28 OMM 1008-1
Compressor On-Board Controllers
Each compressor is equipped with microprocessor controllers and sensors that provide control and data
acquisition. The data is transmitted to other controllers and the OITS via the multi-unit communication
network. The on-board controllers consist of:
• Compressor Controller: the compressor controller is the central processor of the compressor. It is
continually updated with critical data from the motor/bearing controller and external sensors. An
important function is to control the compressor speed and guide vanes operation in order to satisfy load
requirements, to avoid surge and to provide for optimum efficiency. The controller monitors over 60
parameters, including:
Refrigerant pressures and temperatures Line voltage
Phase failure detection Motor temperature
Silicone Rectifier (SCR) temperature Speed
Line currents Guide vane position
• Soft-Start Controller: the soft-start controller limits current inrush by temporarily inserting a charging
resistor between the ac line and the +DC bus. It works in conjunction with the variable-speed function.
• Motor/Bearing Controller: the motor/bearing system provides the measurements and control to calculate
and maintain the desired shaft position. An RS-485 link connects the bearing controller and the
compressor controller.
• Backplane: although not a controller, the backplane connects the on-board control modules with the soft-
start controller, power electronics, motor cooling solenoids and pressure/temperature sensors.
Figure 7, Compressor Electric/Electronic Components
1
2
3
4
5
6
7
8
1. Rectifiers
2. Main Power Block
3. Soft Start Controller
4. Insulated-gate
5. High Voltage DC-DC
Converter
6. Compressor, Bearing/Motor
Controllers
7. Interstage pressure /
temperature sensor
8. Suction Pressure /
temperature sensor
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