JP2909747B2 - Controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a controller having an auto-tuning function by a limit cycle method, and in particular, to find a quick and optimal PID constant even in a special case. Related to what can be done.

<Conventional Technology> As a conventional controller having an auto-tuning function by a limit cycle method, for example, there is a controller as shown in FIG. In this controller, the PID control unit is omitted.

In this controller, 1 is a control amount (PV) input
A / D converter, 2 is a setting unit that sets the set value (SV), 3 is a deviation calculation unit that calculates the deviation between the control amount (PV) and the set value (SV), and 4 is an auto tuning for PID control Reference numeral 5 denotes an ON / OFF control unit of the auto tuning unit 4, and reference numeral 6 denotes a D / A converter that outputs an operation signal (MV).

The auto-tuning unit 4 includes the ON / OFF control unit 5
In addition, it comprises a tuning management unit 10, a limit cycle measurement unit 11, a PID constant calculation unit 12, and a PID constant change unit 13.

As is well known, in a controller of this type, when PID control is performed on a control target, for example, a heating furnace or the like, an optimum P
Since it is necessary to know the ID constant, first, the auto-tuning unit 4 executes auto-tuning to determine the optimal PID.
A constant is obtained, and the target PID control is performed using the constant.

<Problem to be Solved by the Invention> As one method of this auto-tuning, a control object is controlled to be ON / OFF, and a limit cycle for obtaining a PID constant from a cycling waveform (limit cycle) of the control amount (PV). There is a method, which is often used, but in a special case, it may not be possible to quickly and optimally determine the PID constant.

For example, (1) in the case where the auto-tuning is started from a state where the control amount (PV) is almost stable near the set value (SV), the initial deviation (e) is small, so that the amplitude of the limit cycle becomes Since it starts to occur with the amplitude smaller than the original amplitude, it takes a long time (how many cycles) until a stable amplitude limit cycle is obtained.
A decrease in workability is inevitable. However, if the calculation of the PID constant is performed before the limit cycle is stabilized, there arises a problem that an optimum PID constant cannot be obtained.

(2) Some control targets have a very short dead time. On the other hand, when the auto-tuning by the limit cycle method is performed, the limit cycle itself does not occur (is not obtained), or In some cases, only a very small amplitude limit cycle can be obtained. In this case, there are problems that the measurement is difficult and that an optimum PID constant cannot be obtained.

(3) In the auto tuning by the limit cycle method, the sign of the deviation (e) (+
ON / OFF to change the output to ON or OFF by or)
The control is performed to measure the resulting limit cycle to calculate the optimum PID constant. At this time, if there is a large noise, the deviation (e) is affected by the noise and the deviation (e) is instantaneously changed. In some cases. Also, even if the noise is small, if the movement (slope) of the control amount (PV) near the set value (SV) is very gentle,
Similar things can happen. If ON / OFF is changed in response to the instantaneous change of the deviation code, a problem arises that an optimum PID constant cannot be obtained.

The present invention has been made in view of such conventional circumstances.

<Means for Solving the Problems> A feature of the present invention is that an automatic tuning unit using a limit cycle method for PID control is provided.
A PID constant for a control target is obtained by auto tuning, and the controller uses the constant to perform PID control of a control amount (PV) and outputs an operation signal (MV). An ON / OFF output sample / hold unit that samples and holds the output from the / OFF control unit is provided, and the control of this ON / OFF output sample / hold unit is controlled by the dead time and time managed by the output holding time management unit. The hysteresis is performed based on the input dead time managed by the input dead time management unit.

<Operation> Therefore, in the controller of the above configuration, the output from the ON / OFF control unit is controlled using the dead time, the time hysteresis, and the input dead time according to each case.
Even in the above-mentioned unique case, optimal PID control is required.

<Embodiment> FIG. 1 shows an embodiment of a controller according to the present invention.

This controller is the same as the above-described controller of FIG. 10 except for the additional device, and the same components as those of the controller are denoted by the same reference numerals.

The auto-tuning unit 40 of the controller is an ON / OFF control unit that samples and holds the output from the ON / OFF control unit 5 in addition to the ON / OFF control unit 5 in the auto-tuning unit 4 in FIG.
/ OFF output sample / hold unit 41, dead time calculation unit 42 that receives a measurement signal from limit cycle measurement unit 11 and calculates dead time (L), and uses dead time (L) and time hysteresis as output holding time. An output holding time management unit 43 to be managed; a setting unit 44 for setting time hysteresis in the output holding time management unit 43; a control amount (PV) and a set value (SV)
The input dead time management unit 46 to which both the current deviation (e) and the deviation (e) at the time of updating the output held by the deviation sample / hold unit 45 are input, and a setting unit 47 for setting the input dead time Receiving a time lapse signal from the output holding time management unit 43 and a time lapse signal from the input dead time management unit 46,
An ON / OFF output sample / hold unit 41, an output holding time management unit 43, a deviation sample / hold unit 45, and an output update control unit 48 for updating the output by the input dead time management unit 46 are added.

Next, the operation of the controller configured as described above will be described in the second section.
This will be described below with reference to the flowchart in FIG.

When auto-tuning is started, until the auto-tuning is completed, the processing from Step S ₁ to Step S ₉ are repeated every predetermined sampling period. When the processing of each sample in step S ₁ is being started,
In step S _2, the auto-tuning start time determining whether or not.

And in case of YES at the start (first time),
In step S _3, it calculates the output in ON / OFF control unit 5. In step S _4, the calculated value, the signal from the output update control unit 48, and a sample with ON / OFF output sample / hold unit 41, updated and maintained.

In step S _5, it is set as the output hold time to the output holding time management unit 43 the dead time calculated in the dead time calculation unit 42 (L). In step S _6, it performs the initialization processing for the input dead time determination of the input dead time management unit 46. The input dead time is set by the setting unit 47.

The dead time is calculated, for example, under the conditions shown in FIG. 3 as follows. FIG. 3 shows a limit cycle of the control amount (PV) and waveforms of the operation signal (MV) and the set value (SV) when auto tuning is performed by a general limit cycle method.

The dead time (L) is represented by L = (L ₃ + L ₄ ) / 2 (1).

Here, SV is a set value, PV is a control amount, MV is an operation signal, L
_{Reference numerals 1 to 4} denote dead times obtained by measuring the limit cycle generated by the auto tuning by the limit cycle measuring unit 11.

In calculating the dead time (L), the dead time L ₃ ,
L ₄ and that used is because a value when the limit cycle has entered a stable period.

When the auto-tuning is completed in this way, the dead time (L) is calculated. In the second and subsequent auto-tunings, the previously calculated dead time (L) is set as the dead time (L) set to the output holding time at the start of the auto-tuning. L) is used, but when the auto-tuning has not been executed even once, a roughly appropriate value is set depending on the control target.

In step S _7, measurements are taken of the limit cycle auto-tuning, in step S _8, the limit cycle is a predetermined number of cycles, for example, 2 in the cycle has occurred, performs auto tuning completion determination, not ended
If NO, the leads to the end of step S _9, subsequently, repeats the execution of the auto-tuning. Meanwhile, finished
If YES, the Step S _10, and the PID constants of interest,
Calculate the dead time.

Further, in step S _2, the case of NO auto-tuning is not at the start (second and subsequent), the process proceeds to step S _11, whether the output holding time that is managed by the output holding time management unit 43 has elapsed And if NO, step S ₇
Proceed to limit cycle measurement.

If YES the output hold time has elapsed, the process proceeds to step S _12, the input dead time management unit 46, the control amount (PV) and the current deviation (e) and deviation sample / hold unit setting (SV)
45 signs of both the deviation (e) at the time of output updating last held are compared by, in the case of YES in the same sign "=" in step S _13, the initial for the input dead time determination performs processing proceeds to limit cycle measurement in the step S _7.

Both in the case of NO different signs "≠", the flow proceeds to step S _14, wherein, to determine the course of the input dead time. Input dead time in the case of NO not elapsed, the process proceeds to the limit cycle measurement in the step S _7.

If the input dead time has elapsed and the answer is YES, go to step S
_{At 15} , the output of the ON / OFF control unit 5 is calculated. Then, in step S _16, the calculated value, the signal from the output update control unit 48, and a sample with ON / OFF output sample / hold unit 41, updated and maintained.

On the other hand, in step S _17, the time hysteresis setting unit 44, as the output hold time is set to the output holding time management unit 43.

Next, in step S _18, performs initialization processing for input dead time determination of the input dead time management unit 46, and thereafter, the process proceeds to the limit cycle measurement in the step S _7.

In other words, the controller uses the ON / OFF control unit 5 of the auto tuning unit 4 in addition to the normal auto tuning.
Is controlled using the dead time and time hysteresis managed by the output holding time management unit and the input dead time managed by the input dead time management unit. Auto-tuning starts when the setting is almost stable near the set value (SV),
Case where the dead time of the controlled object is extremely short, control amount (PV)
It is possible to optimally cope with a special case such as a case where there are various types of noise.

 Hereinafter, this point will be described more specifically.

(1) The case where auto tuning is started in a state where the control amount (PV) is almost stable near the set value (SV).

For example, when the initial deviation (e) is small, in the conventional controller, the control amount (PV) is immediately changed every time the sign of the deviation (e) of the set value (SV) changes as shown in FIG. ON / OFF
Since the control is repeated, it takes a long time (how many cycles) until the limit cycle is stabilized. Naturally, if the PID constant is obtained at a stage where the limit cycle is not sufficiently stabilized, the optimum PID constant cannot be obtained.

On the other hand, in the present controller, as shown in FIG. 4, the control amount (PV) and the set value (SV) only during the output holding time (dead time (L)) of the output holding time management unit 43. ), The output of the first ON / OFF control unit 5 at the start of auto-tuning by the ON / OFF output sample / hold unit 41 during the dead time (L) even if the sign of the deviation (e) changes As a result, rapid stabilization of the limit cycle can be achieved.

Therefore, an extremely quick and optimal PID constant can be obtained.

(2) A case where the dead time of the control target is extremely short.

For example, when auto-tuning is performed on a control object having a very short dead time using a conventional controller, the amplitude of the limit cycle becomes very small as shown in FIG. In addition, since such a controller is realized using a microcomputer, the dead time is a sampling period (control period).
When the limit cycle is approached, the amplitude and cycle of the limit cycle become unstable depending on the sampling cycle, making stable measurement difficult, and a normal PID constant cannot be obtained.

On the other hand, in this controller, as shown in FIG. 6, the input condition when the output of the ON / OFF control unit 5 is different from the output held by the ON / OFF output sample / hold unit 41. That is, even when the sign of the deviation held in the deviation sample / hold unit 45 differs from the sign of the current deviation when the ON / OFF output sample / hold unit 41 was updated last time, the state is the input dead time. If it is not continuous for more than the input dead time of the management unit 46, the ON / OFF output sample / hold unit
Since the output of 41 is not updated, a stable limit cycle with a reasonable amplitude can be obtained.

In other words, this is the minimum dead time for obtaining a stable limit cycle for the controlled object.
This is equivalent to inserting the input dead time.

Note that, as the input dead time, a small value (about 10 times the sampling period as a guide) is given so that the sampling period can be ignored and does not significantly affect the PID constant.

As a result, it becomes possible to stabilize the limit cycle and to calculate an appropriate PID constant.

(3) Case with noise.

For example, when a large amount of noise is present in the control amount (PV) as shown in FIG. 8, the conventional controller changes the deviation (e) instantaneously,
Since the ON / OFF control is repeated, the output of the ON / OFF control unit 5 takes the form of a waveform 60, and a normal limit cycle cannot be obtained.

On the other hand, in the present controller, even if the sign of the deviation (e) between the control amount (PV) and the set value (SV) changes as shown by the waveform 61 in FIG. The output of the ON / OFF output sample / hold unit 41 will not be updated unless the input dead time (T _{1 in the} figure) of the unit 46 continues for more than the input dead time, so that the operation signal (MV) will not be updated.

Further, the change of the sign of the deviation (e) continues for more than the input dead time (T _{1 in the} figure), and the ON / OFF output sample / hold device
When the output of 41 is updated and the operation signal (MV) is updated,
If the output holding time (time hysteresis, T _{2 in} the figure) of the output holding time management unit 43 has not elapsed from that point, the input dead time is not determined, and the output of the ON / OFF output sample / hold unit 41 is updated again. Operation signal (M
V) is not updated, so it is not affected by noise and the optimal P
ID constant can be obtained.

Even if the noise is small as shown in FIG. 9, when the movement (slope) of the control amount (PV) in the vicinity of the set value (SV) is very gentle, the conventional controller is still used. Each time the sign of the deviation (e) changes, the ON / OFF control is immediately repeated in response to the change, so that the output of the ON / OFF control unit 5 takes the form of a waveform 62 and a normal limit cycle Could not be obtained.

On the other hand, in the present controller, even if the sign of the deviation (e) between the control amount (PV) and the set value (SV) changes as shown by the waveform 63 in FIG. The output of the ON / OFF output sample / hold unit 41 is not updated unless the input dead time (T _{1 in the} drawing) continues for the input dead time of the unit 46, and the operation signal (MV)
Is not updated, so it is not affected by noise.

Therefore, a normal limit cycle can be obtained and an optimal PID constant can be obtained as described above.

In other words, in this controller, at the start of auto tuning, the amplitude of the limit cycle is smaller than the original amplitude, and it takes a long time to obtain a stable limit cycle with a large amplitude, In the case of a control target with a very short time, a long dead time can be set to obtain a stable limit cycle with a large amplitude in a short time. With respect to the change of the deviation signal, the time hysteresis is set so that the optimum limit cycle can be obtained without being affected by the change of the sign of the deviation (e).

Although not shown, the controller of the present invention incorporates a microcomputer as a controller for various calculations and controls.

<Effects of the Invention> As is clear from the above description, according to the controller of the present invention, the auto-tuning section of the controller provided with the auto-tuning section based on the limit cycle method is provided with the auto-tuning ON / OFF control section. An ON / OFF output sample / hold unit that samples and holds the output is provided.
Since the output sample / hold unit is controlled by the dead time and time hysteresis managed by the output holding time management unit and the input dead time managed by the input dead time management unit, the normal auto tuning is executed. Of course, the following excellent effects can be obtained.

(1) Even if auto-tuning is started when the control amount (PV) is almost stable near the set value (SV), a stable limit cycle is quickly obtained and the optimal PID constant is obtained. be able to.

(2) Even if the dead time of the controlled object is extremely short, a stable amplitude limit cycle is obtained and a reasonable PID
Constants can be obtained.

(3) Even in the case where the control amount (PV) includes various noises, an optimum PID constant can be obtained without being affected by the noise.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the controller according to the present invention, FIG. 2 is a flowchart showing an operation flow of the controller, FIG. 3 is a graph for obtaining dead time, FIG.
FIG. 5 is a graph showing the operation state of the present controller when the deviation is small, FIG. 5 is a graph showing the operation state of the conventional controller when the deviation is small, and FIG. 6 is the control target of the present controller. FIG. 7 is a graph showing the operation state when the dead time is short, FIG. 7 is a graph showing the operation state when the dead time of the control target of the conventional controller is short, and FIG. Fig. 9 is a graph showing both the operation state of the controller and the conventional controller. Fig. 9 shows the operation of the controller and the conventional controller when the noise is small and the control amount (PV) moves very slowly. FIG. 10 is a block diagram showing a controller according to a conventional example. In the figure, 2 ... setting unit, 3 ... deviation calculation unit, 5 ... ON / OFF control unit, 40 ... auto tuning unit, 41 ... ON / OFF output sample / hold unit, 42 ... dead time calculation Unit, 43: Output holding time management unit, 44: Time hysteresis setting unit,
45: Deviation sample / hold unit, 46: Input dead time management unit, 47: Input dead time setting unit, 48: Output update control unit

Claims (3)

(57) [Claims] An automatic tuning unit based on a limit cycle method for PID control is provided.
A constant is obtained by auto-tuning, a PID control of the control amount (PV) is performed using the constant, and the controller outputs an operation signal (MV).
ON / OFF output sample / hold unit that samples and holds the output from the / OFF control unit, dead time calculation unit that calculates the dead time from the limit cycle measurement, and output holding that manages the dead time as the output holding time A time management unit and a time lapse signal from the output holding time management unit;
/ OFF Updates the output of the output sample / hold unit and adds an output update control unit that outputs an output holding time initialization signal to the output holding time management unit. A controller characterized in that the first output of the / OFF control unit is held by an ON / OFF output sample / hold unit until a dead time managed by an output holding time management unit has elapsed. 2. An automatic tuning unit according to a limit cycle method for PID control, wherein a PID for a control object is provided.
A constant is obtained by auto-tuning, a PID control of the control amount (PV) is performed using the constant, and the controller outputs an operation signal (MV).
ON / OFF output sample / hold unit that samples and holds the output from the / OFF control unit, and the control amount (PV) and set value (S
Both the present deviation (e) of V) and the deviation (e) at the time of the previous output update held by the deviation sample / hold unit are input, and it is determined that the different sign state of the deviation continues for the input dead time. An input dead time management unit, a setting unit for setting an input dead time, and a time lapse signal from the input dead time management unit, the ON / OFF output sample / hold unit;
The output of the deviation sample / hold unit is updated, and an output update control unit that outputs an input dead time initialization signal is added to the input dead time management unit. When the output of the control unit is inverted, the output before the inversion of the ON / OFF control unit is used by the ON / OFF output sample / hold unit until the input dead time managed by the input dead time management unit elapses. A controller characterized by holding. 3. An automatic tuning unit based on a limit cycle method for PID control, wherein a PID for a control target is provided.
A constant is obtained by auto-tuning, a PID control of the control amount (PV) is performed using the constant, and the controller outputs an operation signal (MV).
An ON / OFF output sample / hold unit that samples and holds the output from the / OFF control unit, a setting unit that sets time hysteresis, an output holding time management unit that manages time hysteresis as the output holding time, and a control amount Both the current deviation (e) of (PV) and the set value (SV) and the deviation (e) at the time of the previous output update held by the deviation sample / hold unit are input. An input dead time management unit that determines that the time is continuous, a setting unit that sets the input dead time, and a time lapse signal from the output holding time management unit. And the function of outputting the initialization signal of the above, and receiving the time lapse signal from the input dead time management unit, updating the outputs of the ON / OFF output sample / hold unit and the deviation sample / hold unit, and An output update control unit having a function of outputting an output holding time initialization signal is added to the output holding time management unit, and when the output of the ON / OFF control unit is inverted during execution of auto tuning. ON
The output before inversion of the / OFF control unit is held by the ON / OFF output sample / hold unit until the input dead time managed by the input dead time management unit elapses,
A controller that holds an output that has been switched once during a time hysteresis managed by an output holding time management unit.