Fast and Fault-Tolerant Model Predictive Control of MMCs Under Selective Harmonic Elimination

Abstract

Modular multilevel converters (MMC) are an attractive choice for various applications, including medium- and high-voltage drives. The large number of semiconductor-based submodules (SM) in an MMC makes it vulnerable to SM switch failures. This paper proposes a fault-tolerant (FT) selective harmonic elimination method to enable seamless operation of an MMC during such failures. The effects of switch failure on phase voltage waveforms are studied first. Then, a method is proposed to design the FT SHE-PWM waveform to preserve its harmonic performance. A model predictive controller (MPC) is also proposed to increase the capacitor voltages during an SM failure to maintain the fundamental component of the faulty phase voltage and balance the line voltages. The advantages of the proposed method are verified through offline and real-time simulation studies on a three-phase nine-level MMC in PSCAD/EMTDC software and RTDS.