The flying-capacitor modular multilevel converter (FC-MMC) has been introduced as a hardware development of the conventional MMC with the aim of reducing the cell capacitor ripple voltage in the application of electrical drive at low speeds. The capacitor ripple voltage More
The flying-capacitor modular multilevel converter (FC-MMC) has been introduced as a hardware development of the conventional MMC with the aim of reducing the cell capacitor ripple voltage in the application of electrical drive at low speeds. The capacitor ripple voltage of the cells in this converter is reduced only by injecting high frequency circulating current between the arms. In the conventional control method of this converter, the circulating current component is injected with the aim of complete elimination of the voltage ripple at low frequencies, which leads to an unnecessary increase of the current amplitude in the converter arms. In this paper, the converter control system is modified by finding the relationship between the cell capacitor voltage ripple and the high frequency circulating current amplitude. Then, by injecting the appropriate amplitude of the circulating current, the voltage ripple is controlled in an acceptable range. It is shown that by partial compensation (instead of full elimination of the voltage ripple), in addition to reducing the amplitude of the arm currents, the losses of the electrical system are significantly reduced. The results of simulations and experiments confirm the successful performance of the proposed method.
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