DC chopper and DC chopping method for doubly fed induction generator system

• US 8,922,173 B2
• Filed: 06/25/2012
• Issued: 12/30/2014
• Est. Priority Date: 08/23/2011
• Status: Expired due to Fees

• Current Assignee: Delta Electronics Company Limited (Delta Electronics Incorporated)
• Original Assignee: Delta Electronics Company Limited (Delta Electronics Incorporated)
• Inventors: Wang, Chang-Yong, Zheng, Jian-Fei, Lu, Fei, Ying, Jian-Ping
• Primary Examiner(s): Patel, Tulsidas C
• Assistant Examiner(s): QUIGLEY, THOMAS K
• Application Number:
  US13/532,356
• Publication Number:
  US 20130049707A1
• Time in Patent Office: 918 Days
• Field of Search: 322/24, 290/44, 290/55
• US Class Current: 322/24
• CPC Class Codes: H02M 3/02 without intermediate conversion into ac
• CPC Class Codes: H02P 6/00 Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor vector control H02P21/00

Abstract

A DC chopper comprising a control unit and a power circuit and a DC chopping method for a DFIG (doubly fed induction generator) system are provided. The input terminal of the control unit is coupled to a DC capacitor of a converter to detect a DC voltage. The power circuit includes input terminals, an overvoltage protection module, a rectifier module and output terminals. The overvoltage protection module comprises at least one discharge unit formed from a discharge resistor and a switch element, and the rectifier module is coupled in parallel to the overvoltage protection module. When a grid voltage drops, the control unit outputs a corresponding control signal to drive the switch element to be ON or OFF, and the output terminal of the power circuit absorbs a portion of rotor inrush current, so as to impose over-current protection.

Claims

1. A DC chopper suitable for a DFIG system comprising a converter and a DFIG, the DC chopper comprising:

a control unit having at least one input terminal and an output terminal, wherein the at least one input terminal of the control unit is electrically coupled to two ends of a DC capacitor of the converter, so as to detect a DC voltage; and

a power circuit electrically coupled to the converter, the DFIG and the control unit, wherein the power circuit comprises;

an input terminal coupled in parallel to the DC capacitor of the converter, wherein the DC capacitor is located between a grid-side inverter and a generator-side inverter of the converter;

an overvoltage protection module coupled to the input terminal of the power circuit, wherein the overvoltage protection module comprises at least one discharge unit formed from a discharge resistor and a switch element which are coupled in series, and the switch element is electrically coupled to the output terminal of the control unit;

a rectifier module coupled to the overvoltage protection module in parallel; and

an output terminal coupled to the rectifier module and the DFIG,

wherein, when a grid voltage of the DFIG system drops, the output terminal of the control unit outputs a corresponding control signal to drive the switch element to be on or off; and

the output terminal of the power circuit absorbs a portion of rotor inrush current from the DFIG, so as to implement over-current protection on the generator-side inverter.

2. The DC chopper of claim 1, wherein when the grid voltage of the DFIG system drops, and the DC voltage detected by the control unit is higher than a first predetermined voltage, the output terminal of the control unit outputs a first control signal to drive the switch element to be on.

3. The DC chopper of claim 2, wherein when the grid voltage of the DFIG system drops, and the DC voltage detected is higher than the first predetermined voltage, another output terminal of the control unit still sends a control signal to the generator-side inverter of the converter to allow the generator-side inverter to be operated normally, and the DFIG system sends reactive power to the electric grid, so as to satisfy the LVRT requirement.

4. The DC chopper of claim 1, wherein the discharge unit further comprises:

a freewheeling unit coupled to the discharge resistor in parallel, so as to provide a freewheeling circuit for the discharge resistor when the switch element is driven off.

5. The DC chopper of claim 1, wherein the overvoltage protection module comprises a plurality of discharge units, and one or more discharge units are turned on according to different sequences so as to drive the overvoltage protection module into operation.

6. The DC chopper of claim 1, wherein the power circuit further comprises:

a first common mode choke arranged between the rectifier module and the output terminal of the power circuit, so as to suppress common mode current.

7. The DC chopper of claim 1, wherein the power circuit further comprises:

a second common mode choke arranged between the input terminal of the power circuit and the overvoltage protection module, so as to suppress the common mode current.

8. The DC chopper of claim 1, wherein when the DC voltage detected by the control unit is lower than a second predetermined voltage, the output terminal of the control unit sends a second control signal, so as to drive the switch element off.

9. A DC chopping method for a DFIG system comprising a converter and a DFIG, wherein the DFIG system further comprises a DC chopper of claim 1, and the DC chopping method comprises:

detecting a DC voltage loaded on a DC capacitor of the converter in real time by using the control unit;

outputting a corresponding control signal from the output terminal of the control unit when a grid voltage of the DFIG system drops, so as to drive a switch element on or off; and

absorbing a portion of rotor inrush current from the DFIG by using the output terminal of the power circuit, so as to implement over-current protection on a generator-side inverter.

10. A DFIG system comprising a converter and a DFIG, wherein the system further comprises:

a DC chopper of claim 1.

11. The DFIG system of claim 10, wherein when the grid voltage of the DFIG system drops, and the DC voltage detected by the control unit is higher than a first predetermined voltage, the output terminal of the control unit outputs a first control signal to drive the switch element to be on.

12. The DFIG system of claim 11, wherein when the grid voltage of the DFIG system drops, and the DC voltage detected is higher than the first predetermined voltage, another output terminal of the control unit still sends a control signal to the generator-side inverter of the converter to allow the generator-side inverter to be operated normally, and the DFIG system sends reactive power to the electric grid, so as to satisfy the LVRT requirement.

13. The DFIG system of claim 10, wherein the discharge unit further comprises:

a freewheeling unit coupled to the discharge resistor in parallel, so as to provide a freewheeling circuit for the discharge resistor when the switch element is driven off.

14. The DFIG system of claim 10, wherein the overvoltage protection module comprises a plurality of discharge units, and one or more discharge units are turned on according to different sequences, so as to drive the overvoltage protection module into operation.

15. The DFIG system of claim 10, wherein the power circuit further comprises:

a first common mode choke arranged between the rectifier module and the output terminal of the power circuit, so as to suppress common mode current.

16. The DFIG system of claim 10, wherein the power circuit further comprises:

a second common mode choke arranged between the input terminal of the power circuit and the overvoltage protection module, so as to suppress the common mode current.

17. The DFIG system of claim 10, wherein when the DC voltage detected by the control unit is lower than a second predetermined voltage, the output terminal of the control unit sends a second control signal, so as to drive the switch element off.