AN2991 Datasheet, PDF (1/14 Pages) STMicroelectronics – Single-phase induction motor drive for refrigerator compressor application

AN2991
Application note
Single-phase induction motor drive
for refrigerator compressor application (formerly AN1354)
Introduction
Up to now, refrigerator compressors have been controlled by electromechanical switches
(thermostat or even electronically controlled relays). This choice was driven by the high
inrush current that can appear when the rotor is stalled. Furthermore, electromechanical
relays were advantageous because they were less sensitive to line voltage disturbances.
Today, new semiconductor devices feature overvoltage protection and high inrush current
capability, allowing their use in cold appliances.
Electronic thermostats can now be implemented, allowing the appliance efficiency to be
improved by more than 20 W, for 150 W compressors. This is possible because of the better
temperature control and the PTC removal.
Hence, at a similar cost to electromechanical thermostats, this technical breakthrough can
allow refrigerators or freezers to fulfill Class A, A+, or A++ consumption requirements,
bringing the following advantages:
 Better reliability
– Higher switching robustness in time of solid-state semiconductor switches compared
with electromechanical solutions
– Higher ACS and ACST overvoltage robustness compared with Triacs, which makes
the metal-oxide varistor redundant
 Temperature regulation curve flexibility (automatic defrost, hysteresis threshold
adaptation)
 Reduction of the temperature ripple (better food preservation, cooling elements
downsizing)
 Possibility to add indication features for the end-user (inside temperature, open door
warning)
 Spark-free operation and EMI reduction (switches can be turned on at zero voltage and
are turned off at zero current)
 Over current protection of the motor winding
This application note presents the different topologies that can be used for induction motor
control, and lists the electrical constraints that result from these different circuits. A
comparison is also made between the different performances of electromechanical or
electronic thermostats.
All numerical examples are based on the specifications for a 150 W compressor, which can
be used in 350 L freezers.
September 2013
Doc ID 15772 Rev 2
1/14
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