Research On The Control Method Of PWM Rectifier Based On LCL Filter

As PWM rectifier has the advantages of net side current sinusoidal, two-way flowof energy and unit power factor etc, now it plays a more and more important role in thefield of electric energy conversion, and it is widely used in high voltage variablefrequency speed regulation, high voltage direct current transmission, wind powergeneration and Static Var Compensator etc. In recent years, some scholars put forwardthe LCL filter used in the ac side of PWM rectifier to replace the traditional L filterapplied in high power occasions, compared LCL filter with the traditiobal L filter, itrequires smaller inductance to obtain the same filtering effect. But the LCL filter has theproblem of resonance, if the parameter design and the control strategy is improper, itwill affect the stability of the system. Therefore, study on the parameter design and thecontrol strategy of LCL filter, has the vital significance.The focus of this paper is the LCL filter parameter intelligent optimization designand direct power control strategy based on virtual flux. The main contents are asfollows:First analyse the advantages of network side current sinusoidal of PWMrectifier, controllable power factor, and two-way flow of energy. At the same time itproposed the harmonic problems brought by the network side single inductor filter, andit lead to the deterioration of dynamic performance of the system. And then proposedthe PWM rectifier based on LCL filter, it uses LCL filter on the AC side to eliminateharmonic and also reduce the inductance volume under the same requirement ofharmonic, improves the dynamic performance of the system. Next it analyses theworking principle of PWM rectifier, deduces the topology and mathematical model ofPWM rectifier with the traditional L filter, builds the mathematical model of the PWMrectifier with LCL filter in the a-b-c, α-β and d-q coordinate system, and compares thetwo, finally, analyzes the causation of resonance. According to the resonance problemsin the system caused by LCL filter, analyses the control method of active damping andpassive damping. As the passive damping requires in series or parallel resistor to eliminate resonance, then it will bring loss to the system, so the study of passivedamping has becomes the current hot. As PWM rectifier based on LCL filter is amultivariable systems of high order, nonlinear, strong coupling, the paper analyses theparameters selection method and the design procedure of LCL filter, introduces thedistribution design method and traditional simple design method, further designs theparameters optimization program of particle swarm optimization using MATLABlanguage. Compared with the traditional design method, the convergence of the particleswarm algorithm is higher.At last the direct power control method of three-phase PWM rectifier based onvirtual flux orientation is proposed and realized, it can not only cancel the grid voltagesensors and improves the reliability of the system, and also as the pure integral linkfilter characteristics, it can run under the condition of non-ideal power grid. Thendiscusses the space vector modulation method combined with direct power controlstrategy based on virtual flux, and analyzes its advantages and disadvantages, thenproves it is a very valuable control method. Further based on the theoretical analysis andsimulation verification, sets the experiment platform of three-phase voltage sourcePWM rectifier based on LCL filter, obtains the preliminary experimental results. Theexperimental results show that the Dc output voltage is stability, the Net side currentdistortion rate is low, the power factor is high, and it has a strong ability to resist loaddisturbance and can satisfy the control requirements, then verify the validity of thecontrol scheme.