New scheme of phase-shifted carrier PWM for modular multilevel converter with redundancy sub-modules

In this paper, various modulation schemes for the Modular Multilevel Converter (MMC) were evaluated in the point of the output voltage harmonics, switching frequency, and operation implementation. It was confirmed that the existing Phase Shift Carrier (PSC) Pulse Width Modulation (PWM) shows better performance. However, this modulation scheme causes difficulty in handling the redundancy SMs involved in operation. This paper proposes a new PSC PWM for the 20MW 24kV MMC, which can provide an effective operation of the redundancy SMs. In order to verify the proposed PSC PWM, computer simulations with Power System Computer Aided Design (PSCAD) and Hardware in the Loop System (HILS) tests with Real Time Digital Simulator (RTDS) were performed. And actual MMC prototype was built and tested to verify the proper operation. The test results confirm that the proposed PSC PWM operates with expected performance.