Abstract : Taking the common variable frequency speed control design in cement plants as an example, this paper proposes a general optimized design scheme for variable frequency speed control based on careful analysis and discussion. Keywords: Variable frequency speed control, design optimization, cement plant 0 Introduction In recent years, the application of variable frequency drives (VFDs) in cement plants has become increasingly common. However, as VFDs are a new type of electrical control equipment, many electrical technicians in cement plants lack sufficient understanding of them and have not fully utilized their powerful functions. The design of VFD speed control is often overly complex, which reduces the reliability of the VFD control system to some extent and even damages the motor. This paper takes the common VFD speed control design in cement plants as an example and proposes a general optimized design scheme for VFD speed control based on careful analysis and discussion, for reference by peers. 1 Common VFD Speed ​​Control Design The VFD speed control design of the rotary motor of a packaging machine in a cement company in Heilongjiang Province is representative. The company uses a VF61 VFD to adjust the speed of the packaging machine's rotary motor. The main circuit consists of an air switch, a frequency converter, a contactor, and a thermal relay; the control circuit consists of an instrument switch, a speed control potentiometer, a start button, and a stop button (see Figure 1). The speed control potentiometer adjusts the output frequency of the frequency converter, used for on-site adjustment of the packaging machine speed. The instrument switch provides the frequency converter with operating commands. The specific operating principle is as follows: At startup, close the air switch Q and press the start button SA. The contactor is energized and self-locked, and the motor is in a ready-to-run state. Turning on the instrument switch SA provides the frequency converter with operating commands, and the frequency converter's output power frequency gradually increases from zero to the set value, while the motor speed gradually reaches the set speed. At shutdown, open the instrument switch and press the stop button SA. The contactor is de-energized, disconnecting the motor power supply. [b][align=center]For more details, please click: Optimized Design of Variable Frequency Speed ​​Control[/align][/b]