Abstract: The integrated CNC contactor described in this paper is a highly integrated contactor product. It consists of main contacts, arc extinguishing device, permanent magnet mechanism, built-in power supply, drive circuit, control circuit, output port and insulating base. It can be directly connected to sensors or controllers through "USB" interface and function expansion module to form a self-cooperating control system. Electronic circuits are designed in the narrow space inside the contactor. While ensuring the close integration of "strong and weak electricity", electromagnetic compatibility is improved. Its highly integrated design breaks the traditional design concept. The integrated CNC contactor is based on high performance, dominated by information technology, and has the technical characteristics of energy saving and environmental protection, which represents the main trend of AC contactor development in the future. Keywords: CNC contactor, highly integrated, permanent magnet mechanism, built-in power supply, output terminal and function expansion module, self-cooperating control system 0 Introduction Low-voltage electrical appliances refer to components that play the role of switching, control and protection in low-voltage power distribution and control systems. There are many varieties and specifications of them. They are widely used in the two major fields of industrial process automation and low-voltage terminal power supply. AC contactors have a solid market foundation, especially mid-to-high-end products have more development potential [2]. The main trend of future AC contactor technology development is to reflect the energy-saving, environmental protection, information technology and multi-functional technical characteristics of the product; reduce operating costs, improve safety and reliability, and make the product more user-friendly. There are a large number of local control and execution mechanisms in the industrial field automation process control system. In engineering design, sensors, controllers, intermediate relays and AC contactors are often selected to form a control system. The control system designed by the traditional method has problems such as complex circuit structure, poor motion controllability, high energy consumption and easy damage of components. This article introduces the design scheme of integrated CNC contactor proposed in reference [5], which can solve the above problems. 1 Scheme implementation concept and difficulties The integrated CNC contactor is a highly integrated contactor product, which consists of main contacts, arc extinguishing device, permanent magnet mechanism, built-in power supply, drive circuit, control circuit, output port and insulating base; through the "USB" interface and function expansion module, it connects to sensors or programmable logic controllers to form a self-cooperating control system. (See Figure 1). Figure 1 1.1 Concept of achieving the goal (1) Select a small transformer with an output voltage of AC9V×2, and use bridge rectification and full-wave rectification to obtain two relatively independent power supplies, which are used to power the drive circuit and the control circuit respectively. (2) The operating frequency of the integrated CNC contactor is designed to be 600 times/hour. During the interval, the energy storage capacitor is charged, and the stored energy is used to smooth the impact of the starting current. (3) Utilize the electric field in the energy storage capacitor group to discharge the excitation coil in a very short time [1], forming a single pulse touch current to excite the pulse magnetic field, achieving the dual purpose of closing the main contacts and magnetizing the permanent magnet. (4) Use the relay control circuit to give full play to its low contact impedance and strong current output capability, so that the excitation current can reach the peak value in the shortest time, and turn off in time when it quickly returns to zero after reaching the peak value. (5) Connect various sensors or programmable logic controllers through the "USB" interface and external function expansion module to perform analog quantity, position, sequence, time and remote control. 1.2 Difficulties in implementing the scheme (1) The control circuit board must be installed inside the contactor (volume: 60mm×60mm×25mm). The design of the DC power supply, control circuit and expansion circuit should be simplified as much as possible. (2) The installation space of the circuit board is sealed, and the temperature rise of the circuit components must be strictly suppressed. (3) Due to the above conditions, a small sealed transformer with a power of 3W is selected as the power supply for the contactor operation and functional expansion module. (4) Designing a product that closely combines "strong current" and "weak current" in the narrow space inside the contactor, the electromagnetic compatibility design is quite difficult. 2 Project technical scheme 2.1 Built-in power supply circuit [5] The power supply circuit (see Figure 2) consists of two relatively independent power supply branches, which are responsible for supplying power to the control circuit and expansion interface respectively. In Figure 2, T1 is a small sealed transformer with a power of 3W and an output voltage of AC9V×2. The power supply VC1 and power supply VC2 are composed of the output terminals 3 and 5 of the transformer T1, the rectifier bridge D1, and the energy storage capacitors C3 and C4. When the contactor is engaged, it is powered by VC2, and when it is disengaged, it is powered by VC1. Another branch is the output terminals 3, 4, and 5 of T1, which are rectified by diodes D2 and D3 and filtered by capacitor C1 to form power supply VC3. Through constant current source circuit and "USB" interface, it provides power supply VC4 for the expansion module. Analysis of the key points of power supply circuit design: (1) The small transformer has a certain overload capacity and the open voltage is 1.6 times the nominal value, which is suitable for charging the energy storage capacitor during the contactor operation interval. (2) T1 is selected with a transformer with a middle tap at the output terminal. Two relatively independent power supplies are obtained through different rectification methods. When the contactor is engaged, the voltage value of VC2 drops sharply. Due to the isolation of D2 and D3 and the energy storage effect of C1, VC3 is not affected, which improves the stability of the control circuit. (3) VC4 is powered by constant current source circuit to avoid overload or short circuit damage to the power supply when the interface is connected. Figure 2 2.2 Drive circuit [5] Figure 3 Figure 3 is the schematic diagram of drive circuit. Its working process is as follows: When the power is turned on, the two ends of the excitation coil KM are grounded through the switching switches JK1 and JK2, and the contactor is in standby state. When the control terminal UB-2 is "1", the trigger diode D5 is turned on → the relay J3 is closed → the relay J2 is closed, the excitation coil KM is energized through the normally open point of the switching switch JK2, and the main contacts are closed by the electric and permanent magnet forces. After a delay, J2 is released, the excitation coil KM is de-energized, and the closed state is maintained by the magnetic force of the permanent magnet. When the control terminal UB-2 is "0", the trigger diode D5 is turned off → the relay J3 is released → the relay J1 is closed, the excitation coil KM is energized through the normally open point of the switching switch JK1, and the reverse magnetic field cancels the permanent magnet force while the main contacts are broken by the force of the reset spring and remain in the broken state [8]. Analysis of key points of drive circuit design: (1) Improve energy efficiency and reduce contactor starting power. According to electromagnetic theory and turn-ampere characteristic analysis [3], when the number of turns of the excitation coil is determined, the strength of the electromagnetic field depends on the current value and slew rate flowing through the excitation coil. That is to say, when the LRC circuit composed of the excitation coil and the energy storage capacitor is working in the resonance state, its energy efficiency value is the highest. (2) Use energy storage capacitor group to realize pulse wave [1] The energy storage capacitor C4 in the figure is a capacitor group composed of multiple electrolytic capacitors connected in parallel, which aims to reduce internal resistance and improve transient current output capability. The lower limit of the capacitor capacity setting should be able to meet the energy required for excitation, and the upper limit should be able to make the excitation current return to zero quickly after reaching the peak value. (3) Select relay control mode [8] The function conversion control of this circuit uses relay control circuit because the relay has the advantages of strong current output capability and low temperature rise compared with transistor, and can meet the technical requirements of the contact current reaching the peak value in the shortest time. The "contact damage" defect of the relay can be solved by switching when the circuit current value is close to the zero point. 2.3 Extension Circuit [5] The integrated control system consists of a built-in DC power supply, drive circuit, "USB" output interface, function extension module and external sensor. The "USB" interface terminal plays a connecting role. The extension interface UB adopts the "USB" interface form, consisting of a DC12V (20mA) constant current power supply, two logic control ports, and a common ground line, and has short-circuit capability. The logic control capabilities of the 2nd and 3rd terminals of the interface are shown in the table below: UB-2 UB-3 Main circuit working state 1 0 On 0 0 Off 1 1 Off 0 1 Off Note: Logic 1 (minimum) DC5V; Logic 0 (maximum) DC2V. In terms of function extension, various integrated sensors such as temperature, humidity, pressure, magnetism (Hall), photosensitive, gas sensitive, etc. can be connected through operational amplifiers or comparators (see Figure 4) to implement analog quantity control. It can also be connected to external digital circuits, microcontrollers, PLCs for position, sequence, and time control; or connected to the fieldbus control system through the fieldbus interface module. Figure 4 2.4 The permanent magnet mechanism of the integrated CNC contactor with permanent magnet mechanism is the same as that of the low power CNC contactor in reference [6], as shown in Figure 5. Its structural features will not be described in detail. Figure 5 Currently, many permanent magnet mechanism schemes are used in the research and development of new contactor products. Each design scheme has its own unique features. The permanent magnet is the core component of the permanent magnet mechanism and is a newly added magnetic source in the magnetic circuit. The requirements of the magnetic field strength for the on and off states of the contactor are completely opposite. The technical feature of this scheme is that the contact current reaches its peak value in the shortest time and can quickly return to zero after reaching the peak value. At the same time as the contactor is on and off, the permanent magnet is magnetized and demagnetized to obtain different magnetic properties. According to actual testing, after the permanent magnet is magnetized by the transient pulse magnetic field (oversaturation), the increase in the attraction force on the moving iron core is not less than 30N. The permanent magnet mechanism is still an electromagnetic operating mechanism. The initial power for the attraction process of the moving iron core mainly comes from electromagnetic fields. The permeability of the iron core composed of silicon steel sheets is better than that of permanent magnets. Based on the anisotropy of magnetic materials, permanent magnets are embedded in the stationary iron core. The silicon steel sheets on both sides of the stationary iron core remain intact, forming a special combination of soft and hard magnetic circuits in the iron core. Through the superposition of multiple magnetic circuits, the dynamic magnetic attraction index reaches the optimal level. 3 Main technical innovations (1) Application innovation of contactor electromagnetic theory Traditional AC contactors directly use AC220V drive. After the main contacts are closed, a large amount of electrical energy is converted into heat and distributed in the excitation coil. The new AC contactor contains electronic circuits and limits the starting time to 100ms. For 50Hz AC, at least 4 cycles are needed to complete the starting process. The rate of change of excitation current (slew rate) depends on the AC frequency. From the analysis of electromagnetic theory, it is known that the generation of pulse magnetic field is not only related to the intensity of current, but also to the rate of change of current; that is, the waveform in which the excitation current can reach the peak value in the shortest time and return to zero quickly after reaching the peak value has the highest effective value. Based on this, the design of the integrated CNC contactor adopts a single pulse drive mode to shorten the start-up time and improve the power utilization rate, thereby reducing the power consumption of large-scale AC contactors by two orders of magnitude and realizing the application innovation of electromagnetic theory. (2) Innovation of contactor design concept When the industry organizes the development of new generation contactor products, it often focuses on improving some technical indicators to shorten the gap with the international advanced level. The design concept of CNC contactor is to lead AC contactors into the fast lane of "informatization". Its characteristics are as follows: First, the carrier of informatization is electronic circuit, and CNC contactor must be compatible with electronic circuit to build a brand-new technical platform for the implementation of informatization[7]. Second, the implementation of informatization will lead to the industrial field control system becoming larger and more complex; as the terminal execution device, the contactor must make breakthrough progress in power consumption, motion controllability and environmental adaptability, and integrate into the information age with a brand-new concept. (3) Breakthrough innovation of contactor core technical indicators All technical indicators of the integrated CNC contactor are superior to those of the existing AC contactor, and its core technical indicators and environmental adaptability indicators have made breakthrough progress. The following is an example of the technical standard for SY type (integrated) CNC contactor [4]: ​​4. Conclusion The development of the social economy has led to an increasing demand for and reliance on electricity, making low-voltage electrical appliances, which are responsible for the transmission and distribution of electricity and the protection and control of electrical equipment, even more important. Countries around the world attach great importance to the development of low-voltage electrical appliances and invest a lot of money in research and development. China is a stable society with a strong innovation culture, and building an innovative country has become a consensus among governments at all levels. With the acceleration of the pace of new industrialization and the improvement of energy-saving and environmental protection standards, a large-scale equipment and fixed asset renewal period is coming, and new electrical components will replace traditional electrical components as the main market. The integrated CNC contactor, based on high performance and dominated by informatization, and with the technical characteristics of energy saving and environmental protection, represents the main trend of future development of AC contactors. Its innovative design concept and technical performance advantages will lead AC contactors into the future of informatization. References [1] LIN Xin. Permanent magnet and vacuum breaker. Beijing: China Machine Press, 2002. [2] WANG Renxiang. Common low-voltage apparatus and its controlling. Beijing: China Machine Press, 2001. [3] CAI Yuanyu. Electrical circuit and magnetic circuit. Beijing: High Education Press, 1992. [4] “The enterprise standard of Sichuan RongGao electrical corporation” Q/78014280-X.2-2006. Filing number B51.1378-2006. Chengdu. Q/78014280-X.2-2006.serial number: B51.1378-2006.Chengdu. [5] LIU Jinping. Integrated digital controlled contactor: China, ZL2005100209164. Authorization date: 2005-12-24. [6] LIU Jinping. Low voltage digital controlled contactor and its controlling system: China, ZL2005100216420. Authorization date: 2006-12-20. [7] Guo Yincheng, Lv Wenhong. The principle of EMC and its application. Beijing: Tsinghua University Press, 2004. [8] Yang Bangwen. Application manual of new type relays. Beijing: Posts And Telecom Press, 2004. Liu Hao (1982), male, master, engineer, research direction is numerical control low voltage electrical appliances and power system stability. Email: [email protected] Liu Jinping (1952), male, university, engineer, research direction is numerical control low voltage electrical appliances. Email: [email protected] Liu Yujie (1982), female, bachelor, assistant engineer, engaged in electronic circuit design and development. Email: [email protected] Integrated digital controlled contactor