Research On Three-phase Energy Feedback Analog Load For Microgrid

With increasingly prominent issues of the global energy and environmental, the microgrid as one of the main way to consume new energy is widely used. In order to meet the requirements of the microgrid experiments, three-phase energy feedback analog load of microgrid is studied in this thesis.The topology and parameters of the three-phase feedback analog load for microgrid system are determined. Reserved for simulating different loads and the quality of grid current, the analog part of the load applies three-phase full-bridge voltage-type PWM converter and the energy feedback part of the load applies three-phase half-bridge voltage-type PWM converter structure. The dq rotating coordinate average model and linear small signal AC model are established. And, the interactions among the DC, front and rear part are analyzed theoretically with the models. The results show that the DC voltage fluctuation is inevitable in simulating nonlinear load and affects the PWM modulation wave. Finally the grid current generates harmonics.In the control system design of three-phase energy feedback analog load, DC voltage fluctuations and their impact on the quality of the feed current of the rear part need be suppressed in simulating nonlinear load, so that a DC voltage decoupling control method is proposed. In the PWM modulation, the DC voltage is decoupled and its fluctuation has not affected the SPWM waveform. The influence of the DC voltage fluctuation on the feed current is eliminated. The simulation results show the effectiveness of the DC voltage decoupling control.On the basis of the three-phase energy feedback analog load, the function of the system is expanded. The compound control of PI + repetitive control is applied and the command value generating method is changed. The system can produce the simulating signals of grid for testing the on-grid performance of micro-source inverter. The simulation results show the accuracy of the signals.