Volt-second-based control method for discontinuous conduction mode flyback micro-inverters to improve total harmonic distortion

Flyback-type micro-inverter is an attractive solution for photovoltaic ac-module applications because of several advantages; such as simple current control, working without ac current sensor and potentially low cost. However, it suffers from the dc-link voltage ripple that causes it to merge with the third and fifth harmonics on the output current. For this reason, a very smooth dc-link voltage is essential in order to keep total harmonic distortion (THD) at a low level. However, the voltage ripple is inevitable in practise for single-phase inverters because of pulsating instantaneous power. This study presents a new volt-second-based current control method for flyback micro-inverters which improves THD caused by the voltage ripple. The proposed method works effectively up to approximately 20% of the dc-link voltage ripple. In addition, the volt-second-based control method is able to allow reduction of the power decoupling capacitor value. Experimental results validating the proposed method are also presented.