Three-Phase ZPUC-MMC Grid Connected Converter

Modular Multilevel Converter (MMC) is a promising topology that gained lot of interest in medium-voltage grid-connected applications due to its modularity, scalability, and adaptability. Although increasing the number of submodules per arm leads to a higher number of voltage levels and better waveforms quality, the size and then the cost of the converter remains a challenge. Therefore, a trade-off between topology complexity and power quality exists. This paper proposes an MMC based on Z Packed U-Cell converter as Submodule (ZPUC-SM) to generate a higher number of voltage levels with reduced number of SMs. When compared to HB-MMC, this topology features reduced components count for generating the same voltage levels. Thus, the candidate topology is considered to be a promising solution for medium-voltage applications connecting the utility. This paper details the design, modeling and control of ZPUC-MMC operating as a three-phase grid-connected converter. The controller task is to regulate output current to fulfill grid connectivity requirements. A Phase shifted-PWM with an integrated voltage balancing algorithm takes in action of controlling the three-capacitors voltages of each arm. Thus, no additional voltage controllers are required. The performance of the proposed converter along with its control system are validated with MATLAB/SIMULINK, and the simulation results validate the robustness and effectiveness of the proposed control during both steady-state and dynamic operations.