Reduced Switching-Frequency Modulation Design for Model Predictive Control Based Modular Multilevel Converters

TL;DR

This paper introduces a new switching algorithm for modular multilevel converters that reduces switching frequency significantly while maintaining control objectives, tested on a seven-level MMC-HVDC system.

Contribution

It presents a novel switching algorithm that considers previous switching states, reducing switching frequency without compromising voltage balancing.

Findings

Switching frequency is significantly reduced.

Submodule capacitor voltages are minimally affected.

Algorithm performs well under various operating conditions.

Abstract

This paper proposes a novel switching algorithm for modular multilevel converters (MMCs) that significantly reduces the switching frequency while fulfilling all control objectives required for their proper operation. Unlike in the conventional capacitor voltage-balancing strategies, in addition to submodule (SM) capacitor voltages, the proposed algorithm considers previous switching statuses during sorting. The algorithm is applied to a seven-level back-to-back MMC-HVDC system and tested under various operating conditions. Significant reduction in the switching frequency with trivial impacts on submodule capacitor voltages are observed.