芝加哥公牛英文闭环控制 中英文对照

2021年1月19日发(作者：interest是什么意思)
英文原文


Closed Loop Control

Many real-time embedded systems make control decisions. These decisions are
usually made by software and based on feedback from the hardware under its control
(termed the plant). Such feedback commonly takes the form of an analog sensor that
can be read via an A/D converter. A sample from the sensor may represent position,
voltage,
temperature,
or
any
other
appropriate
parameter.
Each
sample
provides
the
software with additional information upon which to base its control decisions.

Basics of Closed-Loop Control
Established based on the feedback control system theory. The so-called feedback
principle, in accordance with changes in the information system output control, that is,
by
comparing the system
behavior (output)
and the deviation between the expected
behavior,
and
the
elimination
of
bias
in
order
to
achieve
the
desired
system
performance. In the feedback control system, there was not only the signal from the
input to output prior to the pathway, also contain input from the output to the signal
feedback path,
the two form
a closed loop.
Therefore, the feedback control system,
also
known
as
closed
loop
control
system.
Feedback
control
is
the
main
form
of
control. Most of the feedback control system control system. In engineering often to
run the expectations manipulation to output and consistent feedback control system,
known as automatic adjustment system, to be used to accurately follow or replicate a
process known as feedback control system or servo servo system .




Feedback control system by the controller, the controlled object and the feedback
path
formed. More links,
for subtracting the input and output, error signal
is
given.
This
link
may
be
in
specific
systems,
together
with
the
controller,
referred
to
as
regulators. With temperature control, for example, the controlled object for the stove;
output variables for the actual oven temperature; input variables for a given constant
temperature,
usually
expressed
with
the
voltage.
Temperature
measurement
using
thermocouples, on behalf of the thermal emf and the furnace temperature for a given
voltage compared to the difference between the voltage through the power amplified
to
drive
the
corresponding
actuator
control.



Compared
with
open
loop
control
system,
closed-loop
control
has
a
number
of
advantages.
In
the
feedback
control
system, for whatever reason (external disturbances or changes within the system), as
long
as
the
amount
of
deviation
from
the
specified
value
to
be
controlled,
it
will
generate the appropriate control action to eliminate bias. Therefore, it can inhibit the
ability of interference, not sensitive to the device characteristics and can improve the
system's
response.
However,
the
introduction
of
feedback
loops
to
increase
the
complexity of the system, but choose not to then the gain will cause system instability.
To improve the control precision can be measured in the disturbance variables, they
often also used by disturbance of the control (ie, feedforward control) as a supplement
to constitute a feedback


control complex control systems.
A Closed- Loop system utilizes feedback to measure the actual system operating
parameter being controlled such as temperature, pressure, flow, level, or speed. This
feedback signal is sent back to the controller where it is compared with the desired
system setpoint. The controller develops an error signal that initiates corrective action
and
drives
thefinal
output
device
to
the
desired
value.
In
the
DC
Motor
Drive
illustrated above, the tachometer provides a feedback voltage which is proportional to
the actual motor speed. Closed-Loop Systems have the following features
：

1. A Reference or Set Point that establishes the desired operating point around which
the system controls.

process
variable
Feedback
signal
that
“tells”
the
controller
at
what
point
the
system is actually operating.
3.A Controller which compares the system Reference with the system Feedback and
generates an Error signal that represents the difference between the desired operating
point and the actual system operating value.
4.A Final Control Element or mechanism which responds to the system Error to bring
the system into may be a pneumatically controlled valve, an electronic
positioner, a positioning motor, an SCR or transistor power inverter, a heating element,
or other control device.

Tuning
Elements
which
modify
the
control
operation
by
introducing
mathematical
constants
that
tailor
the
control
to
the
specific
application,
provide
system
stabilization,
and
adjust
system
response
time.
In
process
control
systems
these tuning elements are: Proportional,
Integral, and Derivative (PID) functions. In
electrical
systems,
such
a
generator
voltage
regulators
and
motor
drives,
typical
tuning adjustments include:
(1).Gain, the amplification factor of the controller error amplifier, which affects both
system stability and response time;
(2).Stability which provides a time-delayed response to feedback variations to prevent
oscillations and reduce system “hunting”;

(3).Feedback an adjustment which controls the amplitude of the feedback signal that
is balanced against the system set-point;
(4).Boost which is used in AC and DC motor drives to provide extra low-end torque;

(5).IR
Compensation
which
provides
a
control
signal
that
compensates
for
the
IR
Drop (V
oltage Drop) which occurs in the armature windings in DC machines due to
increased current flow through the armature.

Feedback Polarity
In closed-loop systems, feedback signals may be either Regenerative (in- phase)
or
Degenerative
(out-of-phase).
Regenerative
feedback
exists
when
the
feedback
polarity
or
phase
relationship
acts
to
aid
or
boost
the
main
control
signal.
If
the
amplitude of the feedback is sufficiently large oscillations will be developed. (This is
the principal used in the operation of radio frequency oscillators.) When regenerative
feedback is used in control systems, such in the case of IR Compensation, the effect
of excessive feedback must limited, otherwise instability will result.
Degenerative feedback, on the other hand, will dampen oscillations and produce
system
stability.
In
degenerative
feedback,
the
phase
relationship
or
polarity
of
the
feedback signal acts to cancel or reduce that of the main control signal.
Feedback
polarity
is
critical
and
proper
feedback
polarity
must
be
determined
when
commissioning
equipment
which
consists
of
separate
control
and
feedback
devices. This is not a concern to the installer of a packaged system where the control
and feedback devices are pre-wired as a complete system.
In
the
example
DC
Motor
Drive,
an
operational
amplifier
configured
as
a
summing
inverter
is
utilized.
This
configuration
requires
that
the
reference
and
feedback signals be of the opposite polarity because the amplifier output (error) will
be the mathematical sum of the input voltages (here the reference is positive and the
feedback
is
negative).
When
a
differential
amplifier
is
used,
the
reference
and
feedback will be of the same polarity because the amplifier output (error) will be the
mathematical difference of the two input voltages.
An example of on-off control
Proportional control is the primary alternative to on-off control. If the difference
between the current plant output and its desired value (the current error) is large, the
software should probably change the drive signal a lot. If the error is small, it should
change it only a little. In other words, we always want a change like:

Proportion
where P is a constant proportional gain set by the system's designer.

For example, if the drive signal uses PWM, it can take
any value between 0%
and
100%
duty
cycle.
If
the
signal
on
the
drive
is
20%
duty
cycle
and
the
error
remaining
at
the
output
is
small,
we
may
just
need
to
tweak
it
to
18%
or
19%
to
achieve the desired output at the plant.

If the proportional gain is well chosen, the time the plant takes to reach a new setpoint
will be as short as possible, with overshoot (or undershoot) and oscillation minimized.

Unfortunately,
proportional
control
alone
is
not
sufficient
in
all
control
applications.
One
or
more
of
the
requirements
for
response
time,
overshoot,
and
oscillation may be impossible to fulfill at any proportional gain setting.

The
biggest
problem
with
proportional
control
alone
is
that
you
want
to
reach
new desired outputs quickly and avoid overshoot and minimize ripple once
you get
there.
Responding
quickly
suggests
a
high
proportional
gain;
minimizing
overshoot
and oscillation suggests a small proportional gain. Achieving both at the same time
may not be possible in all systems.

Fortunately, we do generally have (or can derive) information about the rate of
change of the plant's output. If the output is changing rapidly, overshoot or undershoot
may lie ahead.
In that case, we can reduce the size of the change suggested by the
proportional controller.

The rate of change of a signal is also known as its derivative. The derivative at the
current time is simply the change in value from the previous sample to the current one.
This implies that we should subtract a change of:

Differential
where D is a constant derivative gain. The only other thing we need to do is to
save the previous sample in memory.

In
practice,
proportional- derivative
(PD)
controllers
work
well.
The
net
effect
is
a
slower response time with far less overshoot and ripple than a proportional controller
alone.

Integration
A remaining problem is that PD control alone will not always settle exactly to the
desired output. In fact, depending on the proportional gain, it's altogether possible that
a PD controller will ultimately settle to an output value that is far from that desired.

The problem occurs if each individual error remains below the threshold for action by
the
proportional
term.
(Say
the
error
is
3,
P
=
1/8,
and
integer
math
is
used.)
The
derivative
term
won't
help
anything
unless
the
output
is
changing.
Something
else
needs to drive the plant toward the setpoint. That something is an integral term.

An integral is a sum over time, in this case the sum of all past errors in the plant
output
，
Even though the integral gain factor, I, is typically small, a persistent error
will eventually cause the sum to grow large and the integral term to force a change in
the
drive
signal.
In
practice,
the
accumulated
error
is
usually
capped
at
some
maximum and minimum values.
In
summary,
on-off
and
proportional
control
are
the
two
basic
techniques
of
closed-loop control. However, derivative and/or integral terms are sometimes added
to
porportional
controllers
to
improve
qualitative
properties
of
a
particular
plant's
response. When all three terms
are used together, the acronym
used to
describe the
controller is PID.