**Abstract:**
With the rise of the Internet of Things (IoT) era, intelligent remote management of fast chargers has become a reality. The design of monitoring terminals for these systems is a critical technology in this field. This paper presents an overall design scheme for a fast charger monitoring terminal, integrating a single-chip microcontroller STM32 with the real-time operating system μC/OS-II. It explores the formulation of protocols and software design methods for high-power charger CAN bus and GPRS data transmission. Additionally, an economic analysis of GPRS traffic costs is conducted. The results demonstrate that the monitoring terminal ensures the stability of the monitoring network and enables real-time monitoring of the charger's operational status and remote management capabilities.
**0. Introduction**
With strong government support for new energy technologies, electric vehicles have become a key focus in the development of the new energy vehicle industry. As electric vehicles become more widespread, charging stations and fast chargers have become essential infrastructure. A large number of off-board intelligent fast chargers deployed in residential areas and parking lots are expected to become the mainstream solution for efficient, safe, and smart management. Given the unattended operation of current fast charging systems, it is necessary for fast chargers to possess higher reliability, automation, and comprehensive functions, along with remote maintenance capabilities.
This trend has led to the development of distributed, modular, and intelligent fast chargers. High-performance and low-cost charger monitoring terminals are now considered essential technologies. To optimize resource utilization and management across multiple chargers in a given area, it is inevitable that the monitoring terminal must interact with the internet.
**1. Overall Network Monitoring Plan**
As shown in the monitoring network structure diagram of Figure 1, the monitoring terminal acts as a crucial gateway between the charger and the monitoring center. Its communication links include: monitoring center → monitoring terminal; and monitoring terminal → charger (or battery management system (BMS), electric vehicle, etc.).
Through the monitoring terminal, communication links between the monitoring center, the charger, and the electric vehicle are established. The terminal communicates with the charger, BMS, and electric vehicle via the CAN network, collecting relevant node data and storing it. It then feeds back the information to the charger, enabling intelligent battery charging based on the collected data. The terminal also communicates with the monitoring center through a GPRS connection, transmitting data about the charger, battery, and vehicle back to the center. This allows the monitoring center to perform remote control and real-time monitoring of the charger, recording its operational status and any failures. Users can check the location of available chargers through the monitoring center, maximizing resource utilization.
**2. Monitoring Terminal Functional Modules**
**2.1 Overall Design of the Monitoring Terminal**
The monitoring terminal serves as a bridge between the monitoring center and the charger. Its overall design structure is illustrated in Figure 2. The terminal consists of six main components: the STM32ZGT6 core module (based on the Cortex-M3 architecture), a data acquisition module (CAN network), a user charging interaction module, a data storage module, a real-time clock module, and a GPRS communication module.
The terminal uses the STM32ZGT6 microprocessor, which features rich on-chip hardware resources, including a CAN 2.0B controller and up to four serial ports, meeting the requirements for both CAN and GPRS interfaces.
The working process of the monitoring terminal involves the user billing module reading user information and selecting a charging mode, sending corresponding commands to the charging module via the CAN network. At the same time, the terminal reads key data frames from the CAN network, such as the charger’s operational status, and stores them in NAND Flash. User information and operational parameters are periodically sent to the monitoring center via GPRS, and the terminal can print the user’s balance or charging credentials upon request.
**2.2 CAN Bus Module**
To ensure reliable CAN bus communication, the system defines a common application-layer CAN protocol, specifying message IDs for CAN 2.0B. Priority determination is based on the message ID, where smaller IDs indicate higher priority. The CAN bus competition algorithm is non-destructive, making it highly efficient. The protocol defines five-bit source and destination addresses, allowing for up to 31 control nodes, with specific addresses assigned for the monitoring terminal, charger, and BMS.
Segmentation codes are used to handle data larger than 8 bytes, allowing up to 256 × 8 bytes of data per node. For example, the BMS node sends multiple frames to transmit detailed battery information.
**2.3 Data Transmission Module**
The terminal connects to the internet via a serial port using the ZWG-23A GPRS module. After establishing a connection, it sends data to the server according to a defined communication protocol. The protocol includes a message start identifier, version number, command word, message length, data content, and check code. Each data message can be sent up to six times if the receiver fails to respond, with a 30-second interval between attempts.
**3. Software Design**
**3.1 Multi-task Management in μC/OS-II**
μC/OS-II is used as the real-time operating system for the monitoring terminal. It supports multi-tasking, real-time execution, and provides services like semaphores, message mailboxes, and memory management. The system is designed with 13 tasks, each with different priorities based on their relevance, urgency, and real-time requirements. These tasks include display, keyboard input, printing, data storage, GPRS transmission, and alarm handling.
The system uses 13 communication methods, such as semaphores and message queues, to coordinate the tasks. A clock tick of 10 ms ensures real-time performance, and task priorities are planned to allow for future system upgrades.
**3.2 Configuration of ZWG-23A Module**
Since Zhou Ligong does not provide a DTU configuration program for μC/OS-II, a custom configuration program was developed. The flowchart for configuring the DTU is shown in Figure 4. The terminal registers with the center daily and sends heartbeat signals every 30 seconds. Based on the data size, one terminal generates approximately 5 MB of GPRS traffic per day, totaling around 1.7 GB per year—well within a 2 GB monthly data plan.
**4. Conclusion**
This paper analyzes the structure of the electric vehicle fast charger monitoring network and details the communication protocols for CAN and GPRS in the monitoring terminal. The CAN protocol is versatile, while GPRS offers low traffic usage and scalability for broader automation applications. The system demonstrates effective remote monitoring and management of fast chargers, supporting the growth of electric vehicle infrastructure.
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