Research On Flexible Multi-State Switch Control Strategy For Distribution Network

At present,there are many problems in the traditional distribution network,such as the delay of construction,unreasonable structure,limited control means and so on.With the access of a large number of distributed generators and new loads,major challenges have been posed to the safe operation of traditional distribution network.In order to enhance the flexibility of distribution network operation and improving power flow control capability of distribution network,Flexible Multi-State Switch(FMSS)is a new solution.FMSS is a switching equipment based on power electronics flexible switch technology.It can replace the traditional interconnection switch in distribution network,connecting two or more nodes in a distribution system and changing the structure of distribution network.Conpared with traditional switch,FMSS can adjust power function flexibly and continuously.It also has various operation modes,flexible control mode and fast response speed,which can improving the flexibility of distribution network operation greatly.This paper mainly research on Flexible Multi-State Switch control strategy for distribution network.It mainly includes the following aspects:Firstly,the port output power ability of FMSS is analyzed when the AC power supply of the connected power grid is unable to supply power normally.According to the equivalent circuit diagram,voltage and current output range of FMSS are analyzed.Considering the margin in the output current limit and the different load characteristics,the port output power ability of FMSS is researched when there are different kinds of loads.This research can use to confirm the size of loads that FMSS can ensure the uninterrupted power supply.Secondly,aiming at the voltage fluctuation problem caused by distributed generation,this paper proposed a voltage fluctuation suppression strategy based on the flexible regulation ability.The principle of suppressing voltage fluctuation by power flow regulation of FMSS is analyzed.And the distribution network operation model that contains FMSS is established.This paper also proposed a voltage fluctuation index which considered the voltage variation in time series.Then,the objective function is the minimum voltage fluctuation,using particle swarm optimization algorithm to solve the problem.The simulation results shows the voltage fluctuation suppression strategy based on FMSS is realized.Thirdly,aiming at improving the consumption capacity of distributed generation in distribution network,the control strategy of FMSS for maximum consumption of distributed generation is proposed.The principle that FMSS improve the consumption capacity of distributed generation is analyzed and verified by simulation.The estimating method for the maximum accessible capacity of distributed generation at access point is proposed and simulated to verify.For complex system,the multi-objective function for maximizing the consumption of distributed generation is established,and the analytic hierarchy process and entropy weight method were combined to obtain the weight factor.Then,combined with system constraints,the results can be obtain by optimization algorithm.Finally the control strategy of FMSS for maximum consumption of distributed generation is realized and verified in simulation.Finally,the second-harmonic power fluctuation of FMSS under three-phase unbalance is analyzed.By categorizing the different cases of three-phase unbalance.the characteristics of second-harmonic power fluctuation of FMSS under different conditions is discussed.The strategy of FMSS for suppressing the second-harmonic power fluctuation is researched and analyzed in three different situations,and the simulation verified the strategy.