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Equivalent Switch Circuit Model and Proportional Resonant Control for Triple Line-Voltage Cascaded Voltage-Source Converter

This paper studies the modeling and control for a triple line-voltage cascaded voltage-source converter. The unbalanced current of each cascaded unit results in complicated control algorithm and structure due to its structural characteristic, and there exists a double-frequency fluctuation for each dc-capacitor voltage. To solve the aforementioned problems, an equivalent switch circuit model for the converter is established in this paper based on the external circuit characteristic, and a simple proportional resonant control strategy for the model is also proposed. The technique realizes the power factor regulation and the balanced stable transmission of the converter power in a two-phase stationary frame. And by adding an ac-side voltage compensation control for each converter, the double-frequency fluctuation of each dc-link voltage is effectively restrained. Besides, the strategy adopts a carrier phase-shifting space vector pulsewidth modulation suitable for the structural characteristics, which effectively simplifies the modulation algorithm. The proposed strategy has such advantages as less hardware and computation, simpler control structure, better dynamic and static performance, and better robustness. The experimental results have verified the feasibility and availability of the proposed model and its control method.