Aging Detection of Multiple Power Switches in a Live 3-Phase Inverter using Reflectometry

Abstract

Reflectometry-based degradation detection technique designed around spread spectrum time domain reflectometry (SSTDR) for multiple power semiconductor devices in a live 3-phase inverter has been proposed in this paper. Using SSTDR, aging-related impedance variation within the power semiconductor device can be identified without interrupting the circuit's normal operation. The rapid change in the SSTDR propagation path due to the high switching frequency of power switches makes real-time health monitoring challenging. Existing SSTDR based techniques proposed for degradation detection of the DC-DC converter and single-phase grid-tied H-bridge PV inverter require a large number of SSTDR test data acquisition to minimize the error caused by rapid change in the SSTDR propagation path. Moreover, a three-phase inverter may utilize a very complicated switching scheme and multiple impedance paths compared to the other converter topologies used in the previous SSTDR-based degradation detection technique. The proposed method requires significantly less amount of SSTDR data to successfully characterize the device aging by adopting a little modification in the inverter switching scheme. Included experimental results demonstrate that the proposed method can reduce the number of accessible nodes for performing the state of health (SOH) monitoring of all individual devices used in a three-phase inverter, which will eliminate the need for a separate SOH monitoring module for each device. In addition, due to SSTDR's ability to be embedded in the gate signal, the proposed technique can be integrated with the gate driver module, thus making it intelligent.