Research On Three-phase Unbalance Compensation Strategy Of Distribution Network Based On Flexible Multi-state Switch

With the rapid development of power electronics technology,more and more non-linear loads are connected to the distribution network,this has led to a continuous deterioration in power quality.In the process of governance,the traditional means of regulation show obvious deficiencies,and the emergence of flexible multi-state switch provides a new solution.The main research contents of this paper are as follows:In this paper,the three-port flexible multi-state switch is taken as the research object,and the working principle of the switch is analyzed.The dynamic mathematical model of the three-port flexible multi-state switch in the stationary coordinate system and the synchronous rotating coordinate system is established respectively.The symmetrical component method is used to analyze the unbalanced system,and the power characteristics of each current component in the unbalanced load current are studied.Secondly,before studying the compensation strategy for unbalanced load current,command current detection method is the key to the selection of the control scheme.For the problem of three-phase current imbalance in the distribution network system,an improved i_p-i_q detection method is proposed.A phase shifting circuit composed of a second-order generalized integrator is added to the detection link,thereby,the accuracy of unbalanced current component detection is improved and the compensation effect is also improved.The detection circuit mentioned in the paper can simultaneously detect the reactive and harmonic components in the current,and achieve a comprehensive improvement of power quality such as reactive power and harmonics.The control link of the three-port flexible multi-state switch adopts a double closed-loop control structure to achieve accurate tracking of the control commands and ensure the stability of the DC side capacitor voltage of the device.In order to coordinate the normal operation of the flexible multi-state switch three ports,the other ports adopt a constant power control mode to implement the power flow control function.The simulation model is built by Matlab/Simulink,the command current detection method and control strategy of flexible multi-state switch are verified.The feasibility and effectiveness of the method are proved.