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M-SV-001-EN Rev.E
Compressor Fundamentals
Capacity control of the compressor is achieved
primarily by speed modulation. When unloading,
the compressor’s first action is to reduce speed
to slightly above the minimum (surge) speed for
the pressure ratio present at the time. Further
reduction in capacity and an increase in shaft/
impeller stability can be achieved by closing the
IGVs. These are variable angle vanes installed in
the suction inlet ahead of the first stage impeller.
These guide vanes restrict the refrigerant from
entering the impeller inlet, as well as imparting
a “pre swirl” of the refrigerant in the direction of
impeller rotation to increase energy efficiency
during part load operation.
Speed modulation is achieved by the use of
“Inverter” control. To accomplish this, the
incoming 3-phase AC supply is converted to high
voltage DC, incorporating smoothing/storage
capacitors, and then switched by the Inverter,
utilizing 3-phase rectifiers, to give a simulated
3-phase AC supply of variable voltage and
frequency to the compressor motor.
During normal operation, 3-phase power is
required to be connected to the compressor
at all times, even if it is not running. Power is
distributed through the following components to
maintain compressor operation:
• Silicon-Controlled Rectifier (SCR)
• Soft Start Board
• DC Capacitor Assembly
• Inverter
• Stator
• High-Voltage (HV) DC-DC Converter
• Backplane
• Bearing Motor Compressor Controller (BMCC)
• Serial Driver
• Bearing Pulse Width Modulation (PWM)
Amplifier
• Compressor I/O Board
• IGV
• Solenoid actuators
2.3 Capacity Control
2.4 Compressor Energy
and Signal Flow
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