Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 320)

5-12 Functional Description
7000L-UM300I-EN-P – June 2013 7000 “C” Frame
Current Control
The function of the current control block (Figure 5.7) is to determine
the firing angles for the converters Alpha Line (327) and Alpha
Machine (328). The inputs are the torque (Iy Command) and flux
producing (Ix Command) components of the dc link current
command from the speed control and flux control blocks
respectively, and the measured dc link current Idc Feedback (322).
The square root of the sum of the squares of Ix Command and Iy
Command determines the dc link current reference Idc Reference
(321). This is subtracted from the measured dc current feedback is
subtracted to determine Idc Error (323). This is processed by the
current regulator to produce Vdc Error (332). To effectively control
the dc link current an estimate of the motor side dc link voltage is
done to calculate Vdc Feedforward (333) which is added to Vdc
Error to produce the reference voltage for the line side converter Vdc
Reference (326). The line converter firing angle is the inverse cosine
of Vdc Reference. The machine converter firing angle is determined
by taking the inverse tangent of the ratio of Iy Command to the Ix
Command. The quadrant of operation is adjusted based on the signs
of the current commands.