Control Strategy Research On Programmable AC Electronic Load

There are a variety of power equipmemts in our lives,before leaving the factory,these power instruments need to be fully tested to ensure their performance,the testing process includes long time load testing.If we use real loads for load testing,it requires a large experimental spaces and the energy during the test process is wasted.With the development of power electronics technology,electronic load comes into being and replace the traditional energy consuming loads.Different loads can be emulated through modifying the type and value of loads in the program.Using the grid-connected technology,we can feedback the energy generated during the testing process to the grid,as a result,energy saving is achieved.Based on the development of electronic load topology,this paper proposes a new circuit topology,in which three single-phase half bridge PWM rectifiers cascading into three-phase load simulator.The three single-phase half bridge PWM rectifiers in this structure are independent with each other,and there is no couple between them.Therefore,it can simplify the decouping control in the control procedure of traditional three-phase system.To simulate different load types by the cascaded three-phase load simulator,this paper has done the following work:First,in order to design the current closed-loop controller for load simulator,we analyze the principle of single-phase half-bridge PWM rectifier.Since the power transistor turns ON or OFF,the switching converter is a time-varying and nonlinear circuit,the linear control theory could not be used to analyze the system’s stability.In this paper,the state space average method is implemented to establish the small signal model for single phase half bridge PWM rectifier,so that the corresponding state equation is obtained.Then,by the given transfer function which is concluded through small signal model,the system stability is analyzed.The duty cycle D of the power switch can reflect the system stability.When D is less than 0.5,the system is stable;when D is greater than 0.5,the system is unstable.Respectively,proportional-integral and proportional resonant controller served as current closed-loop controller for a load simulator to correct the system,and comparison result on the correction effect of the two current closed-loop controllers are given.Based on the analysis aforementioned,we discuss the influences on the input current of load simulator when the two voltage divider capacitors that on the arm of a single-phase half bridge PWM rectifier is unbalanced,and study the voltage balance control strategy of these two voltage divider capacitors.Finally,based on the theoretical research,Matlab/Simulink Powersystem is used to build the simulation model of load simulator,and simulation work is done on the static and dynamic conditions of differnent loads types.It is proved that the designed parameters of the current closed-loop controller are valid and applicable.To verify the simulation results,an experimental hardware platform is designed.The hardware circuits such as signal conditioning circuit and voltage or current detection circuit are designed;the system software based on DSP(TMS320F2812)is written.From the experiment results,it is proved that the designed electronic load can realize different loads type emulation.