Emerson E300 Series - Page 140

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140 E300 Design Guide
Issue Number: 1
A24 (Symmetrical Current Limit B16)
The symmetrical current limit controls the current when the motor is being accelerated away from standstill during constant speed with changing load
levels and during deceleration towards standstill. The maximum possible symmetrical current limit (+
VM_MOTOR1_CURRENT_LIMIT %) varies
between drive sizes with default parameters loaded.
A25 (Maximum Switching Frequency B13)
This parameter defines the PWM switching frequency. The drive may automatically reduce the switching frequency (without changing this parameter)
if the power stage becomes too hot. A thermal model of the IGBT junction temperature is used based on the heatsink temperature and an
instantaneous temperature drop using the drive output current and switching frequency. The full range of switching frequencies is not available on all
ratings.
The estimated IGBT junction temperature is displayed in J77. If this temperature exceeds 145 °C, the switching frequency is reduced if possible,
based on the current settings. Reducing the switching frequency, reduces the drive losses and the estimated IGBT junction temperature. If the load
condition persists the estimated IGBT junction temperature may continue to rise again above 145 °C and if the drive cannot reduce the switching
frequency any further the drive will initiate an ‘OHt Inverter’ trip.
Every second the drive will attempt to restore the switching frequency to the level set in A25 (Maximum Switching Frequency B13).
The control over the drive switching frequency based upon the estimated IGBT junction temperature can be adjusted using the following parameters
Maximum Switching Frequency (B13), Minimum Switching Frequency (B14) and Switching Frequency Step Size (B15).
A26 (Motor Autotune B11)
A24 {B16} Symmetrical current limit
RW Num US
OL
Ú
+ VM_MOTOR1_
CURRENT
LIMIT %
Ö
165.0 %
RFC-A
175.0 %
RFC-S
Setting the Symmetrical Current Limit (B16) to a low value or zero can result in uncontrolled movement on brake release. Ensure the
Symmetrical Current Limit (B16)is set to a suitable value taking into account both the motor rated current and overload requirement in the
worst case load condition to avoid uncontrolled movement and the risk of damage to the system.
A25 {B13} Maximum Switching Frequency
RW Txt RA US
OL
Ú
2 kHz (0), 3 kHz (1),
4 kHz (2), 6 kHz (3),
8 kHz (4), 12 kHz (5),
16 kHz (6)
Ö
8 kHz (4)RFC-A
RFC-S
Value Text (kHz)
02
13
24
36
48
512
616
A26 {B11} Motor Autotune
RW Txt NC US
OL
Ú
None (0), Static (1),
Rotating (2)
Ö
None (0)
RFC-A
None (0), Static (1),
Rotating (2), Inertia (3)
RFC-S
WARNING