Electronic Load Based On PWM And Its Application In Power System Dynamic Physical Simulation

In dynamic physical simulation of power system, the special custom load isneeded for the trouble-free operation. With the experiment being more complex, theparameter adjustment and modification of load become more difficult, and theaccuracy is decreased. Electronic load can just make up the shortage of classical loaddevice. The AC electronic load studied in this paper can both control the loadcharacteristic precisely and feedback the test engry to the grid.Based on the analysis of three existing kinds of AC-AC converter, theintermediate DC link that has better stability is choosen to be the electronic load maincircuit topology. The framework of three-phase AC electronic load that based on thebasic principles of PWM voltage rectifier is set up. And the select principle of AC sideinductance and DC side capacitor is briefly analysised.The current control method based on double hysteredsis current control and spacevector is taken, so the drawback that the current vector which has bigger change ratecannot be traced quickly can be made up. The current tracing control of three phaseVSR can realized, the switching frequency can be decreased, and the harmonizationcan be suppressed. The approach for determining the reference voltage vector isstudied, and the area of the reference voltage vector of this period can be determinedthrought out the output voltage vector of last period, the error current vector of lastperiod, and the the error current vector of this period.The predicting current control based on BP algorithm is presented. When thesampling frequency isn’t very high, the reference offset current of next time ispredicted using of historical current. So that, the no beating control of SVPWM basedon hysteredsis is realized, and the better tracing is got. The double hysteredsisSVPWM current control and the predicting current control based on BP algorithm areproved to be correct through the test.Double closed loop combined with voltage outer loop and current inner loop isused as control strategy for feeding back engry. The Fuzzy PI controller using involtage outer loop is consisted of fuzzy control technique and traditional PI controlmethod. In order to simplify the Fuzzy inference process and increase the controlspeed, the fuzzy control strategy table is obtained. The anticipation that controlstrategy with fuzzy PI controller can achieve a quicker response speed and a smaller overshoot is proved in the simulation results.The physical simulation method for asynchronous motor and its load, theequivalent model of asynchronous motor and types, and characteristics of all kinds ofmechanical load are discussed. The simulation results of asynchronous motordrugging different kinds of load are obtained in the events that in starting, in steadystate, with disturbances on power supply side and load side. The design withelectronic load in the field of circuit control is proved to be correct and feasible. Someadvices are proposed for the practical application of asynchronous motor electric load.