Dr. Ahmed G. Abo-Khalil

Electrical Engineering Department

Air conditioner in

An inverter in an air conditioner is used to control the speed of the compressor motor to allow continuously regulated temperature. By contrast, traditional air conditioners regulate temperature by using a compressor that is periodically either working at maximum capacity or switched off entirely. Inverter-equipped air conditioners have a variable-frequency drive that incorporates an adjustable electrical inverter to control the speed of the motor and thus the compressor and cooling output.

The variable-frequency drive uses a rectifier to convert the incoming alternating current (AC) current to direct current (DC) and then uses pulse-width modulation of the DC current within an electrical inverter 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 an induction motor is proportional to the frequency of the AC current, the compressors runs at different speeds. A microcontroller can then sample the current ambient air temperature and adjust the speed of the compressor appropriately. The additional electronics add to cost of equipment and operation. Conversion from AC to DC, and then back to AC, can cost as much 4 - 6% in energy losses for each conversion step

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. Ultimately this makes inverter air conditioners less prone to breakdowns, cheaper to run, and the outdoor compressor is generally quieter than a standard air conditioning unit's compressor.

While at the beginning of the 1990s inverter air conditioners had some drawbacks. these have been mostly overcome- the conversion losses are lower and filters suppress most of the electromagnetic interference generated in inverters. Running at full load, a compressor delivers its best efficiency and outperform inverters. Inverter-based air conditioners have their strengths in environments where a partial load is common, as they are significantly more efficient than conventional air conditioners in those situations. For conventional households where each indoor unit is connected to a single dedicated outdoor unit, inverters are the preferred option, as partial loading is the common mode there.[] The higher initial expense is balanced by lower energy bills.[] In a typical setting the pay-back time is about two years (depending upon the usage).[] For more modern installations where an outdoor unit is connected to multiple indoor units there are better options also available

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