Research On Energy Conversion Control Technology Of Doubly-fed Wind Turbine

As a clean energy,wind energy has great exploitation value.However,because of the instability of wind speed,it is difficult to capture wind energy.Doubly-fed wind turbine(DFIG)compensates the frequency,amplitude and phase of stator output voltage according to the excitation process on the rotor side to realize variable speed and constant frequency operation of doubly-fed wind turbine,which greatly improves the utilization of wind energy and makes doubly-fed wind turbine widely used.In this paper,the control process of doubly-fed wind power generation system is studied and explored.Firstly,the mathematical model of doubly-fed induction motor is established and the theoretical control analysis is carried out.Secondly,the control analysis of the rotor side converter and the network side converter,i.e.the inverter circuit and the rectifier circuit,is carried out.The control system and the network side control system of the rotor side converter based on PI controller are established.The simulation model is built under the simulation environment of MATLAB/Simulink to verify the effectiveness of the control system.Then,according to the working condition of DFIG,two kinds of control systems based on PI controller,single-machine operation and grid-connected operation,are established respectively.Similarly,the simulation model is built under the simulation environment.In the control system of single-machine operation,the generator runs on load and achieves stable output of expected voltage.According to the grid-connected demand,the flexible grid-connected process of DFIG is realized.In the control system of grid-connected operation,active power and reactive power are decoupled.The simulation results show that the single regulation of active power and reactive power can be realized effectively.Then,through the overshoot phenomenon of PI controller's dynamic regulation and the complex disadvantage of parameter tuning process,this paper proposes a control scheme based on energy balance.The energy flow process among power electronic devices is analyzed in DC-AC converter,and the energy balance controller in a single PWM cycle is designed.The simulation results show that the energy balance controller can effectively reduce the overshoot in the process of voltage amplitude regulation and improve the dynamic performance of the system.Finally,according to the merits and demerits of PI controller and energy balance controller,the two control schemes are combined and applied in two operating conditions of DFIG single-machine operation and grid-connected operation.In single machine operation,the amplitude of generator load voltage is regulated by energy balance,and the frequency is regulated by PI controller.The total energy of generator output active power and reactive power is controlled by energy balance,and the distribution of active power and reactive power is regulated by controlling the phase angle difference between output voltage and expected voltage.The simulation results verify the proposed control scheme.Compared with the traditional PI controller,it can effectively shorten the grid connection time and reduce the overshoot phenomenon in the regulation process.Finally,the hardware experimental platform of doubly fed wind power generation system is built.According to the working condition of a single machine,the experiments of PI controller and the combination of energy control and PI controller are carried out respectively.The experimental results verify the effectiveness of the proposed control scheme and the superiority in the dynamic adjustment process.