Self-balancing Device And Control Strategy Of Three-phase Load In Low Voltage Grid

The low voltage grid in China belongs to three-phase-four-wire system, using a large number of single-phase loads, which will lead to a serious imbalance situation in three-phase,especially in residential areas and commercial, living and building distribution system. The three-phase imbalanced load will cause many problems, such as increasing the zero line current,the loss ratio is too much in grid, three-phase voltage unbalance, low utilization rate of grid voltage, low utilization rate of three-phase power equipment, neutral line potential rise to endanger personal safety. Three phase load imbalance has become one of the urgent problems in low voltage grid.According to the problem about uneven distribution and randomness use of single-phase load in three-phase, a three-phase load self-balancing device based on power electronic technology and its adaptive balance control strategy are presented in this paper. The self-balancing device is consisting of a plurality of static phase-changing switch and a set of control system. To achieve the best balance state of three-phase system, the control system can provide the best phase-change scheme of the single-phase load by monitoring, analysis and calculation the three-phase equilibrium state, and indicates static phase-changing switch to implement phase-change step automatically. The mainly research work includes:A single phase load static phase-changing switch is designed. It is a kind of intelligent static switch using thyristor zero crossing switching technology, receive communication control commands from the host computer,which can realize single phase load switching in three-phase. Through theoretical analysis and simulation verification, the optimal switching time and switching strategy of the static switch is switched from the current phase to the leading phase or switched to the lagging phase is proposed, the security of the switch phase-changing switch and the shortest of single phase load cut-out time can be ensured.The control system and the adaptive balance strategy of three-phase load balancing device is designed. The control system collects current and current phase of each single-phase load,analysis the degree of three-phase current, determine the optimal adjustment scheme of single phase load by load balancing optimization strategy, sends commutation command to corresponding static phase-changing switch. In order to avoid frequent switching, a load forecasting mechanism based on load history data is introduced. The simulation model of three-phase load balancing system is established, and the effectiveness of the three phase load balancing control strategy is verified.The simulation model of three-phase load balancing system is established, and the effectiveness of the three phase load balancing control strategy is verified. The control system of static phase-changing switch and self-balancing device is developed. The principle circuit and the application program is designed. The experimental studies are carried out. The simulation and experimental results shows the correctness and effectiveness of the three phase load balancing device and its control strategy.