Virtual synchronous generator strategy for suppressing output power fluctuation without additional energy storage

The virtual synchronous generator (VSG) is beneficial to reduce the fluctuation of the output power of the renewable energy sources, but its output power characteristics are sensitive to the disturbance of the grid frequency. Grid frequency disturbance causes the oscillation of the output power of the VSG-controlled grid-tied converter. In order to solve this problem, a virtual inertial control method for renewable energy sources without additional energy storage is proposed. In the view of renewable power generation, the renewable energy source behaves as a VSG, which minimises the impact of power generation disturbances on frequency characteristics. In the view of grid frequency disturbance, the renewable energy source behaves as a droop-controlled grid-tied converter, which adapts to the grid frequency to avoid the power oscillation of grid-tied renewable power source caused by the grid frequency disturbance. Grid frequency is introduced into the closed loop control through feedforward techniques, and the frequency extraction method is implemented based on a frequency-locked loop (FLL) modified by a moving average filter. Based on the small-signal model of the proposed VSG method, the influence of the equivalent FLL gain and time constant is analysed. The experimental results verify the performance improvement of the modified VSG method.