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Analyzing and Designing a Current Controller for Circulating Current Reduction in Parallel Three-Phase Voltage-Source Inverters
Kiryong Kim, Dongsul Shin, Hee-Je Kim, and Jong-Pil Lee
Abstract A circulating current is a major problem caused by directly connecting voltage-source inverters (VSIs) in parallel. This circulating current occurs as a zero-sequence current between the inverters by speci?c switch states. Several studies have presented alternatives using hardware and software methods. When coupled inductors (CIs) are employed for the high-frequency circulating current, a controller is required to prevent the low-frequency circulating current from saturating the CIs. In this study, the zero-sequence circulating current and its alternatives are investigated using hardware and mathematical description. A high-performance circulating current controller is proposed by applying a repetitive controller to the zero-sequence current control loop. The proposed controller can effectively minimize the low-frequency circulating current without any data sharing between the inverters in unfavorable conditions. It can also be applicable to the modular con?guration of parallel three-phase VSIs. Experimental results verify the performance of the proposed controller.
Keyword Circulating current, Parallel operation, Voltage source inverter (VSI)
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