System-Level Investigation of Traction Inverter High-Temperature Operation 2018-01-0464

In this paper, the high-temperature capability of the traction inverter was investigated by applying coolant with temperature much higher than the typical allowed value until the system fails. The purpose of this study is to identify the weakest link of the traction inverter system in terms of temperature. This study was divided into two stages. In the first stage, a series of nondestructive tests were carried out to investigate temperature rise (ΔT) of the key component above coolant temperature as a function of the outside controllable parameters-i.e., dc link voltage, phase current, and switching frequency. The key components include power modules, gate driver board, gate driver power supply, current sensors and dc link capacitor. Their temperatures were monitored by thermocouples or on-die temperature sensors. The result showed that temperature rises of most key components were strongly affected by phase current, moderately affected by switching frequency, and slightly affected by dc link voltage. Therefore, the operating conditions used in the second stage (destructive test) were chosen to stress the phase current only rather than the dc link voltage and switching frequency for better effectiveness. In the second stage (the destructive test), the coolant temperature was controlled to increase every a few hours after the temperature stabilized while maintaining the controllable electrical parameters to be the same. Testing results showed that the traction inverter employed in this study can sustain coolant temperature > 105 °C for more than 10 hours, while the IGBT on-die temperatures were measured to be >200 °C. Under this specific condition, the IGBT module is the first component to fail after the coolant temperature was raised to a certain level (>120 °C). On the contrary, many other components are found to be functioning after the long-time operation at high temperatures. The measurement results were confirmed by the theoretical analysis.