling wind farms · CPC title

• F05B2270/337

  Electrical grid status parameters, e.g. voltage, frequency or power demand · CPC title

• H02M5/458

  using semiconductor devices only · CPC title