Abstract: The electrical and electronic systems of electric vehicles are highly complex. To effectively improve the reliability of electric vehicles and realize their comprehensive control functions, this paper introduces a three-level bus network architecture. This architecture divides the entire electric vehicle's electrical system into three layers: a bottom layer, a middle layer, and an upper layer. These three layers are uniformly controlled and coordinated by the vehicle's integrated controller, realizing functions such as battery voltage monitoring, motor monitoring and fault diagnosis, high-voltage safety detection and emergency control, and communication interfaces for the dispatch service system. This system is currently being applied to the national "863 Electric Vehicle Major Project" and is undergoing trial operation on buses. Keywords: electric vehicle, network, CAN bus[b][align=center]Study of Electric Vehicle synthesizing network system JiangYin Polytechnic College zhang Wei[/align][/b] Abstract: The electric and electronic system is very complex in electric vehicle, to fulfill the integration control function and improving reliability, we designed a three grade network struture, this system partition electric system into three lays: bottom lay, middle lay and top lay. The three lays is controlled by vehicle controller, the system carries out many functions: monitoring battery voltage, motor monitoring and diagnosis, high voltage monitoring and emergency dealing, communication with dispatch system and so on. This system was developed for project of nation high technology plan of 863, and is running in BeiJing 121 Road bus line. Keywords: electric vehicle, network, CAN Bus 1. Overview Due to environmental protection and energy crises, and the fact that traditional automobiles consume large amounts of oil, China needs to import more than 100 million tons of oil annually. Developing electric vehicle technology is a crucial development strategy for China. During the 15th Five-Year Plan, the "863 Electric Vehicle Major Project" was established. This paper focuses on the research of integrated control technology for pure electric vehicles against this backdrop. A pure electric vehicle system includes a battery and its management system, a motor and its control system, and a charger signal monitoring, detection, and control system. Electric vehicles also require communication with a vehicle dispatch system to transmit real-time data such as vehicle location and remaining battery power to the dispatch center. Furthermore, it requires the transmission of various operational data from the electric vehicle to the dispatch center. This data allows the dispatch center to understand the current status of the vehicles, providing raw data for fleet dispatching and fault repair. Therefore, the entire vehicle system must provide a communication interface with the dispatch system. Due to the inherent complexity of electric vehicles, their maintenance and diagnosis are also very difficult. Therefore, an online fault diagnosis and status monitoring window is essential. Developing an onboard information display is necessary, requiring the electric vehicle integrated control system to include an LCD system and button input to achieve a human-machine interface function. Adopting a network solution is key to solving the complex systems of electric vehicles. The development of modern electronic technology has also provided the conditions for realizing integrated network systems for electric vehicles. Powerful microprocessors often have interfaces with various functions, including the universal asynchronous serial port UART and the high-speed communication CAN bus. Differential drive technology can improve the anti-interference performance of these buses in electric vehicles, making their use possible. Electric vehicles not only have complex electrical system logic, but also operate in extremely harsh electrical environments, with voltages reaching over 500 volts. Furthermore, the high-frequency interference caused by the chopper control of the motor often leads to malfunctions of the onboard electrical system. Therefore, the vehicle control system must have high reliability. The development of electric vehicle electrical systems is often carried out in a coordinated and synchronous manner by multiple units. A key aspect is that each unit must adhere to a common communication protocol. In the entire communication system, the vehicle controller is the core, responsible for managing all components. Therefore, the scientific nature of the communication protocol determines the final system performance. 2. Integrated Network Structure of Electric Vehicles This project adopts the three-layer integrated network system structure shown in Figure 1, successfully realizing the integrated control of the entire electric vehicle and integrating all parts of the electric vehicle into a complete organic whole. Figure 1 shows a three-layer structure based on network communication. The bottom layer is the local management system, such as the battery management system, internal battery acquisition and control system, and internal motor acquisition and control system. This layer uses a variety of flexible bus methods. In this project, due to the large number of batteries, the inexpensive but highly reliable RS485 bus is used to reduce costs and facilitate large-scale industrial applications. The middle layer is the vehicle information management system, including communication interfaces with various components, such as the motor controller interface, the front vehicle acquisition and control station interface, and the rear vehicle acquisition and control station interface. It also includes direct acquisition of vehicle signals. The middle layer has very high requirements for communication speed and reliability, therefore a CAN bus interface is used. The top layer is the human-machine interface and communication expansion interface. This part displays the electric vehicle's status, helping the driver understand the electric vehicle's status in real time and monitor for faults, such as the current battery status, motor status, and overall vehicle status. If a fault occurs, the fault information can be displayed in real time. The large-screen color LCD display and operation buttons facilitate the driver's use of the electric vehicle. Meanwhile, the upper-layer network also serves as an interface for comprehensive communication, including communication with ground charging stations to promptly report the current battery status and prevent overcharging hazards. Upper-layer communication also includes communication with the dispatch system to promptly report the current status of the electric vehicle to the traffic system and receive instructions from the comprehensive dispatch system. The upper-layer communication system also functions as a communication interface for electric vehicle debugging and research. Through this interface, a PC can be connected to record various electric vehicle data, such as the electric vehicle's operating conditions and historical data from the battery's usage. To facilitate PC access to the vehicle's comprehensive information system, this project also developed CAN bus and USB bus interfaces, allowing direct connection between the PC's USB interface and the CAN bus. This system also implements the electric vehicle's overall network cabling. Various control signals of the vehicle are not directly connected to the controlled equipment via cables. Instead, the signal is first sent to the front acquisition and control station of the electric vehicle, where it is acquired and then output locally or transmitted to the network via the CAN bus for output by the rear acquisition and control station or other stations. This control method offers the following advantages: (1) The vehicle controller can monitor all vehicle information, enabling comprehensive fault diagnosis; (2) It simplifies vehicle wiring, as the front and rear of the electric vehicle are connected only by the CAN bus, improving reliability and simplifying the manufacturing process; (3) It facilitates electric vehicle maintenance. The core technology of this system is ensuring communication reliability to prevent system malfunctions. This project ensures communication reliability through a customized CAN bus communication protocol and closed-loop communication verification. To prevent system malfunctions and crashes, the application of fault protection and accident handling software and hardware technologies allows the system to recover to normal within 0.1 seconds even in the event of a fault, and ensures the system is in a safe mode in the event of a fatal hardware failure. The battery management system is part of the overall vehicle information system and is fundamental to solving electric vehicle charging safety, usage economy, and increasing driving range. The key technology of this system is resolving the contradiction between the overall battery pack voltage of over 380 volts and the individual cell voltage of less than 3.0 volts. Another crucial issue is reducing the system's hardware cost and improving its reliability. Given the large number of batteries (over 300), minimizing the testing cost per cell is paramount. This project achieves high-speed, high-precision detection of the terminal voltage of each cell and the temperature of the battery pack through the integrated application of high-speed switching technology, high-precision A/D conversion technology, opto-isolation technology, transient interference suppression technology, highly integrated microcontroller technology, digital temperature sensor technology, and high-reliability power supply technology. It also enables control of the battery pack's fan to prevent overheating. [align=center]Figure 1 Composition of the Vehicle Integrated Control System[/align] The division of the vehicle network mainly considers the functional and industrialization requirements of electric vehicles. As shown in Figure 1, some components related to vehicle safety are directly managed by the vehicle controller, belonging to the second layer. For components requiring large amounts of data communication and high real-time performance, this is also done at the second layer. Components with lower real-time requirements are placed at the third layer, such as the human-machine interface, scheduling interface, and debugging interface. For the large number of battery management systems with low real-time requirements, a low-cost RS485 bus is used, which is beneficial for the industrialization of electric vehicles. [align=center]Figure 2 Electric Vehicle Network Wiring Diagram[/align] The system layout on the vehicle is shown in Figure 2. This vehicle is an 11-meter low-floor bus prepared for the Beijing Science and Technology Olympics. It is powered by lithium-ion batteries, which are stored in boxes at the bottom of the vehicle, totaling 10 boxes. Each battery box is equipped with a battery management module, which detects the terminal voltage and temperature of each battery and controls the battery temperature. The battery boxes are connected to the vehicle controller via an RS485 bus. All detection modules 583, the rear detection module 583, the motor controller, and the CAN expansion module are connected to the CAN bus module. This bus is also connected to the vehicle controller and is under its unified control. The vehicle's human-machine interface is connected via an RS232 bus. This interface displays vehicle information and belongs to the third layer of the network. Communication with the dispatch system is achieved through the CAN bus expansion. 3. Composition of the Electric Vehicle Integrated Controller The vehicle controller is the core of the electric vehicle, responsible for signal acquisition and control. It is the communication center, belonging to the second layer of the three-layer network, and is responsible for communication and control with the battery management system, the motor system, and the human-machine interface. This project uses a Motorola DSP as the controller's CPU. The CPU's program memory is entirely internal to the chip, the CAN 2.0B bus is integrated internally, and the chip also has a 12-bit high-precision A/D converter. Adhering to the high reliability of Motorola's MCUs, this CPU is particularly suitable for high-interference applications such as electric vehicles. As shown in Figure 3, this system includes 12 digital inputs, which are transmitted to the CPU via opto-isolation. These digital inputs include brake switch, forward switch, air conditioning switch, and main brake switch. There are also 8 analog inputs, including throttle opening, braking depth, front suspension air pressure, rear suspension air pressure, and low-voltage electrical power supply voltage. Eight pulse inputs are used to collect pulse signals from the wheels to obtain the vehicle's speed and mileage. Relay control outputs control the operation of the high-voltage circuit breaker; if a high-voltage safety fault is detected, the high-voltage power is automatically cut off to ensure system and occupant safety. Communication is a crucial function of the vehicle controller. As shown in Figure 3, the vehicle controller uses three communication methods: CAN bus, RS232 bus, and RS485. To improve system reliability, all communication ports are equipped with safety protection circuits to meet the harsh electrical environment of electric vehicles. [align=center]Figure 3 Block Diagram of Electric Vehicle Controller[/align] 4. Conclusion The integrated network structure of the electric vehicle simplifies the hardware circuitry, allowing this highly complex system to function through different modules connected via a bus. Working under the coordination of the vehicle controller, these modules form an organic whole. This achieves various functions, ensures the safety of the electric vehicle, and lays a technological foundation for its commercial operation. Furthermore, the adoption of networking technology significantly accelerates the development process, modularizing the electric vehicle system and allowing for the development of relatively independent systems by other specialized units. This is crucial for ensuring the development progress and performance reliability of the electric vehicle. Currently, more than 30 electric vehicles equipped with this system are undergoing trial operation on bus routes in Beijing.