Dynamic Performance of a Modular Multilevel Back-to-Back HVDC System

TLDR

The modular multilevel converter (MMC) is a newly introduced switch‑mode topology with promising applications in high‑voltage direct current (HVDC) transmission. This paper investigates the dynamic performance of an MMC‑based back‑to‑back HVDC system. A phase‑disposition sinusoidal pulse‑width modulation strategy with voltage balancing is proposed, a mathematical model for the MMC‑HVDC system under balanced and unbalanced grid conditions is developed, and its dynamic behavior is evaluated through time‑domain simulations in PSCAD/EMTDC. Simulation results demonstrate that the MMC‑HVDC station can satisfactorily respond to system dynamics and control commands while maintaining DC‑capacitor voltage balance under both balanced and unbalanced operating conditions.

Abstract

The modular multilevel converter (MMC) is a newly introduced switch-mode converter topology with the potential for high-voltage direct current (HVDC) transmission applications. This paper focuses on the dynamic performance of an MMC-based, back-to-back HVDC system. A phase-disposition (PD) sinusoidal pulsewidth modulation (SPWM) strategy, including a voltage balancing method, for the operation of an MMC is presented in this paper. Based on the proposed PD-SPWM switching strategy, a mathematical model for the MMC-HVDC system, under both balanced and unbalanced grid operation modes, is developed. Dynamic performance of the MMC-based back-to-back HVDC converter system, based on time-domain simulation studies in the PSCAD/EMTDC environment, is then evaluated. The reported time-domain simulation results show that based on the adopted PD-SPWM switching strategy, the MMC-HVDC station can respond satisfactorily to the system dynamics and control commands under balanced and unbalanced conditions while maintaining voltage balance of the dc capacitors.