The effect of the arm reactance on the modular multi-level converter

One of the most important parts for the renewable energy to be connected to the grid is the design of the converter inside the wind farm or the solar power plant. This paper fully analyzed the influence of the arm reactance on the electro-magnetic transient mathematical model and the control strategy of the modular multi-level converter (MMC). After detailed derivation of equation, a simplified equivalent circuit was given. Then simulation results, based on a MMC model with 9 voltage-levels realized by MATLAB/SIMULINK, indicate that the effect of the inner loop current control is very sensitive to the changes of the reactance value, and that if the arm reactance is too large, the consequent potential drop on it will cause wide fluctuations of the DC voltage, thus affecting the control effect of the DC voltage control. All the simulation results coincide with the theory analysis.