Mitsubishi Electric FR-A700 Instruction Manual page 548

Motor noise, noise reduction
Soft-PWM control (Pr. 240)
Soft-PWM control is a control system that changes the motor noise from a metallic tone into
an unoffending complex tone.
PWM carrier frequency automatic reduction function (Pr. 260)
For PWM carrier frequency automatic reduction function, the following should be noted.
Multiple rating (Pr. 570)
0
1
2 (Initial value)
3
Tab. 6-102: PWM carrier frequency automatic reduction function
When continuous operation is performed at 85% or more of the inverter rated current (the paren-
thesized value of the rated output current on page 420 or more) with the carrier frequency of the
inverter set to 3kHz or more (Pr. 72 ≥ "3"), the carrier frequency is automatically reduced to 2kHz
to protect the output transistor of the inverter. (Motor noise increases, but it is not a failure)
When Pr. 260 is set to"0", the carrier frequency becomes constant (Pr. 72 setting) independently
of the load, making the motor sound uniform.
Note that continuous operation should be performed at less than 85% of the inverter rating.
NOTES
Decreasing the PWM carrier frequency reduces inverter-generated noise and leakage cur-
rent, but increases motor noise.
When PWM carrier frequency is set to 1kHz or less (Pr. 72 ≤ 1), fast response current limit
may function prior to stall prevention operation due to increase in ripple currents, resulting in
insufficient torque. In such case, set fast-response current limit operation invalid using
Pr. 156 "Stall prevention operation selection".
When connecting a sine wave output filter please observe the manufacturer's specifications
for the necessary carrier frequency (the carrier frequency of the inverter).
6 - 368
120%
150%
200%
250%
PWM carrier frequency automatic reduction
Valid
Pr. 260 = 0: Invalid
Pr. 260 = 1 (Initial value): Valid
Invalid
Invalid
Parameter