High Performance Control Of Three Phase PWM Rectifier

The three-phase voltage source PWM rectifier has the advantages of low harmonic distortion of power source current,high power factor(near unity),dc-bus voltage has little ripple and can be adjusted.With the rapid development of science and technology,the requirement of power quality is becoming higher and higher.It is necessary to study the PWM rectifier with low switching loss and low total harmonic distortion.So the harmonic elimination technique under low switching frequency has been paid more and more attention.The specific harmonic elimination method is based on low frequency and can reach the special harmonic elimination.In this paper,the technology is studied in detail.Firstly,the mathematical model of the harmonic elimination based on the three phase voltage source PWM rectifier is established,and a set of nonlinear equations is obtained.The Newton homotopy iteration algorithm is used to solve the nonlinear equations,which combines the advantages of the high convergence precision of the Newton iteration method and the convergence region of the homotopy iteration algorithm.Secondly,the control strategy of the power grid voltage oriented based on the SHE-PWM is studied.This method is based on two-phase rotating coordinate and controlled by current feedforward decoupling,the active current and reactive current can be control independently;Based on the method of harmonic compensation,the feedback current only contains fundamental current,which can reduce the adjusting difficulty of current loop.This method can achieve the purpose of low order harmonic elimination,and the steady-state performance is better than the control strategy of the power grid voltage oriented based on the SVPWM,but the dynamic response speed is slow down.Finally,this paper adopts the method of selective harmonic elimination model predictive control(SHE-MPC)to govern the three-phase voltage source PWM rectifier.The cost function contains the control of grid current errors and the SHE-PWM voltage reference tracking errors,for balancing both dynamic current tracking performance and steady harmonics performance.The traditional SHE-MPC method adopts the filterless reference current method to calculate the SHE voltage reference,the high frequency harmonics caused by switching in rectifier will feedback to control system,distort SHE reference voltage,and introduce 5,7 etc.order nonideal harmonics in current.This paper proposes a method to compensate the harmonics in actual grid currents to calculate the SHE voltage reference,to eliminate switching ripples in actual currents and stabilize SHE reference voltage waveforms.The simulation results show that the nonideal harmonics in currents are eliminated,and the THD performance in steady current and dynamic response of system are good.