Wind Power Generation System Control Based On Quasi-Z Source Inverter

As the worldwide demand for electricity grows,so does the demand for renewable energy.Wind power is a natural gift of clean energy that never dries up.At present,wind power is more and more competitive with other energy sources.Variable-speed wind turbines are known to capture more wind energy than constant-speed ones.However,most loads require the grid to set a fixed frequency.The traditional voltage inverter with dc chopper circuit can meet the requirement of load for voltage and frequency.However,because the traditional voltage inverter can only provide the output voltage lower than the input voltage,the dc chopper circuit must be added to increase the boost function of the inverter.Although the topology circuit is feasible,it increases the cost and complexity of the system.The invention of Quasi-Z source inverters can not only break the limitations of traditional inverters,but also make the circuit topology more simple.In addition,Quasi-Z source inverters have higher efficiency and lower system cost.Therefore,Quasi-Z source inverters are suitable for wind power systems.In this paper,Quasi-Z source inverters have been applied to wind power systems.The Quasi-Z source inverters have been studied.The work is mainly carried out in the following aspects:Firstly,the development status of wind power generation at home and abroad is analyzed.The direct drive permanent magnet synchronous wind generator is selected as the wind power module,and the mathematic model of wind generator system based on Quasi-Z source inverters is established.This paper expounds the different operating conditions of Quasi-Z source inverters,analyzes the operating principle of Quasi-Z source inverters,and obtains the mathematical expressions and boost coefficients of Quasi-Z source inverters.Compared with traditional inverters,Quasi-Z source inverters have simpler structure and higher security and reliability.Secondly,the state space average method is used to establish the small signal model of Quasi-Z source inverters,and the transfer functions of duty ratio to capacitance voltage and duty ratio to inductance current are obtained.A mathematical model of a permanent magnet synchronous wind generator is established.The relationship between wind energy utilization coefficient and blade tip velocity ratio is analyzed.Thirdly,the steady-state power characteristics of Quasi-Z wind power systems connected to the grid are analyzed.The shoot-through time of Quasi-Z source inverters is inserted intothe traditional SVPWM control with certain rules.The output voltage and grid voltage of wind power system are controlled by the technology of grid voltage oriented vector control.Fourthly,the influence of capacitance and inductance in Quasi-Z source inverters on the operation of Quasi-Z source inverters is analyzed.The parameter selection method of LC network capacitance inductance is designed,and the wind power generation system simulation based on Quasi-Z source inverters is given.Fifthly,the adaptive variable step MPPT control technique of current prediction based on Quasi-Z source inverters has been proposed.Based on the different operating conditions of Quasi-Z source inverters,a discrete Quasi-Z equivalent mathematical model is developed.Matlab /Simulink software has been used to simulate parallel connection of Quasi-Z source inverters for the model.The main innovations of this paper are: the adaptive variable step size MPPT control technology based on Quasi-Z source inverter current prediction.A discrete equivalent mathematical model of Quasi-Z source inverter under the algorithm is established.imulating different wind speed conditions,the tracking effect of the algorithm,the grid-connected control method of the algorithm for Quasi-Z source inverter is given.