Please explain in detail the working principle of the variable frequency air pump.

The variable frequency air pump achieves precise control of flow and pressure by dynamically adjusting the motor speed. Its core lies in the collaborative operation of the variable frequency drive (VFD), motor, and the air pump body. The following is an analysis from three aspects: technical principles, control logic, and energy efficiency advantages:

First, core technology: The physical basis of variable frequency speed regulation

The relationship between the speed and frequency of asynchronous motors

The rotational speed of an asynchronous motor is determined by the following formula:

n= 60f(1 - s) of p

n: Motor speed (r/min)

f: Power Supply Frequency (Hz)

s: Slip rate (usually 2% to 5%)

p: Number of magnetic poles of the motor

Key conclusion:

Rotational speed is positively correlated with frequency: for every 1Hz change in frequency, the rotational speed changes by approximately 1.5r/min (taking a 4-pole motor with a power frequency of 50Hz as an example).

The rotational speed can be controlled by adjusting the frequency: The fixed-frequency (50Hz) alternating current is converted into a variable frequency through a frequency converter, achieving stepless speed regulation of the motor.

2. The mathematical relationship between flow rate, pressure and rotational speed

The flow rate (Q), pressure (P) and rotational speed (n) of the air pump satisfy the following relationship:

Q∝n,P∝n squared

Linear flow regulation: When the rotational speed is reduced by 50%, the flow rate decreases simultaneously by 50%.

Pressure square adjustment: Reduce the rotational speed by 50% and the pressure to 25% (note the system back pressure limit).

Example:

Rated operating conditions of a certain air pump: Rotational speed 3000r/min, flow rate 10m³/min, pressure 0.8MPa.

Reduce the rotational speed to 2400r/min (by 20%) :

The flow rate drops to 8m³/min (10×0.8).

The pressure dropped to 0.512MPa (0.8×0.8²).

Second, the composition and control logic of the variable frequency air pump system

Control logic

Pressure closed-loop control

Process:

The pressure sensor detects the outlet pressure and converts it into a 4~20mA signal to be input into the frequency converter.

The built-in PID algorithm of the frequency converter calculates the frequency adjustment amount, making the actual pressure approach the set value.

Constant power control

Principle:

The frequency converter monitors the motor power. When the load decreases, it automatically reduces the frequency to keep the motor always running near the rated power.

It is suitable for intermittent loads (such as intermittent operation of pneumatic tools), avoiding energy waste caused by frequent starts and stops.

Third, energy efficiency advantages and typical applications

Typical application scenarios

Industrial automation

Case: Automobile Painting workshop

Requirements: The spraying robot needs to maintain a stable pressure (0.6MPa±0.02MPa) and flow rate (8m³/min).

Solution:

The screw air pump + vector frequency converter is adopted, and the pressure fluctuation is ≤±1%.

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