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High-performance Resonant Controller Implemented in the Discrete-time Domain for Voltage Regulation of Grid-forming Converters

Grid-forming converters (GFCs) offering sinusoidal voltage supply have been widely employed in a lot of applications. In this work, the dual-loop voltage-current control for GFCs is comprehensively approached. Firstly, optimum tuning of the current loop is addressed to achieve the maximum enhanced active damping from the prospect of the developed equivalent plant, instead of the current loop which has been the focus of the existing literatures. Then, effectiveness of the resonant controllers (RCs), i.e. proportional resonant and vector proportional integral, which are very popular for voltage regulation of GFCs, is addressed. It is found that for GFCs with reasonably designed output filter, specially for high-power applications with a low switching frequency, weakly-damped region exists in the close-loop frequency response with either of the two RCs employed, which can further result in constrained bandwidth and slow transient response. To solve this issue, a discrete resonant controller is developed which avoids the weakly-damped region and a fast response of the output voltage can be achieved. Experimental results have verified the effectiveness of the proposed controller for voltage regulation of GFCs.