The control object of the variable frequency speed controller is an asynchronous motor, and certain rules are followed when frequency modulation, namely the VVVF principle. We know that the rotational speed of an asynchronous motor is n1=60f/P·(1-S)n, where f refers to the power frequency, p refers to the number of pole pairs of the motor, s refers to the slip rate, and n refers to the synchronous speed ; Then in the case of a certain motor, P, S, n are all fixed values. There are only two ways to realize the adjustable speed of the motor: one is to install a mechanical transmission mechanism, and the other is to change the parameter f. Obviously the first method is not suitable for fans and pumps; then, if we want to adjust the flow, we can only achieve this by changing the opening of the inlet or outlet valve or baffle. If there is no special person to adjust according to the actual demand, the motor is completely working under the power frequency state, and a large amount of electric energy, water and gas resources are wasted. The second method, variable frequency speed regulation, just makes up for its shortcomings. When water or gas peaks or valleys are in peak or trough periods (detection elements are added to form closed-loop control), the inverter can increase or decrease the power supply frequency according to the detected signal. Thereby changing the motor speed to achieve the purpose of automatically adjusting the flow. In this way, a large amount of electricity, water and gas resources can be saved.