Abstract : With the development of technology, the variable frequency speed control technology of AC motors has become increasingly sophisticated, and the reliability of frequency converters has also increased. The variable frequency drive has solved the problems of difficult restarting, easy tripping, and poor instantaneous overload capacity that existed in previous frequency converters. To effectively save energy and meet load requirements, using a frequency converter for speed control is an effective energy-saving method. Keywords : frequency converter; speed control and energy saving; parallel operation of multiple pumps [b]1 Principle of Speed ​​Control and Energy Saving by Frequency Converter 1.1 Theoretical Basis of Variable Frequency Regulation[/b] For the same water pump, according to the similarity theory of fluid mechanics, the relationship between flow rate Q, head H, shaft power P, and speed N during speed control can be expressed by the following formula: From the above formula, it can be seen that the flow rate is directly proportional to the speed, the head is directly proportional to the square of the speed, and the shaft power is directly proportional to the cube of the speed. Therefore, compared with the flow control of regulating valves, the speed control of the motor can significantly reduce the shaft power. Thus, using a frequency converter to control the motor speed can fully save energy. When the system load decreases, the frequency converter adjusts the pump speed, thereby reducing water flow and motor power consumption. According to electrical engineering, the relationship between motor speed and input frequency is: n = f/p, where n is the motor speed (RP/m), f is the frequency (Hz), S is the slip ratio, and p is the number of pole pairs. Generally, the variation range of n is small. If the variation of S is negligible, n can be considered directly proportional to f, and changing f can achieve the purpose of changing the motor speed n. The variable frequency speed control closed-loop control system mainly consists of a frequency converter, regulator, sensor, motor, and pump. The control signal can be a voltage signal of 0-5V (or a current of 4mA-20mA). The signal of the variable frequency speed control device can be a temperature signal, a pressure signal, or a combination of several signals. [b][align=center]For more details, please click: A Brief Discussion on the Application of Frequency Converters in Water Pumps[/align][/b]