Passivity Analysis and Enhancement of Voltage Control for Voltage-Source Converters

The grid-forming control is increasingly used with distributed generation systems either in grid-connected mode or islanded mode. The voltage control is essential to a grid-forming converter, which is generally realized with a dual-loop voltage-current control. This paper evaluates the passivity of the output impedance of the dual-loop voltage control, where two voltage regulators are compared, and it turns out that the non-passive region is inevitable in the high-frequency range, which may lead to harmonic instability. An output current feedforward control is then proposed to eliminate the non-passive region below the Nyquist frequency. Lastly, simulations and experimental results corroborate the analysis.