Method and system for controlling electric drive system according to predicted temperature of DC-link capacitor to prevent overheating
An electric drive system includes a power electronics module (PEM) having a DC-link capacitor and an inverter. A controller reduces power output of the inverter while a sensed temperature of an inverter power switch, a sensed current of the PEM, such as a sensed ripple current of the DC-link capacitor, and parameter values of the DC-link capacitor are indicative of a predicted temperature of the capacitor being greater than a threshold to maintain capacitor temperature lower than the threshold. The parameter values are obtainable from a thermal model of the DC-link capacitor. The thermal model may be derived from testing a test version of the PEM under different drive cycles in which for each drive cycle a set of information is recorded including a sensed temperature of the inverter power switch test version, a current of the PEM test version, and a sensed temperature of the DC-link capacitor test version.
1. An electric drive system, comprising:
a power electronics module having a DC-link capacitor and an inverter; and
a controller configured to reduce power output of the inverter while a temperature of the DC-link capacitor, predicted from a thermal equation given a sensed temperature of a power switch of the inverter, a sensed current of the power electronics module, and values of parameters of the thermal equation obtained from a thermal model of the DC-link capacitor, is greater than a threshold to thereby maintain DC-link capacitor temperature lower than the threshold.
2. The electric drive system of claim 1 wherein:
the thermal model of the DC-link capacitor is derived from a test version of the power electronics module being tested under a plurality of drive cycles in which for each drive cycle a set of information is recorded including a sensed temperature of the power switch of the inverter of the test version of the power electronics module, a sensed current of the test version of the power electronics module, and a sensed temperature of the DC-link capacitor of the test version of the power electronics module.
3. The electric drive system of claim 2 wherein:
the sensed current of the test version of the power electronics module is a sensed ripple current of the DC-link capacitor of the test version of the power electronics module.
4. The electric drive system of claim 1 wherein:
the sensed current of the power electronics module is a sensed ripple current of the DC-link capacitor.
5. The electric drive system of claim 1 wherein:
the sensed current of the power electronics module includes either a sensed DC current drawn by the inverter, the sensed DC current drawn by the inverter and a sensed ripple current of the DC-link capacitor, or the sensed DC current drawn by the inverter and a sensed AC current outputted by the inverter.
6. The electric drive system of claim 1 wherein:
the controller is further configured to reduce power output of the inverter by de-rating operation of the DC-link capacitor.
7. The electric drive system of claim 1 wherein:
the electric drive system is of an electric vehicle and further includes a traction battery and a motor, the DC-link capacitor is disposed between the traction battery and the inverter, and the inverter is configured to convert an input electrical power from the traction battery via the DC-link capacitor into an output electrical power and provide the output electrical power to the motor for propelling the electric vehicle.
8. The electric drive system of claim 1 wherein:
the power switch of the inverter is an insulated gate bipolar transistor (IGBT).
9. An electric vehicle comprising:
an electric drive system including a traction battery, a power electronics module having a DC-link capacitor and an inverter, and a motor, the inverter configured to convert an input electrical power from the traction battery via the DC-link capacitor into an output electrical power and provide the output electrical power to the motor for propelling the electric vehicle;
a controller configured to predict a temperature of the DC-link capacitor using a sensed temperature of a power switch of the inverter, a sensed current of the power electronics module, and parameter values obtained from a thermal model of the DC-link capacitor, wherein the thermal model of the DC-link capacitor is derived from a test version of the power electronics module being tested under a plurality of drive cycles in which for each drive cycle a set of information is recorded including a sensed temperature of the power switch of the inverter of the test version of the power electronics module, a sensed current of the test version of the power electronics module, and a sensed temperature of the DC-link capacitor of the test version of the power electronics module; and
the controller is further configured to de-rate the electric drive system while the predicted temperature of the DC-link capacitor is greater than a temperature threshold to prevent overheating.
10. The electric vehicle of claim 9 wherein:
the sensed current of the test version of the power electronics module is a sensed ripple current of the DC-link capacitor of the test version of the power electronics module; and
the parameter values are obtained from the thermal model of the DC-link capacitor by finding which values of a DC-link capacitor temperature thermal equation having variables of power switch temperature, DC-link capacitor ripple current, and the parameters fit the set of information recorded for at least one of the drive cycles.
11. The electric vehicle of claim 9 wherein:
the sensed current of the power electronics module is a sensed ripple current of the DC-link capacitor.
12. The electric vehicle of claim 9 wherein:
the sensed current of the power electronics module includes either a sensed DC current drawn by the inverter, the sensed DC current drawn by the inverter and a sensed ripple current of the DC-link capacitor, or the sensed DC current drawn by the inverter and a sensed AC current outputted by the inverter.
13. A method for an electric drive system including a power electronics module having an inverter and a DC-link capacitor, the method comprising:
sensing a temperature of a power switch of the inverter;
sensing a current of the power electronics module;
obtaining parameter values of the DC-link capacitor from a thermal model of the DC-link capacitor, wherein the thermal model of the DC-link capacitor is derived from a test version of the power electronics module being tested under a plurality of drive cycles in which for each drive cycle a set of information is recorded including a sensed temperature of the power switch of the inverter of the test version of the power electronics module, a sensed current of the test version of the power electronics module, and a sensed temperature of the DC-link capacitor of the test version of the power electronics module; and
reducing power output of the inverter while the sensed temperature of the power switch, the sensed current of the power electronics module, and the parameter values of the DC-link capacitor are indicative of a predicted temperature of the DC-link capacitor being greater than a threshold to maintain DC-link capacitor temperature lower than the threshold.
14. The method of claim 13 wherein:
the sensed current of the test version of the power electronics module is a sensed ripple current of the DC-link capacitor of the test version of the power electronics module; and
obtaining the parameter values of the DC-link capacitor from the thermal model of the DC-link capacitor includes finding which values of a DC-link capacitor temperature thermal equation having variables of power switch temperature, DC-link capacitor ripple current, and the parameters fit the set of information recorded for at least one of the drive cycles.
15. The method of claim 13 wherein:
the sensed current of the power electronics module is a sensed ripple current of the DC-link capacitor.
16. The method of claim 13 wherein:
the sensed current of the power electronics module includes either a sensed DC current drawn by the inverter, the sensed DC current drawn by the inverter and a sensed ripple current of the DC-link capacitor, or the sensed DC current drawn by the inverter and a sensed AC current outputted by the inverter.