Inverter (air conditioning)

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The inverter tag found on some air conditioners signifies the ability of the unit to continuously regulate its thermal power flow.

Traditional reverse-cycle air-conditioners use a heat pump that is either working at maximum capability or switched off, as the compressor's speed cannot be varied. In order to regulate temperature a thermistor is used to measure the ambient air temperature and switch the compressor on when the ambient air temperature is too far from the desired temperature

Air-conditioners bearing the inverter tag use a variable-frequency drive to control the speed of the motor and thus the compressor. The variable-frequency drive uses a rectifier to convert the incoming AC current to DC and then uses pulse-width modulation of the DC current within an inverter (electrical) to produce AC current of a desired frequency. The AC current is used to drive a brushless motor or an induction motor. As the speed of a brushless motor is synchronised to the frequency of the AC current, it is thus possible to build a compressor that can be run at different speeds. Similarly, the voltage and frequency can be varied as needed to efficiently run an induction motor at different speeds. A microcontroller can then sample the current ambient air temperature and adjust the speed of the compressor appropriately.

Eliminating stop-start cycles increases efficiency, extends the life of components, and helps eliminate sharp fluctuations in the load the air-conditioner places on the power supply.

The inverter principle has been applied to a wide range of household appliances including microwave ovens, washing machines, and so on.