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. [ABSTRACT FROM AUTHOR]