Granted Patent B2

US 8,760,120 · App. 14/090,766 · Granted Jun 24, 2014

Abstract

Claims (21)

1. A method for de-energizing a chain-link converter comprising one or more phase legs, each phase leg comprising a number of series-connected converter cells, each converter cell comprising four valves arranged in an H-bridge connection with a DC capacitor, and each valve in turn comprising a semiconductor switch in parallel with a diode, the phase legs being connected to a respective charging resistor, the method comprising the steps of:

opening AC circuit breakers arranged between a power grid and the chain-link converter,

opening charging resistors switches arranged in parallel with a respective one of charging resistors, and

circulating a current within the chain-link converter through the charging resistors and each phase leg, whereby the DC capacitor are discharged.

2. The method as claimed in claim 1 , comprising the further step of bypassing any faulty converter cells after the step of opening the charging resistors switches.

3. The method as claimed in claim 2 , comprising the further steps of:

detecting that the DC capacitor voltage is below a level enabling control of the semiconductor switches, and

using a discharge circuit connected to each of the semiconductor switches for enabling further discharge of the semiconductor switches.

4. The method as claimed in claim 1 , wherein the step of circulating a current within the chain-link converter through the charging resistors and each phase leg comprises sending firing pulses to the semiconductor switches.

5. The method as claimed in claim 1 , wherein the chain-link converter comprises three phase legs connected in a delta connection, the phase legs and the charging resistor thus making up a closed circuit.

6. The method as claimed in claim 1 , wherein the chain-link converter comprises three phase legs connected in a wye connection, and wherein a tuned zero sequence filter is arranged between the star point of the wye connected phase legs and respective points between the AC circuit breakers and a respective charging resistor.

7. The method as claimed in claim 6 , wherein the tuned zero sequence filter comprises a zig-zag transformer, series-connected with a phase reactor, in turn series-connected with a filter device, and wherein the filter device is connected to the star point of the wye connected phase legs, and wherein the zig-zag transformer is connected to each of the phase legs at points between the AC circuit breakers the respective charging resistor.

8. A controller for de-energizing a chain-link converter comprising one or more phase legs, each phase leg comprising a number of series-connected converter cells, each converter cell comprising four valves arranged in an H-bridge connection with a DC capacitor, and each valve in turn comprising a semiconductor switch in parallel with a diode, the phase legs being connected to a respective charging resistor, the controller arranged to:

open AC circuit breakers arranged between a power grid and the chain-link converter,

open charging resistors switches arranged in parallel with a respective one of charging resistors, and

circulate a current within the chain-link converter through the charging resistors and each phase leg, whereby the DC capacitor are discharged.

9. A computer program for de-energizing a chain-link converter comprising one or more phase legs, each phase leg comprising a number of series-connected converter cells, each converter cell comprising four valves arranged in an H-bridge connection with a DC capacitor, and each valve in turn comprising a semiconductor switch in parallel with a diode, the phase legs being connected to a respective charging resistor, the computer program comprising computer program code, which, when run on a controller, causes the controller to perform the steps of:

opening AC circuit breakers arranged between a power grid and the chain-link converter,

opening charging resistors switches arranged in parallel with a respective one of charging resistors, and

circulating a current within the chain-link converter through the charging resistors and each phase leg, whereby the DC capacitor are discharged.

10. A computer program product comprising a computer program as claimed in claim 9 , and a computer readable means on which the computer program is stored.

Assignments (6)