Mitsubishi Electric 800 Series Instruction Manual page 182

 PWM carrier frequency automatic reduction function (Pr.260)
• Setting Pr.260 = "1 (initial value)" will enable the PWM carrier frequency auto-reduction function. If a heavy load is
continuously applied while the inverter carrier frequency is set to 3 kHz or higher (Pr.72  "3"), the carrier frequency is
automatically reduced to prevent occurrence of the inverter overload trip (electronic thermal O/L relay function) (E.THT).
The carrier frequency is reduced to as low as 2 kHz. (Motor noise increases, but not to the point of failure.)
• When the PWM carrier frequency automatic reduction function is used, the operation with the carrier frequency set to 3
kHz or higher (Pr.72  "3") automatically reduces the carrier frequency for heavy-load operation as shown below.
Pr.260 Pr.570
setting setting
1 0 (SLD), 1 Continuous operation with the 85% or higher inverter rated current reduces the carrier frequency automatically.
(LD)
0 0 (SLD) Continuous operation with the 85% or higher inverter rated current reduces the carrier frequency automatically.
1 (LD) Without carrier frequency automatic reduction
(Perform continuous operation with the carrier frequency set to 2 kHz or lower or with less than 85% of the
inverter rated current.)
NOTE
• Reducing the PWM carrier frequency is effective as a countermeasure against EMI from the inverter or for reducing
leakage current, but doing so increases the motor noise.
• When the PWM carrier frequency is set to 1 kHz or lower (Pr.72  1), the increase in the harmonic current causes the fast-
response current limit to activate before the stall prevention operation, which may result in torque shortage. In this case,
disable the fast-response current limit in Pr.156 Stall prevention operation selection.
• During fast-response operation, the carrier frequency automatic reduction function is disabled.
Parameters referred to
Pr.156 Stall prevention operation selection
Pr.570 Multiple rating setting
Pr.800 Control method selection
Carrier frequency automatic reduction operation
page 257
page 167
page 145
5. PARAMETERS
5.4 (E) Environment setting parameters
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