Three-phase boost-type grid-connected inverters

Alternative energy sources, such as solar energy and fuel cells, are desirable due to their pollution-free property. In order to utilize the current infrastructure of the grid for power transmission and distribution, grid-connected dc-to-ac inverters are needed. However, previously proposed voltage source inverters with a two-power-stage structure or a cascaded structure increase the power losses and the complexity of the circuit. The current source type inverter with a large dc side inductor is also not desirable due to its size, weight and losses. A new three-phase boost-type grid-connected inverter, which can be controlled by one-cycle control (OCC) method or the conventional pulse width modulation (PWM) method, is proposed in this paper. The proposed inverter has only a single power stage converting dc power to ac power by injecting three sinusoidal currents into grids, which greatly reduces power losses and the complexity of the circuit. The input dc voltage is lower than the peak grid voltage and can vary in a wide range, which interfaces well with the dc voltage of the photovoltaic or fuel cells. The large dc side inductor is not necessary and the output ac currents are sinusoidal and in phase with grid voltages. With OCC method, the inverter preserves the advantages of simple circuitry, good stability and fast dynamic response. Experiments have been performed with a 1.5kW laboratory prototype to verify the good performance of the inverter.