Lenze 8400 - Manual (Page 153)

Lenze · 8400 protec HighLine · Reference manual · DMS 3.0 EN · 03/2013 · TD05
153
5 Motor control (MCTRL)
5.4 V/f characteristic control (VFCplus)
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5.4.2.2 Defining current limits (Imax controller)
The V/f characteristic control (VFCplus) and the V/f control (VFCplus + encoder) operating modes
are provided with a current limitation control which is decisive for the dynamic behaviour under
load and counteracts exceedance of the maximum current in motor or generator mode. This current
limitation control is called I
max
control.
• The efficiency (motor current) measured by the I
max
control is compared with the current limit
value for motor load set in C00022 and the current limit value for generator load set in C00023 .
• If the current limit values are exceeded, the controller changes its dynamic behaviour.
Motor overload during acceleration
The controller prolongs the acceleration ramp to keep the current on or below the current limit.
Generator overload during deceleration
The controller prolongs the deceleration ramp to keep the current on or below the current limit.
Increasing load with constant speed
• If the motor current limit value is reached:
• The controller reduces the effective speed setpoint until a stable working point is set or an
effective speed setpoint of 0 rpm is reached.
• If the load is reduced, the controller increases the effective speed setpoint until the setpoint
speed is reached or the load reaches the current limit value again.
• When the generator current limit value is reached:
• The controller increases the effective speed setpoint until a stable working point is set or the
maximally permissible speed ( C00909 ) or output frequency is reached ( C000910 ).
• If the load is reduced, the controller reduces the effective speed setpoint until the setpoint
speed is reached or the load reaches the current limit value again.
• If a sudden load is built up at the motor shaft (e.g. drive is blocked), the overcurrent
disconnection may respond (fault message OC1 or OC11).