Control Of Three Phase Voltage Source PWM Rectifier

PWM rectifier has the advantages of sinusoidal input current waveform, high powerfactor, low harmonics distortion of the input current, little output DC voltage ripple, quickdynamic response and also bi-directional power flow. This paper dwells on the research ofthe three phase voltage PWM rectifier.Mathematical modelling is an effective method employed in three phase PWM rectifierresearch. Under the balanced system of three-phase power grid voltage, this paperconstructed the mathematical models of three phase voltage PWM rectifier in staticthree-phase ABC coordinates and also in rotary two-phase coordinates respectively.The grid voltage phase should be dynamically acquired to achieve efficient activepower control as well as reactive power control of the rectifier grid side. Under thecircumstance of a balanced three phase power network, the three-phase digitizedphase-locked loop model and its parameter design are deduced with DSP software.Considering the electromotive force of negative sequence currents under the unbalancedthree-phase voltage condition, the realization algorithm of three-phase phase-locked loopunder the balanced grid system is revamped and improved, with the collected simulationresults that have confirmed its feasibility.Indirect current control of rectifier conducted based on the steady-state equations ownsexcellent static performance, while its current dynamic response is relatively poorer. Fromthe principle of mathematic model we pointe out the unsatisfactory nature of traditionalindirect current control dynamic performance essential reasons.Series Compensation,toimprove the the traditional indirectly current control stability and dynamic response,thisarticle proposes a series compensation of indirect current control scheme by adding LdI/dtwhich adding one pair of zero to compensate the large inertia poles of rectifier naturalcharacteristics in the front of the control loop.Simulation and experimental results showthat adding series compensation has greatly improved the stability of the rectifier andaccelerated the dynamic response of the current speed and decreased the oscillation.This paper elaborates feedforward decoupling double-loop control strategy of PWM rectifier control based on Synchronous rotating coordinate, analysis the parameter designmethod of direct current control dual closed-loop control, and achieves independent controlof the d、 q component current.This paper achieves a variety of unbalanced control strategys based on themathematical model of the three-phase voltage-type PWM rectifier, with the difference ofthe control objective,these strategys can be divided into two categories: one is AC currentsymmetry control strategy, eliminating the negative sequence current to make AC currentsymmetry, and the other is power balance control strategy,aim for eliminating the harmoniccomponent of the dc output voltage. As the three-phase voltage unbalance leads tothree-phase inductor impedance voltage drop unbalanced, although the network side of thepower is balanced, the rectifier bridge side power is still unbalanced, and dc side busvoltage ripple is still large.So this paper also achieves power balance control based on therectifier bridge side. Simulation and experimental results show that the dc voltage pulsationcan be eliminated completely by using the power balance control strategy based on therectifier bridge side.