Research And Design Of Centralized Power Supply Method In Intelligent Low-voltage Distribution System

This topic comes from the research on a new type of thermal-electromagnetic hybrid intelligent miniature circuit breaker and intelligent low-voltage microsystem under the project of national natural science foundation of China.In recent years,intelligent low-voltage power distribution system has become one of the directions of China's smart power grid construction.The system mainly relies on various intelligent electrical apparatus to operate.It can be said that whether the intelligent electrical appliances are stable and reliable directly determines whether the power distribution system can operate safely.Smart appliances are different from traditional power distribution control appliances.They need extra power supply and required to work even if the grid voltage is abnormal.Therefore,how to provide stable electric energy to intelligent electric appliances in case of grid failure is one of the research difficulties.The research in this paper focuses on solving the problem of how to supply power to multi-level intelligent circuit breakers when low voltage distribution network suffer short-circuit and voltage-absent or phase failure.Power supply solution based on fast-saturation current transformer combined with twostage cascade direct current converter is proposed in this paper according to the power supply voltage characteristics of power distribution network under different failure situations.The twostage direct current converter solves the problem of deep voltage drop that ordinary switching power supply can not adapt the fault caused by broken phase.The former is Buck converter and the latter is flyback converter.Fast-saturation current transformer,as the core acquiring-energy element in the state of short circuit loss,directly connect to the back flyback converter.In the study on fast-saturation current transformer,this paper carries out deep analysis on the working characteristics and saturation mechanism and establish the equivalent circuit model of the saturation transformer.The concept of core saturation is put forward and the relationship between the output power of the transformer and its core saturatio is dived into and deduced.Based on this,the design method of transformer parameters based on iron-core saturation is given,including the starting work saturation of iron core,the effective magnetic transversal area of the iron core and the selection of number of secondary winding.In the research on two-stage direct current converter,the basic working principle of front and rear converter is introduced.After analyzing and comparing the characteristics of voltage mode control and current mode control,the peak current control is selected as the control mode of the front and rear converter.The stability criterion of feedback loop and three typical compensation networks are elaborated.This paper offers the parameters of each component in the proposed power supply scheme from the magnetic element design,power level circuit parameter design,feedback loop and compensator design.The steady and transient output waveforms of the power supply scheme in the case of disturbance is simulated by software.The result show that the power supply scheme proposed in this paper has the expected output performance under the short circuit and phase failure of the power grid,verifying the feasibility of the design.