Hitachi RAS-25QH1 Technische Information Seite 157

4. Power Module Circuit
Power module A (QM20TD-H)
a TD
DC compressor
motor
To MAIN P.W.B.
Fig. 4-1
@ The three transistors on the positive © side are called the upper arm, and the three transistors on the
negative © side, the lower arm.
@ The transistors on the upper and lower arms are switched in the specified order and a three-phase
AC voltage is generated at the U, V and W terminals of the compressor motor. When the switching
period is assumed to be T, and the number of rotation of the compressor, N, the following formula is
established. ,
N = 60/2 x 1/T
@ The upper arm transistors perform chopper operation and turn on and off at a frequency of 3.3kKHz.
@ The compressor rotation speed is controlled as follows.
@ The voltage generated between the U, V and W terminals of the compressor motor is input to the
rotor magnetic pole position detector and is then supplied to the micro computer as a rotation speed
signal. ;
@ If the above rotation speed is lower than the speed command value which is input to the micro
computer via the interface, the chopper duty (ratio when the chopper signal is turned on) is widened.
@ As a result, the 3-phase AC voltage generated between the U, V and W terminals of the
compressor motor increases and the rotation speed is raised.
The procedure is then returned to step © and steps @ — @ are repeated to control so the rotation
speed matches the instructed value transferred from the indoor micro computer.
@ The three-phase AC voltage generated between the U, V and W terminals of the compressor motor
changes due to the load and speed.
In case of normal load; approx. 180V at approx. 5700 min™ {rpm.}
approx. 30V at 1300 min" {rpm.}
Other speeds can be calculated by proportional caiculation.
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