Mission Profile Emulator for Individual Submodule in Modular Multilevel Converter With Nearest Level Control

Abstract

The mission profile emulator (MPE) proves to be an effective and cost-efficient tool to validate the design and reliability of the submodule (SM) in a modular multilevel converter (MMC). However, the low-frequency and random switching behaviors of SMs in the MMC with nearest level modulation (NLM) undermine the testing accuracy of MPE in many aspects, including the large ripples in the loading current and the lack of flexibility in control dynamics. To tackle these problems, a MPE with special control structure is introduced in this article to test the individual SM modulated with NLM. The proposed testing method is realized with a common single-phase configuration and the current ripples are suppressed by separating the control functions for two arms in a full-bridge circuit. What's more, the proposed approach gets rid of the need for historical gating signals of the SM under test, and offers a virtual control method to autonomously generate the SM gating signals that can realize the self-balancing of capacitor voltage and the emulation of NLM behaviors in MMC system. Simulations and experimental measurements are also given to validate the proposed method.