Compressor Frequency Control - Mitsubishi Electric PU(H)Y-P250YGM-A Service Handbook

-4- Compressor Frequency Control

Depending on the capacity required, the frequency of the compressor is controlled to bring the evaporation temperature
(Te) close to the target evaporation temperature (Tem) during cooling operation, and to keep constant condensing temper-
ature (49°C =2.88MPa) during heating operation.
The target evaporation temperature (Tem) varies as follows during cooling operation depending on the capacity required.
When lacking in capacity : Tem is lowered
When the capacity exceeds the needs : Tem is raised
Minimum and maximum Tem Valued : -10°C
For P250 model, the capacity is controlled by only the inverter-driven compressor, and for P500 model, the capacity is
controlled by the compressor No.1 (inverter-driven) and No.2 (constant capacity).
The following table shows the frequency change of the inverter compressor during normal operation.
Model
P250 model
P500 model
The maximum frequency during heating operation is affected by the outdoor air temperature to a certain extent.
(1) No. 2 compressor operation/stop (P500 model only)
No.2 compressor changeover from stop to in-operation
When No.1 compressor does not meet the capacity requirement, No.2 compressor will start its operation.
No.2 compressor changeover from operation to stop
When an operation of both No.1 and No.2 compressors exceeds the capacity requirement, No.2 compressor will stop
its operation.
(2) Pressure limit
The maximum limit of high pressure (Pd) is set for each frequency level. If this limit is exceeded, the frequency will be
reduced every 30 seconds.
(3) Discharge temperature limit
The discharge temperature (Td) of the compressor in operation is detected, and if it exceeds the upper limit, the frequency
is reduced by 5 Hz.
Control is performed 30 seconds after compressor start-up and every 30 seconds thereafter.
Operating temperature is 115°C
(4) Periodic frequency control
Frequency control other than the ones performed at start-up, upon status change, and for protection is called periodic
frequency control (convergent control) and is performed in the following manner.
[Periodic control cycle]
Periodic control is performed after the following time has passed
60 seconds after the compressor start-up or 30 seconds after the completion of defrost operation
30 seconds after frequency control based on discharge temperature or pressure limit
[The amount of frequency change]
The amount of frequency change is controlled to approximate the target value based on the evaporation temperature
(Te) and condensing temperature (Tc).
Tem < 25°C
Frequency/cooling
20-60 Hz
20-70 Hz
- 81 -
Frequency/heating
20-60Hz
20-70 Hz
[ VII Control ]
Speed
3 Hz/second
3 Hz/second