| The distribution network in China mostly adopts three-phase four-wire power supply mode.Three-phase unbalance is often caused by factors such as uneven distribution of three-phase load,single-phase random load and three-phase asynchronization of residential electricity.Three-phase unbalance will aggravate the problems of voltage deviation and line loss.In severe cases,it will affect the safe and stable operation of the distribution power grid.In order to reduce the adverse effects of the three-phase unbalanced of the distribution network,the power supply mode of distribution network based on three-phase to single-phase power supply structure is studied in this paper.Firstly,a power supply method for distribution network based on AC/DC/AC converter is proposed.The new method converts the three-phase alternating current into direct current through rectification,and then inverts it into single-phase alternating current to connect to users through a filter.The economics of the proposed power supply method are analyzed from the aspects of construction investment and operation,and the operational reliability is analyzed.On this basis,a switching three-phase to single-phase power supply device is proposed,which can be switched to three-phase to single-phase operation or three-phase four-wire operation according to the three-phase unbalance,and the switching criterion and switching logic are given.Secondly,the three-phase to single-phase power supply method based on power electronic transformer is studied in this paper.The structure and control methods of three-phase to single-phase power electronic transformers are given,and the reliability,power quality and other aspects are studied.The applicable occasions of this power supply method are given.Under the conditions of the same power supply radius and the load distribution,Three models including three-phase four-wire system,three-phase to single-phase power supply based on AC/DC/AC converter and power electronic transformer are established used PSCAD/EMTDC.The simulation calculations under different operating conditions were carried out,and the voltage deviation and line loss of the distribution network were compared and analyzed.Simulation results show that the proposed power supply method is able to improve the power quality and reduce line loss under certain conditions. |
