Research Of Single Phase Power Electronic Load System Based On400Hz Inverter

The single-phase power electronic load based on two-stage voltage-type PWMconverter can be well applied to the performance test and aging test of single or three-phaseAC power supply and DC power supply before delivery. It can simulate different loadcharacteristics and can also feedback the energy generated by the device to be tested duringthe test back to the grid, which can save energy and reduce the required power capacity ofthe test. In this paper, some technical issues are studied in detail on the single-phase powerelectronic load used for the single-phase400Hz inverter.According to the circuit topology of single-phase power electronic load, a concept ofunified power electronic load module is presented in this paper. The basic unit of theunified power electronic load module-single-phase PWM converter is analyzed deeply.Single-phase PWM converter can simulate different load characteristics such as pureresistive, resistive and inductive, resistive and capacitive, negative resistive (feedback),relationship between AC power input voltage, AC side inductor voltage and convertervoltage vector is discussed.According to the technical requirements of the single-phase power electronic loadsystem, a single phase400Hz inverter is designed, including the power circuit and thecontrol circuit. The differences between50Hz inverter and400Hz inverter are compared.Several control methods such as PI control, dual-loop control, state-feedback poleplacement, repetitive control and intelligent control are discussed. In this paper, dual-loopcontrol structure composed of outer loop voltage PI control and inner loop current PIcontrol and load current feedback is verified on a single-phase400Hz inverter used ofexisting laboratory materials. The control effect is excellent.The power harmonics sources of the DC-bus voltage in the single-phase powerelectronic load system are investigated in details. The mathematical relationship betweenthe power harmonics order of the DC-bus voltage and the frequency of the two AC powersources is conducted based on the analysis of power balance in both steady and transientstates. The resultant power harmonics in the DC-bus voltage due to the voltage fluctuatingshows no connection with the frequency of the AC power source in this PEL. A doubleclose-loop control strategy of voltage and current is adopted for the converter control, andthen the power harmonics in the DC-bus voltage is found to aggravate the sinusoidaldistortion of the combined grid-connected current reference and deteriorate the resulting current quality since the current reference of the inner current loop comes from the outervoltage loop. A hysteresis control strategy of the DC-bus voltage is then proposed to dealwith this problem. A load simulator based experimental system is established with a400Hzsingle-phase inverter for testing power source. The improved performance of thegrid-connected current is validated with simulation and experimental results.In the industrial operation site，the grid voltage of PCC might have low power qualitysuch as sudden voltage drop and so on. Grid voltage is feed-forward in the control systemin order to eliminate the impact on the current quality caused by the non-sinusoidal PCCvoltage. The LCL filter offers a much better suppression of the high frequency currentripple than a simple inductor filter, and in the PEL operation, an LCL filter system absorbsless active power especially when the power rate of the tested source is high. However anLCL filter causes a stability problem due to the sudden phase change around the resonancefrequency， passive damping or active damping is needed to stabilize the resonant system.In this paper, six kinds of passive damping method are studied and characteristics andshortcomings are compared to each other. Active damping methods such as capacitorcurrent feedback can reduce the resonance peak and compared to passive damping, don’tneed the damping resistor, which can reduce energy loss on the resistor. Simulation iscarried out in Matlab, and the reliability and validity of the controller are verified evenwhen the voltage of PCC is heavily distorted.