Sinusoidally Modulated AC-Link Microinverter Based on Dual-Active-Bridge Topology

In this article, a bidirectional single-stage ac-link microinverter is proposed with a novel sine pulsewidth modulation. The proposed microinverter operates on the principles of dual-active-bridge converter modulation and thus allows seamless bidirectional power flow with soft switching. Contrary to the traditional two-stage microinverter interfacing a variable input voltage source, the proposed converter integrates dc-dc and dc-ac into a single stage, retaining functionality over a wide input-to-output voltage ratio. The synthesis of the sinusoidal output is achieved by applying a new composite modulation scheme that utilizes phase-shift modulation schemes used in the dual-active-bridge converter. Different parameters of the phase-shift modulation (namely, triple-phase-shift modulation) affect the overall composite modulation in terms of its ability to achieve soft switching and the average power flow. The mode analysis was carried out to demonstrate different modulation segments and its overall effect on the output power, efficiency, total harmonic distortion, etc. Previous works on a similar topology requires computationally intensive optimal modulation methods, which update every switching cycle. However, the proposed modulation parameters are analytically determined; hence, the controller only updates every line cycle, which is a significant reduction of control complexity. The proposed converter modulation scheme is designed and simulated in PSIM environment, which supports the theoretical analysis. A prototype was built for an experimental study. Results verifying the modulation scheme and the working principles of the converter are presented.