Fault Diagnosis of Open Switch Failure in Voltage Source Inverter Using Average and RMS Phase Voltages

For a VSI in a grid-connected renewable energy system, there are several failure modes that can occur. In this paper, a new method is proposed and implemented to detect and localize open switch faults in a three-phase VSI. The proposed technique utilizes a series of measurements of both average and RMS phase voltages at the output terminals of the inverter. Using MATLAB/Simulink, the proposed fault diagnosis system is designed and tested for each type of open switch fault in an attempt to detect the presence of both single and double open switch faults. The study covers a total number of 16 fault cases including the normal operation condition. The method is tested for its robustness and reliability against variation of load, transient condition, and noisy signals added directly to the phase voltages under testing. As a result, advantages and limitations are discussed according to several important criteria such as effectiveness, time taken for fault detection, implementation effort, tuning effort, and the diagnostic variables required. Finally, after identifying the faulty phase(s), remedial measures are employed that include a rapid and safe turnoff of the power switches and a fail-safe reconfiguration operation to avoid failures that are more dangerous.