Research And Design Of Intelligent Capacitor

In recent years,with the development of modern industry and power electronic technology,a large number of devices having lower power factor,nonlinearity,asymmetry and other characteristics are used in the access network,such as motors,welders,thyristors,etc.They will produce a great quantity of reactive power in the operation of power system.However,a great quantity of reactive power will cause line loss,voltage drop,affect power quality.Consequently,the research and development of reactive power compensation device will have a great significance to the power network.This thesis aim at the controller,capacitor and switch are separated and easy to produce inrush current and arc of traditional reactive power compensation device,a new type of low voltage reactive power compensation device which is composed of controller,capacitor and synchronous switch is designed,that is intelligent capacitor.This device can be switched in the voltage zero crossing and cut off in the current zero crossing,to achieve the purpose of switching without current and arc.The main fruits of this thesis are as follows:1.The principles of reactive power compensation,no inrush current switching and no arc removal are analyzed.The method of power system parameter measurement based on FFT algorithm is introduced.2.The whole design scheme of the intelligent capacitor is introduced,and the system functional requirements and technical specifications are defined.3.The hardware circuits of power network parameters acquisition and processing,switching control,temperature detection,data communication and so on.A novel zero crossing detection method is designed.In this method,the zero crossing detection circuit and the DSP capture interrupt function are used to detect the zero crossing point exactly,it makes up for the defect of single optical coupling detection of zero crossing error.Moreover,This system use the voltage zero crossing to calculate the current zero crossing time saving the use of current sensor,and the equipment cost is reduced.4.The ideology of modular programming is adopted.The programming principles of no delay,no wait cycle,break up the whole into parts are followed,to design the signal acquisition and processing,switching control,data communication,key and display modules,makes the system program clear and smooth.5.The prototype of intelligent capacitor was tested,and the results showed: this design of intelligent capacitor network parameter measures exactly,high precision of zero crossing detection.It can realize the goal of switching no inrush current and cutting off no arc of capacitor,and meet the requirements of the technical indicators.The results of this study have high engineering application value.