This paper presents a new procedure for the speed changing of the two-speed compressor driven by the single-phase Permanent Split Capacitor (PSC) motor. The use of the two-speed motor for compressor is one of the effective ways for their capacity control. But the two speed compressors now in use are driven by three-phase motors. It is because a single-phase, two-speed motor has rather a small starting torque, thus making it difficult to change the number of poles from four to two, unless it is connected with a starting capacitor of comparative large value. We have developed new procedure for the compressor driven by the two speed motor with no starting capacitor. This motor has main and auxiliary windings for 2-pole running as well as for 4-pole running. The speed changing from 4-pole to 2-pole running is made by the following procedure. If the speed is to be changed during the 4-pole running, the 2-pole windings are energized without the 4-pole windings being de-energized. In other words, at this stage, both 2-pole and 4-pole windings are supplied with the power simultaneuously. After several tens of milliseconds, however, the 4-pole windings are de-energized, the 2-pole windings remianing energized alone.
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