Research On Smooth Switching Method Of Coordinated Control Mode Of Multi-Terminal Flexible Multi-State Switch

Compared with the traditional tie switch,multi-terminal flexible multi-state switch has the advantages of bidirectional power flow control,reactive power compensation and fault isolation.It is regarded as the key equipment to realize the distribution network reconfiguration technology and self-healing technology.The stability of DC bus voltage is the key to the normal operation of multi-terminal flexible multi-state switch,but there are many working modes of flexible multi-state switch,and the switching between modes is more common,which poses a great challenge to maintain the bus voltage quality.The hard switching between multiple modes produces large disturbance,resulting in severe fluctuation of bus voltage.The research on smooth switching is the most effective way to realize bus voltage stability.Firstly,the topology of multi-terminal flexible multi-state switch is designed,the mathematical model in dq rotating coordinate system is established,the working principle of multi-terminal flexible multi-state switch is analyzed,and the working mode of multi-terminal flexible multi-state switch is introduced in detail.Then,the basic control mode of flexible multistate switch under master-slave control is studied,and the coordinated operation control strategy of multi-terminal flexible multi-state switch is analyzed.Then,the switching between different modes is divided into hard switching and smooth switching.The control structure and switching principle of steady-state inverse model smooth switching are emphatically analyzed.It is pointed out that steady-state inverse model smooth switching can effectively improve the response speed of the system and make the system quickly adapt to the new power demand,but it still brings new interference to the system.In view of the deficiency of smooth switching of steady-state inverse model,a smooth switching technology of radial phase basis function neural network(RBFNN)steady-state inverse model is proposed,the basic principle of RBFNN algorithm is expounded,and the control model of improving smooth switching of steady-state inverse model by using RBFNN is given,while using the steady-state inverse model to improve the system response speed,the influence of disturbance on the system dynamic performance is compensated by adjusting the PI output,which further smoothes the bus voltage fluctuation during switching.Finally,a three-terminal flexible multi-state switch simulation model is built in Matlab/Simulink,and detailed simulation verification is carried out.Simulation results show that,compared with hard switching and smooth switching of steady-state inverse model,smooth switching of RBFNN steady-state inverse model compensates the influence of disturbance on the system by controlling the corrected PI output of RBFNN,and then superposition the corrected PI output and steady-state inverse model output to generate the inner loop reference value,which further flattens the oscillation of DC bus voltage.It can realize the advantages of small fluctuation of bus voltage,fast response speed,good dynamic characteristics and wide adaptability to working conditions.