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Conventional centralized control strategies may reduce the flexibility and expandability of a modular multilevel converter (MMC) system. To tackle this issue, this paper proposes a distributed control architecture that is capable of assigning certain control tasks to distributed local controllers and improves the modularity of an MMC system. A central controller dealing with the output current regulation based on sensed arm currents is adopted. The control of MMC internal dynamics and the pulsewidth modulation (PWM) generation are distributed into local controllers. Unlike the conventional MMC control that needs all submodule capacitor voltages for capacitor voltage averaging, the proposed capacitor voltage control only relies on local submodule voltage measurement. Consequently, communication-intensive capacitor voltage transmission in each control cycle is not required and the communication burden of the control system can be significantly reduced. The control loops and possible control conflicts among submodules are presented and considered for system stability analysis. The effectiveness of the proposed distributed control architecture and capacitor voltage control for an MMC are confirmed by the start-up, steady state, and transient experimental results. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel H-bridge structured ac–ac pulsewidth modulation (PWM) converter topology based on two-level non-differential ac chopper legs, which can work at the non-inverting and inverting modes for the utility voltage compensation. Compared to the traditional bipolar-type H-bridge ac–ac converter, no bidirectional switches are switched in a complementary manner to overcome the commutation problem due to the delayed response of electronic circuits and semiconductor switching devices. The detailed PWM control signals and operational principles are presented to regulate the output voltage in a bipolar manner. Especially the main advantage is that the proposed ac–ac converter has the same buck/boost operation process for non-inverting and inverting modes, which ensures the continuously average current supply to the low-voltage output side without a high-value capacitor to support power. Additionally, due to the common sharing ground of the input and output, the feature that output can reverse or maintain phase angle with input is supported well. Then, the detailed analysis, design conditions, and experimental verification based on a 1 kW experimental prototype are presented. [ABSTRACT FROM AUTHOR]