Menu 4
66
Commander SK Advanced User Guide
www.controltechniques.com Issue Number: 9
This parameter defines the current limit as a percentage of the rated active current. When the motor rated current is set lower than the drive rated
current, the maximum value of this parameter increases to allow larger overloads.
Therefore, by setting the motor rated current to a lower value than the drive rated current, it is possible to have a current limit greater than 165%. An
absolute maximum current limit of 999.9% is applied.
In frequency control mode (Pr
4.11
= OFF), the drive output frequency is modified if necessary to keep the active current within the current limits as
shown below:
The active current limit is compared with the active current and if the current exceeds the limit the error value passes through the PI controller to give
a frequency component which is used to modify the ramp output. The direction of the modification is always to reduce the frequency to zero if the
active current is motoring, or to increase the frequency towards the maximum if the current is regenerating. Even when the current limit is active the
ramp still operates, therefore the proportional and integral gains (Pr
4.13
and Pr
4.14
) must be high enough to counter the effects of the ramp. For
method of setting the gains see Pr
In torque control mode the current demand is limited by the active current limit. For operation of this mode see Pr
When the current limit becomes active, the display will flash AC.Lt
This is the main torque reference parameter. A positive value is required for torque to be applied in the forward direction, and a negative value is
required for torque to be applied in the reverse direction.
For a negative value, program a digital input to the analog input invert bit. This will give a negative value on the analog input destination parameter.
This will allow the direction of rotation to be controlled by the polarity of the analog input.
If operating in torque control, due to small errors in current measurement at low frequencies, with zero torque reference and light loads, the drive may
allow the motor to rotate. The direction of rotation while in torque control is determined by the polarity of the torque reference. Therefore, at power-up
with zero torque reference and with the drive enabled, the motor may rotate in either direction. This is because any error in the current feedback
maybe a positive or negative value. If the error is positive, the motor will rotate in the forward direction and if the error is negative, the motor will rotate
in the reverse direction.
If it is necessary to guarantee the direction of rotation at power up while in torque control, a small positive or negative error must be present in Pr
4.08
.
0
: OFF Torque mode disabled
1
: On Torque mode enabled
If this parameter is OFF(0) normal frequency control is used.
If this parameter is set to On(1) the current demand is connected to the current PI controller giving closed loop torque/current demand as shown
below.
The current error is passed through proportional and integral terms to give a frequency reference. In motoring conditions and regeneration, the
frequency reference is allowed to go up to the maximum programmed in menu 1 + 20% to allow for current control close to maximum speed.
4.08
Torque reference
Coding
Bit
SP
FI
DE Txt VM DP ND RA NC NV
PT
US RW BU PS
1
1
1
1
Range
±
USER_CURRENT_MAX%
Default
0.0
Update rate
Background
4.09 to 4.10
Unused parameters
4.11
Torque mode selector
Coding
Bit
SP
FI
DE Txt VM DP ND RA NC NV
PT
US RW BU PS
1
1
1
Range
OFF(0) or On(1)
Default
OFF(0)
Update rate
Background
P Pr
4.13
I Pr
4.14
Current limit
active
1
0
Active
current
limit
Post ramp
reference
Ramp
Active
current
-
+
Summary of Contents for 2202
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