Power Quality Control Strategy of MMC Inverter as Solid State Transformer on Distribution Network

The massive penetration of EV, rooftop PV and other power electronic-based loads will be a challenge in the distribution network. Even though conventional transformers are equipped with voltage regulators, they are passive towards harmonics, power quality problems (sag, swell) and reverse power flow due to future distribution network loads. One of the solutions currently being developed is the solid state transformer (SST). This research will focus on the LV stage SST using Modular Multilevel Converter (MMC) topology. MMC was chosen as the inverter topology because it provides the most features. The MMC topology provides a feasible and cost-effective approach for a DC/AC converter with a very high number of levels. MMC can control active/reactive power independently and easily control the magnitude, phase and frequency of the AC voltage. The most attractive feature is modularity. The two main control schemes Nearest Level Control (NLC) and Voltage-Frequency Control (VFC) are used as converter control algorithms in the designed MMC inverter. The results of the SST model simulation, the built MMC inverter can transmit and absorb reactive power. MMC inverter can maintain the voltage back to steady state when sag and swell events occur.