Study On The PWM Rectifier And It's Control Strategies

With the fast developing technology of green energy, an ever-enhanced attention has been focused to the PWM rectifier in the field of power electronics. PWM rectifier might become an ideal electric appliance or a linkage between grid -line and other electric facilities,characterized of pollution-free and adjustable power factor. With this regards,the dissertation comprehensively studied the theoretical and practical aspects concerning the voltage -source PWM rectifier (VSR) and the current-source PWM rectifier (CSR), covering the basic principle, mathematical model, control strategy, system design, parameter calculation and engineering application etc.. The author explored some key problems about VSR &?CSR and developed his own clues of thinking, viewpoints, and approaches that are based on the work done in the following aspects.· A depiction of the basic principle and characteristics of the four - quadrants operation of PWM rectifier according to the grid side vector relation.· A quantitative analysis of the PWM VSR & CSR's commutation and the characteristics of the waveforms.· The introduction of the equivalent transformer model and a detailed d -q model based static and dynamic performance analysis of VSR & CSR.· The development of the design method of grid -side inductor of VSR to meet the requirements on active or reactive power in four-quadrants operation, as well as the calculation method of the parameters of DC - side energy storage elements (inductor & capacitor) to meet the requirements on system control performance such as tracking ability and robustness.· The selection and quantitative analysis of several key attributes that affect the current control of VSR based on a study on the current control strategy.· According to the definition and the distribution of VSR's voltage space vector, the introduction of a rule -based SVPWM current control strategy, with non -fixed switching frequency and dual hysteresis loops, that obviously improves the performance of current control.· Based on two kinds of control strategies of VSR under unbalanced grid condition,the introduction of a new VSR control strategy featuring undamped -oscillation that simplifies the controller structure and effectively improves VSR's performance under unbalanced grid condition.· A systematic description of the state switching in trilogic PWM signal generation of three-phase CSR by using the conversion between bilogic and trilogic switching functions.· Referenced to the CSR's trilogic PWM signal generation, an approach to achieve low-stress natural commutation of switching devices by reshuffling the vector composition sequence, resulting reduced switching loss.With the background of and well instanced by the Xinjiang Autonomous Region's Key Sci-Tech Project "Solar Photovoltaic grid -connected inverter" ,the dissertation work implemented the new approach of a grid -connected PV inverter that was of single -phase VSR topology and with MPPT (Maximum Power Point Tracking). An algorithm of dead -beat current control with introduced zero -vector modulation was put forward and a PID algorithm with variable - integration-rate was adopted in the control strategy that not only enhanced the dynamic performance but also e-liminated the grid-side harmonic current.With the support of National key Scientific Engineering Project "HT -7U Super -conductive Tokmak Nuclear Fusion Experimental System", the dissertation work also implemented a CSR of new topology to fulfill the task of "Fast Control Power Supply (FCPS)" to control the plasma's displacement. The approach was of a parallel topology of multi AC -DC -AC current-source PWM converter and with phase-shifting PWM control, achieved satisfactory high -current fast response in the field coil loads. Furthermore, the control strategy of the low-stress SVPWM is realized to further reduce the switching losses.Tentative engineering designs were presented. The approaches put forward in the dissertation were verified as expected by both simulations an...