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Motor noise, EMI measures
4.20 Motor noise, EMI measures
4.20.1 PWM carrier frequency and Soft-PWM control (Pr. 72, Pr. 240)
(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 motor or on EMI measures or on leakage current reduction caused by the PWM switching.
⋅ Carrier frequencies under Real sensorless vector control or vector control are as shown below.
(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.
You can change the motor sound.
Parameter
Number
Name
Initial
Value
Setting Range Description
72 *1 PWM frequency selection 2
55K or lower 0 to 15
PWM carrier frequency can be changed.
The setting displayed is in [kHz]. Note
that 0 indicates 0.7kHz, 15 indicates
14.5kHz and 25 indicates 2.5kHz.
(Setting value "25" is for the sine wave
filter.)
75K or higher 0 to 6, 25
240
*1 Soft-PWM operation selection 1
0 Soft-PWM is invalid
1
When Pr. 72 = "0 to 5" (
"0 to 4" for 75K or
higher), soft-PWM is valid.
*1 The above parameters allow its setting to be changed during operation in any operation mode even if "0" (initial value) is set in
Pr. 77 Parameter write selection.
Pr. 72 Setting
Carrier Frequencies (kHz)
55K or lower 75K or higher
0 to 5 0 to 5 2
6 to 9 6 6
10 to 13 ⎯ 10
14, 15 ⎯ 14
⋅ When using an option sine wave filter (MT-BSL/BSC) for the 75K or higher, set "25" (2.5kHz) in Pr. 72.
REMARKS
When "25" (available with the 75K or higher) is set in Pr. 72, V/F control is forcibly selected.
CAUTION
⋅ When operating the inverter of 75K or higher with a value larger than 2kHz set in Pr. 72 PWM frequency selection, derate the
inverter rated output current. (Refer to page 442)
⋅ When operating the inverter of 55K or lower with a value larger than 2kHz set in Pr. 72 PWM frequency selection, the carrier
frequency will automatically decrease as low as 2kHz if the inverter is overloaded during low speed operation (output frequency
is 3Hz or less). This may cause the motor noise to increase, but not a fault.
⋅ Decreasing the PWM carrier frequency effect on EMI measures and on leakage current reduction, 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 harmonic currents depending on the motor, resulting in insufficient torque. In such case, set fast
response current limit operation invalid using Pr. 156 Stall prevention operation selection.
♦ Parameters referred to ♦
Pr. 156 Stall prevention operation selection Refer to page 152