Grid-forming (GFM) converters can support system voltage and frequency, which promotes the integration between distributed generations and power grid. Due to the time delay of digital control, the virtual impedance exhibits opposite damping characteristics on both sides of 1/6 of the sampling frequency ( fs /6). The stable operation of GFM converters can be achieved by setting a reasonable damping feedback coefficient in each separate frequency interval. However, the load or line impedance variation may cause the resonant frequency of LC filter to cross the frequency boundary, so GFM converters will not be stable when the resonant frequency is near the frequency boundary. In this paper, an improved active damping control with a lead compensator is proposed to achieve positive damping from 0 to fs /4, which eliminates the instability resonant frequency region, and the stability of GFM converters is significantly improved. Then, the procedures of parameter tuning for obtaining the maximum system damping is presented. Furthermore, the discrete-time domain resonant controller is proposed to acquire a high-performance voltage control, which brings a fast transient response without overshoot for output voltage. Finally, experimental results verify the effectiveness of the analysis.     «

Grid-forming (GFM) converters can support system voltage and frequency, which promotes the integration between distributed generations and power grid. Due to the time delay of digital control, the virtual impedance exhibits opposite damping characteristics on both sides of 1/6 of the sampling frequency ( fs /6). The stable operation of GFM converters can be achieved by setting a reasonable damping feedback coefficient in each separate frequency interval. However, the load or line impedance varia...     »