Optimal Voltage Control; How To Determine The Optimal Voltage - Mitsubishi Electric Mr.Slim MSZ09UN Service Manual

3. Frequency control by estimated discharge temperature (for protecting the discharge temperature in case the
estimated discharge temperature is 212 °F or higher)
By calculating the difference between the current discharge temperature and the discharge temperature 15 seconds
before, a discharge temperature in one minutes is estimated. As a result, the frequency and LEV are controlled as
shown the table below.
Esimated discharge
temperature(°F )
241 or higher
232 to 241
219 to 232
212 to 219
212 or lower

8-11. Optimal voltage control

The purpose of optimal voltage control is to operate the compressor at optimal
voltage that meets the load detected by the power factor of the compressor.
1. Optimal
As shown on the right the efficiency (ratio of output against input) of the
motor in the compressor becomes optional when the sliding (ratio of differ-
ence between the actual number of rotation and the number of synchronous
rotation of motor) is one fixed value. The value of sliding can be calculated
from the power factor since the sliding and the power factor are mutually
related as shown the table on the right. To make the value of sliding so that
the efficiency of motor is optimal, the power factor of the compressor is
detected. Then the detected power factor is controlled so that its efficiency
can be high. As a result, it is possible to operate the compressor at optimal
voltage.

2. How to determine the optimal voltage

Compare the detected power factor with the target power factor so that the efficiency of motor is optimal, the voltage
correction value is changed and the optimal output voltage is determined.
Optimal output voltage[V]= Standard voltage at certain frequency [V]x voltage correction value(%)
Target power factor minus detected power factor
(Calculated value is supposed to be "A".)
-2%<A<+2%
Frequency control
Lowered by 12Hz
Lowered by 6Hz
Regulated so that the
frequency will not rise
No correction
No correction
A[-2%
A]+2%
LEV control
Opened by 30 pulse
Opened by 20 pulse
Opened by 20 pulse
Opened by 20 pulse
No correction
Calculation of voltage
correction value (%)
Previous voltage correction value minus 1
Same as previous voltage correction value
Previous voltage correction value plus 1
36
Power factor
1 slip
efficiency
0