Research On Micro Grid-connected Photovoltaic Inverter

With the development of economic and industry, energy crisis and pollution have become moreserious. Now renewable energy resources are researched to solve these problems. In green energies,photovoltaic power generation attracts more attention because of its pollution-free.Nowadays, there are two potential markets for electric power generation from photovoltaicsystems: large-scale power plants sized up to several megawatts and small-scale residentialapplications (0.1to5kW). Micro photovoltaic system combines PV modules and single-phasegrid-connected inverter together, ensuring that every panel works at MPP even under partially shading.Beyond that, the installed power module can be easily upgraded; it has the possibility to plug and play.Standardize design can improve reliability and reduce costs, and grid-connected inverter doesn’t takespecial installation space. Moreover, by optimizing the cooling and removing the fan, the reliability ofmicro PV system improves from5years to20years; one micro PV modules failure will not affect thewhole PV system.Micro PV inverter requires high efficiency and high-power density, low cost and high reliability,the so-called flyback inverter is rather an attractive solution. The inverter operates in DCM so as tobehave as a current source. Dual interleaved flyback is designed to reduce the switch stress andcurrent harmonic, RCD and active clamping is compared to absorb the leakage energy. There are strictstandards for Interconnecting Distributed Resources with the Electric Power System especially withthe current, so PR control with harmonic compensation is applied for current loop of the inverter. Asthe output of PV panel changes with illumination and temperature, the inverter is able to track themaximum point of panel’s power, and two methods are researched to solve the DC voltage breakdownproblem. European efficiency is an import indicator in grid-connected PV system considering thewhole range of load, while inverter performs low efficiency under low load, so a pulse skippingcontrol strategy is designed to improve European efficiency. Based on the design and simulation, a230W micro grid-connected PV inverter prototype controlled by DSP28035is built for experimentaljustification. Also the design methods of hardware circuit and software program are presented.