Research On The Control Strategy For PWM Rectifier With LCL Filter

The three-phase voltage-source PWM rectifier has the advantages of sinusoidalgrid-side currents, unit power factor, constant output, which made it has been widelyused in the fields of electrical drives, renewable energy for power generation, highDC-voltage transmission, and so on. But PWM rectifier will produce high frequencyharmonic and this harmonic brokes in power grid will influence the load that sensitiveto electromagnetic interference and will generat loss. With the increase of the single-Lfilter will reduce harmonic, but it will influence the requirement of power quality andwill increase the cost effectiveness. The PWM rectifier with the LCL filter is moreeffective at reduce harmonic distortion and the inductance can inhibit impulse current,and fast dynamic, low cost and small volume. As a result, research on control strategyof the three-phase voltage-source PWM rectifier with LCL filter has the vitalsignificance.At first, it analyses the topology of the three-phase voltage-source PWM rectifierwith LCL filter, and builds the mathematical model in the a-b-c, α-β and d-q coordinatesystem, and analyses the properties of LCL filter, the ways of parameter design and themethods of dampers. Secondly, introduces the principle and properties of fixedswitching frequency control method, and The LCL filters will bring resonance andstability problem. In order to solve the problem, an undamp control method for PWMrectifier with LCL filter is proposed based on the analysis of mathematical model for thethree-phase voltage source PWM rectifier with LCL filter. This method uses systemdelay and the dampers in fixed switching frequency control and then adjusts thesampling time of the PI regulator to achieve stability of the system and withoutincreasing capacitance sensors and the system structure is optimized. The simulationand result analysis show that the system has excellent dynamic performance and thecurrent harmonics on grid side reduces significantly and the resonance of the filter canbe effectively suppressed. The third, it analysises the traditional direct power control strategy of PWM rectifier with L filter, and then it analysises the undamp direct powercontrol strategy of PWM rectifier with LCL filter, and the results show that the systemhas superiority properties of the undamp direct power control strategy of PWM rectifierwith LCL filter.The last, it designs the experiment platform of three-phase voltage-source PWMrectifier control system with LCL filter and analysises the hardware circuit and gives thedesign method of software. The experimental results show that the output DC-voltage isstability, the grid side current harmonic rate is low, and the resonance of the LCL filtercan be effectively suppressed, and the control effects are mostly carried out.