| As one of the commonly used AC-DC power conversion topology,single-phase PWM rectifier has become a research hotspot in the field of power supply as a result of its sinusoidal input current and unit power factor.Due to the instantaneous power imbalance between the input and output port,there is inherent double power frequency ripple in the output voltage of single-phase PWM rectifier.The ripple enters the control loop through feedback loop,causing the distortion of current reference and input current.The traditional scheme to suppress the current distortion is reducing the bandwidth of voltage loop,which would synchronously reduce the dynamic performance of the converter.In view of this problem,this paper,from the control level,explores to solve the harmonic distortion problem of single-phase PWM rectifier caused by the double power frequency ripple,while taking the improvement of the dynamic performance of the converter into account.The main work and achievements are as follows:(1)In view of the unclear formation mechanism of harmonics in single-phase PWM rectifier,the related analysis is done by theoretical derivation,which provides the basis and train of thought for solving the harmonic distortion problem of single-phase PWM rectifier.Based on the power balance of the main circuit as well as the control reference composition,the close relationship between the output voltage ripple and the input current harmonic is analyzed.At the same time,by analyzing the relationship between the loop bandwidth and the dynamic response of the system,the restriction of the traditional low bandwidth harmonic suppression scheme on the dynamic performance of the system is highlighted.According to the analysis above,the contradiction between the dynamic and steady-state performance of the converter is introduced,which lays the foundation for the follow-up work of this paper.(2)In order to solve the contradiction between the dynamic response and the steadystate waveform quality of single-phase PWM rectifier,a current-harmonic feedforward compensation control strategy considering the dynamic and steady-state performance of the system is proposed,whose establishment is based on the idea of harmonic disturbance elimination.Specifically,according to the trigonometric function algorithm,the undesired third harmonic of the input current along with the fundamental input voltage are selected to construct the second harmonic compensation variable,which is feedforward to the output point of the voltage loop to suppress the distortion of the current reference.Finally,the dynamic and stable-state performance of the converter is unified.On the basis of theoretical analysis,the feasibility and effectiveness of the proposed control strategy are verified by simulation and experiment.(3)A virtual impedance control strategy based on D-Q rotating coordinate system for single-phase PWM rectifier is proposed.Aiming at the single-phase PWM rectifier controlled by D-Q average current mode,the two port model of D-axis control system of the converter is derived by using small signal modeling and feedforward decoupling control,and the impedance correlation between output voltage and input current of Daxis is clarified.Based on the two port model of D-axis control system,the amplitude at twice power frequency of transfer admittance from output voltage to input current of Daxis is reduced by introducing a series virtual impedance,so as to reduce the second harmonic component of input current of D-axis and then naturally suppress the harmonic distortion of input current.In this paper,the experiment of single-phase PWM rectifier with D-Q average current control is carried out,and the effectiveness of series virtual impedance control on improving the waveform quality of input current in single-phase PWM rectifier with high bandwidth is verified. |
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