IN-SITU INSTRUMENTATION FOR DEGRADATION MONITORING OF POWER SEMICONDUCTOR DEVICES IN POWER ELECTRONICS CONVERTERS

Power electronics converters are an integral part of modern power and energy system. Power semiconductor switching devices are the most significant component in a power electronics converter. Power semiconductor devices such as MOSFETs/IGBTs age through different degradation mechanisms in long-term applications. Failure of MOSFETs/IGBTs is one of the primary causes of power electronics failure. And MOSFETs on-state resistance (RDSON) is a key health-indicating parameter. This dissertation presents sensing circuit designs that enable real-time monitoring of on-state voltage of the MOSFETs/IGBTs. In addition a complete online in-situ health monitoring system of the MOSFETs in a three-phase inverter is presented. A new on-state drain-source voltage (VDSON) sensing circuit has been used to monitor the RDSON of the high-side MOSFETs. This sensor references the drain of the high-side transistors for their VDSON measurement and allows VDSON measurement of multiple high-side transistors with respect to the same ground reference. The high-side VDSON measurement circuits combined with low-side VDSON measurement circuits have been used for a complete RDSON monitoring of all the MOSFETs in the inverter. The drain current (IDS) is captured from measurements using an off-the-shelf current sensor located at the output filter inductor. Accounting for propagation delays in the measurement circuitry, both the VDSON and IDS are sampled and converted into digital data multiple times in a switching cycle, filtered, and stored in a digital signal processor (DSP). The DSP, originally used for the inverter control, then processes the sensor data captured over one grid cycle and calculates the average RDSON of the MOSFETs of the inverter. Validations of all the sensing circuits, using theoretical analysis and hardware experiments along with the software implementation for data processing and handling are presented in the dissertation for this real-time, in-situ RDSON measurement. Furthermore, a method of mapping the MOSFET's RDSON to the junction temperature is presented which can be used for real-time accurate junction temperature estimation of the MOSFETs.