MPPT Control Strategy Of Grid Connected Direct Driven Wind Power Generation Based On PMSG

Because of the superiorities of low noise, low loss, high reliability and the high running efficiency, direct drive permanent magnet synchronous generator(PMSG) system is considered to be an important research direction in the field of high power variable speed constant frequency wind power generation. The topological structure including diode rectifier, DC-DC circuit and PWM inverter is regarded as the main one. It is provided with high practical value because of the advantages of simple structure, high reliability and the appropriate control algorithm. This article focus on above-mentioned topology structure, and discusses the system how to realize the maximum power point tracking(MPPT) control in grid circumstances. In the precondition of the grid requirements, the maximum power point tracking control is studied, which is achieved by generator side converter and the grid side converter respectively.Firstly, the working principle and the function of each component of the grid-connected permanent magnet synchronous generator system are researched. Meanwhile, the characteristics of the wind turbine is analyzed in detail.The mathematical model of permanent magnet synchronous generator is established, and the control structure of full power converter is introduced.Secondly, the mathematical model of full power converter is established. For generator side converter, the change of input current and voltage of uncontrolled rectifying circuit and Buck-Boost circuit, besides the output one, are analyzed detailedly. For another, the mathematical model of the grid side inverter in three-phase stationary coordinate is established, and the mathematical model of grid side inverter is obtained base on the coordinate transformation technology in the two-phase synchronous rotating coordinates.Thirdly, the generator side type maximum power point tracking control strategy including the maximum power point tracking control which achieved by using generator side convertor and grid-connection control is adopted and researched. The basic principle of the maximum power point tracking is also analyzed. The DC decoupling control strategy for grid side inverter is studied. The transfer function of inner current loop and outer voltage loop are established, and the tuning method of PI regulator parameters in the control structure is provided.Fourthly, the gride side type maximum power point tracking control strategy which achieve MPPT by using gride side inverter is adopted and researched, and the basic principle of the maximum power point tracking is also analyzed. Based the reference value of the grid power on input, direct decoupling control strategy for grid side PWM inverter is studied; Compared with the generator side type maximum power point tracking control system, this system is simpler and could easily be achieved because of the lack of outer voltage loop.Finally, the simulation platform of grid-connected and direct-drive permanent magnet synchronous generator system has been built by Matlab/Simulink, including the motor-side type maximum power tracking control system and the grid side type one. The correctness and effectiveness of the two kinds of control system are verified. The simulation results show that the two kinds of control system is same on efficiency and tracking speed with the condition of the maximum power point tracking, but in the second control system, the DC bus voltage is more stable and smaller fluctuating.