Modeling and Capacitors Voltage Balancing Control of STATCOM Based on Modular Multilevel Converter

Modular multilevel converter (MMC) provides a new concept in a wide range of applications due to its simple topology and high reliability. In this paper, a three phase four legs modular multilevel converter is used as a compensator in a four-wire network which feeds an unbalanced and distorted custom load. The purpose is to compensate this unbalance load currents by injection suitable currents besides the capacitors voltage balancing control in individual legs. In this paper, designing of compensator current controller will be done based on a composite control model (CCM) combined of average model and predictive control method. Also an independent controller has been proposed for capacitors voltage balancing whose task is to eliminate the circulating current oscillations in each leg. In order to control total energy stored in converter and also to remove the zero sequence current, two simple control schemes have been presented based on PI controller and closed loop controller, respectively. Finally simulation results have been presented in MATLAB/Simulink to confirm effectiveness and accuracy of proposed controller.

Keywords:

imbalance and harmonic compensation , predictive control model , averge model