Study On Control Strategy Of PV Three-Phase Grid-Connected Inverter Base On Smart Grid

Rapid non-renewable fossil energy consumption caused increasingly serious environmental pollution problems, it is urgent to find a clean alternative energy. On the one hand, the clean energy can alleviate the energy crisis; on the other hand it can effectively inhibit the greenhouse effect caused by burning fossil fuels and other environmental problems. Solar energy as a clean, renewable energy, it's pollution-free, wide distribution of available resources, renewable. The ultimate form of photovoltaic (PV) power generation is grid-connected photovoltaic inverter. Power of PV cells can be transmit a long distance by grid. The power of PV power generation is not instable, for its output power is vulnerable to environmental impact. The PV power generation system will infect the grid's steady running. Resolving this contradiction, we must rely on the development of smart grid. To ensure the reliability of power grid, meet the technical requirements of grid-connected photovoltaic inverter and reduce the adverse impact on the grid, we must study the grid-connected PV inverter base on smart grid. Based on the analysis of the running mode and characteristics of smart grid, this thesis studied the grid-connected three-phase inverter for PV cells, the main contents are as follows:(1) The electrical output characteristics of photovoltaic cells are analyzed by actual parameters. Because of the change of external environment, the output power is nonlinear. Photovoltaic inverter will affect the stability of the grid when connecting on grid, but adverse effects can be reduced by using smart grid.(2) This thesis analysis the grid-connected three-phase inverter technology. Using dq transformation and PLL, the grid side of the voltage amplitude, frequency, and phase are accurate tracked. If PV inverter is connected with grid, the only parameter can be controlled is current. This thesis calculates the state space equations of three-phase inverter LCL filter, and then uses the small signal model of linear equations to realize the decoupling control of voltage and current. On this basis, we designed a new three-phase inverter grid current control methods, which outer side is power grid voltage, the inner side is the inverter current and voltage synchronous control. Then a grid-connected three-phase inverter simulation model is established to implement the grid-connected three-phase inverter current control simulation.(3) Three-phase inverter for photovoltaic island phenomenon is analyzed. This thesis suggests three pattern of connect with grid. If island phenomenon occurs, the electrical parameters of load will change. A three-phase PV inverter islanding detection simulation model is established to detect and control the island phenomenon.