Abstract : This paper details the use of CAN bus to implement a remote centralized monitoring and control strategy for frequency converter systems. Keywords : Fengguang Converter, CAN Bus, Remote Monitoring System Overview : In recent years, with the national emphasis on building a conservation-oriented society, the importance of energy conservation and power saving has increased, especially in the energy-saving renovation of large electrical equipment in state-owned enterprises. The use of frequency converters in large state-owned enterprises such as oil fields, coal mines, power plants, and steel plants is growing rapidly. Particularly in oil fields, power electronic equipment such as pumping unit frequency converters, submersible pump frequency converters, water injection pump frequency converters, and heating power supplies are being widely adopted. Given the unique characteristics of field operations in oil fields—the distance between each piece of equipment is relatively far, yet they are relatively concentrated—centralized control based on various fieldbuses is becoming increasingly necessary. The CAN bus demonstrates significant advantages in the centralized management and control of frequency converters, with its ultra-long-distance transmission and superior anti-interference capabilities unmatched by other buses. Most importantly, it features a master-slave network topology throughout the control system, allowing for easy addition and removal of communication nodes. Shandong Xinfengguang Electronic Technology Development Co., Ltd.'s medium and low-voltage frequency converters and heating power supplies offer stable performance, comprehensive protection functions, and RS232 and RS485 communication interfaces. As of June 2007, the total number of these devices in use at Daqing Oilfield and Shengli Oilfield exceeded 700, with approximately 500 located at Shengli Oilfield, and this number is rapidly increasing. Additionally, Xinxiang Pharmaceutical Group has hundreds of sets of frequency converter equipment for its fermentation tanks. This represents a substantial market share for frequency converters of the same brand within the same field. This provides a significant market opportunity for CAN bus-based remote centralized monitoring systems and necessitates their promotion. Furthermore, this system can be flexibly applied in production sites with multiple frequency converter devices. CAN Bus Introduction : CAN uses the CSMA/CD (Carrier Sense Multiple Access/Collision Detection) communication protocol. Each node on the network listens to the bus's status to check if it's idle before sending data. If no collision is detected (i.e., the bus is idle), each node sends data with an equal opportunity—this is Carrier Sense Multiple Access. If two nodes send data simultaneously, a collision is detected, and lossless arbitration is performed. After a collision, the data remains unchanged, and the node continues listening to the bus, waiting for the next transmission. The CAN protocol is message-format based, not solely node ID-based, eliminating traditional station address encoding. Based on this protocol, message transmission isn't just from one node to another according to address; multicast and broadcasting are also possible. During broadcasting, each node in the system receives data transmitted on the bus and confirms that each message has been correctly received. Each node can also determine whether received data should be saved or discarded immediately. Error detection in CAN communication mainly includes: acknowledgment errors, format errors, bit errors, and stuffing errors. Key error states include error activation, error acceptance, and bus shutdown. The CAN bus has the following characteristics : (1) CAN can be a peer-to-peer structure, that is, a multi-master working mode. Any node on the network can actively send information to other nodes on the network at any time, without master-slave distinction, and the communication method is flexible. (2) Nodes on the CAN network can be divided into different priorities to meet different real-time needs. (3) CAN adopts non-destructive arbitration technology. When two nodes transmit information to the network at the same time, the node with lower priority will automatically stop transmitting, and the network will not be paralyzed when the network load is heavy. (4) CAN can send and receive data in point-to-point, point-to-multipoint, and point-to-network modes. The communication distance is up to 10km, and it can reach 5Kbps at a distance of 10km. The transmission rate within 40m is 1Mbps, and the number of nodes can reach 110. (5) CAN adopts a short frame structure. Each frame has 8 effective bytes and has CRC check and other detection measures, so the probability of data error is small. In the event of a serious error, the CAN node has an automatic shutdown function, which will not affect the operation of other nodes on the bus. (6) The communication medium uses inexpensive twisted-pair cable, with no special requirements. The user interface is simple and easy to form a user system. System topology : The entire system consists of three parts: node information acquisition card, CAN-RS232/485 conversion interface and monitoring computer. Inverter node information acquisition : Node information mainly refers to the various operating parameters and operating status of the inverter. Commonly used parameter settings for wind and solar inverters include: operating frequency, maximum frequency, starting frequency, acceleration time, deceleration time, rated current, V/F curve selection, open-loop/closed-loop setting, multi-speed setting, actual input current and voltage, actual output current and voltage, low-frequency compensation; in addition, there are various fault protection monitoring: short circuit protection (instantaneous current exceeds 1.8 times the rated current), overcurrent protection (current exceeds 1.5 times the rated current and lasts for 1 minute), overvoltage protection (input voltage exceeds 1.2 times the rated voltage), undervoltage protection (input voltage is lower than 0.8 times the rated voltage), temperature rise protection (internal temperature of the inverter is higher than 75 degrees Celsius), phase loss protection, external abnormal protection, etc. Currently, there are two data acquisition methods: For the original model, the main control chip is N87C196MC, and the main control board's external communication method is RS485. Therefore, an external RS485-CAN conversion circuit must be added when communicating with the CAN bus. With product upgrades, the application of DSP has made communication easier. TI's TSMLF2407A chip integrates a CAN communication interface, eliminating the need for the above circuit. The upgraded wind and solar inverter will then have a simpler CAN bus communication implementation. Data transmission and conversion : After data is sent to the bus, it needs to be transmitted through a medium. The CAN protocol itself has optimized error control algorithms, so it doesn't have high requirements for the medium; ordinary twisted-pair cable can achieve a transmission distance of 10km. However, considering the absolute reliability of inverter operation and equipment control, we use twisted-pair cable within a 5km transmission range, and optical fiber as an intermediate transmission medium beyond 5km to improve anti-interference capabilities. When CAN transmits data to the control computer, an external level converter must be added to complete the data exchange with the main control computer. The conversion principle is shown in Figure 2. In addition, there are relatively mature products of this type of conversion device on the current market. Figure 3 shows the conversion interface launched by Zhou Ligong. It is essentially a transparent device to the user, making it convenient to use. Human-Machine Interface : The monitoring computer's monitoring program configuration has two types: specific system and general system. Below is a general-purpose human-machine interface for centralized monitoring of 20 sets of equipment. The entire human-machine interface system consists of two parts: equipment monitoring and equipment control. When a device is added to the system, a device number can be manually assigned and stored in the system, thus activating the device number. When a device is removed from the system, the device number can be deleted and reused. The activated device number is the operable number; otherwise, the number is inoperable. When the equipment is running normally, the green indicator light is on; when an abnormality occurs, the red light is on. For ease of operation, multiple devices in the system can be divided into several control groups for management. When operating by group, corresponding operations can be performed simultaneously on all devices in that group: power on, power off, emergency stop, parameter setting, frequency adjustment, etc. Common parameter settings within the group can be viewed simultaneously. Double-clicking the device number allows you to view the operating status and curve of the device, and also allows you to easily perform various operations on a single device. You can also operate on all devices in the system at the same time. Conclusion: The design of the entire system is based on the principle of flexibility and convenience, and is designed to adapt to multiple work sites. After a hardware node fails, the data can be uploaded in the shortest time. The host computer can also observe and control each device in real time, realizing the purpose of remote monitoring, facilitating operation, enhancing the reliability of the system, and saving production costs. References : (1) Design and Implementation of Intelligent Systems Based on Microcontrollers, Shen Hongwei, Electronic Industry Press (2) Fieldbus and Its Application Technology, Li Zhengjun, Machinery Industry Press (3) Fieldbus Technology, Wu Kuanming, Beijing University of Aeronautics and Astronautics Press (4) Some References and Papers from Guangzhou Zhou Ligong Microcontroller Website (5) Visual Basic Serial Communication and Measurement and Control Application Technology Practical Explanation, Li Jiangquan, People's Posts and Telecommunications Press About the Author : Zhang Changyuan, male (1983-), graduated from Chongqing Jiaotong University, and is currently working at Shandong Xinfengguang Electronic Technology Development Co., Ltd., engaged in research and development.