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The "Inverter" is an electric apparatus that changes direct current (DC) to alternating current (AC).  It is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for an inverter are Variable Frequency Drive (VFD), variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive and micro-drive.

Frequency (or hertz) is directly related to the motor’s speed (RPMs). In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement.

Why the output current & voltage of Inverter will be proportional changed?
The torque of an asynchronous motor is generated by the interaction between the magnetic flux of the motor and the current flowing through the rotor. At the rated frequency, if the voltage is fixed but only the frequency is reduced, then the magnetic flux will be too large, the magnetic circuit will be saturated, and the motor will be damaged.Therefore, the frequency and voltage should be changed proportionally. The frequency should be changed at the same time to control the output voltage of the frequency inverter. It keep the magnetic flux of the motor constant and avoid the phenomenon of weak magnetism and magnetic saturation.This kind of control mode is mainly used in energy-saving inverter of fan and pump.
How long is the lifetime of the Inverter?
Although the inverter is a fixed device, it has some consumption components, such as filter capacitor and cooling fan. If they are maintained regularly and operating at regulate conditions, they can be expected to have a life of more than 10 years.
What means V/f control model?
Standard VFD will sometimes be referred to as a "V/Hz" drive to differentiate it from a vector drive. It maintains a certain V/Hz ratio to the motor at all times. For example, a 230 Vac, 60 Hz motor wants to see a V/Hz ratio of 3.83 (230/60 = 3.83). When a V/Hz drive changes speed (frequency), it also changes the output voltage to keep the ratio constant. So, at 30 Hz (half speed), the same 230 Vac motor will only see 115 Vac output from the drive. For most applications this works great, as long as you operate from about 6-60 Hz (10:1 speed range). Below 6 Hz, a motor on a V/Hz type VFD can't generate much torque, because at those low speeds, the V/Hz ratio to achieve maximum torque is different than at higher speeds. If you try to run at those low speeds with a V/Hz drive, you will typically see the motor shaft "cogging" as it tries to turn.
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