Research on intelligent control of CJX2 AC contactor

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1. Control skill of phase selection and closing


The size of the coil voltage and current is related to the initial phase angle φ 0. It takes about 20ms for CJX2 AC contactor to move from the beginning of the iron core to close, while the frequency of the control voltage is 50Hz, that is, a voltage waveform period is 20ms, so the initial phase has a greater impact on the dynamic process of the contactor closing. The results show that: under different closing phase angle, the change laws of the electromagnetic mechanism's suction, armature's movement speed and displacement are different, which may lead to the situation of no closing; In other phase angles, although it can be closed reliably, the closing speed is too high, which leads to the increase of contact bounce and affects the mechanical life and electrical life of the contact. In order to change the influence of closing phase angle on the dynamic characteristics of contactor, the control skill of selecting phase and closing is put forward. The skill of phase selection and closing is based on the control system with single chip microcomputer as the core. After the zero crossing point of closing voltage is collected, the power electronic switch device is driven to turn on after the delay time t, and then the purpose of phase selection and closing is achieved. As for the confirmation of the delay time t, the better closing phase angle is generally obtained through experiments, and then set through the human-computer interface.


2 current breaking control skills


The additional arc closing and breaking process of AC contactor will be affected by the additional arc closing and breaking current of AC contactor Reliability. Communication current has the characteristic of current zero crossing, so the electromagnetic mechanism of AC contactor can be controlled to make it break near the current zero crossing, which can complete the micro arc less arc breaking control, namely the so-called zero current breaking control. To complete the zero current breaking control of the three-phase contact system of AC contactor, the researchers put forward the following control plans: (1) through the control of microcomputer and software, the three-phase contact is randomly broken at the current zero crossing point, so that only one phase contact can complete the zero current breaking in each breaking process. (2) Change the structure of the contact, so that the opening distance between the three-phase contacts is different, so that the three-phase contacts are not synchronized when breaking. Assuming that the contact opening distance of the central phase is greater than that of the other two phases, and its separation time is just ahead of the other two phases by a certain time t, then only the central phase needs to be operated when breaking, so that it can break at the zero crossing point of the current, and the other two phases can also reach the power point after the time delay t In this way, the zero current breaking of the three-phase contacts of the contactor is completed. (3) Combined contactor is selected to perform split phase control. A single pole AC contactor and a north-south pole AC contactor are combined. The single pole contactor replaces the first open contact in plan (2) and is responsible for breaking the first open phase. The north-south pole AC contactor is responsible for other two phases. The zero current breaking of contactor three-phase circuit is completed by microcomputer control system. These three plans all need to be controlled by microcomputer control system, and there are some problems in their completion: due to mechanical factors such as contactor structure and process, the breaking dynamic process of contactor has great dispersion with the mechanical and electrical wear of contact, and it is unable to ensure that the breaking time of contact is stable at a certain value every time, which makes the control parameters set by microcomputer may be invalid It affects the reliability of contactor.


3 open loop control skills


The open-loop control of CJX2 AC contactor generally adopts the time-sharing or subsection PWM control skill of electromagnetic system. The MCU control system announces the duty cycle of the PWM drive signal switch tube after the power circuit is detected, so that the DC voltage after rectification and filtering is changed into the high frequency square wave voltage applied to two ends of the coil. After controlling the duty cycle of each period, the excitation of the two ends of the coil can be adjusted, and then the dynamic characteristics of the electromagnetic mechanism can be adjusted. The closing process is divided into 3 segments at equal intervals. Each segment of 10ms is applied with different duty cycle driving signals at each time period, so that the coil obtains different sizes of excitation, and then the contact curve of the contactor is adjusted. As for the selection of duty cycle, the dynamic characteristics of contactors are tested under different duty cycle combinations. According to the experimental data, the support vector machine regression method is used to establish the PWM control model and optimize the control parameters. This model can predict the closing time of contactors and the closing speed of moving iron core according to the duty cycle combination.


4 closed loop control skills


As mentioned above, the cooperation between the suction and reaction characteristics of contactor is very important, which determines the function of CJX2 AC contactor. The reaction force of the contactor includes the breaking reaction force supplied by the mechanical tension spring, the reaction force supplied by the over travel tension spring installed in the contact system, the reaction force of the auxiliary contact system to recover the tension spring, and the resultant force of a series of forces that hinder the closing of the iron core, such as the friction generated by the moving parts. The mechanical dispersion of the resultant force of so many mechanical forces makes the cooperation between the suction and reaction force of the contactor unstable. At this time, if the closed-loop control system is selected, the size of the electromagnetic suction can be adjusted according to the real-time effective response signal, so that the contactor can be closed reliably, and the excessive suction will not aggravate the contact bounce and mechanical wear. Closed loop control requires effective response signals, which mainly include coil voltage, current, iron core movement speed, iron core displacement, etc. The author designs a control system with single chip microcomputer as the core. After collecting the coil voltage, he controls the voltage regulator to make its output stable at a certain value. In this way, the dynamic characteristics of the contactor will remain stable even though the grid voltage fluctuates (within 85% - 110% of the additional voltage scale specified in the national standard). The experiment proves that the control effect is good.


Although the energy-saving control plan proposed by early scholars can save a certain amount of operation energy consumption, the reliability of control is reduced, which has adverse effects on the closing and breaking functions, and is gradually screened in practical application. With the wide application of microprocessor and related power electronic skills, the intelligent control of contactor will be more and more perfect. In theory, the existing intelligent control plan can improve some aspects of the function index of the contactor, but the practical application also needs to consider the characteristics of the dynamic parameter dispersion in the process of using the contactor. The selection of closed-loop control and related parameter self calibration skills can improve this problem

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