| To prevent the hazard of inverter’s leakage current, electrical isolation measure should be takeninto account in inverter’s designation. However, the big size of isolation transformer would greatlyincrease the weight of inverter.Accordingstudying the cause of common mode current, the topology ofsix switches single-phase inverter with dc bypass could effectively suppress the leakage current.Therefore, the text adopted this topology as the main circuit.According the analysis of three different filters, LCL filter is found that it has betterhigh-frequency filtering effect than L filter and LC filter. So the LCL filter is adopted as the maincircuit of the text, and each parameter of the filter is designed according the prototype indicators intext. However, LCL filter has a resonance peak at the resonant frequency in gird-connected inverterand the resonance peak would lead to steady-state error and waveform distortion of output current. Tosuppress the resonance peak, the damping coefficient of system should be reasonably designed. Thedouble-current loop is a method to add capacitive current control into grid-connected current control,and it can effectively suppress the resonance peak. The math model of double-current loop system isbuilt, and the analysis of control theory and design process of correction parameters are given in thetext. Then each control parameter is calculated out and given in the text.To verify validity of the control method, the simulation model of main circuit and control circuitis built in MATLAB environment. Then simulation analysis is completed and outcome of simulationis given in the text.A300W prototype is built and the programs of phase locked loop(PLL) and PIDcontrol are written with the digital signal processor(DSP) TMS320F2812. In addition, the softwareand prototype joint debug are completed in the experiment. All results of the experiment indicate thewaveform of output current is good and the phase of output current can track the grid phase rapidly. |
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