Mitsubishi Electronics FR-D740-012 ユーザーズマニュアル
148
Motor noise, EMI measures, mechanical resonance
4.15 Motor noise, EMI measures, mechanical resonance
4.15.1 PWM carrier frequency and Soft-PWM control (Pr. 72, Pr. 240, Pr. 260)
(1) PWM carrier frequency changing (Pr. 72)
You can change the PWM carrier frequency of the inverter.
Changing the PWM carrier frequency produces an effect on avoiding the resonance frequency of a mechanical system or
Changing the PWM carrier frequency produces an effect on avoiding the resonance frequency of a mechanical system or
motor or on EMI measures or on leakage current reduction caused by the PWM switching.
(2) Soft-PWM control (Pr. 240)
Soft-PWM control is a control method that changes the motor noise from a metallic tone into an unoffending complex tone.
(3) PWM carrier frequency automatic reduction function (Pr. 260)
When Pr. 260 = "0" (initial value), the carrier frequency becomes constant (Pr. 72 setting) independently of the load,
making the motor sound uniform.
When continuous operation is performed at 85% or more of the inverter rated current with the carrier frequency of the
inverter set to 3kHz or more (Pr.72
≥ "3") while Pr.260 = "1", the carrier frequency is automatically reduced to 2kHz to avoid
E.THT (inverter overload shutoff). (Motor noise increases, but it is not a failure.)
Purpose of Use
Parameter that should be Set
Refer to Page
Reduction of the motor noise
Measures against EMI and leakage
currents
Measures against EMI and leakage
currents
Carrier frequency and
Soft-PWM selection
Soft-PWM selection
Pr. 72, Pr. 240, Pr. 260
Reduce mechanical resonance
Speed smoothing control
Pr. 653
You can change the motor sound.
Parameter
Number
Name
Initial Value
Setting Range
Description
72 *
PWM frequency selection
1
0 to 15
You can change the PWM carrier frequency.
The setting is in [kHz].
Note that 0 indicates 0.7kHz and 15
indicates 14.5kHz.
The setting is in [kHz].
Note that 0 indicates 0.7kHz and 15
indicates 14.5kHz.
240 *
Soft-PWM operation
selection
selection
1
0
Soft-PWM is invalid
1
When Pr. 72 = "0 to 5", Soft-PWM is valid.
260
PWM frequency
automatic switchover
automatic switchover
0
0
PWM carrier frequency is constant
independently of load.
independently of load.
1
Decreases PWM carrier frequency
automatically when load increases.
automatically when load increases.
The above parameters can be set when Pr.160 Extended function display selection = "0". (Refer to page 162)
* The parameters in the table allow its setting to be changed during operation even if "0" (initial value) is set in Pr. 77 Parameter write selection.
* The parameters in the table allow its setting to be changed during operation even if "0" (initial value) is set in Pr. 77 Parameter write selection.
NOTE
Decreasing the PWM carrier frequency affects on EMI measures and on leakage current reduction, but increases
motor noise.
When PWM carrier frequency is set to 1kHz or less (Pr.72
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 .
response current limit operation invalid using Pr. 156 Stall prevention operation selection .
Parameters referred to
Pr. 156 Stall prevention operation selection