EV Propulsion Drive Converter SiC Power Device Over-Temperature Protection under Low Motor Speed Operation

Monitoring power device temperature in an electric vehicle propulsion drive converter is extremely important to achieve full power delivery within the maximum power capability envelope. Usually, on-die temperature sensors are installed on Si-IGBT power devices in electric vehicle propulsion drive converters to enable monitoring device temperature and achieve over-temperature protection. Currently, SiC MOSFET is a promising power device in power converters of electric drives because of its lower loss, higher switching speed, higher voltage capability, and higher junction temperature limit in comparison with widely used Si-IGBT. However, SiC MOSFET is a more expensive device, so the present technology trend is trying to reduce its chip size. Installation of an on-die temperature sensor on SiC MOSFET will significantly increase its cost and complexity. So presently, there is no junction temperature sensor installed in SiC MOSFET due to which there is great difficulty protecting SiC MOSFET from over temperature. Till date, the junction temperature estimation method is used to monitor SiC MOSFET temperature. As a result, the power loss computation of SiC MOSFET is a key factor in achieving its purpose. However, the existing loss calculation method assumes motor operating at high speed, and loss is computed/estimated with rms current as one of the inputs. For motor low speed operation, it is not practical because the power converter output current has a long fundamental period. The instantaneous power losses and hence the junction temperatures of the six power converter switches are not the same under such operating conditions. Hence, the junction temperature obtained with loss computed using the rms current value does not correspond to the actual device junction temperature, resulting in the failure of power device over-temperature (OT) protection. This paper proposes a power device over-temperature protection method under low motor speed operation to solve the above issues. The proposed method allows a reduction of system cost and complexity. It computes/estimates instantaneous loss and junction temperature for each individual power device of the power converter enabling over temperature detection at the motor low fundamental frequency and imbalance phase operation. The full paper will disclose the technical principle of the proposed instantaneous power loss and junction temperature estimation method, over-temperature protection for SiC MOSFET, its model details, simulation and experimental test results to verify the new method.