Research On Energy Feedback Three-phase AC Electronic Load Control System

All kinds of power supply devices(UPS(uninterruptible power supply),ac/dc power supply,car power)have to undergo a rigorous aging experiments and related dynamic and static load experiments before leave factory,traditional power test equipment is connected by passive components,such as wire resistance,inductance,capacitance,etc.,which has the disadvantage of high energy consumption,large volume,simulation of load characteristics is not flexible,simulation precision of load is not high.The energy feedback type power electronic load can solve the above shortcomings,and conform to the concept of sustainable development advocated by the society today,which has attracted the attention and research of scholars from different countries.In this paper,three-phase ac energy feedback type electronic load is researched,load simulator of the system is flexible to simulate pure resistance load and inductive load,capacitive load and nonlinear load;grid-connected converter feedback energy to the grid without pollution.This can solve the shortcomings of traditional testing.This paper analyses the work principle and common topology structure of the Electronic Load device(PEL),then the mathematical model of PEL under three-phase static coordinate system and synchronous rotating coordinate system is established.For Control coupling between repetitive controller and PI controller,load current is distorted in the dynamic process,a modified PI + repetitive control is proposed,this method using Zero Phase Error Tracking Control(ZPETC)makes the transfer function of input to output is 1,which ensure the rapidity of control system and provide the structure foundation of inhibit control coupling,and then the command signal of repetitive controller is process with "dynamic delay",which can realize the redistribution of error in the dynamic process,reduce the error peak of the repetitive controller,inhibit control coupling,reduce the total harmonic distortion rate of current.Due to the traditional nonlinear load simulation have the disadvantage of big volume,simulation of characteristics is not flexible,calculation is complicated,simulation precision of is not high,a method of digital implementation is proposed,based on mathematical relationship between three-phase uncontrollable rectifier bridge input voltage instantaneous value and the DC side voltage and diode conduction conditions,the criteria of 7 working stage is obtained,the differential equations of circuit are solved by use the backward difference method,then command signal is obtained.Simulation model of the system is established in Matlab/Simulink,the result of simulation verify the effectiveness and correctness of the algorithm.Three-phase PEL experiment platform is builted,and carries on the experiment on the experiment platform,respectively,the dynamic and steady-state experiments of system with traditional PI + repetitive control and modified PI + repetitive control the system is conducted,the results and date of experimental results and is analyzed,and come to a conclusion.