Simplified Power Estimation Feedforward to Reduce DC-Link Capacitance in Single-Phase Dual-Stage Full-Bridge Microinverter

Abstract

To enhance the reliability and lifetime of a single-phase dual-stage full-bridge microinverter, the film capacitor may be preferably used instead of a DC-link electrolytic capacitor. However, concern to hold the DC-link voltage during transients, this expectation needs an input current sensor for conventional feedforward power balance compensation in the voltage control loop, increasing whole system cost. Moreover, the inherent double-line frequency of single-phase AC instantaneous power still appears on the DC-link voltage that is the adverse cause of grid-injected third-order harmonic current of the inverter. For overcoming all the obstacles described above, without any use of an input current sensor, this paper proposes a modified notch filter to function with an input DC power estimation feedforward for the voltage control loop. Consequently, using the film capacitor can be used without any system performance reduction, which can reduce system cost. The simulation results show that the proposed power estimation feedforward can cope with a dip of DC-link voltage, while the good quality of grid-injected current is not significantly different from using the conventional feedforward.