Method and apparatus for controlling thermal cycling

1. A method comprising, in a gate drive unit of a power converter during operation of the power converter:

obtaining a first value indicative of a junction temperature of a power switch within the power converter;

obtaining a second value indicative of the junction temperature of the power switch;

selecting a gate drive voltage time function for the power switch from a plurality of pre-determined gate drive voltage time functions, based on at least the first and second values indicative of the junction temperature of the power switch; and

reducing thermal cycling of the power switch, relative to the thermal cycling that would be present during operation at a constant gate voltage, by providing gate drive voltage to a gate of the power switch, according to the selected gate drive voltage time function wherein reducing thermal cycling includes providing the gate voltage according to the selected gate drive voltage time function by which switching losses are increased above the losses that would be present during operation at the constant gate voltage.

2. A method as claimed in claim 1 , wherein at least one of the values indicative of the junction temperature is obtained based on measurements of at least a DC link voltage of a DC link to which the power switch is attached and a power converter output current of a power converter that includes the power switch.

3. A method as claimed in claim 1 , wherein at least one of the values that is obtained is a measurement of a power switch temperature of the power switch at an associated case.

4. A method as claimed in claim 1 , wherein at least one of the values that is obtained is an estimate of an output load current into a load that is at least partially provided with the load current by the power switch.

5. A method as claimed in claim 1 , wherein the gate drive voltage time function is selected based also on an updated value of an operator control signal that is received at the gate drive unit while the gate drive unit is obtaining the first and second values indicative of the junction temperature.

6. A method as claimed in claim 1 , wherein reducing thermal cycling of the power includes providing gate voltage according to a gate voltage time function by which gate voltage is reduced at a time when switching losses otherwise would diminish.

7. A gate drive unit comprising:

an output stage controllable to provide an adjustable gate drive voltage to an output terminal;

a signal connection configured to receive a sequence of values of a parameter indicative of a junction temperature of a power switch; and

a controller coupled to the signal connection and to the output stage, the controller configured to control the output stage to adjust the gate drive voltage in response to the sequence of values of the parameter indicative of the power switch junction temperature so as to mitigate temperature cycling that would be present in case the gate drive voltage was not adjusted wherein the controller is configured to mitigate temperature cycling by reducing gate voltage at a time when switching losses otherwise would diminish.

8. A gate drive unit as claimed in claim 7 , wherein the controller is configured to control the output stage based on searching a lookup table to identify one or more pre-determined values of gate drive voltages corresponding to at least one of the sequence of values of the parameter indicative of the power switch junction temperature.

9. A gate drive unit as claimed in claim 8 , wherein the lookup table includes a plurality of gate drive voltage time functions corresponding to pre-defined ranges of voltages across the power switch driven by the output stage.

10. A gate drive unit as claimed in claim 8 , wherein the lookup table includes a plurality of gate drive voltage time functions corresponding to pre-defined ranges of current through the power switch driven by the output stage.

11. A gate drive unit as claimed in claim 8 , wherein the lookup table includes a plurality of gate drive voltage time functions corresponding to pre-defined ranges of power switch junction temperatures.

12. A gate drive unit as claimed in claim 8 , wherein the controller is configured to adjust the gate drive voltage according to an updated value of an operator control signal that is received at the gate drive unit while the gate drive unit is receiving the sequence of values.

13. A power converter comprising:

at least one gate drive unit comprising an adjustable output stage configured to provide an adjustable gate drive voltage to at least one of a plurality of power switches composing the power converter;

and

at least one controller coupled to the adjustable output stage of the at least one gate drive unit, the controller configured to control the adjustable output stage to adjust the gate drive voltage in response to receiving a sequence of values indicative of a junction temperature of the at least one of the plurality of power switches so as to mitigate temperature cycling that would be present in case the gate drive voltage was not adjusted wherein the controller is configured to mitigate temperature cycling by reducing gate voltage at a time when switching losses otherwise would diminish.

14. A power converter as claimed in claim 13 , wherein the controller is configured to control the adjustable output stage based on searching a lookup table to identify pre-determined values of gate drive voltages corresponding to the received value indicative of the junction temperature.

15. A power converter as claimed in claim 14 , wherein the lookup table includes a plurality of gate drive voltage time functions corresponding to pre-defined ranges of voltages across the at least one of the plurality of power switches.

16. A power converter as claimed in claim 14 , wherein the lookup table includes a plurality of gate drive voltage time functions corresponding to pre-defined ranges of current through the at least one of the plurality of power switches.

17. A power converter as claimed in claim 14 , wherein the lookup table includes a plurality of gate drive voltage time functions corresponding to pre-defined ranges of the junction temperature of the at least one of the plurality of power switches.

18. A power converter as claimed in claim 14 , wherein the controller is configured to adjust the gate drive voltage according to an updated value of an operator control signal that is received at the gate drive unit while the gate drive unit is receiving the sequence of values.