Optidrive
ODV
‐
2
User
Guide
Revision
1.00
www.invertek.co.uk
51
14.2.3.
PID
Operating
Mode
Selection
For
default
operation
the
drive
response
to
an
increase
in
feedback
signal
is
to
decrease
motor
speed
and
vice
versa
to
adjust
the
feedback
signal
back
to
the
set
‐
point.
This
is
referred
to
as
‘Direct
Mode’
PID
control.
For
example
when
pressure
increases
in
a
pumping
system
and
the
feedback
signal
increases
then
the
drive
response
is
to
slow
the
pump
to
reduce
the
pressure.
This
mode
of
operation
is
the
default
drive
behaviour
and
can
be
selected
by
setting
P3
‐
04=0
(User
PID
operating
mode
=
Direct
Mode).
The
alternative
operating
mode
is
when
an
increase
in
feedback
signal
requires
an
increase
in
motor
speed.
This
is
referred
to
as
‘Inverse
mode’
PID
control.
For
example
on
a
condenser
fan
control
where
the
feedback
signal
increases
with
the
load
on
the
condenser
increases
and
the
fan
is
reduced
to
operate
at
a
higher
speed.
This
mode
of
operation
can
be
selected
by
setting
P3
‐
04=1
(User
PID
operating
mode
=
Inverse
mode).
PID
operating
mode
selection
is
summarised
in
the
following
table.
Parameter
P3
‐
04
Setting
Mode
Selected
Feedback
Behaviour
Motor
Behaviour
0
Direct
Mode
Signal
Increases
Speed
decreases
Signal
decreases
Speed
increases
1
Inverse
Mode
Signal
Increases
Speed
increases
Signal
decreases
Speed
decreases
14.2.4.
PID
Controller
Output
Limits
The
output
from
the
PID
controller
can
be
limited
by
settings
within
the
drive
unassociated
with
the
maximum
and
minimum
speed
limits
set
in
drive
parameters
P1
‐
01
and
P1
‐
02.
This
means
that
different
maximum
and
minimum
values
can
be
applied
when
the
drive
switches
from
PID
control
to
a
preset
speed
(via
digital
input)
or
variable
limits
can
be
applied.
Parameter
P3
‐
09
–
PID
Output
Limit
Control
sets
the
method
used
for
determining
the
PID
output
limits.
The
following
options
are
available.
Parameter
P3
‐
09
Description
0
Digital
preset
limit
value
(P3
‐
07
and
P3
‐
08)
will
be
used
to
limit
PID
controller
output
1
Analog
input
1
(terminal
6)
will
be
used
as
the
maximum
output
limit
2
Analog
input
1
(terminal
6)
will
be
used
as
the
minimum
output
limit
3
Analog
input
1
(terminal
6)
will
be
used
as
an
offset
value
and
added
to
the
PID
controller
output
The
basic
PID
block
diagram
shown
in
section
14.1
shows
the
limits
applied
when
P3
‐
09
is
set
to
0.
When
other
values
are
set
for
P3
‐
09
the
limits
for
the
PID
output
are
defined
by
the
methods
listed
in
the
table
above.
When
P3
‐
09=0
(default)
the
limits
are
set
digitally
by
parameters
P3
‐
07
and
P3
‐
08
and
limits
for
the
PID
controller
are
calculated
as
follows.
Upper
Limit
=
P3
‐
07
*
P1
‐
01:
(A
value
of
100%
limits
the
maximum
speed
of
the
PID
controller
to
the
maximum
speed
limit
defined
in
P1
‐
01).
Lower
Limit
=
P3
‐
08
*
P1
‐
01
14.2.5.
PID
Controller
Ramp
Rates
The
drive
standard
ramp
rates,
as
defined
by
P1
‐
03
and
P1
‐
04
are
normally
active
whilst
the
drive
operates
in
PID
mode.
P3
‐
11
(Maximum
PID
error
to
enable
ramps)
can
be
set
to
define
a
threshold
PID
error
level,
whereby
ramps
are
enabled
or
disabled
based
on
the
magnitude
of
the
PID
error.
If
the
difference
between
the
set
‐
point
and
feedback
values
is
less
than
the
threshold
set
in
P3
‐
11
then
the
internal
ramp
times
of
the
drive
are
disabled.
Where
a
greater
PID
error
exists,
the
ramp
times
are
enabled.
This
allows
the
rate
of
change
of
motor
speed
on
large
PID
errors
to
be
limited,
whilst
smaller
errors
are
reacted
to
quickly.
Setting
P3
‐
11
to
0
means
that
the
drive
ramps
are
always
enabled.
Caution:
Care
must
be
taken
in
adjusting
P3
‐
11.
Disabling
the
ramps
may
cause
the
motor
to
react
dramatically
to
larger
errors
in
the
PID
control
and
tuning
of
the
PID
controller
might
be
adversely
effected.
14.2.6.
PID
Controller
Gains
values
and
Tuning
As
with
any
PID
controller,
the
response
and
behaviour
of
the
system
is
controlled
by
the
Proportional
Gain
(P3
‐
01),
the
Integral
Time
Constant
(P3
‐
02)
and
the
Differential
Time
Constant
(P3
‐
03).
Correct
setting
of
these
parameters
is
essential
for
stable
and
reliable
system
operation.
There
are
many
methods
and
text
books
available
explaining
how
these
terms
work
and
how
they
can
be
tuned,
and
so
only
a
brief
summary
is
given
below.
P3
‐
01
Proportional
Gain:
Range
0.1
to
30.0,
Default
Setting
1.0
Proportional
gain
acts
as
a
multiplier
of
the
difference
between
the
Feedback
and
Set
‐
point
signals.
The
PID
controller
firstly
determines
the
PID
Error,
assuming
direct
operation
PID
Error
=
PID
Set
‐
point
–
PID
Feedback
The
proportional
gain
is
then
used
to
multiply
this
error.
If
the
Integral
and
Differential
Time
constants
are
both
set
to
zero,
PID
Output
=
Proportional
Gain
x
(PID
Set
‐
point
–
PID
Feedback)
A
large
value
of
P
‐
gain
will
cause
a
greater
change
in
output
frequency
for
a
small
difference
between
the
Feedback
and
Set
‐
point.
If
the
value
is
too
large,
the
system
is
likely
to
be
unstable,
and
motor
output
speed
will
often
overshoot
the
set
‐
point.
Higher
values
are
acceptable
on
dynamic
applications
requiring
fast
response.
Lower
values
should
be
used
for
slower
responding
systems,
such
as
fan
and
pump
control
applications.
If
the
system
tends
to
overshoot,
reducing
the
P
gain
will
have
an
effect
of
reducing
the
overshoot.
P3
‐
02
Integral
Time
Constant:
Range
0.0
to
30.0,
Default
Setting
1.0
The
integral
time
constant
is
a
time
based
function,
which
modifies
the
output
of
the
PID
controller
based
on
the
change
in
PID
Error
over
a
defined
time
period.
The
effect
of
the
Integral
Time
Constant
is
always
to
try
to
reduce
the
PID
Error
towards
zero
(so
that
Feedback
=
Set
‐
