Improved Elimination Scheme of Current Zero-Crossing Distortion in Unipolar Hysteresis Current Controlled Grid-Connected Inverter

In this paper, the generation reason and the improved elimination scheme of the current zero-crossing distortion (ZCD) of single-phase grid-connected inverter controlled by unipolar hysteresis current control containing band are investigated in detail. A current ZCD elimination scheme by exchanging the control signal of low-frequency leg of inverter ahead of the zero-crossing points of grid voltage is proposed. The effect of the variation of the amplitude and frequency of tied grid and the filter inductor on the optimal leading exchanging phase angle (LEPA) is analyzed. A single-phase hybrid filter-based enhanced phase-locked loop is proposed to estimate accurately the information of the grid, even under nonideal input conditions. Then, an online filter inductor estimation scheme is proposed to obtain the accurate actual inductor value. The former estimated parameters are used to calculate the exact optimal LEPA online to improve the performance of the current ZCD elimination scheme. Comprehensive experimental results are represented to verify the accuracy and feasibility of the theoretical analysis and the proposed improvement.