Multi-motor soft start system based on single chip microcomputer
With the rapid development of the national economy, AC motors play an extremely important role in industrial production. As the main drag motors in various industries, they are more widely used. It is well known that when the AC motor is started at full voltage, the starting current reaches 5 to 7 times of the rated current, which will cause an impact on the power grid; the starting torque is about twice the rated torque, which aggravates the mechanical structure wear. In order to solve the problem of starting the AC motor, it is usually necessary to use a soft starter for soft start.
The monitoring of current soft starters is generally carried out by separate monitoring units, which do not provide complete control and monitoring of the entire system. Therefore, it is necessary to establish a data communication system to connect the soft start monitoring nodes to form a complete monitoring network.
Compared with communication standards such as RS-485, the CAN (Controller Area Network) bus has been applied in many fields with its many advantages. The CAN bus is a multi-master LAN introduced by Bosch in Germany in the early 1980s. The CAN communication network is a fully distributed, all-digital intelligent two-way, multi-variable, multi-point, multi-station distributed communication system. High reliability, good stability, strong anti-interference ability, communication speed block, low cost and many other advantages. The CAN bus is a communication method that is very suitable for the harsh environment of industrial sites. This paper introduces an AC motor soft start communication system based on CAN bus.
CAN communication system structure
The AC motor soft start communication system consists of an industrial computer as the monitoring host. The industrial computer accesses the CAN bus through the CAN bus interface. Each node is an AC motor soft starter with CAN bus data transmission and reception function controlled by the single chip microcomputer.
The various parts of the communication system provide different functions. Among them, the industrial computer controls the working state of the AC motor soft starter, such as soft start, soft stop, etc., and displays various parameters of the soft start such as starting voltage and starting current. The soft starter controls the soft start of the AC motor according to the command of the industrial computer, and collects the parameters such as the starting current and voltage of the motor, and sends it to the industrial computer through the CAN bus.
CAN communication protocol
In this communication system, the length of data transmitted is not fixed. The control command issued by the industrial computer to the soft starter is only a few bytes, and the soft start real-time data uploaded by the soft starter to the industrial computer generally has several tens of bytes. Therefore, the CAN communication protocol needs to have a large amount of data transmission capability, and it must be fast and efficient. Since CAN communication adopts a short frame structure, the effective data length per frame is at most 8 bytes. When the amount of transmitted data is large, the data is split into multiple frames for transmission. If all the information and data are placed in the 8-byte data field, the effective data in the transmission frame will be less, and the communication information will be more, which will reduce the communication efficiency of the CAN bus. Therefore, this paper adopts a method of using the arbitration field in the message identifier to contain communication control information, and the data field contains actual data to improve communication efficiency.
Soft starter CAN communication program design
After the soft starter is powered on, the self-test is first performed. After the self-test is completed, the self-test result is sent to the industrial computer. If the self-test is successful, the industrial computer sends the soft start initialization parameter and the “allow start” command to the soft starter, and the motor starts to soft. Start; during soft start, the soft starter sends soft start data every 100ms, including three-phase voltage, three-phase current, motor speed and other information; when the motor runs, the industrial computer sends a "soft stop start" command, soft starter Start to control the motor soft stop; when the soft starter fails, the industrial control machine receives the fault alarm signal and displays the cause of the fault.
Conclusion
This paper designs a reliable and efficient AC motor soft start communication system. It uses CAN bus technology to realize the remote control and monitoring function of motor soft start. The system has been successfully applied to the soft start system of a pump station motor. It has been proved that the system has strong anti-interference ability, good real-time performance and stable operation, and meets the design requirements.
