Design And Experimental Research Of AC Electronic Load With DC Energy Feedback

The power supply unit needs to be tested before leaving the factory.The use of traditional analog loads has serious problems such as serious energy loss and single load forms.Based on the research purpose of replacing the simulated load,for an inverter power supply factory test,this paper designs an AC electronic load that feeds energy back to the DC power supply terminal.According to the DC input characteristics of the power supply under test,this paper uses energy feedback to the input end of the power supply under test.The whole system adopts a cascaded structure of load simulation unit and energy feedback unit.The front-stage load simulation unit uses a single-phase voltage-type PWM rectifier,and the back-stage energy feedback unit uses a phase-shifted full-bridge DC/DC converter.Combined with the system technical indicators,complete the parameter design of the main circuit components.The load simulation unit is the front stage of the system and adopts a single current loop control to achieve precise control of the input current.Based on the mathematical model of the static coordinate system,PI control is used as the current loop controller to design,and the steady-state error of the PI controller is theoretically analyzed.Therefore,this paper improves the classic sliding mode control strategy,analyzes the accessibility of the system,establishes a mathematical model of the rotating coordinate system,and designs a sliding mode controller based on feedback linearization.Comparing the input current waveforms of PI control and sliding mode control through matlab simulation,the results show that the use of sliding mode control strategy can achieve no static error tracking of the input current,and there are few harmonic components and basically no chattering.The energy feedback unit is the latter stage of the system.Select the double closed-loop PI control strategy of bus voltage outer loop and output current inner loop.Use the pole placement method to theoretically calculate the controller parameters.It is analyzed that the double frequency ripple on the bus voltage has a disturbing effect on the output current,and the notch filter has a small amount of low-frequency and high-frequency ripples that cannot be filtered out.Therefore,this paper chooses the current inner loop input power feed-forward control strategy to offset the double-frequency ripple on the bus voltage with the double-frequency component of the input power.Through matlab simulation analysis,the dual closed-loop control strategy can realize the control of bus voltage and output current under several working conditions.Combine the main circuit structure and technical indicators to make an experimental prototype.The control circuit is divided into an electronic load control board and a main control board based on a modular design method.The system control chip is composed of the main control chip DSP and the auxiliary chip CPLD.According to the program structure diagram,the software design of DSP and CPLD is carried out respectively,and the function debugging is completed.The AC electronic load is subjected to experiments under simulating different load characteristics and load sudden changes,and the key point waveforms of the front and rear units are analyzed.The results show that the AC electronic load has better steady-state and dynamic performance.