A Currentless Submodule Individual Voltage Balancing Control for Modular Multilevel Converters

Abstract

The capacitor voltage balancing is one of the most important issues for safe and reliable operation of the modular multilevel converters (MMC). This article proposes a currentless submodule individual voltage balancing control (SMIVBC) to realize capacitor voltage balancing in the MMC. Through regulating the dc component in each submodule (SM) capacitor current by modulation index mbased SMIVBC or phase angle θ-based SMIVBC, each SM capacitor voltage can be individually controlled to follow a reference value, which can realize capacitor voltage balancing in the MMC. The proposed SMIVBC not only requires no sorting technique to select the SMs in the MMC avoiding sorting algorithm, but also requires no knowledge of current in the MMC, which reduces the sensors and sampling signals, saves the cost, and improves the reliability. Simulation studies with professional tool power systems computer aided design for electromagnetic transients including DC (PSCAD/EMTDC) and experiment studies with a down-scale prototype in the laboratory are both conducted and their results confirm the effectiveness of the proposed SMIVBC for the MMC.