Reserach On Three Phase PWM Rectifier’s Control Method And Its Application

The traditional circuit of diode rectification’s power factor can’t be adjusted andits’ output value can’t be adjusted too.So a large number of harmonics is poured in thesystem leads the power factor low and a great pollution on electric fence.The mostuseful method to eliminate this pollution is adjust the current of line side to be sine.PWM rectifier came out at90th of last century which based on pulse-widthmodulation.Because the current’s waveform of AC side is sine with low harmoniccontent,high power factor and its energy bidirectional flow,so it is widely used in a lotof areas in national economy.Through the PWM rectifier’s characteristic of fourquadrant operation,it is easy to see that if the voltage’s value of AC side is big enough,AC side’s voltage can be controled to make the system to get an idea outputcharacteristic in four quadrant operation.The voltage and current can be maked with asame phase so that the reactive power and harmonic can be removed. Three phasePWM rectifier’s Nonlinear control method is researched here in order to obtain agood performance on response time, anti-jamming ability and make the power factorof PWM rectifier can be adjusted.The research content will be shown as follows:In order to get the ideal result, PWM rectifier’s math model has been buid.Theidea of switching function is introduced and the system‘s math model is buildedbased on three-phase static frame of axes and then transform the equation based onthree-phase static frame of axes to the equation based on the two-phase rotatingcoordinate system with PARK transform. Found this math model is strong couplingand non-linear characteristics. The linear control methods can’t get a good result.In order to control the phase and amplitude of current. Direct current technologyis analyzed that include: hysteresis control and SVPWM control. Then thesemethods have been compared.At last PI control, VSC (variable structure control) and FVSC (Fuzzy variablestructure control) based on SVPWM are analyzed and a conclusion between them isgotten.PI control is very easy to understand but when the interfence is very strong thesystem can’t have a good performance. VSC don’t have a relation with systemparameter so it is good at anti-jamming after reach the sliding surface but theswitching gain can’t compliance oversteer so a contraction between Rapid andstability have come out. In order to resolve this problem. Fuzzy control and VSC are combined.The simulation result demonstrate that this new method is very useful.At last APF（Active Power Filter）is designed based on the PWM rectifier. Firstthe harmonic content and wattles current are detected by Real-time compensationcurrent technology which based on reactive power compensation. Then VSC is usedto control PWM rectifier and engender the Real-time current and pour it in to theelectric fence.In order to demonstrate these methods are useful MATLAB is used tosimulation the methods have designed and the result demonstrate the APF caneliminate the reactive power and harmonic in the electric fence.