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A fan is a mechanical device that consumes energy (usually electricity) and transports gas (usually air).
Generally speaking, the fan is actually composed of a fan and a motor. The fans commonly used in civil building ventilation systems include centrifugal, axial, mixed, and cross-flow, and the motor usually refers to the cage type that uses AC power. Induction motor (the old standard is called squirrel cage asynchronous motor).
The electric motor is based on the principle of electromagnetic induction to realize the conversion or transmission of electric energy, so it is called an induction motor. Under normal circumstances, the rotor speed of induction motors is always slightly lower or slightly higher than the speed of the rotating magnetic field (synchronous speed), so induction motors are also called "asynchronous motors". The power source that generates the induced current comes from a three-phase AC power source, so induction motors are usually also called AC induction motors, or AC motors for short.
The motor speed is calculated by the following formula:
In the formula: n—motor speed, p—number of pole pairs, f—power frequency, k—slip coefficient
Therefore, as long as you change the power supply frequency "f" or the number of pole pairs "p", you can change the motor speed.
The inverter is an electrical device that changes the frequency of the power supply.
The working principle of the inverter: AC-DC-AC, that is, three-phase 50Hz power frequency alternating current is rectified by the rectifier bridge into pulsating direct current, filtered by electrolytic capacitors, and then transformed into smooth direct current. The control system then inverts the smooth direct current into three Alternating currents with variable phase frequency.
During the frequency conversion process of the frequency converter, there will be a loss of 4% to 8%. Generally speaking, the greater the motor power, the relatively small loss, and vice versa, the greater the loss.
In the inverter inversion process, high-order harmonics will be generated, and harmonics are a kind of pollution to the power grid, transformers, and electrical equipment. To reduce harmonic damage, it is necessary to select an inverter that meets the relevant standards and avoid excessive use of inverters in sensitive situations.