Analysis of Grid Current Distortion and Waveform Improvement Methods of Dual-Active-Bridge Microinverter

Due to its merits of fewer power switches, a wide zero-voltage switching range, and high efficiency, the dual-active-bridge (DAB) microinverter is drawing growing interest. However, it has an inherent issue of grid current distortion and spikes, which deteriorate the total current distortion. Existing literature mainly focuses on modulation strategies and barely analyzes the underlying causes, let alone the methods to improve grid current quality. This article fills this blank by revealing the dead-time effect on grid current distortion from two aspects. Several methods are proposed to improve the grid current quality and are compared in detail. Besides, a complete set of grid current closed-loop control methods is proposed based on the DAB microinverter modeling. The control method not only provides the correct control logic but also eliminates the immanent time-varying and condition-dependent features of the control loop, making the proposed current control method self-adaptive and universal. The analyses and the proposed control method are all validated by experimental results.