Rockwell Automation SD3000 Drive Configuration, Programming - Manual (Page 91)

Appendix C
SD3000 Control Algorithm
Armature and field current regulation in SD3000 Drives is performed by the PMI Processor. Application tasks
on the UDC module and AutoMax Processor are used to intiate auto-tuning, run and stop the current
regulation algorithms, monitor the PMI Processor for warnings and faults, and coordinate with higher-level
control tasks.
The PMI Processor operating system regulates armature and field current based on the results of auto-tuning
and on the configuration parameters entered by the programmer. The PMI Processor calculates firing angle
values for the D-C Technology module, which in turn provides the firing signals to the armature and l-phase
field Power Module SCR gates for variable speed control of D-C motors.
For armature current regulation, the PMI Processor compares the desired current reference to the measured
armature current and voltage integrated from SCR firing to SCR firing. The armature current reference is
calculated in a UDC task and sent to the PMI Processor at the end of each UDC scan. Voltage-to-frequency
converters are used to compute average current and voltage in order to avoid errors inherent in sampling,
e.g., measuring during noise spikes or A-C line dips. Armature feedback and CEMF are used to determine
the proper gate firing time for SCR pairs every 1/6th of the line (every 2.78 msec. on average at 60Hz). The
armature current regulation algorithm provides for linear regulation over a full range of operating conditions,
such as A-C line fluctuations, continuous and discontinuous conduction, and speed changes.
For field current regulation, the PMI Processor compares the desired output current reference calculated in a
UDC task to the measured field feedback. The PMI Processor uses current error and CEMF to determine the
proper gate firing time for the 1 -phase field Power Module SCR thyristor pairs every 1/2 cycle of the line
(every 8.33 msec. on average at 60 Hz). Field current regulation is programmable which provides for field
weakening, field trim, field economy, and field loss protection.
The PMI Processor scans its Resolver & Drive l/O module, D-C Technology module, and rail I/O in concert
with armature and field current regulation so that I/O data can be integrated into both the PMI control
algorithms and into UDC tasks as required.
The following figures show block diagram representations of both the armature and field current regulation
algorithms.
C-l