How the system works

AN2446

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3.4

Stall rotor detection

The system performs the stall rotor detection immediately after the compressor is turned on.

The monitoring lasts 5 seconds. During this time, the system monitors the temperature of

the AC switch driving the RUN winding.

After a normal turning on, meaning when the compressor regularly spins, the current flowing

through the RUN winding is the nominal one. Of course at the very beginning, the in-rush

current is higher than the nominal one, but after a while the current flowing is the nominal

one.

Therefore the increase of the AC switch temperature is smooth.

Attempting to turn on the compressor while the rotor is stalled will result in a higher current

flowing through the RUN winding. Therefore the temperature of the AC switch will increase

faster.

By reading the trend of the temperature, the system is able to determine if the compressor

rotor is stalled or not. In stall rotor condition, the compressor is immediately turned off and

the dead-time is set.

Moreover, the compressor is not turned on when the AC switch temperature goes over 85

°C or goes below 0°C. Dead-time is set as well.

By reading the trend of the temperature, the compressor can be turned off faster than any

mechanical device, saving in power consumption. Moreover, the system prevents the AC

switch temperature from reaching the blowing point.

Figure 4.

Temperature behavior in normal condition and in stall rotor condition

AC switch temperature

Blowing point

Stalled rotor control

AC switch temperature