A Novel PQ Control Strategy for Non Phase-Locked Loop based on Hilbert Transform

The feed-forward decoupling PQ control strategy is widely used in the grid-connected control for the micro-grid inverter. When the grid voltage is unbalanced, the output of the inverter usually contains the negative sequence components, the third harmonic and other components which will affect active and reactive power stabilization with PQ control. A novel PQ control strategy with non phase-locked loop (PLL) is proposed in this paper. By presetting a synchronous rotation frequency, the negative errors for the specified frequency can be converted each other. With Hilbert transform of the amplitude and phase, the positive sequence harmonic components, the fundamental negative sequence component and the negative sequence harmonic components can be eliminated. Even under the abominable grid conditions, it can extract the synchronization signal and improve the performance of the PQ control. Simulation results verify the effectiveness and feasibility of the proposed strategy.