Static VAR compensator with multilevel converter

• US 9,130,458 B2
• Filed: 03/15/2010
• Issued: 09/08/2015
• Est. Priority Date: 03/15/2010
• Status: Expired due to Fees

• Current Assignee: Alstom Technology Ltd. (Alstom SA)
• Original Assignee: Alstom Technology Ltd. (Alstom SA)
• Inventors: Crookes, William, Trainer, David Reginald, Oates, Donald Colin Murray
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): RIVERA-PEREZ, CARLOS O
• Application Number:
  US13/634,205
• Publication Number:
  US 20130094264A1
• Time in Patent Office: 2,003 Days
• Field of Search: 363 15- 17, 363/21.02, 363/21.03, 363 35- 38, 363 40- 46, 363/71, 363123-128, 363/131, 363/132, 363135-137, 323205-211, 323271-275, 323282-285, 323/351, 318/107, 318/108
• US Class Current: 1/1
• CPC Class Codes: H02J 3/1835 with stepless control
• CPC Class Codes: H02J 3/1857 wherein such bridge converter is a multilevel converter
• CPC Class Codes: H02M 1/0095 Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
• CPC Class Codes: H02M 7/217 using semiconductor devices only
• CPC Class Codes: H02M 7/4835 comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

A static synchronous compensator for use in reactive power compensation, the static synchronous compensator comprising at least one primary compensator limb including first and second DC terminals, and an AC terminal for connection in use to an AC network, the or each primary compensator limb defining first and second limb portions, each limb portion—including at least one switching element connected in series with a chain-link converter—between a respective one of the first and second DC terminals and the AC terminal, the switching elements of the first and second limb portions being operable to switch the respective chain-link converters in and out of circuit between the respective DC terminal and the AC terminal and the chain-link converters being operable to generate a voltage waveform at the AC terminal; and a secondary compensator limb including at least one DC link capacitor connected between the first and second DC terminals, the secondary compensator limb being connected in parallel with the or each primary compensator limb.

Claims

1. A static synchronous compensator for use in reactive power compensation, the static synchronous compensator comprising at least one primary compensator limb including first and second DC terminals, and an AC terminal for connection in use to an AC network, the or each primary compensator limb defining first and second limb portions, each limb portion including at least one switching element and a chain-link converter connected in series at a common point, said common point being shared only by the switching element and the chain-link converter, the switching element and the chain-link converter being mounted between a respective one of the first and second DC terminals and the AC terminal, wherein the switching elements of the first and second limb portions being operable to switch the respective chain-link converters in and out of circuit between the respective DC terminal and the AC terminal, wherein the switching elements of the first and second limb portions being operable to switch the chain-link converters into circuit at the same time and wherein the chain-link converters being operable to generate a voltage waveform at the AC terminal;

and a secondary compensator limb including at least one DC link capacitor connected between the first and second DC terminals, the secondary compensator limb being connected in parallel with the or each primary compensator limb.

2. The static synchronous compensator according to claim 1 wherein the secondary compensator limb includes two DC link capacitors connected in series, a junction between the DC link capacitors being connected in use to ground.

3. The static synchronous compensator according to claim 1 wherein the secondary compensator limb includes a DC link capacitor with a center tap, the center tap being connected in use to ground.

4. The static synchronous compensator according to claim 1 wherein each chain-link converter is operable when the respective limb portion is switched out of circuit to generate a voltage to offset a voltage across the limb portion and thereby minimize the voltage across the respective switching element.

5. The static synchronous compensator according to claim 1 wherein the chain-link converter of each of the limb portions includes a chain of modules connected in series, each module including at least one pair of secondary switching elements connected in parallel with an energy storage device, the secondary switching elements being operable in use so that the chain of modules defines a stepped variable voltage source.

6. The static synchronous compensator according to claim 5 wherein the or each module of the chain-link converters includes two pairs of secondary switching elements connected in parallel with the respective energy storage device in a full-bridge arrangement to define a 4-quadrant bipolar module that can provide positive or negative voltage and can conduct current in both directions.

7. The static synchronous compensator according to claim 5 wherein the or each module of the chain-link converters includes a pair of secondary switching elements connected in parallel with the respective energy storage device in a half-bridge arrangement to define a 2-quadrant module that can provide positive or zero voltage and can conduct current in both directions.

8. The static synchronous compensator according to claim 5 wherein the or each energy storage device includes a capacitor, a fuel cell, a battery or an auxiliary AC generator with an associated rectifier.

9. The static synchronous compensator according to claim 1 wherein the or each switching element of each limb portion includes a semiconductor device.

10. The static synchronous compensator according to claim 9 wherein the or each semiconductor device includes an insulated gate bipolar transistor, a gate turn-off thyristor or an integrated gate-commutated thyristor.

11. The static synchronous compensator according to claim 1 wherein the chain-link converter of each limb portion includes at least one semiconductor device.

12. The static synchronous compensator according to claim 1 including multiple primary compensator limbs, each primary compensator limb including an AC terminal for connection in use to a respective phase of a multi-phase AC network.

13. The static synchronous compensator according to claim 1 wherein the chain-link converter of each limb portion is operable to generate a voltage to oppose the flow of current created by a fault, in use, in the secondary compensator limb or the AC network.

14. The static synchronous compensator according to claim 1 wherein, in each limb portion, a voltage rating of the chain-link converter and a voltage rating of the or each switching element are equal.

15. The static synchronous compensator according to claim 1 wherein, in each limb portion, a voltage rating of the chain-link converter and a voltage rating of the or each switching element are not equal.

16. The static synchronous compensator according to claim 1 wherein the switching elements in the first and second limb portions are operable to switch the chain-link converters into circuit at the same time to reset any drift in voltages in the chain-link converter elements.