Low switching loss and harmonics PWM for three-phase grid-connected PV inverter

Photovoltaic (PV) power generation has become viable alternative due to the advantages of no fuel cost and abundance of sunlight. In a grid-connected PV inverter system, besides stability and reliability, the efficiency is always an important factor. To generate active power effectively, the grid-side current must be in phase with the grid voltage. Further, the current harmonics must be low enough to avoid excessive losses. At the inverter side, the efficiency is inverse proportional to the summation of switching loss and conducting loss. Further, for the switching frequency higher than several Kilo-Hz, the dominant loss is switching loss. This means that to have high efficient grid-connected PV power generation system, a low switching loss switching strategy for inverter to produce low harmonics currents is essential. In this paper, a fixed injection PWM is proposed to achieve both low current harmonics and low switching losses. The proposed method can be directly applied to the three-phase two-level grid-connected inverters without any circuit modification. In the simulation, a 30.8% reduction in the current total harmonics distortion is obtained comparing with the conventional switching strategy. Further the 14.78% improvement of inverter efficiency is achieved.