The Key Technology For Modern Design Of AC Contactor

As a type of control electric apparatus and an important part of the security and stability operation of power grid, AC contactors are widely used in low-voltage distribution systems. With the development of computer technology, modern design techniques for electric apparatuses combined with multi-disciplinary theories and methods gradually become the core of the advanced manufacturing technology. In general, the modern design techniques in the field of electric apparatuses consist of the virtual prototype technology, finite element analysis, optimization design, reliability design, intelligent computer-aided design, dynamic design and analysis, value engineering, robust design, reverse engineering and intelligent engineering, etc. As mentioned above, some key techniques and methods of modern design for electric apparatuses have been researched and used in different aspects of designing, testing and analyzing intelligent AC contactors, in order to provide examples in the field of low-voltage electric apparatuses for spreading modern design applications. The main contents of the study include the following aspects.(1) This paper studies a numerical method to solve the coupled equations of the AC contactors based on static magnetic analysis. Specifically, the electromagnetic variables are solved, and substituted into mechanical dynamic governing equations in the form of a numerical grid. So the coupling calculation results are archived. By using static and discrete current and displacement sequences, the method above cannot reflect the influence of induced current of system and dynamic inductance caused by the action of the electromagnetic mechanism. The thesis proposes an integrated modeling framework to optimize the finite element analysis technology for magnetic contactors. The air gap field is meshed with the moving mesh method in the time domain so that the electromagnetic governing equation can be coupled with the mechanical dynamic governing equation. The electromagnetic variables and the mechanical variables can be solved in the same time for the dynamic response of an actuator. Meanwhile the electromagnetic energy, dynamic inductance and other parameters can also be solved.(2) The relevant factors that affect the dynamic characteristics of intelligent AC contactors include the dynamic inductance of the coil, the closing initial phase angle and temperature. These factors can be studied by means of simulation and experimentation. On this basis, a mathematical model of temperature and minimum closing duty cycles is developed, which can compensate the error on the dynamic characteristics of the contactor because of the change of the working condition temperature.(3) Based on the reliability optimization design of structure parameters of the main contact springs and electromagnetic system by the improved genetic algorithm, this paper discusses a modeling process under the nonlinear constrained multi-objective conditions, and tests the characteristics of the main contact spring and electromagnetic system after optimization. The experimental results show that the mass of the spring decreases 16.2% after the reliability optimization design than before, the reliability upgrades from 94.5% to 99.9% compared to a non-optimized one. The steady-state temperature of an optimized electromagnetic system falls to 28.8℃, decreasing significantly compared to that before optimization(55.1℃). In the conditions of ensuring the contactor stability, the end closing velocity of the actuator of the electromagnetic mechanism is significantly reduced after optimization than before. The experimental results prove that the method of reliability optimization design is efficient and feasible.(4) A time-shared control strategy is developed to optimize the performance of intelligent AC contactors. PWM time-shared control is proposed to test the dynamic characteristics of an intelligent AC contactor by using different duty cycles. Based on the results, Support Vector Machine for regression is employed to develop the PWM control model and optimize the control parameters accordingly. The prediction samples are evaluated by using the model. Comparisons show that the model can predict the inherent relationship between duty cycles, end velocity and closing time properly. Meanwhile, the PWM time-shared control model and the judgment methods of initial closing phases have been applied to the control algorithm of the intelligent AC contactor. The experimental results show that in the holding process the DC current is limited under a low level so that the energy can be saved,and the dynamic characteristics can be optimized by adjusting the anti-suction force relationship.