Control Techniques unidrive sp User Manual

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52 Unidrive SP Advanced User Guide
www.controltechniques.com Issue Number: 7
This is the final speed demand at the input to the speed regulator formed by the sum of the ramp output and the hard speed reference (if the hard
speed reference is enabled). If the drive is disabled this parameter will show 0.0.
The speed feedback can be taken from the drive encoder port or a position feedback module fitted in any slot as selected with Pr 3.26. Parameter
03.02 shows the speed feedback used by the speed controller. The FI attribute is set for this parameter, so display filtering is active when this
parameter is viewed with one of the drive keypads. The value held in the drive (accessible via comms or an option module) does not include this filter,
but is a value that is obtained over a sliding 16ms period. The speed feedback value includes encoder quantisation ripple given by the following
equation:
Ripple in parameter 03.02 = 60 / 16ms / (ELPR x 4)
where ELPR is the equivalent encoder lines per revolution as defined below.
For example a 4096 line Ab type encoder gives a ripple level of 0.23rpm.
The 16ms sliding window is not normally applied to the speed feedback used by the speed controller, but a filter may be applied as defined by Pr 3.42.
The encoder ripple seen by the speed controller is given by:
Encoder speed ripple = 60 / Filter time / (ELPR x 4)
It is not advisable to use the speed feedback filter unless it is specifically required for high inertia applications with high controller gains because the
filter has a non-linear transfer function. It is preferable to use the current demand filters (see Pr 4.12 or 4.23) as these are linear first order filters that
provide filtering on noise generated from both the speed reference and the speed feedback. It should be noted that any filtering included within the
speed controller feedback loop, either on the speed feedback or the current demand, introduces a delay and limits the maximum bandwidth of the
controller for stable operation. If Pr 3.42 is set to zero (no filter) the ripple seen by the speed controller is given by:
Encoder speed ripple = 60 / 250µs / (ELPR x 4)
The speed ripple can be quite high, for example with a 4096 line encoder the speed ripple is 14.6rpm, but this does not define the resolution of the
speed feedback which is normally much better and depends on the length of the measuring period used to obtain the feedback. This is shown in the
improved resolution of the value accessible in Pr 3.02 which is measured over 16ms, i.e. a resolution of 0.23rpm with a 4096 line encoder. The speed
controller itself accumulates all pulses from the encoder, and so the speed controller resolution is not limited by the feedback, but by the resolution of
the speed reference. If a SINCOS encoder is used the encoder speed ripple is reduced by a factor of 2
( 2 - INTERPOLATION BITS)
For example with the
nominal 10 bits of interpolation information, the speed ripple is reduced by a factor of 256. This shows how a SINCOS encoder can reduce noise
caused by encoder quantisation without any filtering in the speed feedback or the current demand, so that high gains may be used to give high
dynamic performance and a very stiff system.
The speed error is the difference between the final speed demand and the speed feedback in rpm. This does not include the effect of the D term in the
speed controller feedback branch.
3.01 Final speed reference
Drive modes Closed-loop vector, Servo
Coding
Bit SP FI DE Txt VM DP ND RA NC NV PT US RW BU PS
1 11111
Range Closed-loop vector, Servo ±SPEED_MAX rpm
Update rate 4ms write
3.02 Speed Feedback
Drive modes Closed-loop vector, Servo
Coding
Bit SP FI DE Txt VM DP ND RA NC NV PT US RW BU PS
1 11111
Range Closed-loop vector, Servo ±SPEED_MAX rpm
Update rate 4ms write
Position feedback device ELPR
Ab, Ab.Servo number of lines per revolution
Fd, Fr, Fd.Servo, Fr.Servo number of lines per revolution / 2
SC.Hiper, SC.EnDat, SC, SC.SSI number of sine waves per revolution
3.03 Speed error
Drive modes Closed-loop vector, Servo
Coding
Bit SP FI DE Txt VM DP ND RA NC NV PT US RW BU PS
1 11111
Range Closed-loop vector, Servo ±SPEED_MAX rpm
Update rate 4ms write
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Control Techniques unidrive sp Specifications

General

Brand	Control Techniques
Model	unidrive sp
Category	Controller
Language	English