An improved grid voltage observation method for grid-connected inverter

The voltage observation method via sliding mode observer (SMO) is widely used in the predictive control of grid-connected inverter (GCI) without AC voltage sensor. However, conventional methods not only need complex phase and amplitude compensation, but also are greatly affected by low-order harmonics of grid voltage. Therefore, a simple method of voltage phase and amplitude compensation is proposed, which is based on the conventional SMO. Besides, an improved phase-locked loop (PLL) is also adopted to reduce the interference of low-order harmonics in power grid. The improved PLL eliminates the interference of 5th and 7th harmonics and realises the accurate observation of power grid frequency and angle. The effectiveness of the proposed method is verified by MATLAB/Simulink simulation.