RC-IGBT switching pulse control

1. A method of controlling a first and a second reverse-conducting insulated gate bipolar transistor, RC-IGBT, electrically connected in series, wherein:

a collector of the first RC-IGBT is electrically connected to a positive pole of a direct current, DC, voltage source and an emitter of the second RC-IGBT is electrically connected to a negative pole of the DC voltage source; and

an emitter of the first RC-IGBT is electrically connected to a collector of the second RC-IGBT to form an alternating current, AC, terminal,

the method comprising the steps of:

comparing a magnitude of an output current on the AC terminal with a selected threshold; and

applying a gate voltage to respective gates of the first and second RC-IGBTs,

wherein said gate voltage is controlled based on a direction of the output current on the AC terminal, the comparison of the magnitude of the output current on the AC terminal with the selected threshold and on a command signal indicating targeted turn-on and turn-off instants for the respective RC-IGBTs, and wherein, if said comparison indicates that the magnitude of the output current on the AC terminal exceeds the selected threshold and the direction of the output current indicates that one of the RC-IGBTs is operated in IGBT mode and the other RC-IGBT is operated in diode mode, high-level and low-level gate voltage pulses are applied respectively to the RC-IGBT operated in IGBT mode during respective targeted turn-on and turn-off instants as indicated by the command signal, and

wherein the method further comprises: if said comparison indicates that the magnitude of the output current on the AC terminal exceeds the selected threshold and the direction of the output current indicates that one of the RC-IGBTs is operated in IGBT mode and the other RC-IGBT is operated in diode mode, applying and maintaining a low level gate voltage to the other RC-IGBT except during a time period prior to a targeted turn-off instant for the other RC-IGBT indicated by the command signal, during which time duration a high-level gate voltage pulse is applied to the other RC-IGBT.

2. The method according to claim 1 , further comprising:

if said comparison indicates that the magnitude of the output current on the AC terminal does not exceed the selected threshold,

applying high-level and low-level gate voltage pulses respectively to both RC-IGBTs during respective targeted turn-on and turn-off instants for the respective RC-IGBTs as indicated by the command signal.

3. The method according to claim 2 , wherein gate voltages are applied to the first and second RC-IGBTs such that application of the high level gate voltage to one of said RC-IGBTs and application of the high level gate voltage to the other RC-IGBT is separated by a blanking time during which blanking time the low level gate voltage is applied to both of said RC-IGBTs.

4. The method according to claim 1 , wherein gate voltages are applied to the first and second RC-IGBTs such that application of the high level gate voltage to one of said RC-IGBTs and application of the high level gate voltage to the other RC-IGBT is separated by a blanking time during which blanking time the low level gate voltage is applied to both of said RC-IGBTs.

5. The method according to claim 1 , further comprising:

if said comparison indicates that the magnitude of the output current on the AC terminal does not exceed the selected threshold,

applying high-level and low-level gate voltage pulses respectively to both RC-IGBTs during respective targeted turn-on and turn-off instants for the respective RC-IGBTs as indicated by the command signal.

6. The method according to claim 1 , wherein gate voltages are applied to the first and second RC-IGBTs such that application of the high level gate voltage to one of said RC-IGBTs and application of the high level gate voltage to the other RC-IGBT is separated by a blanking time during which blanking time the low level gate voltage is applied to both of said RC-IGBTs.

7. The method according to claim 1 , wherein the DC voltage source is an energy storage element.

8. The method according to claim 1 , wherein the first and the second RC-IGBTs are in half bridge configuration, or are included in a full bridge configuration, and electrically connected to a storage element.

9. The method according to claim 1 , wherein the first and the second RC-IGBTs are included in a cell of a branch of cascade connected cells and wherein a measurement of the output current on the AC terminal is obtained by measuring the current through the branch.

10. The method according to claim 1 , wherein each of the first and second RC-IGBTs is a bi-mode insulated gate transistor (BIGT).

11. The method according to claim 1 , wherein the command signal is complementary for the first RC-IGBT and the second RC-IGBT.

12. A computer program product comprising a non-transitory data carrier with computer executing computer readable instructions for causing a programmable processing unit, connected to a first and a second RC-IGBT, to perform the method according to claim 1 to control both the first RC-IGBT and the second RC-IGBT, wherein:

the first and second RC-IGBTs are electrically connected in series;

a collector of the first RC-IGBT is electrically connected to a positive pole of a direct current voltage source and an emitter of the second RC-IGBT is electrically connected to a negative pole of the DC voltage source; and

an emitter of the first RC-IGBT is electrically connected to a collector of the second RC-IGBT at an alternating current terminal.

13. A controller for controlling a first and a second reverse-conducting insulated gate bipolar transistor, RC-IGBT, electrically connected in series, wherein:

a collector of the first RC-IGBT is electrically connected to a positive pole of a direct current voltage source and an emitter of the second RC-IGBT is electrically connected to a negative pole of the DC voltage source;

an emitter of the first RC-IGBT is electrically connected to a collector of the second RC-IGBT to form an alternating current terminal; and

the controller comprising:

an input circuit adapted to receive a command signal indicating targeted turn-on and turn-off instants for the respective RC-IGBTs;

a processor, adapted to:

receive information from a current meter on a magnitude and direction of a measured output current on said AC terminal;

compare the magnitude of the measured output current on the AC terminal with a selected threshold; and

determine, based on the received command signal, the received information on the direction of the measured output current and the comparison of the magnitude of the measured output current on the AC terminal with the selected threshold, a gate voltage for application to respective gates of the first and second RC-IGBTs; and

an output circuit connected to respective gates of the first and second RC-IGBT,

wherein the output circuit is further adapted to apply a determined gate voltage to respective gates of the first and second RC-IGBTs, wherein the controller is configured to, if said comparison indicates that the magnitude of the output current on the AC terminal exceeds the selected threshold and received information on the direction of the output current indicates that one of the RC-IGBTs is operated in IGBT mode and the other RC-IGBT is operated in diode mode, apply high-level and low-level gate voltage pulses respectively to the RC-IGBT operated in IGBT mode during respective targeted turn-on and turn-off instants as indicated by the command signal,

wherein the controller is further configured to, if said comparison indicates that the magnitude of the output current on the AC terminal exceeds the selected threshold and received information on the direction of the output current indicates that one of the RC-IGBTs is operated in IGBT mode and the other RC-IGBT is operated in diode mode, apply and maintain a low level gate voltage to the other RC-IGBT except during a time period prior to a targeted turn-off instant for the other RC-IGBT indicated by the command signal, during which time duration a high-level gate voltage pulse is applied to the other RC-IGBT.

14. The controller according to claim 13 , wherein the controller is configured to, if said comparison indicates that the magnitude of the output current on the AC terminal does not exceed the selected threshold,

apply high-level and low-level gate voltage pulses respectively to both RC-IGBTs during respective targeted turn-on and turn-off instants for the respective RC-IGBTs as indicated by the command signal.

15. The controller according to claim 13 , wherein the first and second RC-IGBTs are bi-mode insulated gate transistors (BIGTs).

16. The controller according to claim 13 , wherein the command signal is complementary for the first RC-IGBT and the second RC-IGBT.

17. The controller according to claim 13 , wherein the controller is embodied by a computer executing computer readable instructions to control both the first RC-IGBT and the second RC-IGBT.

18. A voltage source converter for converting between AC and DC current, comprising:

an arrangement of connected RC-IGBTs comprising at least a first and a second RC-IGBT electrically connected in series, wherein:

a collector of the first RC-IGBT is electrically connected to a positive pole of a direct current voltage source and an emitter of the second RC-IGBT is electrically connected to a negative pole of the DC voltage source; and

an emitter of the first RC-IGBT is electrically connected to a collector of the second RC-IGBT at an alternating current terminal; and

the controller according to claim 13 which is electrically connected to the arrangement of RC-IGBTs.