Siemens SINAMICS DCM 6RA80 Faq page 22

The current controller adjusts the setpoint/actual value difference of the current via its PI
characteristic curve by forming the suitable firing angle for the gating unit.
Precontrol: The precontrol acts simultaneously with the current controller and ensures the
dynamic response of the current control loop both for discontinuous and continuous current.
Above all, the precontrol ensures that the firing angle for the existing non-linear control
characteristic and the varying firing angle requirement for a change in the actual current
value for discontinuous and continuous current is calculated and precontrolled to the correct
extent.
From Firmware V1.2 an adaption for the current controller is implemented. See List manual
chapter 2 sheet 6853.
Control
Uctrl
characteristic
curve
Discontinuous
current
Uctrl1
Uctrl2
I
To effect a current change I a firing angle change Uctrl must be applied. If I is equal, the
necessary control firing angle Uctrl1 in the discontinuous current range is much higher than
Uctrl2 in the continuous current range. The firing angle change only has to take account of
the armature-current-related linear voltage drop I * R in the continuous current range.
The point of transition from discontinuous to continuous current (see below) is determined by
the inductance in the load circuit and the current motor EMF.
The control characteristic above applies to a particular motor EMF, the curve moves up or
down depending on the current EMF.
The precontrol calculates the firing angle depending on the current setpoint and the EMF of
the motor, uses it to compensate the above non-linearities and sets the required firing angle
without delay for the following gating unit. The current controller now only has to correct by a
small amount. This ensures that even for greater dynamic requirements such as cross-
cutters, for example, the required dynamic response of the current control can be provided.
p50153 = 0, The precontrol is not active
p50153 = 1 Factory settings, precontrol dependent on current setpoint and EMF active
p50153 = 2 Current-setpoint-dependent precontrol active, EMF influence not active, with
torque direction change or on start via controller enable, the I component of the current
controller is set to the firing angle component as a condition of the EMF. Recommended
Point of transition from
discontinuous to continuous
current
I
I * R
Control characteristic
curve
Continuous current
22
Current