Research On Control Strategies Of Three-phase Voltage Type PWM Rectifier Based On Active Disturbance Rejection Control

Nowadays,green and sustainable developments are important pursuits of the industrial production and manufacturing.To achieve the goal of using energy more efficiently,new energy technologies,microgrid technologies and smart grid technologies have gradually entered our vision,and they have received more and more attention from researchers and technicians in the industry.As an important interface of AC-DC energy conversion,three-phase voltage type pulse width modulation(PWM)rectifier has the characteristics of high energy density,low AC current harmonics and small DC voltage ripple.Thus,it has a wide range of applications in industrial production.With the increasingly strict requirements of power quality,the traditional control strategies of PWM rectifiers have obvious insufficiencies in phase-locked accuracy,grid-side current quality and output voltage stability,etc.As a result,these strategies cannot satisfy the actual production and application requirements.Linear active disturbance rejection control(LADRC)has the characteristics of low model dependence,strong disturbance rejection capability and good robustness.Accordingly,this dissertation conducts the research on control strategies of three-phase voltage type PWM rectifier based on LADRC,through in-depth research and analysis of the limitations of the existing PWM rectifier control strategies.The dissertation concentrates on the design of phase-locked loop with the non-ideal grid voltage,the grid-side current harmonic suppression strategies,and the DC-link voltage stability control.The main work of this dissertation is as follows:(1)Aiming at the deteriorative accuracy of phase-locked loop based on LADRC(LADRCPLL)under non-ideal grid voltage conditions,a LADRC phase-locked loop based on improved moving average filter(IMAF-LADRC-PLL)are proposed in this dissertation.Firstly,the influence of non-ideal grid voltage on the design of PLL is analyzed from many aspects.On the basis of studying the design principle and limitations of traditional LADRC-PLL,the improved moving average filter(IMAF)with phase compensation is designed and incorporated into a specific position of the LADRC-PLL.By using the phase compensation and frequency attenuation characteristics of IMAF,the dynamic performance and phase-locked accuracy of LADRC-PLL under non-ideal grid voltage conditions are improved.Then,the extracted frequency variation is utilized to modify the IMAF-LADRC-PLL parameters in real time to ensure the frequency adaptability.Furthermore,the fractional-order phase lag is adopted to guarantee the accuracy requirements of the frequency-adaptive IMAF-LADRC-PLL.The proposed IMAF-LADRC-PLL can be used in applications with non-ideal grid voltage or large frequency variation,and has better dynamic performance and steady-state phase-locked accuracy,which provides a reliable basis for PWM rectifier to realize unity power factor control.(2)Aiming at the problem that space vector pulse width modulation(SVPWM)method introduces error voltage and causes harmonic distortion of the grid-side current in PWM rectifiers,a fractional-order LADRC strategy based on adaptive harmonics compensation(AHCFOLADRC)is presented.By studying the error voltage characteristics caused by SVPWM modulation,dead time effect and zero-current clamping,an adaptive harmonic compensation(AHC)algorithm is constructed.The adaptive fitting and compensation of error voltage are realized by using the truncated Fourier series and the accurate phase information obtained by IMAFLADRC-PLL.In order to solve the problems of decreased fitting accuracy and poor parameter applicability of AHC algorithm caused by model parameter uncertainty and incomplete decoupling,a fractional-order linear extended state observer(FOLESO)is designed and combined with the AHC algorithm to further optimize the harmonic suppression capability and robustness of AHC algorithm.Compared with traditional control strategies,the proposed AHC-FOLADRC algorithm can achieve better performance in terms of total harmonic distortion,robustness and insensitivity to the grid frequency variations.Therefore,it can be used in complex application scenarios and obtain ideal sinusoidal current.(3)Aiming at the problems of the deterioration of DC-link voltage control performance caused by the perturbation of the PWM rectifier model parameters and the poor practicability of existing control strategies in engineering applications,a novel DC-link voltage LADRC strategy of PWM rectifiers based on the reduced-order linear extended state observer(ROLESO)is proposed.Firstly,the grid-side current,achieved by AHC-FOLADRC,is utilized as the equivalent control input of ROLESO to eliminate the influence of the dynamic characteristic of the current loop and further simplify the design of the observer.Then,a ROLESO is designed to observe and even compensate the model variations caused by grid voltage fluctuations and load transients or tracking task differences.In this way,the proposed method can not only suppress the transient overshoot in DC-link voltage caused by grid voltage and load variations,but also solve the problem of dynamic performance degradation in DC-link voltage caused by tracking task changes.The proposed strategy has the characteristic that the control parameters can be adjusted arbitrarily with the stability ensured,which greatly reduces the difficulty in LADRC design and parameter tuning.Thereby,the stability of the DC-link voltage under different working conditions can be guaranteed,which provides a more stable DC power supply for the downstream loads.(4)According to the practical application requirements,an experimental application platform of three-phase voltage type PWM rectifier is built with DSP+CPLD as the core architecture.A variety of protection circuits are designed to ensure the safe and reliable operation of the platform.Moreover,human-computer interaction tools such as panel display,key input and host computer communication are established to facilitate the actual parameter debugging and experimental result observation.The experimental application platform provides a basis for the effective application and performance verification of the control strategies proposed in this dissertation.The experimental results verify that the methods can be effectively applied to the PWM rectifier system and improve the overall performance of the system,such as phase-locking accuracy,grid-side current quality and DC-link voltage stability,etc.Furthermore,the satisfactory control performance could be maintained under different working conditions,which is of great significance for practical engineering applications.