Research On The High Efficiency Photovoltaic Grid-connected Inverter Device

Fossil fuels in power generation can produce large amount of harmful gase on the environment. It may be result in high levels of pollution, as well as damage to human health. Free-carbon, green and renewable energy will become the best choice in the future. Solar energy resource with inexhaustible features will be widely distributed in the world, with good prospects for development. Solar panels are used to convert solar energy to suitable DC voltage, photovoltaic inverter device converts electrical energy into alternating current that identifies frequency and phase with grid, and deliver to the public grid. An isolation transformer three-phase photovoltaic inverter, its device selection, switching topology, MPPT, SVPWM control method and islanding detection technology are studied in the paper.The silicon carbide(Si C) Schottky Barrier Diodes(SBD) and Si C Metal Oxide Semiconductor field-effect transistors(MOSFET) are used as switching device in PV grid power generation device. Compare with silicon devices, Si C-type devices have unparalleled advantages, such as Si C SBD minimal zero reverse recovery time and reverse leakage currents, Si C MOSFET operating ambient temperature from 50 ℃to 150 ℃, the on-resistance change is small, so it has good high temperature properties. In addition, on-time and off-time of Si C MOSFET are less than silicon MOSFET and IGBT. Thus, the total switching losses are reduced effectively and the efficiency of the inverter device is improved well.PV grid solar modules are grouped in series to reduce the hot spot effect caused by solar panels blackout of light. Boost topology is used in DC side circuit, the MPPT(Maximum Power Point Tracking) is used as its control method. SVPWM control method is used in three-phase inverter bridge circuit side to enhance the use ratio of DC voltage, and produce approximately sinusoidal current waveforms. LCL filter is used in Output-side to reduce size of the filter and public grid harmonic components.Software phase lock loop(SPLL) is essential part of the photovoltaic inverter device access of the utility grid. Only to ensure the frequency and phase of the real-time tracking can delivered to the utility grid by photovoltaic power. Focus on balanced and unbalanced three-phase grid operation, the paper analyzes both of a single synchronous reference frame phase-locked loop(SSRF-SPLL) and decoupled double synchronous reference frame software phase-locked loops(DDSRF-SPLL). Photovoltaic Grid-connected inverter device can threat safety and electrical equipment when it’s operating in island operation statutes. Therefore, the detection and prevention of islanding protection has become a necessary means of PV grid. This paper analyzes the passive and active islanding detection method, and simulation results show the feasibility of frequency offset method islanding detection methods.On the basis of theoretical study and simulation analysis, the Photovoltaic Grid-connected inverter device is designed. Efficiency tests show that the Boost circuit conversion efficiency of 93% on the low voltage experiment platform.