Research On Harmonic Suppression Strategy Of Permanent Magnet Generator Based On Optimal Control

In Compared with other motors,PMSG has excellent operating efficiency and low loss in wind power system,Therefore,it is widely used in the field of onshore wind power and offshore wind power.However,due to the harmonic of air gap magnetic field,the advantages and disadvantages of generator design and some nonlinear factors,the harmonic voltage and current will be generated.Most of the harmonics come from the PWM converter on the machine side and the magnetic field distortion in the air gap of the motor.These harmonics will lead to the increase of the loss and heat of the motor,as well as the torque ripple,which reduces the stability of the control system.Firstly,the paper makes a mathematical model analysis of the harmonic voltage and current generated by the converter to provide the necessary theoretical support for the next step of harmonic suppression.In order to reduce the insulation damage of generator stator windings caused by high-frequency pulse harmonics generated by PWM converter and reduce the generator loss caused by harmonic current,based on the determination of LCL filter parameters,a damped（Series Resistance of Filter Capacitor Branch）LCLLC filter was designed for the transformer end.Damped LCLLC filter not only has excellent high order harmonic attenuation characteristics,but also has the same amplitude-frequency characteristics and resonance frequency as damped LCL filter in the frequency range below 2/3 switching frequency^[11].When designing the damping LCLLC filter,therefore,assumes that the damping of the LCL filter inductance capacitance parameter with the same type damping LCLLC filter,in this condition,the type of damping type LCL filter and damping LCLLC filter filter characteristic analysis,analysis,compared with the traditional type damping LCL filter harmonic mode,damping type LCLLC filter not only has the ability of anti-resonance,and can keep good in high and low frequency harmonic attenuation.Secondly,in order to further study the attenuation of the amplitude of the terminal voltage of the generator and the distribution of the inter-turn voltage in the winding after the attenuation of the rich harmonics in the PWM high-frequency pulse wave by the filter and the optimization of the control strategy.In this paper,the finite element software is used to calculate the single-slot model of permanent magnet wind generator,and the distribution parameters of inductance and capacitance of windings are obtained.The influence of filter performance difference on overvoltage of generator windings is analyzed,and the suppression effect of overvoltage under different filters is obtained by building the simulation model.Finally,Finally,in view of the harmonic current generated in the permanent magnet synchronous generator,based on the classical current closed-loop control theory,this paper analyzes the advantages and disadvantages of the closed-loop control of ac signal,and analyzes the factors that lead to the poor harmonic suppression ability from the aspects of controller stability,current tracking performance and harmonic suppression performance.Based on the traditional PI control strategy on the basis of the resonance controller（R）with two degrees of freedom（2DOF）PID controller in hybrid control mode,design of resonant two degree of freedom PID controller（R-2DOF PID）,and through the PSO（particle swarm optimization）to optimize the controller parameters,strong ability of the current tracking,stable control and good harmonic current suppression effect.Compared with the traditional PI control harmonic suppression strategy,the proposed controller can not only suppress the current harmonics and realize the zero difference control of the current loop,but also reduce the influence of the external disturbance and enhance the dynamic stability of the controller.But considering the complexity of the controller parameter design.On this basis,an improved repetitive controller is introduced,and a hybrid controller（QRC-IRC）is designed by combining a quasi-resonant controller（QRC）with an improved repetitive controller（IRC）.The simulation results of R-2DOFPID controller are compared and analyzed.The model was built on Matlab platform,and the simulation was carried out.