Research And Design Of Digital Grid Connected Inverter In Energy-fed DC Electronic Load

Energy-fed dc electronic loads have received more and more attention as a new type of DC power supply test product.It can not only continuously simulate the load characteristics,but also recover the energy of the power supply under tested,so that the energy can be recycled and saved.Its digital control further improves the reliability and performance of the electronic load.The inverter is an important part of energy-fed DC electronic Load for feeding the energy into the public power grid under tested.It must up to the grid connection standard,ensure that the harmonic waves of the incoming current are small and have minimal impact on the grid and realizes grid connection of incoming current under unit power factor,the inverter DC voltage must be stabilized to ensure the stable operation of the front and rear circuits.The efficient and stable operation of the inverter directly affects the energy recovery efficiency of the feedable DC electronic load and the degree of pollution to the power grid.Therefore,for obtaining the high-quality feedback and high efficiency operation of the grid-connected inverter in the feedable electronic load,the research has certain practical significance and economic value.The paper introduces the research status of energy-fed DC electronic loads,grid-connected inverter topology and control technology,and analyzes the topology structure and working principle of T-type three-phase three-level inverter circuit based on LCL filtering in detail.The mathematical model of T-type three-phase three-level inverter topology in three coordinate systems is established.On this basis,the grid-connected control strategy and algorithm of "voltage and current double closed loop + DDSRF-SPLL" are proposed and verified the feasibility of its algorithm on MATLAB.The overall scheme of T-type three-phase three-level inverter with DSP(TMS320F28379D)is the core control,including the hardware circuit of the inverter and DSP control software are designed.The hardware circuit includes a main power circuit,a switching tube drive circuit,a sampling circuit,and an auxiliary power supply circuit that supplies power to the switching tube drive circuit and the sampling circuit.The DSP control software includes a PWM modulation module,a DDSRF-SPLL module,an SDFM sampling module,and an interrupt module program.An experimental platform was built to test the drive waveform of the switch and the voltage and current waveform of the grid,and the conversion efficiency of the inverter was analyzed.Experiments show that the designed grid-connected current waveform of the inverter is a sine wave with the same frequency and phase as the grid voltage,and the harmonic content is low,and the efficiency can reach 97.8%,which proves the correctness and effectiveness of the entire design.