34 of 282 M-SV-001-EN Rev. G
Figure 2-5 Serial Cooling Path - TTS300/TGS230
2.3 Capacity Control
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.
2.4 Compressor Energy and Signal Flow
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 Bus Bar Assembly
• Inverter
• Stator
• High-Voltage (HV) DC-DC Converter
• Backplane
• Bearing Motor Compressor Controller (BMCC)
• Serial Driver
BMCC
From Motor
Cavity Temp.
Sensor
From Motor
Winding Temp.
Sensor
Motor/Rotor
cooling gas and
leakage
BMCC
From Inverter
Temp. Sensor
From SCR
Temp. Sensor
Inverter
SCR
ORIFICEORIFICE
Solenoid
E
Solenoid
M
Liquid
Refrigerant
Inlet
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