Research On The Control Strategy Of Vacuum Circuit Breaker Based On The Dynamic Behavior Of Permanent Magnetic Actuator

When opening or closing a circuit breaker, the phase of grid current or voltage is uncertainty, which may generate inrush current or overvoltage and impact greatly on the grid. Synchronous control technology provides a good solution for this problem. The importance of synchronous control technology and its implementation mechanism was analyzed in this thesis, and it was clear that the dispersion of closing or opening time of circuit breaker is the main difficulties to achieve synchronous control technology. Since vacuum circuit breaker (VCB) with permanent magnetic actuator (PMA) has a simple structure, fewer parts, little opening or closing dispersion, high reliability, long life and many other advantages, it had become the ideal component to achieve synchronous control technology. However, the dispersion of VCB operation will be affected by the changing of environment temperature and control voltage, aging of the actuator and other factors. In order to reduce the dispersion of the operation and its power consumption, and also to improve the dynamic behavior of the moving contact in VCB, a new control technology for general VCB with permanent magnetic actuator was proposed in this thesis. The main work which had been done in this thesis is shown as follows:The dynamic behavior equation of PMA with capacitor as the excitation source was analyzed and based on which the dynamic behavior equation of PMA with current excitation was deduced. To analyze the difference between the two excitation modes^the simulation model was established with Ansoft. The dynamic behavior using two different sources was analyzed and compared. Since the action time of VCB can not be affected by the changing of the control voltage or capacitance of the capacitor, it will contribute to maintaining the stability of the time for opening and closing VCB.To achieve closed-loop control based on the coil current of PMA, the principle of hysteretic control was analyzed in detail, and an improved control strategy based on linear interpolation PID control strategy was proposed to overcome the shortcoming of traditional hysteretic control. The differences between the linear interpolation PID control strategy proposed in this paper and the traditional PID control strategy was analyzed. With the control strategy based on linear interpolation PID hysteretic control which provided a powerful tool for achieving stable and efficient current source, the coil current can be effectively tracked. By analyzing the current in coil when closing VCB, a method for obtaining optimum reference current curve to get better dynamic behavior of moving contact was proposed. With the reference current curve and the new PID hysteretic control strategy, the dispersion of opening and closing time of VCB can be limited to±0.3ms.In order to improve the dynamic behavior of the moving contacts in VCB, a method of varying voltage and varying output energy (VVVE) was proposed. Features of the current when closing VCB under open looped control were analyzed, and the current equation for closing VCB was given by curve fitting way. The method for solving the equation parameters was introduced in detail, and the corresponding example was given in this thesis to demonstrate the accuracy of the fitting method. Based on the method, VVVE control strategy was proposed, by varying the initial voltage (VV) with the condition that the output energy of the capacitor were maintained, the closing time could be regulated coarsely and the speed of moving contact could be limited; and by varying the output energy (VE) with the condition of maintaining the initial voltage of the capacitor, the closing time could be regulated finely, and the speed of the moving contact could also be regulated. Since reducing the collision energy between the contacts when closing VCB and increasing speed of the moving contact in order to reduce the closing time has been always a contradiction, VVVE control strategy provides an effective method for reducing the influence of the contradiction.A controller for controlling VCB was designed to achieve synchronous controlling technology and the main structure of the hardware was described. VVVE controlling strategy had exhibited excellent performance in the realization of synchronous controlling. Although VVVE controlling strategy was concluded from the experiments with12kV VCB, it had been successfully used to control40.5kV VCB with the controller. Many experiments were done at different temperatures with40.5kV VCB to analyze the dispersion of closing time. Based on the experiments, the compensation method for closing time changed by temperature varied was implemented.