Control Strategy Research Of Converters In Wind Power System With DFIG

With its significant advantages such as high energy conversion efficiency and good power quality,Doubly-fed wind power generation system with variable speed constant frequency has become a popular model in wind power market.The control method research of doubly-fed wind power generation system also has been a hot spot at the domestic and international research.The core of the control of doubly-fed wind power generation system is the control of the converters.In order to utilize the flexibility of the converters fully and ensure the stability of the power supply system,the converters of the system are controlled in this thesis.And to avoid that the traditional vector control relies too much on the generator parameters,the direct power control strategy of the converters are studied.The main contents are as following:Firstly,the development status and trends of wind power industry at home and abroad on the research are well understood.Then the maximum power point tracking control strategy of the wind turbine and the control strategy of the converters in the current doubly-fed wind power generation system are analyzed in detail.Secondly,The power tracking mechanism of the doubly-fed wind power generation system is analyzed.And the mathematical model of doubly-fed induction generator(DFIG)is introduced under the three-phase stationary coordinate system.In order to simplify the design of the control system,the mathematical model of DFIG is simplified to the synchronously rotating frame.It can provide the foundation for the following power control in the direct power control system of the rotor-side converter.Then,the sliding mode control is introduced in the direct power control system of the rotor-side converter.To weaken the chatter of the sliding mode control,the sliding mode controllers using a novel approach law are designed.This method can weaken the dependence of the system on the parameters,realize the fast tracking object and smooth the power of the DFIG stator side.And then,the simulation results verify that the designed controller has fast power tracking performance,can smooth power fluctuations effectively,and has good robustness.Finally,because the stable operation of the grid-side converter is the basis of the power control of the rotor-side converter for the doubly-fed induction generator.And,to ensure theunit grid power factor and the stability of the DC bus voltage,the direct power controllers of the grid-side converter and the DC bus voltage controller are designed on basis of a novel approach low of sliding mode control.It can implement the power smooth control of the grid-side converter,and realize the stable operation of the system.And then,Simulation results verify that the designed controller can stabilize the DC bus voltage effectively,smooth the power fluctuation of the grid-side converter successfully,and has good robustness.