Current Zero Crossing Distortion Control Strategy for Three-Phase Dual Buck Grid-Connected Inverter Based on Duty Cycle Compensation

Compared with the traditional three-phase full-bridge inverter, the three-phase dual Buck grid-connected inverter does not need dead zone, which can avoid the extra low-frequency current harmonics. Half cycle control is often used, but it makes the inductor current discontinuous when the current is near zero and results in zero crossing distortion of grid-connected current. Usually, the full cycle control near the zero-crossing area of the current can suppress the distortion, but it increases current ripple that is not conducive to the design of the inductor and brings extra power losses. This paper analyzes the reason of the current zero crossing distortion under half cycle SPWM (sinusoidal pulse width modulation) controlled three-phase dual Buck grid-connected inverter. In addition, this paper changes the switching conditions for half cycle control and proposes the duty cycle compensation method with the detailed derivation of the ideal modulation wave function under the discontinuous current region. As a result, the duty ratio is changed near the switching point of the half cycle to make the average value of the inductor current sinusoidal. Thus, the current distortion can be suppressed, and the efficiency of the whole system can be ensured. The theoretical analysis is verified by the simulation and experiment. © 2018, Electrical Technology Press Co. Ltd. All right reserved.