In an inverter AC, the 50 cycles per second or 50Hz alternating current in our power supply is first converted into a Direct Current DC and then it is reconverted into an alternating current where the frequency is infinitely variable, from say 10 cycles per second or HZ to say 100 cycles per second. This variable frequency enables the main compressor motor of the AC to turn at different speeds. With the fixed 50Hz AC of our electric supply, the compressor motor of normal air conditioner can only turn at one speed, but with a variable frequency, the compressor motor of the AC can run at different speeds, from very low to very high speeds. There are many advantages of the AC compressor to be run at different speeds as explained below.
The problem with the fixed 50Hz power supply is that it will turn electric motors only at only a fixed speed depending on the number of poles. Then you may ask, but we can have our fans running at different speeds without an inverter? Yes true, but the fan speed control is limited and is achieved by the use of changing the number of poles or by changing the voltage which can only have a very limited speed control and is not very efficient.
Since the speed of any electric motor depends on the frequency of the voltage applied to it, so to control the speed of an electric motor, the most efficient way is to control the frequency of the power supply voltage. To achieve this, the AC power supply to our houses has to be first converted into DC and this DC power converted back to AC voltage with the ability to infinitely control the frequency of the AC voltage. The device that converts DC voltage to AC voltage is known as an inverter.