Multi-string single-stage grid-connected inverter for PV system

The objective of this paper is to propose a multi-string single-stage grid-connected inverter (MSG-inverter) for PV power generation system. The proposed MSG-inverter can improve the power conversion efficiency, increase the overall PV array output power, reduce the output inductor size, eliminate the input current sensor, and simplify the control circuit. The proposed MSG-inverter is composed of distributed buck-boost type dc-ac inverters (BBIs) and an ac-ac filter. The distributed BBIs can eliminate the shading effect while fulfill the functions of dc-ac conversing and the maximum power point tracking (MPPT). The ac-ac filter is realized by 4 active switches operated at low switching frequency and an output inductor. It can convert the high frequency pulsating ac current generated by the distributed BBIs into a sinusoidal one with utility line frequency. Based on the developed equations, the MPPT feature of the proposed BBI can be achieved without the need of input current sensor. Also, with the interleaved operation between distributed BBIs, the current ripple of the output inductor can be reduced too. The computer simulations and hardware measurements are shown to confirm the validity of the operation principle of the proposed MSG-inverter.