Speed Controller Set-Up Method - Emerson unidrive sp User Manual
Universal variable speed ac drive for induction and servo motors
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Menu 3
Parameter
Keypad and
Closed-loop
structure
display
To analyze the performance of the speed controller it may be represented as an s-domain model as shown below.
w*(s)
+
-1
rads
_
Speed controller
Where:
Kc is the conversion between the speed controller output and the torque producing current. A value of unity at the output of the speed controller gives
a torque producing current equal to Kc. The drive automatically compensates the torque producing current for flux variations in field weakening, and
so Kc can be assumed to have a constant value even in field weakening. See menu 4 for the value of Kc each drive size).
Kt is the torque constant of the motor (i.e. torque in Nm per amp of torque producing current). This value is normally available for a servo motor from
the manufacturer, however for induction motors the value must be calculated from
Kt = Motor rated torque / Motor rated torque producing current
= Motor rated torque / √(Motor rated current
L(s) is the transfer function of the load.
The s-domain system above may be used to determine the performance of systems with a relatively low bandwidth. However, the real drive system
also includes non-ideal delays due to the torque controller response, and speed measurement and control delays. These delays, which can be
approximated with a simple unity gain transport delay (T
w*(s)
+
Kp+Ki/s
_
The speed controller gains used in previous Unidrive products were in internal drive units. Conversion between the previous internal units and the SI
units used in this product are given in the table below.
Gain
Conversion from previous internal units to new SI units
Kp
Ki
Kd
Speed controller set-up method
3.17
Drive modes
Closed-loop vector, Servo
Bit
SP
Coding
Range
Closed-loop vector, Servo
Default
Closed-loop vector, Servo
Update rate
Background (1s) read
The user may enter the required speed controller gains into Pr 3.10 to Pr 3.15. However, if the load is predominantly a constant inertia and constant
torque, the drive can calculate the required Kp and Ki gains, provided a value of motor plus load inertia (Pr 3.18) and the motor torque per amp
(Pr 5.32) are set-up correctly. The gain values are calculated to give a required compliance angle or bandwidth. The calculated values for Kp and Ki
are written to Pr 3.10 and Pr 3.11 once per second when one of these set-up methods is selected (i.e. Pr 3.17 = 1 or 2). The values are calculated
from a linear model assuming a pure inertia load, not including unwanted delays in the speed and current controllers. The Kd gain is not affected. If
Pr 3.17 is set to 3 automatic gain set up is not active, but Kp is boosted by a factor of 16.
62
Parameter
Parameter
x.00
description format
Kp
+
+
Ki
1/s
2
- No load current
) as shown below, should be taken into account for more accurate results.
delay
+
Kc.Kt
_
Ki.Kd
T
delay
Kp_old / 17103
Ki_old / 94.41
Kd_old / 46376
FI
DE
Txt VM DP
ND
0 to 3
0
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Advanced parameter
Macros
descriptions
Kc
Kt
_
Ki.Kd
2
)
w(s)
L(s)
RA NC
NV
PT
US RW BU
1
Serial comms
Electronic
protocol
nameplate
w(s)
-1
rads
L(s)
PS
1
1
Unidrive SP Advanced User Guide
Performance RFC mode
Issue Number: 10
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