Danfoss Turbocor Twin-Turbine TTS Series Applications And Installation Manual page 26

3.4.3 Bearing Motor Compressor Controller
3.4.4 Compressor Control
3.4.5 Capacity Control
3.4.6 Expansion Valve Control
3.4.7 Motor/Bearing Control
3.4.8 Monitoring Functions
3.4.9 Abnormal Conditions
3.4.10 Bearing PWM Amplifier
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M-AP-001-EN Rev. Q
The hardware and software for the compressor controller and the bearing/motor controller physically
reside in the BMCC. The BMCC is the central processor of the compressor.
The Compressor Controller is continuously updated with critical data from external sensors that
indicate the compressor's operating status. Under program control, the compressor controller can
respond to changing conditions and requirements to ensure optimum system performance.
One of the Compressor Controller's primary functions is to control the compressor's motor speed and
IGV position in order to satisfy load requirements and to avoid surge and choke conditions. However,
the majority of capacity control can be achieved via motor speed.
The onboard Electronic Expansion Valve (EXV) driver uses manual control only. Depending on the
application, a load balancing (hot gas bypass) valve can be manually driven by the auxiliary EXV
output. Load balancing allows the compressor to obtain lower capacities at higher pressure ratios. The
valve opens to lower the overall pressure ratio and thereby reduces the lift, enabling the compressor
to reduce speed/unload.
The magnetic bearing system physically supports a rotating shaft while enabling non-contact
between the shaft and surrounding stationary surfaces. A digital bearing controller and motor
controller provide the PWM command signals to the Bearing PWM Amplifier and Inverter, respectively.
The bearing controller also collects shaft position inputs from sensors and uses the feedback to
calculate and maintain the desired shaft position.
The compressor controller monitors more than 60 parameters, including:
• Gas pressure and temperature monitoring
• Line voltage monitoring and phase failure detection
• Motor temperature
• Line currents
• External interlock
The compressor controller responds to abnormal conditions by monitoring:
• Surge RPMs
• Choke RPMs
• Power failure/phase unbalance
• Low/high ambient temperature
• High discharge pressure
• Low suction pressure
• Motor-cooling circuit failure (over temperature)
• Refrigerant loss
• Power supply
• Overcurrent
The Bearing PWM Amplifier supplies current to the radial and axial magnetic bearing actuators.
The PWM Amplifier consists of high-voltage switches that are turned on and off at a high frequency,
as commanded by the PWM signal from the BMCC.