Abstract : This paper discusses the problems existing in DC speed control systems commonly used in the dyeing and printing industry, and introduces a simple and reliable frequency conversion retrofit scheme to replace the system. Keywords : DC motor; AC motor; frequency converter; synchronizer; synchronization sensor 1 Overview The control system of the 102-108 three-column water-pressing dryer is used in pre-treatment mechanical equipment (oxygen bleaching machine, mercerizing machine, singeing machine, scouring machine, etc.), dryer and setting machine in the dyeing and printing industry. This project comes from the frequency conversion technology retrofit project of the 102-180 type three-column water-pressing dryer of Guangzhou Huangpu Changhui Dyeing and Printing Co., Ltd. The system diagram is shown in Figure 1: [align=center] Figure 1 System Principle Diagram [/align] In the production process, the fabric first passes through the sizing tank, then enters the first column drying under the drive of the main motor M, then enters the second column and third column drying, and finally completes the fabric output function under the action of the fabric discharge motor. The four motors M1, M2, M3 and M4 are the first column, second column, and third column drying cylinder motors and the fabric discharge motor, respectively. The system requires strict synchronization of motors M, M1, M2, M3, and M4. The original system was a three-phase semi-controlled bridge rectifier device, a stepless speed regulation system composed of speed negative feedback and current cutoff negative feedback. It rectified the three-phase AC power frequency into DC to power the armature of the DC motor. The system was designed with a guide speed and could smoothly accelerate and decelerate. The guide speed, acceleration, and deceleration times could be easily adjusted as needed. The device had an independent silicon rectifier power supply for the excitation of the DC motor. [b][align=center]For details, please click: Variable Frequency Drive Retrofit of 102-180 Three-Column Water Rolling Dryer[/align][/b]