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Motor noise, EMI measures, mechanical resonance
4.16 Motor noise, EMI measures, mechanical resonance
4.16.1 Carrier frequency and Soft-PWM selection under general-purpose motor
control (Pr. 72, Pr. 240, Pr. 260)
<V/ F><S MFVC>
(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.
⋅ When using an option sine wave filter (MT-BSL/BSC) for the 75K or higher, set "25"(2.5kHz) in Pr. 72.
(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)
⋅ If continuous operation is performed at 85% or higher of the rated inverter current (the value in the parenthesis on
page 346) with Pr.260 = "1 (initial setting)" and Pr.72 ≥ "3 (inverter carrier frequency is set to 3kHz is higher)," E.THT
(Inverter overload trip) is likely to occur. To avoid that, the carrier frequency is automatically lowered to as low as
2kHz. (Motor noise increases, but not to the point of 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.
Purpose Parameter that must be Set
Refer to
Page
Reduction of the motor noise
Measures against EMI and leakage currents
Carrier frequency and Soft-PWM
selection under general-purpose motor
control
Pr. 72, Pr. 240, Pr. 260 182
Reduction of the motor noise
Measures against EMI and leakage currents
Carrier frequency and Soft-PWM
selection under IPM motor control
Pr. 72, Pr. 240, Pr. 260 183
Reduce mechanical resonance Speed smoothing control
Pr. 653, Pr. 654 184
You can change the motor sound.
Parameter
Number
Name
Initial
Value
Setting Range Description
72 *
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.
(25 is exclusively for a sine wave filter.)
75K or
higher
0 to 6, 25
240 *
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.
260
PWM frequency
automatic switchover
1
0
PWM carrier frequency is constant independently of
load.
When the carrier frequency is set to 3kHz or more (Pr.
72 ≥ "3"), perform continuous operation at less than
85% of the rated inverter current.
1
Decreases PWM carrier frequency automatically when
load increases.
The above parameters can be set when Pr. 160 User group read selection = "0". (Refer to page 201.)
* This parameter allows its setting to be changed during operation even if "0" (initial value) is set in Pr. 77 Parameter write selection.
CAUTION
⋅ Decreasing the PWM carrier frequency is effective 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 ripple currents, 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 91
V/F
V/F
V/F
S
MFVC
S
MFVC
S
MFVC