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NSGA-III Based Controller Parameter Design for Optimizing Impedance of VF Controller MMC

The positive damping characteristic of a modular multilevel converter (MMC) is important for improving the stability of an MMC based system. However, it is difficult to optimize the impedance characteristics of the MMC by adjusting the controller parameters, due to the complexity of the existing impedance model. This paper investigates the influence of the voltage-frequency(VF) controller on the impedance of an MMC, in which the relationship between open loop controlled impedance and VF controlled impedance is established. Based on the proposed impedance model, Non-dominated sorting genetic algorithm III (NSGA-III) is used to optimize the parameters of the VF controller, which makes the MMC positive damping in chosen frequencies. The time domain simulations in PSCAD/EMTDC verify the proposed impedance model and the optimized results.