Advanced static var compensator control system

• US 5,329,221 A
• Filed: 08/12/1992
• Issued: 07/12/1994
• Est. Priority Date: 08/12/1992
• Status: Expired due to Term

• Current Assignee: Electric Power Research Institute
• Original Assignee: Electric Power Research Institute
• Inventors: Schauder, Colin D.
• Primary Examiner(s): Voeltz, Emanuel T.
• Application Number:
  US07/928,971
• Time in Patent Office: 699 Days
• Field of Search: 323/207, 323/212, 363/64, 363/131, 363/132, 363/97, 363/98
• US Class Current: 323/207
• CPC Class Codes: G05F 1/70 Regulating power factor; Regulating reactive current or power

Abstract

An advanced static VAR (volt ampere reactive) compensator (ASVC) system for coupling with and compensating a transmission line of a power system includes an ASVC controller. A voltage-sourced inverter has an AC side coupled through a series inductance to the transmission line, and a DC side coupled to a capacitor. By monitoring the DC side voltage, two line-to-line voltages and two line currents between the series inductance and the transmission lines, the ASVC controller determines an instantaneous reactive current component of the line current. The ASVC controller adjusts the phase angle of the inverter AC output voltages to compensates the transmission line by negating the instantaneous reactive current, and thus, the undesirable instantaneous reactive power on the transmission line. A method is also disclosed of compensating the instantaneous reactive power flowing over the transmission line.

Claims

1. An advanced static VAR compensator system for coupling to an AC power line for compensating reactive power losses of the line, the control system comprising:

a voltage sourced inverter having a DC side and an AC side for coupling to the line, the inverter responsive to an inverter phase angle control signal for drawing a selected magnitude of reactive power from the line;

a series inductance coupled to the AC side of the inverter for coupling the inverter to the line;

a voltage supporting device coupled to the DC side of the inverter;

a DC voltage sensor apparatus for monitoring a DC voltage across the voltage supporting device;

an AC parameter sensor apparatus coupled between the inverter and the line for monitoring an electrical characteristic, including AC current, therebetween; and

a controller responsive simultaneously to the monitored AC current and DC voltage for generating an instantaneous reactive current signal and for generating in response thereto the inverter phase angle control signal.

2. An advanced static VAR compensator system according to claim 1 wherein the controller is responsive to the DC voltage sensor for generating a dynamic inverter phase angle control signal for dynamically controlling the inverter.

3. An advanced static VAR compensator system according to claim 2 wherein the controller is responsive to the DC voltage sensor and the instantaneous reactive current signal for synthesizing a dynamic stabilizing feedback signal and for generating in response thereto the inverter phase angle control signal.

4. An advanced static VAR compensator system according to claim 1 wherein the AC parameter sensor apparatus comprises:

a pair of AC voltage sensors for monitoring two line to line voltages of the AC power line; and

a pair of AC current sensors for monitoring two phases currents flowing between the inverter and the line when coupled therewith.

5. An advanced static VAR compensator system according to claim 4 wherein the pair of AC voltage sensors monitor two line to line at the line side of the series inductance.

6. An advanced static VAR compensator system according to claim 4 wherein the controller comprises:

a input portion responsive to the pair of AC voltage sensors and the pair of AC current sensors for generating the instantaneous reactive current signal to be synchronized with the line voltage;

a comparator portion responsive to the instantaneous reactive current signal and an instantaneous reactive current reference signal for generating a first error signal; and

an output portion responsive to the first error signal and the DC voltage sensor for generating the inverter phase angle control signal.

7. An advanced static VAR compensator according to claim 1 wherein the series inductance comprises the inductance of a coupling transformer for coupling the inverter to the line.

8. An advanced static VAR compensator system according to claim 1 wherein the voltage supporting device comprises a capacitor.

9. An advanced static VAR compensator system according to claim 1 wherein the voltage sourced inverter comprises a simple inverter having only phase angle control capability.

21. An advanced static VAR compensator controller system according to claim 1 wherein the controller is responsive vectorially to the monitored AC current and DC voltage on an instantaneous basis for generating the inverter phase angle control signal.

22. An advanced static VAR compensator system according to claim 1 wherein the controller is responsive to the monitored AC current and DC voltage on an instantaneous basis in a nonlinear fashion for generating the inverter phase angle control signal.

10. An advanced static VAR compensator system for coupling to a power line for compensating reactive power losses of the line, the control system comprising:

a voltage sourced inverter having a DC side and an AC side for coupling to the line, the inverter responsive to an inverter phase angle control signal for drawing a selected magnitude of reactive power from the line;

a series inductance coupled to the AC side of the inverter for coupling the inverter to the line;

a voltage supporting device coupled to the DC side of the inverter;

an AC parameter sensor apparatus coupled between the inverter and the line for monitoring an electrical characteristic therebetween, with the AC parameter sensor apparatus comprising a pair of AC voltage sensors for monitoring two line to line voltages of the line, and a pair of AC current sensors for monitoring two phase currents flowing between the inverter and the line when coupled therewith;

a DC voltage sensor for monitoring a voltage of the voltage supporting device; and

a controller responsive to the AC parameter sensor apparatus for generating an instantaneous reactive current signal and for generating in response thereto the inverter phase angle control signal, with the controller including;

a vector resolver portion responsive to the pair of AC voltage sensors for generating direct and quadrature voltage signals;

a vector phase locked loop portion responsive to the direct and quadrature voltage signals for generating a first angle signal;

a rotating axis transformation portion responsive to the pair of AC current sensors and the first angle signal for generating the instantaneous reactive current signal;

an instantaneous reactive current feedback portion responsive to the instantaneous reactive current signal and a reactive current reference signal to generate an instantaneous reactive current feedback signal;

a synthesized feedback portion responsive to the DC voltage sensor and the instantaneous reactive current signal for generating a synthesized feedback signal; and

an output portion responsive to the first angle signal, the instantaneous reactive current feedback signal, and the synthesized feedback signal for generating the inverter phase angle control signal.

11. A method of compensating reactive power losses of a power line, comprising the steps of:

coupling an AC side of a voltage sourced inverter to the transmission line through a series inductance, and coupling a DC voltage supporting device to a DC side of the inverter, the inverter responsive to an inverter phase angle control signal;

first monitoring the AC current flowing between the inverter and the power line;

second monitoring the AC line voltage of the power line;

third monitoring the DC voltage across the DC voltage supporting device; and

controlling a phase displacement angle between an AC terminal voltage at the AC side of the inverter and the line voltage by generating an instantaneous reactive current signal in simultaneous response to the first, second and third monitoring steps for generating the inverter phase angle control signal.

12. A method of compensating reactive power losses of a power line according to claim 11 wherein:

the method further includes a third monitoring step of monitoring a DC voltage of the voltage supporting device; and

the controlling step comprises the step of generating the inverter phase angle control signal in response to the third monitoring step.

13. A method of compensating reactive power losses of a power line according to claim 12 wherein:

the controlling step comprises the step of comparing the instantaneous reactive current signal with a reference signal to generate a reactive current error signal; and

the controlling step comprises the step of generating the inverter phase angle control signal in response to the reactive current error signal.

14. A method of compensating reactive power losses of a power line according to claim 13 wherein:

the controlling step comprises the step of synthesizing a synthesized feedback signal in response to the instantaneous reactive current signal and the third monitoring step; and

the controlling step comprises the step of generating the inverter phase angle control signal in response to the synthesized feedback signal.

15. An advanced static VAR compensator controller inverter apparatus for coupling between a DC voltage supporting device and an AC power line, comprising:

a voltage sourced inverter having a DC side for coupling to the DC voltage supporting device and an AC side for coupling to the line, the inverter responsive to an inverter phase angle control signal for drawing a selected magnitude of reactive power from the line;

an AC parameter sensor apparatus coupled between the inverter and the line for monitoring an electrical characteristic, including AC current, therebetween;

a DC voltage sensor apparatus for monitoring a DC voltage across the voltage supporting device; and

a controller for simultaneously combining the monitored AC current and DC voltage on an instantaneous basis in a nonlinear fashion for generating an instantaneous reactive current signal and for generating in response thereto the inverter phase angle control signal.

16. An advanced static VAR compensator controller for controlling an inverter coupled between a DC voltage supporting device and an AC power line, the inverter responsive to an inverter phase angle control signal, with a pair of AC voltage sensors for monitoring two line to line voltages of the AC power line, a pair of AC current sensors for monitoring two phase currents flowing between the inverter and the line, and a DC voltage sensor for monitoring a DC voltage across the voltage supporting device, the controller comprising:

an input portion responsive to the pair of AC voltage sensors and the pair of AC current sensors for generating an instantaneous reactive current signal;

a comparator portion responsive to the instantaneous reactive current signal and an instantaneous reactive current reference signal for generating a first error signal; and

an output portion responsive to the first error signal and the DC voltage sensor for generating the inverter phase angle control signal.

17. An advanced static VAR compensator controller according to claim 16 wherein the input portion comprises:

a vector resolver portion responsive to the pair of AC voltage sensors for generating direct and quadrature voltage signals;

a vector phase locked loop portion responsive to the direct and quadrature voltage signals for generating a first angle signal; and

a rotating axis transformation portion responsive to the pair of AC current sensors and the first angle signal for generating the instantaneous reactive current signal.

18. An advanced static VAR compensator controller according to claim 17 wherein:

the comparator portion comprises an instantaneous reactive current feedback portion responsive to the instantaneous reactive current signal and a reactive current reference signal to generate an instantaneous reactive current feedback signal; and

the controller further includes a synthesized feedback portion responsive to the DC voltage sensor and the instantaneous reactive current signal for generating a synthesized feedback signal.

19. An advanced static VAR compensator system for coupling to a power line for compensating reactive power losses of the line, the control system comprising:

a voltage sourced inverter having a DC side and an AC side for coupling to the line, the inverter responsive to an inverter control signal for drawing a selected magnitude of reactive power from the line;

a voltage supporting device coupled to the DC side of the inverter;

a DC voltage sensor for monitoring a DC voltage of the voltage supporting device;

an AC parameter sensor apparatus coupled between the inverter and the line for monitoring an electrical characteristic, including AC current, therebetween; and

a controller simultaneously responsive to the monitored AC current and the DC voltage on an instantaneous basis for making a combination in a nonlinear fashion for generating the inverter control signal.

20. An advanced static VAR compensator system according to claim 19 wherein the controller generates an instantaneous reactive current signal in response to the AC parameter sensor apparatus, and a synthesized feedback signal in response to the instantaneous reactive current signal and the DC voltage sensor for generating the inverter control signal.