Research On Grid-Connected Inverter For Wind Power Generation System

Wind power is attracting more attention due to its performance of environmental protection, economy, flexibility and so on, and is rapidly developing in the world. Grid-connected inverter is a energy interface between wind power generation system and the grid, and its performance has a direct impact on the output of wind power generation system and power quality of the grid. In this paper, the model, detection and control of low-voltage grid-connected inverter, and its realization of hardware and software etc. were investigated, the work mainly includes the following aspects:First of all, power circuit topology of grid-connected inverter was determined based on voltage and power grade of wind power generation system. Its static mathematic model in the three-phase coordinate, equivalent controlled resource model in d-q rotating coordinate and dynamic small-signal model were analysed and derived, which provided theoretical basis for parameter selection of the main circuit and compensation and correction of control section.Next, the instantaneous reactive power theory was applied in the detection and control section, which avoided the complex calculation of decoupling for the active power and the reactive power in traditional synchronous rotating coordinate. The instantaneous reactive power theory was combined with PID control strategy, by which dual-loop control of voltage loop and current loop of the grid-connected inverter was achieved. Under the premise of keeping the balance of power generation and feed, in order to reduce or avoid the negative impact on the grid induced by the wind power generation system, parameters of compensation and correction in control section were calculated and optimized.The key parameters of coupled inductor and DC bus capacitance in the power circuit were calculated based on the foregoing theory. According to the dual-loop control structure of the system, taking TMS320LF2407 as core processor, modules of signal sampling, phase locked tracking, PI regulation, SPWM formation etc were realized. To avoid repeat detecting and missing detecting of zero-crossing led by analog circuit oscillation in the conventional realization of phase locked tracking, an improved software method was presented. The method effectively improved the accuracy of phase locked tracking.Finally, power circuit and control section of the grid-connected inverter were simulated with MATLAB/SIMULINK. A 10kVA/380V grid-connected inverter prototype was set up in the laboratory, with which dynamic and steady-state tests were done. The simulation and experiment results met the predetermined technical index, showing the feasibility of the design scheme.The grid-connected inverter for wind power generation system developed in the paper could play promoting role for changing the backward situation of wind power grid-connection control technology in China.