Research On Voltage Control Strategy Of The Gird-Off Inverter In The Microgrid

The operation control mode of the microgrid is taken as the research background in this paper.The control strategy of the inverters in the microgrid and the voltage controlled method of islanding operation are mainly studied.The three-phase combined inverter is applied as the interface inverter in the microgrid.According to the operation condition of the inverter,the droop control with no communication interconnection is chosen.The power supply is polluted and power quality decreases due to a number of the nonlinear loads in the microgrid.The output voltage of the inverters is easily affected by the load characteristics in the islanding mode.Therefore,the nonlinear load has to be taken into account for the voltage control of the inverters.Two control methods are studied to improve the output voltage quality of the inverters.One is the proportional complex integral(PCI)control.A circuit model of the system is built and a voltage loop with harmonic suppression function based on proportional complex integral controller and a current loop with proportion control are designed.The multi-resonant PCI control is presented to improve the power quality and the load current feed-forward control is introduced to further suppress the harmonic.The other control method is the sliding mode variable structure control,which has the strong robustness and the ability to suppress the load disturbance,hence the control is applied to the inverter control.Reasonable sliding mode surface parameters can guarantee output voltage of the inverter to become sinasoidal waveform under the condition of the linear or nonlinear loads.Two methods are applied to single-phase full-bridge inverters to verify the above voltage control methods,and finally two methods are used for the combined three-phase inverter with the power droop loop in the islanding mode.The simulation model of the three-phase combined inverters is established by the PSIM simulation software.And the experimental platform of three-phase combined inverters is built with the Infineon XE164 MCU as the control core.The effectiveness and feasibility of the presented control strategy is proved by simulation and experimental results.