Study On Power Control Strategy Of Variable-Speed Fixed-Pitch Wind Power Generation System Based On Z-Source Inverter

With the energy shortage and environmental deterioration,the development of wind power industry has become the consensus of many countries in the world.To solve the problem of electricity consumption in remote areas and less developed areas,as well as to support the developing of distributed generation and micro-grids,it is more important to develop the small-to medium-scale wind energy conversion system rather than the large-scale ones.The small-to medium-scale wind energy conversion system usually adopts variable-speed fixed-pitch wind turbine with its simple structure,high reliability and low cost.At the same time,the Z-source inverter has obvious advantages in the wind power generation system because of its advantages.Therefore,this paper applies Z-source inverter to variable-speed fixed-pitch wind power generation system and its power control method is studied.Firstly,it discusses the topological structure of variable-speed fixed-pitch wind power system based on Z-source inverter.Then,the aerodynamic characteristics of the wind turbine are analyzed.Based on the analysis of the working principle of the Z-source inverter,the mathematical relationship between the input voltage of the DC side of the Z-source inverter,the capacitor voltage of the Z-source network,the DC voltage of the inverter bridge and the shoot-through duty cycl are obtained.Then,the mathematical model of Z-source grid connected inverter in synchronous rotating coordinate system is established,and designs double closed loop grid connected control strategy of capacitor voltage outer loop and current loop.Then,based on the analysis of the working principle of the wind power system of Z-source inverter,it is concluded that the speed of generator can be controlled by adjusting its shoot-through duty cycle,providing the basis for maximum power tracking control.By analyzing and comparing some common maximum power point tracking(MPPT)control technology,it is concluded that the aerodynamic power feedback method has good tracking performance.Then,combined with the characteristics of variable speed constant frequency wind power system based on Z-source inverter,maximum power point tracking(MPPT)control strategy for wind energy conversion system based on Z-source inverter was proposed in this paper.The optimum speed is calculated by aerodynamic power,and to control the speed of generator,to realize the maximum power point tracking control.Finally,the main circuit of the Z-source system is designed and building a simulation model in MATLAB/Simulink.The SVPWM modulation strategies of the Z-source inverter,the working state of Z-source inverter,the grid connected control strategy and the full range power control strategy are simulated and analyzed.The simulation results show the correctness of the theoretical analysis.In the simulation of grid connected control strategy,the capacitor voltage is stabilized at the set value,the grid connected current is sinusoidal,and the unity power factor control is realized.In the simulation of maximum power point tracking control strategy,validated by step wind speed and random wind speed.The simulation results show the speed of generator can be well adjusted with the speed of the wind and the capacitor voltage can be stably controlled at the set value,the maximum power point tracking control is realized.