A Three-Phase Load Imbalance Control And Monitoring System In Low-Voltage Distribution Area

With the improvement of residents’ living standards,more and more electrical appliances have entered resident’s home.While bringing convenience to people’s lives,the surge of single-phase loads has also resulted in the three-phase load imbalance in low-voltage distribution networks.Load balancing devices such as STATCOM and APF are installed in the load side or grid side to suppress the three-phase imbalance of the power grid traditionally.However,this method has high input costs and cannot solve the three-phase unbalanced problem of the whole circuit of low-voltage distribution network.This dissertation introduces a three-phase load imbalance control and monitoring system,which adjusts the phase sequence allocation and the loads are distributed in three phases equally by the load commutation terminal.The advantages and disadvantages of several kinds of load commutation topology are compared in this dissertation and the anti-parallel structure based on thyristor has been finally chosen.A control strategy of seamless commutation based on the thyristor is proposed and it can change the load phase in 0ms.The commutation operation is required at the right time to avoid the commutation failure and reduce the adverse effect of the abrupt change of voltage on the load,SSRF-PLL technology is introduced.Aiming at reducing the adverse effect of phase abrupt change on the non-variable frequency induction motor during the commutation phase,an obstacle avoiding commutation strategy has been adopted in this project.The load is excluded from the current load commutation operation when the motor is identified in the working state with non-intrusive load identification technology.In this dissertation,the switch function matrix of the commutation terminals in the low-voltage distribution area is taken as the independent variable to establish a two-objective mathematical model with the objective of minimizing the load unbalance and switching times of the load commutation terminals.The multi-objective genetic algorithm was used to solve the problem and the non-dominated sorting genetic algorithm(NSGA-Ⅱ)with elitist strategy based on vector gene was studied in this dissertation.An example is given to verify the feasibility of NSGA-Ⅱ to solve this problem.Based on the above research,this dissertation further introduces the communication network design and server program design of the remote monitoring platform of unbalanced management system.The prototype of the control center and load commutation terminal are developed and installed in several distribution areas.The experimental results show that the seamless phase commutation control strategy can change phase of load in 0ms and the commutation process has little effect on common household appliances.Three-phase load imbalance control and monitoring system can effectively suppress the unbalance in the low-voltage distribution network,reduce line loss,improve power quality and it verifies the feasibility and effectiveness of the system.