Abstract: This paper introduces the characteristics of the iCAN fieldbus protocol and describes the hardware platform and software flow of the iCAN-based distributed supercapacitor monitoring system. Keywords: iCAN fieldbus; supercapacitor monitoring The supercapacitor monitoring system is a key technology for supercapacitor trolleys. The supercapacitor monitoring system can monitor the status of supercapacitors in real time, such as voltage, charging and discharging current, and operating temperature; predict the internal resistance and capacitance of supercapacitors, and prevent overcharging and over-discharging, thereby improving the performance and lifespan of supercapacitors and enhancing the reliability and safety of supercapacitor trolleys. This design uses NXPARM as the main body to build the hardware platform of the supercapacitor monitoring system, and embeds the C/OS-11 real-time operating system inside the ARM to form an iCAN-based distributed supercapacitor monitoring system, which improves the stability and real-time response capability of the system and enhances the scalability and portability of the system. [b]1 Introduction to iCAN Protocol[/b] The iCAN protocol is an application layer protocol based on CAN-bus independently developed by Guangzhou Zhiyuan Electronics Co., Ltd. It provides an easy-to-build CAN-bus network for the industrial control field and provides a low-cost solution for the connection between industrial field devices (sensors, instruments, etc.) and management devices (industrial control computers, PLCs, etc.). The iCAN protocol defines in detail the allocation and application of IDs and data in CAN messages, and defines the I/O resources and access rules of devices. The iCAN protocol communication layer structure is shown in Figure 1. The iCAN protocol specification mainly describes the following: iCAN message format definition: specifies the CAN frame type used in the iCAN protocol, as well as the frame ID, message data usage, etc.; Message transmission protocol: specifies the communication method between devices based on the iCAN protocol; Device definition: device identifier, device application unit, device communication and application parameters, and defines standard device types to distinguish different functions or product types of devices on the network; Network management: specifies device communication monitoring and error management. 1.1 iCAN Protocol Network Topology The topology of the iCAN network conforms to the high-speed standard of CAN [ISO99-2]. The iCAN network supports a maximum of 64 nodes, and the nodes are connected to the network cable using branch lines. In practical applications, the branch lines in the network should be as short as possible. At a speed of 1 Mbps, the longest branch line is 0.3 m. At lower speeds, the branch lines can be extended. The maximum communication distance in an iCAN network is related to the communication rate within the network. Table 1 below shows the relationship between the bit rate and the maximum bus length in an iCAN network. 1-2 Addressing of iCAN Network Devices In the iCAN protocol specification, each node in the network has a unique identifier, MACID, used to distinguish different devices in the network. The numerical range of MACID is defined in Table 2 below. Each node in an iCAN network has a specific MACID; therefore, data exchange between different nodes in an iCAN network is based on node addressing. In a CAN network, information is distinguished by message identifiers; therefore, various identifiers can be assigned to establish information connections. CAN data frames transmitted in the network contain the destination and the source address of the node. Therefore, each frame is sent to a specified node or a group of nodes. Nodes in the network determine whether to process the message by judging the node address in the network message. Furthermore, the iCAN protocol also reserves specific addresses for addressing a group of nodes or all nodes (broadcast) and transmitting frames. The iCAN protocol's node-addressing-based communication method is based on data communication through connection and acknowledgment. 1.3 iCAN is a connection-based communication protocol. iCAN-based networks are master-slave networks. An iCAN network typically has a master device that manages other devices on the network and monitors the entire network. Slave devices cannot communicate with each other. Communication between devices in an iCAN network is connection-based, facilitating communication between the master and slave devices. Communication between the master and slave devices in an iCAN network is not random. A communication connection must first be established between the master and slave devices. Only after establishing the connection can the master device communicate with the slave devices. 2 Hardware Structure 2.1 System Overall Structure This system (Figure 2) is used to detect the operating voltage of each capacitor in the supercapacitor bank, as well as the total voltage and current of the capacitor bank, and connects to the vehicle's instrument system via a CAN bus conforming to the SAE J1939 protocol. The system consists of a monitoring system master node (hereinafter referred to as the master node), capacitor detection sub-nodes (hereinafter referred to as sub-nodes), an LCD diagnostic instrument, and a CAN bus network. The system consists of one master node and 27 sub-nodes. Each child node communicates with the master node via the iCAN network and can detect the voltage of 18 capacitors, with a detection voltage range of 0-5V and an error of <10mΩ. Each child node has one temperature input for detecting the battery surface temperature, with a range of 0-100°C and an error of <1°C. The master node has a CAN bus interface with the SAE J1939 protocol. It supports a 320x240 monochrome LCD diagnostic instrument for displaying system operating status and inputting alarm threshold parameters. It has two relay outputs at contact points, which can drive two fans. The total voltage measurement interface can be connected to an external NCV1-1000V voltage sensor to measure (0-650V, +5V) DC voltage. The total current measurement interface has an input current of 0-120mA and can be connected to an external NT300-S current sensor to measure (rated current 300-3A, maximum measurement range ±300A) DC current. The system power supply is DC24V/2A. The intelligent monitoring sub-node uses the LPC2119 as the controller. Peripheral modules include a temperature measurement module, a voltage measurement module, and a node address selection module. The LPC2119 has a built-in CAN interface module. The voltage measurement module processes the voltage of each battery cell in the series capacitor by introducing it into a voltage divider circuit via analog switches. After impedance transformation by a voltage follower, the voltage is sent to the differential input of the ADC. The converted digital voltage output is isolated and then sent to the P1 port of the microcontroller. The temperature measurement module uses the DS18S20 series single-wire digital thermometer from Dallas Semiconductor, requiring only one wire to connect the microcontroller and the DS18S20. To fully utilize the interface resources of the LPC2119, serial interface devices are used, reducing circuit size and hardware costs. The master node uses the LPC2368 as the controller. The LPC2368 uses a high-performance 32-bit ARM7 core and can operate at frequencies up to 72MHz. Each device contains up to 512KB of on-chip Flash and 58KB of on-chip SRAM memory. It includes one 10/100 Ethernet MAC interface, one USB 2.0 full-speed (12Mbps) device, two CAN 2.0B channels, one general-purpose DMA controller, one 10-bit A/D converter, and one 10-bit D/A converter. Peripheral modules include: a total voltage detection module, a total current detection module, an output relay module, and a power isolation module. The two CAN interface modules are built into the LPC2368, enabling iCAN and J1939 communication. This design utilizes the LPC2368's IAP function to store configuration parameters in the on-chip Flash. 3. Software Design 3.1 Software Development Zhiyuan Electronics provides users with dedicated development project templates, simplifying the software development process. The industrial control module has a built-in file system, TCP/IP protocol stack, USB protocol stack, iCAN library, basic driver library, and iC/OS-II operating system. Users do not need to configure the IC/OS-II kernel; they can only use the pre-set configuration information. The main software development tool is ADSv1.2, or ARM Developer Suite. It is a new generation of ARM integrated development tools launched by ARM. ADS consists of a command-line development tool, an ARM real-time library, a GUI development environment (CodeWarrior and AXD), utilities, and support software. With these components, users can write and debug their own applications for ARM series RISC processors. The ADS software itself includes the AXD debugger software, supporting debugging operations such as viewing variables and controlling breakpoints in the running executable code, facilitating debugging of target programs and improving program development efficiency. 3-2 Software Flowchart Main Node: The software design adopts modular programming. The system software is mainly divided into the main program, data acquisition (voltage, current) processing program, alarm processing, J1939 message communication, and iCAN scanning communication program. The main program is the system control program, which implements the initialization of system data processing (including system self-test, reading the local node address, and capacitor voltage type) and the overall scheduling of each module software. Sub-nodes: The data acquisition and processing program includes voltage acquisition and temperature acquisition. Because the DS18S20 has a relatively long temperature conversion time (750ms), temperature conversion and voltage acquisition are performed first, followed by temperature acquisition, in each data acquisition cycle. Temperature conversion and voltage acquisition are performed simultaneously. After each round of acquisition, the data is processed to determine if it exceeds the limit value. The iCAN communication program is responsible for sending the acquired data to the CAN controller, as shown in Figure 4, and then the CAN controller is responsible for sending the data to the CAN bus. The main subroutines include: CAN initialization, CAN transmission, CAN reception, ADC subroutine, DS18S20 reset, and startup. 4 Hardware Anti-interference Measures As part of the vehicle, the capacitor monitoring system is frequently subjected to various electromagnetic interferences. Its actual working environment is quite harsh, so it is necessary to take certain anti-interference measures in the hardware design. 1) Suppressing interference sources. When the IGBTs and power diodes in the motor equipment of electric vehicles are working, they will generate strong electromagnetic interference, and shielding should be strengthened. 2) Isolated power supply. The capacitor monitoring system design uses several DC/DC conversion modules to provide stable isolated power supplies, which can effectively eliminate power supply interference and interference caused by common ground. 3) Opto-isolation. In the design of the capacitor monitoring system, an optocoupler is used to isolate the external communication interface (CAN communication, RS232 communication) from the internal CPU circuit, preventing electromagnetic interference caused by circuit coupling. 5 Conclusion The iCAN-based distributed capacitor monitoring system has a high degree of intelligence, accurate measurement, and can detect early faults in supercapacitor banks in a timely manner. It has been successfully applied to our company's supercapacitor buses. [b]References:[/b][1] Zhou Ligong. iCAN Fieldbus Principles and Applications [M]. Beijing: Beijing University of Aeronautics and Astronautics Press. 2007 Click to download: Distributed Supercapacitor Monitoring System Based on iCAN Protocol Editor: Chen Dong