1. Introduction
Among various industrial water pumps, multi-stage pumps, deep well pumps, centrifugal pumps, etc., most of them operate at rated power. The design of fan flow is based on the maximum air volume requirement, and its adjustment methods are controlled by baffles, air doors, reflux, start stop motors, etc., which cannot form a closed-loop control and rarely consider power saving; The design of the water pump flow rate is also the maximum flow rate, and the pressure regulation can only be achieved by controlling the size of the valve, the start stop of the motor, and other methods. The electrical control adopts direct or Y △ start, which cannot change the motor speed, cannot have soft start function, has large mechanical impact, short transmission system life, high vibration and noise, and low power factor.

2. The energy-saving significance of variable frequency speed regulation
Variable frequency speed regulation is a new technology that has emerged in recent years. It adjusts the speed by changing the power frequency. Due to its characteristics of smooth speed regulation, high transient stability, and energy saving, it is increasingly valued by people. With the continuous maturity of variable frequency speed regulation technology, the application of variable frequency speed regulation devices in fan and water pump equipment is becoming increasingly widespread.
Using a frequency converter to directly control fan and pump loads is the most scientific control method. By using the built-in PID regulation software in the frequency converter, the speed of the motor can be directly adjusted to maintain a constant water and air pressure, thereby meeting the pressure requirements of the system. Due to the fact that frequency converters can achieve soft stop and soft start of large motors, avoiding voltage surges during startup, reducing motor failure rates, extending service life, and reducing capacity requirements and reactive power losses on the power grid, the operating conditions of the equipment have been significantly improved, and the safety, reliability, and equipment utilization of the system have been enhanced, resulting in a significant energy-saving effect.    

3. Energy saving principle of variable frequency speed regulation for water pumps
According to the basic laws of fluid mechanics, pump equipment belongs to square torque loads, and its speed n is proportional to flow rate Q, pressure H, and shaft power P as follows: Q ∝ n1, H ∝ n2, P ∝ n3; that is, flow rate is proportional to speed, pressure is proportional to the square of speed, and shaft power is proportional to the cube of speed.

Q2=Q1（n2／n1）

H2=H1（n2／n1）

P2=P1（n2／n1）
Therefore, ideally, there is the following relationship:

As shown in the table above, adjusting the speed can save a lot of energy when the demand flow decreases. For example, when the motor is running at 80% of its rated speed, theoretically it consumes 51.2% of its rated power, which is 80% of the rated power. After removing the effects of mechanical losses, motor copper, iron losses, etc., the energy-saving efficiency is also close to 40%. At the same time, closed-loop constant voltage control can also be achieved, and the energy-saving efficiency will be further improved. If traditional baffle and valve methods are used for regulation, although energy consumption can be correspondingly reduced, the saving effect is vastly different from that of frequency conversion.

4. Functions and characteristics of frequency converter
Variable frequency energy-saving equipment has the following technical characteristics:
Using a frequency converter to control the motor speed, eliminating the need for baffles and valve adjustments, reduces equipment failure rates, and achieves significant energy-saving effects.
The soft start of the motor has been achieved, extending the service life of the equipment and avoiding impact on the power grid.
The motor will operate at a speed lower than the rated speed, reducing the impact of noise on the environment.
It has automatic protection functions for overload, overvoltage, overcurrent, undervoltage, and power shortage.
The operation status is flexible and diverse, and can be manually controlled or fully automated. It can also be electrically interlocked with other automatic control devices of the equipment to achieve automatic protection and computer control of the equipment, without affecting production due to accidents.
Installation can be carried out without damaging the existing power distribution facilities and environment, and without affecting production.
Simply adjust the potentiometer knob to adjust the flow rate, making it easy to operate.

The use of variable frequency speed regulation technology to achieve energy-saving operation in equipment such as fans and pumps is a key promotion technology for energy conservation in China. Article 39 of the Energy Conservation Law of the People's Republic of China lists it as a universal technology for promotion. Practice has proven that frequency converters have achieved significant energy-saving effects in driving and controlling fan and pump equipment, and are an ideal speed control method. It not only improves equipment efficiency, but also meets production process requirements, greatly reduces equipment maintenance and repair costs, and lowers downtime. The direct and indirect economic benefits are very significant, and the one-time investment in equipment can usually be fully recovered within 9 to 16 months of production.