121 - 23/May/97
5.5 Speed Loop
The speed control loop is implemented by the Digital Signal Processor fitted into the DBM
module control board. The speed reference normally comes from a CNC in the form of
+10V/-10V analog signal. Alternatively, the speed reference might be set by a dumb terminal
or a PC computer, through the RS485 serial link. Speed control loops of the axes are
completely independent of each other. The feedback for the speed loop error discrimination
is obtained from the velocity observer, illustrated in Fig. 4. Simplified block diagram of the
speed control loop is given in Fig. 5, presented in a form suitable for easier understanding of
feedback gains. This block diagram should be used for the estimation of the drive
performance in the stage of system selection and sizing.
Σ
Ko
Speed
reference
[rad/s]
+
-
Ko
observer
p + i/s
KD
1/(Js)
T [Nm]
ω
[rad/s]
Fig. 5
Gain correlator and AWU
The speed observation constant Ko in Fig. 5 is Ko=50.06 [1/(rad/s)]. The K1 block in Fig. 5
approximates the drive power section and the motor. It is assumed that the response of the
current control loop may be neglected with respect to the dynamics of the speed loop.
Notice: As the result of more detailed analysis, that takes into account the interaction of both
loops, it is concluded that said simplification results in an error of less than 2%. Hence, the
user is encouraged to use Fig. 5 simplification as a toll for the system performance
estimation.
The value of the parameter K1 may be calculated from the drive peak current (25 A in the
case of DBM 10/25) and the motor torque constant Kt:
K Nm
I
A
K Nm A
e
peak
t
1
1 6
[
]
[ ]
[
/
]
=
∗
(6)
K1
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