Abstract : In the field of industrial automation, there is often a requirement for long-distance variable frequency speed control of multiple motors. This paper introduces a circuit based on a 1:n multi-branch communication network composed of a Mitsubishi PLC and its frequency converter to realize long-distance variable frequency speed control, which can well meet the above requirements. Keywords : PLC; frequency converter; communication adapter 0 Introduction Synchronous control systems, proportional control systems, and same-speed control systems using variable frequency drives as speed controllers have been widely used in the automation control fields of metallurgy, machinery, textile, and chemical industries. However, in many large-scale automated production lines, when it is often necessary to control the operation and speed of multiple motors that are distributed far apart, the traditional method of PC or PLC driving D/A converters to control variable frequency drives suffers from reduced system stability and reliability due to the attenuation of speed command signals during long-distance transmission and external interference; at the same time, the large number of D/A conversion modules increases system cost and has many drawbacks. To address this, we propose a multi-branch communication control network composed of a PLC and a variable frequency drive. Taking a proportional control system as an example, the system structure is shown in Figure 1. The PLC issues speed commands to the variable frequency drives (VFDs), causing each VFD to operate the motors at a specific speed ratio. The actual speed of each motor is collected in real-time by rotary encoders installed behind each motor and compared with the speed of the main motor. Fine-tuning is then performed on each motor to achieve synchronous tracking. This system is low-cost, has a long signal transmission distance, and strong anti-interference capabilities, making it particularly suitable for long-distance, multi-motor control. [b][align=center]For details, please click: Constructing a Multi-Motor Variable Frequency Speed ​​Control System with Mitsubishi PLC and its Inverters[/align][/b]