Open Circuit Fault Identification Technique for Switch and Diode in a Reduced Sensor Based Medium Voltage MMC

The modular multilevel converter (MMC) is a popular choice for various medium voltage applications. Recently, several works have focussed on reducing the number of sensors and thereby reducing the hardware complexities in an MMC. Although the normal operation of MMC with a reduced sensor scheme showed some decent performance, the detection of a switch or diode fault and its localization with a reduced sensor operation remains challenging. There is very few literature that deal with fault identification in MMC with reduced sensor operation, but they lack either due to complexity in fault identification technique or due to dependency on additional measurement. In this work, for the first time, both switch and diode open circuit faults are identified based on certain measurements such as arm voltages, observed arm current, and switching status. As these measurements are being used for the healthy operation of MMC, additional sensor is avoided for the proposed fault identification technique. The fault identification also avoids a computationally intensive software based approach. Extensive simulation and experimental studies are carried out to identify single and multiple switch and diode faults. It is also verified that there is no false trigger in open circuit submodule fault identification due to step change in output current.