Case Sensitive Condition Monitoring of an IGBT Inverter in a Hybrid Car

In view of ever-increasing power densities of voltage source inverters the implementation of condition monitoring functions will gain greater importance. This paper presents a concept to determine the health state of the IGBT power module and the cooling-system within a short diagnosis phase. For a short time, the IGBTs are heated with repetitive halfsinusoidal, low-frequency power losses. After thermal equilibrium is reached the amplitude and the minimum value of the temperature cycles are measured and averaged across several periods. An increased cycle amplitude indicates a degraded chip- or system-solder. If the minimum cycle temperature increases a contamination of the cooling system is identified. It is shown that the half-sinusoidal excitation of the power module solves the timing and accuracy problem of today's health-monitoring systems and has great potential to be implemented in a real voltage source inverter.