Mitsubishi Electric FR-A760 Series Instruction Manual page 280

(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)
For PWM carrier frequency automatic reduction function, the following should be noted.
Multiple rating (Pr. 570)
0 SLD
1 LD
2 (initial setting) ND
3 HD
⋅ When continuous operation is performed at 85% or more of the inverter rated current (the parenthesized value of
the rated output current on page 424 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.
CAUTION
⋅ Decreasing the PWM carrier frequency reduces inverter-generated noise and leakage current, but increases motor noise.
⋅ When PWM carrier frequency is set to 1kHz or less (
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
♦ Parameters referred to ♦
Pr. 156 Stall prevention operation selection
Pr. 570 Multiple rating setting
PWM carrier frequency automatic reduction
valid
Pr. 260 = "0" : invalid
Pr. 260 = "1" (initial setting) : valid
invalid
invalid
≤ 1), fast-response current limit may function prior to stall prevention
Pr. 72
Pr. 156
Stall prevention operation selection
Refer to page 138
Refer to page 143
Motor noise, noise reduction
.
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