Danaher Motion Kollmorgen Speciality Electronics System Operation
SERVOSTAR CD-LITE User Manual 17
Torque Loop
Most applications use the SERVOSTAR CD-Lite in torque mode configuration. The SERVOSTAR CD-
Lite has many internal variables that can be used to examine and dictate system operation. Many of these
variables and their locations in MOTIONLINK are presented graphically in the following discussions to
help disclose meanings and relationships.
Analog Torque
The SERVOSTAR CD-Lite is most often configured to operate as an analog torque loop controller
(OPMODE=3). In this case, the current loop receives its input from the analog-to-digital (A/D)
conversion system. After conversion, the input command signal is processed through an algorithm that
adjusts the signal (ANOFF1, ANDB, ANZERO), filters it (ANLPFHZ) and scales it (ISCALE), before
developing the current command. The current (or torque) command is checked against the peak (IMAX,
ILIM) and continuous (FoldBack features, ICONT) current clamp limits. Sinusoidal commutation
modulation is added to the command and fed to the three-phase current loop regulator, which calculates a
current error. This error is fed through a digital pole-placement compensation algorithm. The output of
the compensator is converted to a PWM signal and fed to the power transistor bridge. The power bridge
uses the high voltage DC BUS Module (325 VDC bus typical) to supply the required current to the motor
windings. The actual motor current is updated and the process begins again.
Current Sampling
The current loop receives corrective feedback from the current sampling circuitry. The current sensors
use closed-loop hall sampling techniques in all units.
The current sample is used by the current loops to regulate the current in each of the three motor phases.
Two phases (A and C) of the current signal are sampled by the microprocessor at a 16 kHz rate. The
momentary A phase current and C phase current are monitored by examining the IA and IC variables,
respectively. The microprocessor calculates the equivalent absolute current, which can be monitored as I.
This value can be averaged for 2, 4, 8, 16, 32, or 64 samples.
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