Power module based on normally-on semiconductor switches

1. A power module, comprising:

a plurality of normally-on semiconductor switches based on a wide bandgap substrate, the normally-on semiconductor switches connected in parallel;

a balancing unit comprising a capacitor and a balancing semiconductor switch connected in series, which are connected in parallel to the normally-on semiconductor switches;

a controller adapted for providing a gate signal for the normally-on semiconductor switches and for providing a gate signal for the balancing semiconductor switch;

wherein the controller is adapted for turning the normally-on semiconductor switches on and off with a given switching frequency;

wherein the controller is adapted for turning off the balancing semiconductor switch, when the normally-on semiconductor switches are turned on and for turning on the balancing semiconductor switch, when the normally-on semiconductor switches are turned off.

2. The power module of claim 1 ,

wherein the given switching frequency is higher than 50 Hz;

wherein a time interval between turning off the balancing semiconductor switch and turning on the normally-on semiconductor switches is smaller than 1 μs;

wherein a time interval between turning off the normally-on semiconductor switches and turning on the balancing semiconductor switch is smaller than 1 μs.

3. The power module of claim 2 ,

wherein the controller is mechanically integrated in the power module.

4. The power module of claim 3 , wherein the normally-on semiconductor switches are based on a SIC substrate; and

wherein the normally-on semiconductor switches are JFETs.

5. The power module of claim 2 , wherein the normally-on semiconductor switches are based on a SiC substrate; and

wherein the normally-on semiconductor switches are JFETs.

6. The power module of claim 2 ,

wherein the balancing semiconductor switch is a normally-off semiconductor switch.

7. The power module of claim 6 , wherein the balancing semiconductor switch is based on a Si substrate; and

wherein the balancing semiconductor switch is an IGBT, a MOSFET or a JFET.

8. The power module claim 2 , wherein the normally-on semiconductor switches comprises gates, all of which gates are electrically connected with each other for receiving a single gate signal from the controller.

9. The power module claim 8 , further comprising a base plate to which the normally-on semiconductor switches are bonded and a top plate to which for each normally-on semiconductor switch an electrically conducting spring element is attached, which presses against the respective normally-on semiconductor switch.

10. The power module of claim 1 ,

wherein the normally-on semiconductor switches are based on a SiC substrate;

wherein the normally-on semiconductor switches are JFETs.

11. The power module of claim 1 ,

wherein the balancing semiconductor switch is a normally-off semiconductor switch.

12. The power module of claim 1 ,

wherein the balancing semiconductor switch is based on a Si substrate;

wherein the balancing semiconductor switch is an IGBT, a MOSFET or a JFET.

13. The power module of claim 1 ,

wherein the normally-on semiconductor switches comprises gates, all of which gates are electrically connected with each other for receiving a single gate signal from the controller.

14. The power module of claim 1 , further comprising:

a base plate to which the normally-on semiconductor switches are bonded and a top plate to which for each normally-on semiconductor switch an electrically conducting spring element is attached, which presses against the respective normally-on semiconductor switch.

15. The power module of claim 1 , further comprising:

an auxiliary unit for providing auxiliary power to the controller,

wherein the auxiliary unit comprises a battery for providing power to the controller in the case of a stark-up of the power module.

16. The power module of claim 1 , further comprising:

an auxiliary unit for providing auxiliary power to the controller,

wherein the auxiliary unit comprises an inductive power supply for providing power to the controller in the case of a start-up of the power module.

17. A power module stack, comprising:

at least two power modules according to claim 1 connected in series.

18. A method for controlling a power module, the power module comprising a plurality of normally-on semiconductor switches based on a wide bandgap substrate, the normally-on semiconductor switches connected in parallel; a balancing unit comprising a capacitor and a balancing semiconductor switch connected in series, which are connected in parallel to the normally-on semiconductor switches; a controller adapted for providing a gate signal for the normally-on semiconductor switches and for providing a gate signal for the balancing semiconductor switch; wherein the controller is adapted for turning the normally-on semiconductor switches on and off with a given switching frequency; the method comprising:

turning the normally-on semiconductor switches on and off with a given switching frequency;

turning off the balancing semiconductor switch, when the normally-on semiconductor switches are turned on and turning on the balancing semiconductor switch, when the normally-on semiconductor switches are turned off.