Research On Precision Current Control Method In Digital Detection Of Circuit Breaker Protection Characteristics

Circuit breaker is an important protective equipment in distribution network,which is responsible for closing,carrying and breaking normal circuit current.When there are electrical faults such as overload,over-current and short circuit,the circuit breaker breaks off the abnormal current within the specified time,and provides the ability to protect the line and power supply.It is an important electrical equipment to maintain the stable and reliable operation of the power grid and ensure the safety of personal and property.The protection characteristic of circuit breaker is an important index to measure its comprehensive performance.In the process of production,the traditional method needs a lot of labor,which leads to poor product consistency,low efficiency and accuracy.It seriously restricts the development of high performance circuit breaker products and the digital upgrading of manufacturing methods.It is an important method to check the protection characteristics of circuit breaker by using high precision constant current source system.The system control of the existing scheme only deals with the error and the error accumulation,which cannot judge the influence of the error change on the system accuracy.The system control accuracy is limited and the system response time is slow.At the same time,the test response time problem caused by impedance difference seriously restricts the efficiency and accuracy of circuit breaker protection characteristic test.To solve the existing problems,this paper studies the precision current control method in digital detection of circuit breaker protection characteristics,and puts forward the control algorithm based on PI like sugeon fuzzy system.Combined with load impedance compensation algorithm,the current output accuracy and response speed of the detection system are improved.The main studies include:(1)The principle of constant current generator in digital circuit breaker detection is analyzed.The problems of low precision,slow response and serious harmonic pollution in the current constant current generator are pointed out.Combined with the development trend of future technology,it is pointed out that the current constant current source should have reliable protection mechanism,various human-computer interaction,high intelligence degree and small harmonic pollution.(2)The protection characteristic of circuit breaker is analyzed and the hardware and software design of the whole system are determined.In hardware,in order to realize the whole constant current output and reduce the harmonic pollution of the system,the current conversion circuit with the main topology of the previous power factor correction circuit and the rear inverter circuit is determined.In software,the operating system based on preemptive task priority scheduling is designed to coordinate the multi-task operation of system sampling,control,protection,man-machine interaction and improve the real-time response of the whole system.(3)To improve the precision and response time of the output current of the whole system,the PI like sugeno fuzzy control scheme is developed,and the control quantity is obtained according to the current sampling information.In order to further improve the output accuracy of the constant current device,a sliding window sampling algorithm based on the first-order inertial filtering algorithm is proposed.The real-time performance of the sampling algorithm is greatly enhanced.Meanwhile,in the face of the contradiction between time and space under the digital SPWM generation algorithm,a linear expansion SPWM digital generation algorithm with phase information is proposed.(4)The simulation model under the proposed constant current output scheme is built.Besides,the physical prototype is developed,and the proposed control scheme is verified and compared with the traditional control scheme.Simulation and experimental comparisons show that compared with the traditional control strategy,the output current accuracy of the system is less than 0.2%,the maximum performance is more than 87%and the response time of the system is increased with 60%.Different parameters including the current output accuracy,the system response time and the reliability of the circuit breaker protection characteristics can be greatly improved.