UC800 AFD Operation
AFDE-SVU02F-EN
41
Surge Recovery
When surge occurs, the pressures in the evaporator and
condenser shells can become erratic. Surge recovery is
needed to force conditions out of this unstable operating
point. This is accomplished by reducing the pressure
coefficient every 90 seconds of continuous surge. In
addition, when the surge flag is set, the compressor speed
command is increased by 1 Hz every 5 seconds until the
surge condition clears. When the surge flag is removed,
the speed command will relax back to the speed needed to
raise the pressure coefficient to the new surge boundary.
Surge Detection
Surge detection control logic monitors changes in
compressor motor current. A surge occurrence leaves a
characteristic motor current signature as shown in
This signature is formed because the transitory
pressure breakdown between the condenser and
evaporator causes a sudden reduction in compressor
motor load. As the pressures equalize, the compressor
begins to quickly load, increasing the motor current.
Figure 17.
Boundary re-optimization
0.0
0.6
0.7
0.8
0.9
1.0
1.1
1.2
10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0
Pressure Coefficient Optimization
Pressure Coeff
icient
Surge detected
IGV % Capacity
Figure 18.
Motor current signature representing surge
Present
Sampled
Value
Previous
Sampled
Value
Rectified
Motor
Current
Transitory
Pressure
Breakdown
Pressure
Rebuilding
1 Surge
Occurrence
Time
