Abstract: This paper introduces the development of an automotive relay control system with a CAN bus control module, and describes the hardware and software design of the system. The system uses a PIC18F2480 microcontroller and a CAN bus transceiver as its control core, employing an optimized hybrid control scheme. It can connect and disconnect large currents without arcing, and achieve intelligent control and real-time protection functions. Keywords : automobile relay; CAN bus; hybrid control scheme; microcontroller [b][align=center]Research of High-Current Automobile Relay Control System Based on CAN Bus WANG Zhi-qiang, LIU Xiang-jun (College of Electrical Engineering & Automation, Fuzhou University, Fuzhou 350108, China)[/align][/b] Abstract: This paper introduces an automobile relay control system based on a CAN bus control module. The hardware and software design are discussed in detail. The control core, based on a PIC18F2480 microcontroller and a CAN bus transceiver, is built with an optimized hybrid control plan. The relay can switch high-current circuits with non-arc signals to realize the functions of intelligent control and real-time monitoring. Key words: automobile relay; CAN bus; hybrid control plan; microcontroller 0 Introduction With the rapid development of the automobile industry, people's requirements for the safety, comfort, and multi-functionality of automobiles are increasing. The current problems of automotive electrical systems are as follows: (1) There is a problem of battery current leakage when the car is stored, transported and parked, which affects the service life of the battery. (2) When the car malfunctions or a violent collision causes a short circuit, if the battery cannot be effectively disconnected from the entire electrical system, there is a risk of fire or even explosion. The main power switch of the car is a very important component installed between the battery and the automotive electrical system. It can cut off the main circuit power when the car malfunctions or the driver leaves the car, effectively protecting the battery and the automotive electrical system [1]. Currently, there are two types of main power switches: electromagnetic switches and battery relays. They are installed near the battery, and the control switch is installed on the dashboard near the driver, which is convenient to operate [2]. However, the electromagnetic switch is a manually operated switch and cannot play a real-time protection role for faults. The contact capacity of a general relay is limited. When cutting off the short circuit current, an arc will be generated. In severe cases, a welding phenomenon will occur, which will damage the switch or shorten the electrical life. Nowadays, there are more and more electrical appliances in the car. Various signal control lines make the length of the wiring harness longer, the weight greater, and the complexity higher. At the same time, the circuit failure rate will also increase, and the hardware cost and production efficiency of the whole vehicle will also increase accordingly. The application of CAN bus can solve these problems, and its application in automobiles is becoming increasingly mature. Through CAN bus, the control of automotive electrical systems will achieve intelligent operation. Therefore, developing a power master switch with a CAN bus control module capable of switching high currents has become an urgent task. This paper studies a high-current automotive relay based on CAN bus, realizing arc-free switching, short-circuit protection, and intelligent control functions. 1 Basic Principles The high-current automotive relay based on CAN bus designed in this paper uses a single-coil magnetic latching relay as its body. The advantage of magnetic latching relays is that only a few milliseconds of pulse drive are needed to put the switch in the on or off state, thus requiring very little power and the coil heating is negligible. Since magnetic latching relays themselves cannot switch high currents, this paper combines power electronic devices with magnetic latching relays, and by reasonably selecting the on and off times of the power electronic devices, enables the magnetic latching relay to achieve arc-free switching. The overall structure is shown in Figure 1. The existing hybrid control scheme is to connect power electronic devices and contacts in parallel. Power electronic devices bear the main circuit current during the transient process of contact connection and disconnection, while contacts bear the main circuit current during steady state [3]. This avoids the contact from generating an arc due to bouncing and interrupting large currents. The timing sequence of the excitation coil current, MOSFET drive pulse, and contact voltage is shown in Figure 2. The MOSFET operates in high-frequency conduction mode. Under the premise of ensuring reliability, the conduction time of the MOSFET should be minimized to reduce heat generation and improve service life. Therefore, this paper optimizes the existing hybrid control scheme and uses mathematical methods such as slope calculation to control the MOSFET's initial conduction time near point A in Figure 2, which greatly shortens the MOSFET's conduction time. The relay system uses a microcontroller and a CAN bus transceiver as the core of the intelligent control module. The module receives instructions from the vehicle's central control unit through the CAN bus and sends the current relay parameters to the central control unit through the CAN bus to realize intelligent control and play the role of real-time control and protection. 2 Hardware Design The relay designed in this paper uses PIC18F2480 microcontroller and CAN bus transceiver MCP2551 to form the core of the intelligent control module. PIC18F2480 comes with a CAN communication module and together with the CAN bus transceiver, it forms a CAN bus communication module [4]. The functional circuit is mainly composed of DC/DC isolation converter circuit, MOSFET drive circuit, coil drive circuit, coil sampling circuit and current sampling signal processing circuit. The overall block diagram of the hardware circuit is shown in Figure 3. In order to achieve electrical isolation between the main circuit and the control circuit, the MOSFET is driven by optocoupler isolation drive. Therefore, the power supply of the drive circuit and the power supply of the microcontroller system must be isolated from each other. The power supply system design in this paper uses DC/DC isolation converter to obtain two mutually isolated power supply systems. The current sampling of the main circuit is the key to realizing real-time short circuit protection. The intelligent control module calculates the current of the main circuit through A/D sampling, thereby determining the corresponding action of the relay. In order to achieve high precision and fast current detection, this paper uses ACS754 current sensor as the current detection element of the main circuit. ACS754 is a high-precision, bidirectional current sensor that can linearly convert the main circuit current into a logic level of 0-5V. 3 Software Design The accurate determination of the engagement and release time of the magnetic latching relay is the key problem that the software needs to solve. The software mainly includes a bus command recognition subroutine, an excitation coil current sampling subroutine, and a main circuit current sampling subroutine, etc. [5]. The software flowchart is shown in Figure 4. The specific process is as follows: When the relay is in the open state, the intelligent control module is in the state of waiting to receive commands. When the relay is in the closed state, the intelligent module samples the current of the main circuit at certain intervals and determines whether the current exceeds the set threshold of the short circuit current, and decides whether to perform the protection action. In the normal state, the current parameters are sent to the central control unit through the CAN bus so that they can be displayed on the instrument. The relay connection and disconnection commands are received by interrupt mode. After the command is recognized, the connection (disconnection) subroutine is called according to the command. When the main circuit has excessive current due to short circuit, the module automatically calls the disconnection subroutine to realize short circuit protection. 4. Implementation of a High-Current Automotive Relay Based on CAN Bus To verify the feasibility of the scheme, this paper uses a JE12-G magnetic latching relay as the main body and a PC to simulate the automotive central control unit, sending commands to the relay's intelligent control module and receiving relevant parameters from the module. A control system is built using Visual Basic 6.0 software. Since the PC does not have a CAN bus interface, the transmission of command data must be through an RS232/CAN intelligent protocol converter. The main interface of the PC-simulated control system is shown in Figure 5. The waveform displayed on the main interface is the current waveform of the main circuit, where the vertical axis represents current and the horizontal axis represents time, with each unit representing 0.5 seconds (during system operation, the waveform automatically shifts from right to left, so the origin of the horizontal axis is not necessarily zero). Figure 5 shows the current waveform when the main circuit voltage is 42V and the current is 10A, and the current is suddenly increased to the short-circuit current threshold of 60A, resulting in short-circuit protection by the relay. Experiments demonstrate that the high-current automotive relay with a CAN bus control module can reliably connect and disconnect under different load current conditions, effectively realizing the relay's arc-free switching and real-time protection functions. 5. Conclusion The high-current automotive relay with bus control function employs an optimized hybrid control scheme to achieve intelligent control. Using it as the main power switch for the automotive electrical system overcomes the shortcomings of current electromagnetic main power switches, reliably protecting the automotive electrical system and showing great application potential. [align=center][b] References[/b][/align] [1] Gu Yongqi. A new type of main power switch for storage batteries[J]. Automotive Electrical Appliances, 1995(3): 10-12. [2] Gu Yongqi, Zhao Ming. Research on a new type of main power switch for storage batteries[J]. Bus Technology and Research, 1995, 17(1): 16-20. [3] Ren Xiaoxia, Lin Chunyang, Liu Xiangjun. 42V hybrid automotive relay based on single-chip microcomputer control[J]. Low Voltage Electrical Appliances, 2008(3): 29-32. [4] Yang Xianhui. Fieldbus Technology and Applications[M]. Beijing: Tsinghua University Press, 2000. [5] Li Xuehai. Practical Tutorial on PIC Single-Chip Microcomputers[M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2002. Original text: Research on High Current Automotive Relay Control System Based on CAN Bus