On the grid side, the half‐bridge topology of the microinverter is of interest for solar rooftop applications because of its high efficiency, low component count, and cost‐effectiveness. However, it has an inherent double‐line frequency ripple voltage on the dc‐link, which causes the injection of a third‐order harmonic current when the voltage control loop is closed. Furthermore, in practice, different average voltages or different capacitances of the two capacitors at the dc‐link produce a second‐order harmonic current that flows into the grid. In this paper, the analytical details of these harmonics are comprehensively described, and a simple and effective low‐cost technique using the cascaded connection of two modified notch filters is proposed in the voltage control loop to mitigate their effects. The simulation and experimental results of a 300 W microinverter indicate that the proposed filters represent an effective low‐cost solution and perform well in accordance with the IEEE 1547 standard, even if the capacitances at the dc‐link are mismatched by 20%. Besides, the prototype is tested when occurring of the changing +1% of the line frequency, or appearing of the distorted waveform of grid voltage with the composition of 6% of fifth‐order harmonic.

A single-phase phase-locked loop (PLL) is popular for line frequency estimation. However, the line voltage may not be a pure sinusoidal waveform in practice, which causes high noise in the estimated frequency signal generated from the PLL. An increasing system order using a digital RST controller is presented to enhance high-frequency rejection. Consequently, the estimated frequency signal is significantly improved to be precise and smooth, even under a distorted line voltage. The proposed control strategy was verified by simulation results.

Nowadays power electronics converter that uses for emulate electrical characteristic V-I curve of renewable dc power source are widely interested in research fields. This paper concerns with a photovoltaic (PV) array simulator using a classical dc/dc buck converter as power stage. The inductor current of the converter is used as control variable that is characterized by digital R-S-T controller, so the converter can emulate accurately the V-I curve, even under partial shading condition. Fundamental of controller design is presented with the technique of canceling discrete zero of plant. The details of PV array model are also investigated in order to prepare an appropriated current loop command signal. The design concept is realized by 330 Watts of prototype. Finally, the experimental results validate the proposed controller.