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PROGRAMMING GUIDE
SINUS PENTA
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35. LIMITS MENU
35.1. Overview
The
Limits Menu defines the current/torque limits applied to the control functions (IFD, VTC or FOC controls) selected
for the three connected motors.
For IFD control, current limits are used. Three limit current levels are available, which are expressed as a percentage of
the motor rated current:
1) Current limit while accelerating;
2) Current limit at constant rpm;
3) Current limit while decelerating.
Two special parameters are also available; one sets the decrease of the limit current value when the motor runs at
constant power (field weakening), while the other parameter disables the frequency decrease in case of acceleration
current limit (this is useful for inertial loads).
If a VTC control or a FOC control is used, limits are expressed as a percentage of the rated motor torque.
Values set in the two parameters relating to min. torque and max. torque represent the limits for saturation of the control
torque demand. If an external torque limit is set (
C147 in the CONTROL METHOD MENU), the values set in the
parameters above represent the range of the source used for limitation; the torque ramp times set in the RAMPS MENU
will be applied to the preset limit torque reference.
When in field weakening mode, such as when the system operates at a higher speed than the rated motor speed set in
C016 , the torque limits defined by parameters C047 / C048 are decreased following a law 1/speed at speed exceeding
the rated speed, to limit the maximum mechanical power required to the motor. The external torque limit programmed
via
C147 is not re-scaled to 1/speed, but is saturated between the two limits defined above, as shown in Figure 46.
Figure 46: Torque limit for VTC and FOC controls in field weakening mode
The Ipeak current load is available (see Table 81 and Table 85) for a maximum time of 3 seconds and only if the preset
carrier frequency is lower than/equal to the default frequency value (see Table 81 and Table 85). When operating with
synchronous modulation, the current peak value dynamically decreases when the output frequency increases.
Manually enabling/disabling that function can be done only when using the IFD control with current limit parameters
C043/C044/C045 . When using the VTC or FOC control, the system will automatically handle the maximum current value
that can be used also based on the torque limit configured with C047/C048 .