Research On Smooth Switching Of Microgrid Operation Mode Based On Master-Slave Structure

With the continuous development of society,the problem of energy shortage has become more and more prominent,and clean and renewable distributed energy has gradually been paid attention to.However,there are many problems in these distributed energy sources,such as uncontrollability,intermittence and so on.Microgrid can just solve these problems,so in recent years,more and more research on Microgrid has been done.But at present,most of the research only focuses on off-grid operation control or grid-connected operation control.The research on smooth switching of micro-grid operation mode is still insufficient,so it is necessary to study smooth switching of offgrid operation of microgrid.Firstly,the basic concept of microgrid is analyzed.According to the need of distributed generation,the three-phase inverters of microgrid inverters are designed,the suitable filter circuit is selected,the traditional control strategy of inverters is introduced,and the improvement strategy is put forward.For the parallel control of microgrid inverters,a PQ control strategy based on improved proportional resonance(PR)controller is proposed.The transfer function of the control system is analyzed.It is shown that the improved PR controller can not only improve the control accuracy of the system,but also greatly reduce the oscillation caused by insufficient damping.For the off-grid control of microgrid inverters,the traditional droop control is pointed out in this paper.Based on these problems,an improved droop control strategy is proposed.Finally,the off-grid operation control of the micro-grid inverters is realized by combining the voltage and current double closed-loop control.Secondly,aiming at the problem of switching operation modes of microgrid,this paper analyses in detail the problems existing in the process of switching off-grid,and then puts forward corresponding solutions to these problems.Among them,in order to find out that the microgrid is separated from the large grid in time,the principle and method of islanding detection are analyzed,and the detection scheme is given.In order to reduce the phase mutation of the microgrid when it is off-grid,an off-grid phase locking control strategy is proposed.In order to eliminate the current shock and voltage oscillation in the process of grid-connected,a voltage amplitude and phase pre-synchronization strategy is proposed.Finally,the simulation model of micro-grid and control system is built under the environment of MATLAB/Simulink,and the control strategy proposed in each chapter is simulated.Through the simulation results,the advantages and disadvantages of the control strategy are found,and the appropriate parameters are gradually debugged.The simulation results show that the main control inverters of microgrid can operate stably in the mode of grid-connected and off-grid,and can realize smooth seamless switching between them,which improves the reliability of power supply,thus verifying the correctness and feasibility of the smooth switching control strategy of microgrid based on master-slave structure proposed in this paper.Figure [60] Table [3] reference [61]...