An analysis of improved current control strategy for DC-AC modular multilevel converters

SUMMARY This paper deals with an improved decoupling control of the current components applied to three‐phase modular multilevel converter (MMC) via rotating d‐q frame theory based on the mathematical model of the system. In order to apply independent controllers for the two axes in d‐q coordinates, the impact of the q‐axis on the d‐axis component and vice versa has to be removed. This is done by creating a decoupling block consisting of modified coupling terms. The feed‐forward ac‐side voltages compensation can effectively reduce any harmonic disturbance of the load side. Furthermore, we employed the strategy to reduce the capacitor voltages variation in each arm. A comparison of simulation results for both existing and improved decoupling current control algorithms using a (6.6 kV, 6 MW) induction motor drive verifies the superior performance of the proposed controller especially for good current reference tracking and disturbance rejection properties despite the variations in the system parameters. Copyright © 2013 John Wiley & Sons, Ltd.