A novel topology and control strategy for maximum power point trackers and multi-string grid-connected PV inverters

The number of grid-connected photovoltaic (PV) systems is increasing noticeably. However, the high initial cost of such systems impedes their wide spread commercialization. This paper presents a new multi-string grid-connected converter topology and a-simplified control strategy with a minimum number of components that considerably lowers the initial investment and increases the life time of the system. The proposed system consists of two stages. The first stage is a new robust maximum power point (MPP) tracker circuit that can rapidly follow the given reference signal of the MPP under any irradiation or temperature condition. This stage also decouples the output power pulsation from the input-power generation to minimize the deviation-from the MPP. The multi-string topology enables the circuit to extract the maximum available power from each string independently for partially shaded conditions. The second stage is a current source inverter using a modified modulation strategy to inject a current with minimum harmonic components into the grid at unity power factor. Simulation results are provided to demonstrate the performance of the converter and to prove the validity of the proposed control system.