JP7840220B2 - Methods for feedback control, programs for feedback control, and filter systems - Google Patents

Description

This invention relates to a feedback control method and program for feedback control used in the control of a rotary filter device, as well as a filter system.

Rotary filter systems used in wastewater treatment and other applications are devices equipped with an endless strip filter consisting of multiple connected panel filters. By rotating this endless strip filter, the system regenerates the filter while separating solid matter from the treated water. In this type of system, the processing capacity can be adjusted by controlling the rotation speed of the endless strip filter.

For example, Japanese Patent Publication No. 8-177030 (Patent Document 1) discloses an operating method for a screen-type dust removal machine, which controls the machine to operate at high speed and then gradually reduce the operating speed when it detects that the water level has risen to a set level, and to stop or operate at a slow speed and remain in standby mode when the water level is below the set level. According to the operating method of Patent Document 1, unnecessary high-speed operation can be avoided.

Japanese Patent Application Publication No. 8-177030

However, in the technology described in Patent Document 1, the speed change when switching operating speeds is discontinuous. For example, a change in drive speed in a very short time can cause the chain and sprocket to become misaligned, increasing the risk of tooth skipping. This can lead to increased load on rotating equipment such as rotors. Therefore, there was a risk of shortening the lifespan of the rotary filter device.

Therefore, even when it is necessary to switch to operating conditions with different processing capacities, a control system for rotary filter devices that minimizes the load on the equipment is desirable.

The feedback control method according to the present invention is a feedback control method for a rotary filter device provided with an endless strip filter that is movable by the rotation of a rotor, wherein the feedback control is PI control or PID control, and the parameter set for the feedback control is set in advance to include at least a first parameter set and a second parameter set which is a parameter set in which the contribution of proportional operation is greater than that of the first parameter set, and the feedback control using the first parameter set is performed when at least one of the conditions represented by the following equations (1) and (2) is not satisfied, and the feedback control using the second parameter set is performed when the conditions represented by the following equations (1) and (2) are simultaneously satisfied.
L(t) > a (1)
L(t)-L(t-Δt)>b (2)
In the formula, L(t) is the water level on the primary side of the endless strip filter at a certain time t, Δt is a predetermined unit period relating to the period for determining the parameter set to be used, a is a predetermined threshold determined based on the configuration of the rotary filter device, and b is a predetermined threshold determined based on the capacity of the water level gauge that measures the water level.

Furthermore, the present invention relates to a program for feedback control of a rotary filter device provided with an endless strip filter that is movable by the rotation of a rotor, wherein the feedback control is PI control or PID control, and a first parameter set and a second parameter set which is a parameter set in which the contribution of proportional operation is greater than that of the first parameter set are set in advance as the parameter set of the feedback control, and the program realizes a determination function which determines whether each of the conditions represented by the following equations (1) and (2) is satisfied when executed by a computer, a first control function which performs feedback control using the first parameter set when the determination function determines that at least one of the conditions represented by the following equations (1) and (2) is not satisfied, and a second control function which performs feedback control using the second parameter set when the determination function determines that each of the conditions represented by the following equations (1) and (2) is satisfied simultaneously .
L(t) > a (1)
L(t)-L(t-Δt)>b (2)
In the formula, L(t) is the water level on the primary side of the endless strip filter at a certain time t, Δt is a predetermined unit period relating to the period for determining the parameter set to be used, a is a predetermined threshold determined based on the configuration of the rotary filter device, and b is a predetermined threshold determined based on the capacity of the water level gauge that measures the water level.

Furthermore, the filter system according to the present invention is a filter system comprising a rotary filter device provided with an endless strip filter that is movable by the rotation of a rotor, and a control device that performs feedback control of the rotary filter device, wherein the feedback control is PI control or PID control, and the control device is pre -set as a parameter set for the feedback control, a first parameter set and a second parameter set which is a parameter set in which the contribution of proportional operation is greater than that of the first parameter set, and the control device is configured to perform feedback control using the first parameter set when at least one of the conditions represented by the following equations (1) and (2) is not satisfied, and to perform feedback control using the second parameter set when the conditions represented by the following equations (1) and (2) are simultaneously satisfied.
L(t) > a (1)
L(t)-L(t-Δt)>b (2)
In the formula, L(t) is the water level on the primary side of the endless strip filter at a certain time t, Δt is a predetermined unit period relating to the period for determining the parameter set to be used, a is a predetermined threshold determined based on the configuration of the rotary filter device, and b is a predetermined threshold determined based on the capacity of the water level gauge that measures the water level.

With these configurations, feedback control is always performed regardless of which of the two parameter sets is used, allowing for continuous changes in the operating conditions of the device. Therefore, even when it is necessary to switch to operating conditions with different processing capacities, the device is less likely to be overloaded. With these configurations, operating conditions can be changed in accordance with the rise in water level, making it easier to prevent overflow on the primary side of the endless strip filter. With these configurations, the use of feedback control with the second parameter set can be limited to cases where there is a particularly high need. With these configurations, feedback control can be performed using an appropriate parameter set according to the degree of disturbance suppression required.

Further features and advantages of the present invention will become clearer through the following description of exemplary and non-limiting embodiments, with reference to the drawings.

This is a diagram showing the configuration of the filter system according to the embodiment. This is a flowchart illustrating the procedure of the feedback control method according to the embodiment.

Embodiments of the feedback control method, program, and filter system according to the present invention will be described with reference to the drawings. Below, an example of applying the feedback control method according to the present invention to the control of a rotary filter device 1 provided in a filter system 100 will be described.

[Filter system configuration]
The filter system 100 includes a rotary filter device 1 and a control device 2 (Figure 1).

The rotary filter device 1 is a rotary filter type sludge separation device having a filter unit 11. The filter unit 11 is provided in the form of an endless strip filter, for example, consisting of multiple panel filters with mesh sizes of 0.1 to 1.0 mm connected together. The rotary filter device 1 also has multiple rotors 12 for moving each panel filter of the filter unit 11. The rotors 12 are electrically connected to a control device 2 and transmit information regarding the operating status of the rotors 12 (such as rotational speed and current value) to the control device 2, and can also receive control signals from the control device 2 that determine the operating conditions of the rotors 12.

In the rotary filter device 1, a filter unit 11 is provided in a manner that crosses the flow path of the water to be treated W1 flowing into the rotary filter device 1. The filter unit 11 is positioned so as to be inclined from the upstream to the downstream side of the flow path of the water to be treated W1, and the panel filter moves from bottom to top on the primary side where the water to be treated W1 flows in due to the rotation of the rotor 12. The residue S contained in the water to be treated W1 is blocked by the filter unit 11, and the filtered water W2, which is the water in the water to be treated W1, passes through the filter unit 11. The residue S remaining on the panel filter of the filter unit 11 is transported as the panel filter moves and is detached from the filter unit 11 by the cleaning mechanism 13. The cleaning mechanism 13 includes, for example, a scraper 13a that scrapes off the residue S from the filter unit 11, and a spray 13b that sprays cleaning water from the back side of the filter unit 11 to detach the residue S from the filter unit 11.

A water level gauge 14 is provided on the primary side of the filter unit 11 of the rotary filter device 1, allowing detection of the water level on the primary side of the filter unit 11. The output of the water level gauge 14 is input to the control device 2.

The control device 2 is implemented as a known computer. Therefore, the control device 2 includes common computer components such as an arithmetic unit, memory device, and input/output device. The control device 2 has a control program installed for performing feedback control of the rotary filter device 1, and this control program is an example of a program according to the present invention. The control device 2 is electrically connected to the rotor 12 and the water level gauge 14, and can receive information regarding the operating state of the rotor 12 (rotation speed, current value, etc.) and the water level detected by the water level gauge 14, as well as transmit control signals that determine the operating conditions of the rotor 12. Such control signals are generated by the feedback control described below.

[Feedback control method]
The feedback control method according to this embodiment is implemented by executing a control program installed in the control device 2. In this embodiment, the feedback control is implemented as PI control, and two sets of PI control parameters are pre-set. The first set of parameters is used for normal control, and the second set of parameters is used for emergency control. An emergency is when the load on the rotary filter device 1 suddenly increases due to external factors such as rainfall or cleaning of the pumping station, and normal conditions are when there is no emergency. The two sets of parameters are stored in the memory of the control device 2 and are read as needed.

Comparing the two parameter sets, the second parameter set is configured to be more sensitive to disturbances than the first parameter set. Specifically, the second parameter set has a larger contribution from proportional motion (larger proportionality constant) compared to the first parameter set. Furthermore, while the integration time is shorter with the second parameter set than with the first, the variable is larger when the second parameter set is applied compared to when the first parameter set is applied. Therefore, the product of the variable and the integration time is equivalent in both cases. In other words, the contribution of integral motion is equivalent in both the first and second parameter sets. While adopting the second parameter set increases the effect of suppressing disturbances, regular use may lead to overshoot and increased load on the device itself (especially the rotor 12) due to repeated short-interval starts and stops. Therefore, in this embodiment, the second parameter set is adopted only when there is a strong need for disturbance suppression, i.e., in emergencies, and the first parameter set is adopted at all other times (normal operation).

The determination of whether it is a normal or emergency situation is made based on the output of the water level gauge 14 (water level on the primary side of the filter unit 11). Specifically, an emergency situation is determined when the conditions expressed in the following equations (1) and (2) are met simultaneously.
L(t) > a (1)
L(t)-L(t-Δt)>b (2)
In the formula, L(t) is the water level on the primary side of the filter unit 11 at a certain time t, Δt is a predetermined unit period, and a and b are predetermined thresholds.

Specifically, the determination is made according to the procedure shown in the flowchart 200 of Figure 2. The first determination is determination 201 based on equation (1), which is a determination regarding the current water level on the primary side of the filter unit 11. When the water level L(t) at a certain time t is below a predetermined threshold a (determination 201: no), it can be said that there is sufficient capacity on the primary side of the filter unit 11 to accept the water to be treated W1. In this case, even if the inflow rate of the water to be treated W1 increases due to a disturbance, the acceptance of the water to be treated W1 can continue, and therefore, a transition to emergency control is not necessary. Therefore, if the condition of equation (1) is not met, it is determined that it is a normal situation without performing the determination of equation (2) (process 205), and feedback control using the first parameter set is continued (process 206). On the other hand, if the condition of equation (1) is met (determination 201: yes), the determination of equation (2) is then performed.

The second determination is determination 202 based on equation (2), and concerns the rate of rise in water level. When the amount of rise in water level L(t) - L(t - Δt) in the unit period Δt immediately preceding a certain time t is less than or equal to a predetermined threshold b (determination 202: no), it can be said that the balance of the treated water W1 is roughly balanced. In this case, even if the water level is greater than threshold a, the possibility of a sudden rise in the water level is small, and therefore, a transition to emergency control is not necessary. Therefore, even if the conditions of equation (1) are met, if the conditions of equation (2) are not met, it is determined that it is a normal state (process 205), and feedback control using the first parameter set is continued (process 206).

On the other hand, if the condition of equation (2) is met (Judgment 202: Yes), then both equations (1) and (2) are met simultaneously, the water level is relatively high, and the inflow of treated water W1 is greater than the processing rate (the balance of treated water W1 is not balanced). In this case, it is determined to be an emergency (Process 203). At this time, it is necessary to temporarily increase the processing rate of the rotary filter device 1 to prevent overflow of treated water W1, so feedback control using the second parameter set is performed (Process 204). As described above, the second parameter set is more sensitive to disturbances than the first parameter set, so it can react sensitively to a rapid rise in water level and increase the output of the rotor 12, thereby smoothly and quickly increasing the processing rate of the rotary filter device 1.

Subsequently, the same flow of judgment is repeated to appropriately select the parameter set used for feedback control according to the situation at the time the judgment was made.

The threshold value a can be set considering conditions such as the capacity of the rotary filter device 1, the normal inflow rate of the water to be treated W1 at the installation location of the rotary filter device 1, the rated capacity of the rotor 12, and the processing capacity of the control device 2. As an example, the threshold value a may be 60-70% of the full water level on the primary side of the filter unit 11.

The threshold b and unit period Δt can be set considering the capabilities of the water level gauge 14. For example, if we want to determine that an emergency has occurred when the rate of rise in the water level exceeds 0.5 cm per second in the second determination (determination 202), the combination of threshold b and unit period Δt is not limited as long as b = 0.5 Δt, so there are infinitely many combinations such as 1 cm and 2 seconds, 2 cm and 4 seconds, 3 cm and 6 seconds, etc. Here, it can be said that adopting a combination with a short unit period Δt is preferable in that the determination of an emergency is less likely to be delayed. On the other hand, if the threshold b is excessively small, the amount of rise in water level L(t) - L(t - Δt) compared with the threshold b will fall below the smallest unit of difference in water level that the water level gauge 14 can detect, and the reliability of the detected value of the amount of rise in water level L(t) - L(t - Δt) will be impaired, thus reducing the accuracy of the second determination (determination 202). Therefore, the threshold b and the unit period Δt can be determined as a combination of threshold b and unit period Δt that gives an appropriate value for threshold b considering the accuracy of the water level gauge 14, while also providing the rate of water level rise when an emergency is determined.

For example, the unit period Δt can be the period used to determine whether a situation is normal or an emergency. In this case, the rise in water level L(t) - L(t - Δt) can be defined as the difference between the water level L(t) at the time of determination in a given period and the water level L(t - Δt) at the time of determination one period prior to that period. That is, by repeatedly recording the water level at intervals of unit period Δt, the condition of equation (2) can be determined to be satisfied when the difference between the latest water level and the water level one period prior exceeds the threshold b.

[Other Embodiments]
Finally, other embodiments of the feedback control method, program, and filter system according to the present invention will be described. Note that the configurations disclosed in each of the following embodiments may be applied in combination with configurations disclosed in other embodiments, provided that this does not create a conflict.

In the above embodiment, an example was described in which the predetermined conditions for determining the parameter set used for feedback control are expressed by equations (1) and (2). However, in the feedback control method according to the present invention, the predetermined conditions for determining the parameter set used for feedback control are not limited. That is, the conditions may be based on the water level, as in the above embodiment, or they may be based on other physical properties of the water to be treated (such as flow rate, suspended solids (SS), turbidity, etc.).

In the above embodiment, a configuration in which the second parameter set contributes more to proportional operation than the first parameter set was described as an example, but the invention is not limited to this configuration. In the feedback control method according to the present invention, the relationship between the first parameter set and the second parameter set is such that it is possible to realize control suitable for each of the two states separated by predetermined conditions, according to the purpose of setting predetermined conditions for determining the parameter set to be used for feedback control.

In the above embodiment, a configuration in which feedback control is implemented as PI control was described as an example. However, the feedback control according to the present invention is not limited to PI control; for example, it may be PID control.

Regarding other configurations, the embodiments disclosed herein are illustrative in all respects, and it should be understood that the scope of the present invention is not limited thereto. Those skilled in the art will readily understand that modifications can be made as appropriate without departing from the spirit of the invention. Therefore, other embodiments modified without departing from the spirit of the invention are naturally included within the scope of the present invention.

This invention can be used, for example, for sludge separation in activated sludge treatment facilities.

100: Filter system 1: Rotary filter device 11: Filter unit 12: Rotor 13: Washing mechanism 13a: Scraper 13b: Spray 14: Water level gauge 2: Control device S: Debris W1: Water to be treated W2: Filtered water

Claims (3)

A method for feedback control of a rotary filter device equipped with an endless strip filter that is movable by the rotation of a rotor,
The aforementioned feedback control is PI control or PID control,
As the parameter set for the feedback control, at least a first parameter set and a second parameter set which has a greater contribution to proportional operation compared to the first parameter set are set in advance .
If at least one of the conditions expressed by the following equations (1) and (2) is not met, feedback control using the first parameter set is performed.
A feedback control method that performs feedback control using the second parameter set when the conditions expressed by the following equations (1) and (2) are simultaneously satisfied.
L(t) > a (1)
L(t)-L(t-Δt)>b (2)
In the formula, L(t) is the water level on the primary side of the endless strip filter at a certain time t, Δt is a predetermined unit period relating to the period for determining the parameter set to be used, a is a predetermined threshold determined based on the configuration of the rotary filter device, and b is a predetermined threshold determined based on the capacity of the water level gauge that measures the water level. A program for feedback control of a rotary filter device equipped with an endless strip filter that is movable by the rotation of a rotor,
The aforementioned feedback control is PI control or PID control,
As the parameter set for the feedback control, a first parameter set and a second parameter set, which is a parameter set in which the contribution of proportional operation is greater than that of the first parameter set , are set in advance.
When executed by a computer,
A determination function that determines whether each of the conditions expressed by the following equations (1) and (2) is met,
When the determination function determines that at least one of the conditions represented by the following equations (1) and (2) is not met, a first control function performs feedback control using the first parameter set,
A program that implements a second control function that performs feedback control using the second parameter set when the determination function determines that the conditions expressed by the following equations (1) and (2) are simultaneously met.
L(t) > a (1)
L(t)-L(t-Δt)>b (2)
In the formula, L(t) is the water level on the primary side of the endless strip filter at a certain time t, Δt is a predetermined unit period relating to the period for determining the parameter set to be used, a is a predetermined threshold determined based on the configuration of the rotary filter device, and b is a predetermined threshold determined based on the capacity of the water level gauge that measures the water level. A filter system comprising: a rotary filter device provided with an endless strip filter that is movable by the rotation of a rotor; and a control device that performs feedback control of the rotary filter device,
The aforementioned feedback control is PI control or PID control,
The control device is pre-configured with a first parameter set and a second parameter set, which is a parameter set whose contribution to proportional operation is greater than that of the first parameter set , as the parameter sets for the feedback control.
The control device,
If at least one of the conditions expressed by the following equations (1) and (2) is not met, feedback control using the first parameter set is performed.
A filter system configured to perform feedback control using the second set of parameters when the conditions expressed by equations (1) and (2) below are simultaneously satisfied.
L(t) > a (1)
L(t)-L(t-Δt)>b (2)
In the formula, L(t) is the water level on the primary side of the endless strip filter at a certain time t, Δt is a predetermined unit period relating to the period for determining the parameter set to be used, a is a predetermined threshold determined based on the configuration of the rotary filter device, and b is a predetermined threshold determined based on the capacity of the water level gauge that measures the water level.