Programming
Page
D-160
890CS Common Bus Supply - Frames B & D; 890CD Common Bus Drive and 890SD Standalone Drive - Frames B, C & D
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A
B
C
D
E
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Functional Description
The speed error (speed demand minus speed feedback) is calculated and processed via a propor integral (PI) controller.
The output of the PI controller is a torque demand, which is passed directly to the torque control block.
The speed demand is derived from the Setpoint Scale block. The speed feedback is derived from the encoder when the drive is
in CLOSED-LOOP VEC mode. This mode gives the best control, as the feedback is fast and accurate. When the drive is in
SENSORLESS VEC mode, the speed feedback is calculated from the voltages and currents flowing in the motor, and the
motor model.
The parameters COMPENSATION F1 and COMPENSATION F2 perform different functions depending upon the setting of
the COMPENSAT'N TYPE parameter:
COMPENSAT'N TYPE:
MAX ATTENTUATION
This applies a first order filter with 3db attenuation frequency given by parameter “COMPENSATION F1”.
This form of compensation has a more efficient roll off characteristic, falling to zero at the Nyquist limit (see “Nyquist
limit” below). The Nyquist limit is equal to half the loop operating frequency, it has the disadvantage that it adds additional
phase delay equal to a time delay of half a sample period to the transfer function. This delay is equal to 1/(4 * switching
frequency). For example, if the switching frequency is 4kHz, the delay is equal to 62.5uS.
Nyquist Limit: This is defined as half the control loop operating frequency. The control loops operate at twice the stack
switching frequency, so the Nyquist Limit is equal to the stack switching frequency.
MINIMUM PHASE
This applies a simple first order recursive filter with 3db attenuation frequency given approximately by parameter
COMPENSATION F1. This type of compensation has a less efficient roll off characteristic, but has less phase shift than the
MAX ATTENTUATION filter, as there is no additional time delay.
