PLC-based sewage and flue gas desulfurization collaborative control method and system

Abstract

The application discloses a sewage and flue gas desulfurization collaborative control method and system based on PLC, and relates to the technical field of industrial process automatic control, and comprises the following steps: when the limited state of a first control loop is removed and a control demand corresponding to a control amount not executed still exists, obtaining a safety margin of a second control loop relative to a preset unsafe boundary and a resource margin of a power supply resource; storing the control amount not executed during the limitation period separately, so as to separate the control amount from an integral amount of a closed-loop controller; combining the safety margin of another loop and the available margin of the shared power supply resource, and periodically and conditionally releasing the historical unexecuted amount; and according to an actual action increment of an executing mechanism, the released amount is reduced, so that the historical demand after the limitation is removed is smoothly released, the released amount strictly corresponds to the actual completed amount of the executing mechanism, and the determination of the collaborative control in the scene where the multiple loops share the limited resource is improved.

Description

Technical Field

[0001] This invention relates to the field of industrial process automatic control technology, and in particular to a PLC-based method and system for coordinated control of wastewater and flue gas desulfurization. Background Technology

[0002] With the continuous deepening of industrialization, wastewater treatment and flue gas desulfurization have become two core links in the field of environmental protection. Programmable logic controllers (PLCs) have been widely used in the above-mentioned process systems due to their high reliability, strong real-time performance and flexible configuration capabilities.

[0003] In the field of wastewater treatment, PLCs have been deeply integrated into various stages, including influent systems, aeration systems, chemical dosing systems, effluent systems, pretreatment, biological treatment, sedimentation, and posttreatment. This has resulted in a mature control architecture based on closed-loop PID regulation, sequential control, and interlocking protection. Currently, most wastewater treatment plants both domestically and internationally employ PLC-based automatic control systems, achieving decentralized control and centralized management through multiple PLC subsystems. Similarly, in the field of flue gas desulfurization, PLCs are widely used in the control of key components such as absorption tower systems, absorbent preparation and supply systems, and sulfur dioxide absorption and oxidation systems.

[0004] However, existing integral separation or anti-integral saturation strategies have shortcomings in scenarios where multiple loops share limited resources: During periods of resource constraints, the "saturation quantity" accumulated by the integrator will be mixed with the normally generated integral components after the constraints are lifted, making them indistinguishable. Furthermore, the system does not use a separate data structure to specifically record the control quantities that could not be actually executed due to resource constraints, nor does it perform closed-loop verification between the "quantities to be released" and the "actually executable quantities." As a result, the integral quantity written to the control output during the saturation period is directly regarded as having been executed, and even if the actuator does not respond at all due to insufficient resources, this part of the output will not be rolled back. Summary of the Invention

[0005] In a first aspect, the present invention provides a PLC-based method for coordinated control of wastewater and flue gas desulfurization, wherein the wastewater treatment control loop and the flue gas desulfurization control loop share a power supply resource with an available upper limit, comprising: The control loop in the restricted state is designated as the first control loop, and the other control loop is designated as the second control loop. The system obtains the requested control quantity of the first control loop and the actual execution representation quantity fed back by the actuator. It converts the actual execution representation quantity into an actual execution quantity with the same dimension as the requested control quantity. It updates the unexecuted control quantity based on the uncompleted difference between the requested control quantity and the actual execution quantity, and stores the unexecuted control quantity independently of the closed-loop control integral quantity of the first control loop. When the restricted state of the first control loop is lifted and the control requirement corresponding to the unexecuted control quantity still exists, obtain the safety margin of the second control loop relative to the preset unsafe boundary and the resource margin of the power supply resources. The allowable release amount is determined based on the unexecuted control amount, safety margin, and resource margin. The allowable release amount is then superimposed on the current control output of the first control loop to form the target control output, which is then sent to the actuator of the first control loop. Obtain the actual execution increment of the first control loop actuator corresponding to the allowable release quantity, and deduct the unexecuted control quantity according to the actual execution increment; When the safety margin or resource margin does not meet the release conditions, the release of the remaining unexecuted control quantities is suspended, and the release continues after the safety margin and resource margin meet the release conditions again.

[0006] Preferably, the power supply resource is the available active power capacity of the power supply bus shared by the sewage treatment control loop and the flue gas desulfurization control loop, and the occupancy of the power supply resource by the two control loops is expressed by the actual active power of the corresponding actuators. The restricted state includes at least one of the following: actuator failure, manual control, local control, output limiting, limited output rate of change, and insufficient power supply resources.

[0007] Preferably, when the control direction of the unfulfilled difference is consistent with the current adjustment demand direction of the first control loop, the unexecuted control increment corresponding to the unexecuted difference is accumulated to the unexecuted control quantity; When the control direction is opposite to the current adjustment demand direction, the accumulation stops, and the unexecuted control quantity is reduced according to the control quantity corresponding to the current adjustment demand in the opposite direction, and the reduction amount does not exceed the remaining unexecuted control quantity.

[0008] Preferably, a storage limit and validity period are set for unexecuted control quantities; When the amount of unexecuted control reaches the storage limit, stop accumulating new unexecuted control increments and maintain the amount of unexecuted control at the storage limit. When the controlled parameter of the first control loop recovers to the preset stable range, the release stops and the unexecuted control quantity corresponding to the disappeared control requirement is cleared; When the corresponding control requirements are fulfilled by other implementing agencies, the amount of unexecuted control shall be reduced according to the amount of control actually completed by the other implementing agencies. When the validity period expires, any remaining unexecuted control quantities will be cleared.

[0009] Preferably, when the second control loop is a wastewater treatment control loop, the safety margin is determined based on the difference between the measured dissolved oxygen value in the biological treatment tank and the minimum allowable dissolved oxygen value. When the second control loop is a flue gas desulfurization control loop, the safety margin is determined based on the difference between the maximum allowable concentration of sulfur dioxide in the outlet flue gas and the actual measured concentration of sulfur dioxide in the outlet flue gas.

[0010] Preferably, the safety margin is corrected according to the direction and rate of change of the controlled parameter of the second control loop relative to the preset unsafe boundary. Specifically, when the controlled parameter changes toward the preset unsafe boundary, the safety margin is reduced according to the rate of change, and when the controlled parameter changes away from the preset unsafe boundary, the safety margin is increased according to the rate of change. The larger of the current resource occupancy of other loads, the current basic requested resource occupancy of the first control loop, and the actual resource occupancy, and the current requested resource occupancy of the second control loop, is subtracted from the available upper limit of power supply resources. The resulting non-negative result is determined as the resource reserve.

[0011] Preferably, according to a preset conversion relationship, the safety margin and resource margin are converted into a first release limit and a second release limit with the same dimension as the unexecuted control quantity, respectively. The third release limit is determined based on the execution quantity that the first control loop actuator can increase in a single release cycle. The minimum value among the remaining unexecuted control quantity, the first release limit, the second release limit, and the third release limit is determined as the allowable release quantity. The unexecuted control quantity is then allocated to multiple release cycles for release.

[0012] Preferably, during the feedback sampling period for determining the actual execution increment, the basic control output of the first control loop without superimposed additional control output remains unchanged; Before the target control output is sent, the reference execution rate of the first control loop actuator is obtained, and the reference execution amount is determined based on the reference execution rate and the feedback sampling duration. The actual cumulative execution amount of the first control loop actuator is obtained during the feedback sampling period. The smaller of the non-negative difference value that is consistent with the direction of the additional control output and the allowable release value obtained by subtracting the reference execution amount from the actual cumulative execution amount is determined as the actual execution increment. The unexecuted control quantity is deducted based on the actual executed increment. When no actual executed increment is generated, the unexecuted control quantity is not deducted.

[0013] Preferably, when the safety margin of the second control loop is lower than the pause threshold, the power supply is restricted again, or the execution feedback of the first control loop is abnormal, the release quantity will be set to zero and the remaining unexecuted control quantity will be retained. When the safety margin reaches the recovery threshold above the pause threshold, the power supply resources meet the release conditions again, the execution feedback is normal, and it is reconfirmed that the control demand corresponding to the remaining unexecuted control quantity still exists and its control direction is consistent with the current adjustment demand direction of the first control loop, the remaining unexecuted control quantity continues to be released.

[0014] Secondly, the present invention provides a PLC-based wastewater and flue gas desulfurization coordinated control system, comprising: The control loop determination module is used to determine a control loop in a restricted state as the first control loop and another control loop as the second control loop. The unexecuted management module is used to obtain the requested control quantity of the first control loop and the actual execution representation quantity fed back by the actuator, convert the actual execution representation quantity into an actual execution quantity with the same dimension as the requested control quantity, update the unexecuted control quantity according to the unfinished difference between the requested control quantity and the actual execution quantity, and store the unexecuted control quantity independently of the closed-loop control integral quantity of the first control loop. The release condition acquisition module is used to acquire the safety margin of the second control loop relative to the preset unsafe boundary and the resource margin of the power supply resources when the restricted state of the first control loop is released and the control requirement corresponding to the unexecuted control quantity still exists. The release output generation module is used to determine the allowable release amount based on the unexecuted control amount, safety margin and resource margin, convert the allowable release amount into an additional control output with the same dimension as the current control output of the first control loop, superimpose the additional control output onto the current control output of the first control loop to form the target control output, and send the target control output to the actuator of the first control loop. The incremental deduction module is used to obtain the actual execution increment of the first control loop actuator corresponding to the additional control output, and deduct the unexecuted control quantity according to the actual execution increment; The pause and recovery module is used to control the release output generation module to pause the release of the remaining unexecuted control quantities when the safety margin or resource margin does not meet the release conditions, and to control the release output generation module to continue releasing the remaining unexecuted control quantities after the safety margin and resource margin meet the release conditions again.

[0015] The beneficial effects of this invention are as follows: By storing the control quantities that were not executed during the restricted period separately, separating them from the integral quantities of the closed-loop controller, and combining the safety margin of another loop and the available margin of shared power supply resources, the invention conditionally releases the historical unexecuted quantities in stages. At the same time, the release quantity is deducted based on the actual incremental action completed by the actuator, thus achieving a smooth release of historical demands after the restriction is lifted. This avoids the resource impact caused by a one-time concentrated output, ensures that the release quantity strictly corresponds to the actual amount completed by the actuator, and does not consider the unexecuted portion as written off, thereby improving the certainty and security of collaborative control in scenarios where multiple loops share restricted resources. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a structural diagram of the wastewater and flue gas desulfurization collaborative control system module based on PLC in the embodiment.

[0018] Figure 2 This is a flowchart illustrating the actual execution of the incremental reduction and pause / recovery process in the embodiment. Detailed Implementation

[0019] To make the above-mentioned objectives, features and advantages of the present invention more readily understood, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0020] In this embodiment, a three-phase AC power supply bus with a rated line voltage of 380V, which is jointly connected to the wastewater treatment control circuit and the flue gas desulfurization control circuit, is used as a shared power supply resource. The upper limit of the active power that the power supply bus can carry is taken as the upper limit of the available power supply resource.

[0021] The aforementioned power supply bus is powered by a transformer with a rated capacity of 1000kVA. Based on the on-site operating power factor of 0.90, the available active power is calculated, and a 10% operating reserve capacity is reserved. The upper limit of available active power is set at 810kW to withstand the start-up of the actuator and short-term load fluctuations, and to avoid triggering the power supply protection during the coordinated release process.

[0022] The rated voltage of the power supply bus and the rated capacity of the transformer are read from the equipment nameplate, while the operating power factor and the actual active power of the bus are read from the bus power measurement device.

[0023] The actuator for the wastewater treatment control loop is an aeration blower, while the actuator for the flue gas desulfurization control loop is a slurry circulation pump. It should be noted that within the calibration operating range of the aforementioned correspondence between control commands and active power, both actuators use active power to represent their resource occupancy, and use the product of active power and control cycle duration to represent the control quantity, so that the requested control quantity, actual execution quantity, resource reserve and release quantity of the two control loops can be processed in a unified dimension.

[0024] The PLC reads the current control commands of the two control loops, the actual active power of the actuator, the operating status of the actuator, the actual total power of the power supply bus, the dissolved oxygen concentration in the biochemical tank, and the sulfur dioxide concentration in the outlet flue gas according to a fixed control cycle of 5 seconds.

[0025] The 5-second control cycle ensures that the power, dissolved oxygen, and flue gas sulfur dioxide detection results can all be updated within one control cycle, and the release process that no longer meets the safety conditions can be stopped in time.

[0026] The current control command is read from the output of the corresponding closed-loop controller, the actual active power and operating status of the actuator are read from the frequency converter, the dissolved oxygen concentration in the biochemical tank is read from the dissolved oxygen detection device, and the sulfur dioxide concentration in the outlet flue gas is read from the flue gas continuous monitoring device.

[0027] Before the actuator is put into operation, control commands within the allowable range are sent to the aeration blower and slurry circulation pump in sequence, and the corresponding actual active power is recorded after the actuator is running stably, thus forming a correspondence table between control commands and active power.

[0028] Specifically, the control commands of the actuator are divided into 11 calibration points according to 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%. Each calibration command is held for 30 seconds. The transition data of the first 20 seconds is discarded, and the arithmetic mean of 10 active power values ​​read at 1-second intervals in the last 10 seconds is taken as the active power corresponding to the calibration command.

[0029] The current control command is converted into the requested active power according to the correspondence table; when the current control command is located between two recorded commands, the requested active power is obtained by linear interpolation.

[0030] Specifically, subtract the adjacent lower calibration command from the current control command, and then divide by the difference between the upper and lower calibration commands to obtain the position ratio of the current control command between the two calibration commands; Multiply the position ratio by the difference between the upper and lower rated power, and add it to the lower rated power to obtain the requested active power.

[0031] When the current control command is the same as a calibration command, the active power corresponding to the calibration command is read directly.

[0032] Within each control cycle, the PLC multiplies the requested active power by the control cycle duration to obtain the requested control quantity for the corresponding control loop; the average value of the actual active power of the actuator within the control cycle is multiplied by the control cycle duration to obtain the actual execution quantity.

[0033] When the requested control quantity is greater than the actual executed quantity, and the status of the actuator or the power supply bus indicates that the difference is caused by actuator failure, manual control, local control, output limiting, output rate of change limitation, or power supply capacity limitation, the corresponding control loop is recorded as a restricted control loop to be determined. When the difference between the requested control quantity and the actual executed quantity is greater than or equal to 2% of the product of the actuator's maximum continuous operating power and the 5s control cycle duration, and this condition is met for two consecutive control cycles, the corresponding control loop is determined to be in a restricted state.

[0034] When two or more restricted states occur simultaneously in the same control loop, only one restricted record is established, and all valid states are saved in the restricted record. Unexecuted control quantities are not generated repeatedly.

[0035] When only one control loop is in a restricted state, that control loop is designated as the first control loop, and the other control loop is designated as the second control loop.

[0036] When two control loops are simultaneously restricted within the same control cycle, the control loop with the larger difference between the requested control quantity and the actual executed quantity is identified as the first control loop.

[0037] When the two differences are the same, the control loop that generates the restricted state signal first is determined as the first control loop; when the restricted state signals are generated simultaneously, the wastewater treatment control loop is determined as the first control loop according to a pre-fixed order.

[0038] After the first control loop is determined, the PLC subtracts the actual executed quantity from the requested control quantity of its current control cycle to obtain the unfinished difference for this control cycle. When the unfinished difference reaches the aforementioned 2% judgment value, the PLC uses the entire value of the unfinished difference as the unexecuted control increment for this control cycle and adds the unexecuted control increment to the previously unexecuted control quantity that has not yet been cleared. When the requested control quantity is not greater than the actual executed quantity, the unfinished difference for this control cycle is recorded as 0.

[0039] The PLC stores the updated unexecuted control quantities in a separate storage area and synchronously records the control loop identifier, formation time, and control direction.

[0040] Unexecuted control quantities are not written into the closed-loop control integral of the first control loop, nor are they directly added to the actuator output during the duration of the restricted state.

[0041] It should be noted that the closed-loop control integral is the control quantity formed by the existing closed-loop controller after accumulating the deviation between the controlled parameter and the set value over time, and is used to generate the current closed-loop control output.

[0042] Unexecuted control quantities are set as data items independent of the closed-loop control integral quantity, used to distinguish between historical unfulfilled demands formed during the restricted period and closed-loop control quantities generated by the closed-loop controller based on the current controlled parameters.

[0043] While storing unexecuted control quantities, the PLC also records their corresponding control directions.

[0044] The first control loop is the wastewater treatment control loop. When the dissolved oxygen in the biological treatment tank is lower than the dissolved oxygen control setpoint and the requested active power of the aeration blower is greater than the actual active power, the control direction will be determined to increase the aeration output direction. The first control loop is the flue gas desulfurization control loop. When the sulfur dioxide concentration in the outlet flue gas is higher than the sulfur dioxide control setpoint and the requested active power of the slurry circulation pump is greater than the actual active power, the control direction will be determined to increase the desulfurization output direction.

[0045] After the restricted state is lifted, the PLC reads the current controlled parameters of the first control loop and reconfirms the control requirements corresponding to the unexecuted control quantities.

[0046] When the actuator of the first control loop resumes automatic control, the fault signal disappears, and the actual total active power of the bus is below 810kW for three consecutive control cycles, the restricted state is recorded as released.

[0047] The reason for setting three consecutive control cycles is to eliminate short-term fluctuations in bus power near the upper limit.

[0048] When the first control loop is the wastewater treatment control loop, the measured dissolved oxygen value in the biological treatment tank is lower than the dissolved oxygen control setpoint, indicating that there is still a need to improve the aeration capacity; when the first control loop is the flue gas desulfurization control loop, the measured sulfur dioxide concentration in the outlet flue gas is higher than the sulfur dioxide control setpoint, indicating that there is still a need to improve the desulfurization capacity.

[0049] In this embodiment, the dissolved oxygen control setting is 2.5 mg / L, and the sulfur dioxide control setting for the outlet flue gas is 25 mg / m³. Both data are read from the original process control settings.

[0050] If the above conditions are no longer met for three consecutive control cycles, it means that the current controlled parameter no longer needs to be adjusted in the direction recorded by the unexecuted control quantity, that is, the corresponding control requirement has disappeared.

[0051] It should be noted that when the corresponding control requirement has disappeared, the unexecuted control quantity will not enter the current control output.

[0052] If the corresponding control requirements still exist, the PLC calculates the safety margin of the second control loop.

[0053] In this embodiment, the minimum allowable dissolved oxygen value is set at 1.8 mg / L, so that a safe range of 0.7 mg / L is maintained between it and the control set value of 2.5 mg / L.

[0054] When the second control loop is a wastewater treatment control loop, the difference between the measured dissolved oxygen value in the biological treatment tank and the minimum allowable dissolved oxygen value is used as a safety margin. When the second control loop is a flue gas desulfurization control loop, the difference between the maximum allowable sulfur dioxide concentration in the outlet flue gas and the measured sulfur dioxide concentration in the outlet flue gas is used as a safety margin.

[0055] In this embodiment, the maximum allowable concentration of sulfur dioxide in the flue gas is set to 35 mg / m³, leaving a safe range of 10 mg / m³ between it and the control set concentration of 25 mg / m³.

[0056] The minimum and maximum allowable concentrations mentioned above are written into the process safety setting table before the system is put into operation and can be directly read by the PLC.

[0057] If the safety margin is greater than 0, it means that the second control loop has not yet reached the preset unsafe boundary; if the safety margin is less than or equal to 0, the PLC will set the allowable release amount to 0 and continue to save the unexecuted control amount.

[0058] In this embodiment, the safety margin is only used to determine whether release is allowed, and it is not directly compared with the power or the unexecuted control quantity.

[0059] After obtaining the safety margin of the second control loop, the PLC calculates the resource margin of the shared power supply resources.

[0060] First, subtract the actual active power of the first and second control loops from the actual total active power of the bus to obtain the current power occupied by other loads. Then, subtract the larger of the current power occupied by other loads, the current basic active power requested by the first control loop, and the actual active power from 810kW, and the larger of the current active power requested by the second control loop and the actual active power. The resulting non-negative result is used as the resource margin.

[0061] It should be noted that during the period when the control quantity is not released, the current basic requested active power of the first control loop is still determined based on the basic control output without superimposed additional control output; the actual active power of the first control loop is determined based on the actual active power fed back by the actuator in real time, and includes the increase in actual active power caused by the additional control output.

[0062] Therefore, after the additional control output is applied, the actual resource occupancy of the first control loop is updated according to the change in the actual active power of the actuator, and the change in the actual resource occupancy is reflected in the calculation result of the resource reserve.

[0063] The larger of the requested active power and the actual active power in the second control loop is deducted to ensure that the currently occupied resources and the normal control needs that have not yet been completed are reserved first.

[0064] When both the safety margin and resource margin are greater than 0, the PLC reads the maximum active power allowed by the actuator in the first control loop, and subtracts the requested active power corresponding to the current closed-loop control output of the first control loop from the maximum active power to obtain the power that the actuator can currently increase.

[0065] It should be noted that when the continuous operating power recorded on the equipment nameplate is inconsistent with the maximum allowable power set by the frequency converter, the smaller of the two values ​​shall be used as the maximum allowable active power.

[0066] The PLC divides the unexecuted control quantity by the preset release cycle duration to obtain the remaining historical demand corresponding to the power to be released.

[0067] In this embodiment, the release cycle is set to 20s. This time is obtained by adjusting the longer actual response time of the aeration blower and slurry circulation pump upward to an integer multiple of the 5s control cycle, so that the actuator can form a measurable actual response within one release cycle.

[0068] It should be noted that the control cycle is the period during which the PLC updates the sampled data and control status, while the release cycle is the duration of one additional release output and its execution feedback sampling. The release cycle is an integer multiple of the control cycle.

[0069] According to the conversion relationship described later, the PLC converts the corrected safety margin and resource margin into the first release limit and the second release limit with the same dimension as the unexecuted control quantity, respectively, and determines the third release limit based on the execution quantity that the first control loop actuator can currently increase; the minimum value among the remaining unexecuted control quantity, the first release limit, the second release limit, and the third release limit is determined as the allowable release quantity for this time.

[0070] Multiply the additional release power by the release cycle duration to obtain the allowable release amount; add the additional release power to the requested active power corresponding to the current closed-loop control output of the first control loop to form the target active power; then, according to the correspondence table between control commands and active power, convert the target active power into a target control command and send it to the actuator of the first control loop.

[0071] When the target active power is located between two adjacent calibration powers, first calculate the position ratio of the target active power between the two calibration powers, then multiply the position ratio by the difference between the two corresponding calibration commands and add it to the lower calibration command to obtain the target control command; when the target active power exceeds the highest calibration power, the target control command is limited to 100%.

[0072] It should be noted that when the safety margin or resource margin is less than or equal to 0, the additional release power is 0, and the first control loop only executes the current closed-loop control output.

[0073] Before sending the target control command, the PLC reads the actual active power of the actuator of the first control loop for N consecutive control cycles, and uses the arithmetic average of the N actual active power as the reference power before release.

[0074] The value of N is an integer between 3 and 8.

[0075] It should be noted that the minimum value of N is set to 3 because the actual active power of a single control cycle may be affected by grid voltage fluctuations, instantaneous load changes of the actuator, measurement errors of the power detection device, and data sampling disturbances. When only the actual active power of one or two control cycles is used, occasional fluctuations have a significant impact on the baseline active power, which may cause the actual execution increment calculated later to be too large or too small. Using the arithmetic average of the actual active power of no less than three consecutive control cycles can reduce the impact of a single abnormal sampling or short-term power fluctuation, making the obtained baseline active power closer to the actual stable operating power of the actuator before the additional control output is applied.

[0076] The maximum value of N is set to 8 because too many sampling periods will prolong the statistical time of the reference active power, causing power data from earlier control periods to be included in the calculation of the current reference active power. When the actuator load, basic control output, or process status changes during the statistical period, an excessively long statistical time may cause the obtained arithmetic mean to fail to accurately represent the current operating status before the target control output is sent, and it will also reduce the response speed of the coordinated release control.

[0077] During feedback sampling, the basic control output of the first control loop, which does not include additional release power, is kept unchanged so that the execution quantity corresponding to the basic control output can be used as a benchmark for determining the actual execution increment.

[0078] Maintaining the basic control output of the first control loop, excluding additional release power, means that the basic control command corresponding to the original closed-loop control output of the first control loop remains unchanged during this feedback sampling period. It does not mean that the actual active power of the actuator of the first control loop, the actual total active power of the power supply bus, or the resource margin remains unchanged.

[0079] After the additional release power is superimposed on the basic control output, the increase in the actual active power of the first control loop actuator is included in the actual resource occupancy of the first control loop.

[0080] The PLC still reads the actual total active power of the power supply bus, the actual active power of the first control loop, the actual active power of the second control loop, and the currently requested active power of the second control loop according to the 5-second control cycle, and updates the resource reserve according to the aforementioned resource reserve calculation method.

[0081] The longest feedback sampling period is a 20-second release cycle.

[0082] Safety margin, resource margin, and execution feedback status are continuously updated according to a 5-second control cycle. When any of the safety margin, resource margin, or execution feedback status no longer meets the release condition, the PLC sets the additional release power to 0, causing the first control loop to resume executing the basic control output without the superimposed additional release power, and the moment when the additional release power is canceled is determined as the end time of this feedback sampling.

[0083] After the target control command is sent, the PLC reads the control command feedback value returned by the actuator. If the difference between the control command feedback value and the target control command does not exceed 1% of the full scale of the actuator's control command, the target control command is recorded as having been received by the actuator.

[0084] The starting point for feedback sampling is the moment when the target control command is confirmed to be received, and the ending point is the end of the current release cycle; when the release process is paused early, the ending point is the moment when the additional release power is canceled.

[0085] The PLC reads the cumulative active energy consumed by the actuator during the feedback sampling period, and multiplies the baseline power before release by the actual feedback sampling duration to obtain the baseline execution amount. The baseline execution amount is then subtracted from the cumulative active energy consumed to obtain the additional execution amount in the same direction as the additional release. If the additional execution amount is less than 0, it is recorded as 0. The smaller value between the additional execution amount and the current allowable release amount is determined as the actual execution increment.

[0086] The PLC deducts the remaining unexecuted control quantities based on the actual executed increment; no deduction is made when the actual executed increment is 0, and only the actually completed portion is deducted when the actuator has only completed part of the allowed release quantity. Target control instructions that have already been issued or received by the actuator are not used as a separate basis for deducting unexecuted control quantities.

[0087] After each release cycle, the PLC reconfirms the control requirements corresponding to the first control loop and recalculates the safety margin of the second control loop and the resource margin of the shared power supply.

[0088] When the first control loop is in the state of not executing control release, the PLC updates the corrected safety margin of the second control loop every 5-second control cycle.

[0089] When the corrected safety margin is greater than the pause threshold, the resource margin is not lower than the resource pause threshold, and the execution feedback is normal, the current additional release output is maintained; when the corrected safety margin is less than or equal to the pause threshold, the resource margin is lower than the resource pause threshold, or the execution feedback of the first control loop is abnormal, the PLC cancels the additional release power, so that the first control loop resumes the execution of the current closed-loop control output without the superimposed additional release power, and retains the remaining unexecuted control quantities.

[0090] The above-mentioned abnormal execution feedback means that after the target control command is sent, no effective active power feedback is obtained from the first control loop actuator for two consecutive control cycles, or the active power feedback exceeds the range of 0 to the maximum allowable active power of the actuator.

[0091] When the additional release power has been cancelled and the corrected safety margin of the second control loop is lower than the recovery threshold, the PLC remains in a suspended state and does not immediately resume the additional release output even if the safety margin is higher than the suspension threshold.

[0092] When the corrected safety margin of the second control loop is greater than or equal to the recovery threshold, the resource margin is not less than the minimum additional output power, the execution feedback is normal for three consecutive control cycles, and the control demand corresponding to the remaining unexecuted control quantity still exists and its control direction is consistent with the current adjustment demand direction of the first control loop, the PLC recalculates the allowable release amount based on the remaining unexecuted control quantity, the corrected safety margin, the resource margin, and the increaseable power of the actuator of the first control loop, and restarts the release.

[0093] It should be noted that the release will continue after the above recovery conditions are met for three consecutive control cycles to prevent repeated start and stop of the release process due to fluctuations in a single measurement.

[0094] Once the remaining unexecuted control quantities are reduced to 0, the process of releasing historically unfulfilled demands ends, and the first control loop reverts to closed-loop control based solely on the current process status.

[0095] Furthermore, in the wastewater treatment control loop, when the dissolved oxygen in the biological treatment tank is below 2.5 mg / L and the requested power of the aeration blower is higher than the actual power, the unexecuted control increment is recorded as an increase in aeration direction.

[0096] In the flue gas desulfurization control loop, when the sulfur dioxide concentration in the outlet flue gas exceeds 25 mg / m³ and the requested power of the slurry circulation pump is higher than the actual power, the unexecuted control increment is recorded as an increase in desulfurization capacity. Only when the control direction of the uncompleted difference is consistent with the current adjustment demand direction, the unexecuted control increment of this cycle is accumulated to the original unexecuted control quantity.

[0097] When the dissolved oxygen concentration in the wastewater treatment control loop is higher than 2.7 mg / L, the current adjustment demand direction is recorded as reducing aeration. When the sulfur dioxide concentration in the flue gas at the outlet of the flue gas desulfurization control loop is lower than 23 mg / m³, the current adjustment demand direction is recorded as reducing desulfurization output. A 0.2 mg / L direction switching interval is established between 2.7 mg / L and 2.5 mg / L, and a 2 mg / m³ direction switching interval is established between 23 mg / m³ and 25 mg / m³. This is to avoid frequent changes in the control direction when the controlled parameter fluctuates slightly around the control setpoint.

[0098] When the current adjustment demand direction is opposite to the control direction of the stored unexecuted control quantities, the accumulation of unexecuted control quantities in the original direction is stopped. The PLC reads the requested active power of the current control cycle and the previous control cycle, multiplies the reduction of the two requested active power in opposite directions by 5s, obtains the control quantity corresponding to the current control demand in the opposite direction, and uses the smaller value between this control quantity and the remaining unexecuted control quantity as the deduction amount for this cycle.

[0099] The minimum number of unexecuted control quantities after reduction is 0, and the current control requirements in the opposite direction are no longer stored as new reverse unexecuted control quantities.

[0100] Furthermore, each unexecuted control increment retains its formation time and is stored in chronological order of formation time.

[0101] In this implementation, the effective period for unexecuted control quantities is set to 300 seconds. This period is longer than the maximum time required for the controlled parameter to reach the monitoring position and produce a stable and identifiable change after a change in the output of the aeration blower or slurry circulation pump. At the same time, it limits the long-term retention of historical demands formed too early, and avoids the loss of correspondence between historical demands and the current process status.

[0102] The upper limit for storing unexecuted control quantities is the product of the maximum increaseable active power of the actuator and the 300s validity period. The maximum increaseable active power of the actuator is obtained by subtracting the minimum stable operating power from the maximum continuous operating power of the equipment; both power values ​​are obtained from the continuous operation technical parameters of the equipment. Once the unexecuted control quantity reaches the storage upper limit, no new unexecuted control increments are accumulated, and the already stored unexecuted control quantities and their formation times remain unchanged.

[0103] When the wastewater treatment control loop stores unexecuted control quantities for increasing aeration capacity, and the dissolved oxygen concentration remains between 2.5 and 2.7 mg / L for three consecutive control cycles, it indicates that the current process state has entered the control set range, and the historical need to increase aeration capacity has disappeared. When the flue gas desulfurization control loop stores unexecuted control quantities for increasing desulfurization capacity, and the outlet flue gas sulfur dioxide concentration remains between 23 and 25 mg / m³ for three consecutive control cycles, it indicates that the historical need to increase desulfurization capacity has disappeared. Three consecutive control cycles correspond to 15 seconds, used to exclude fluctuations from single measurements. After the control need disappears, the release stops and the corresponding unexecuted control quantities are cleared.

[0104] When parallel actuators are connected in the same control loop, and other actuators have already completed control requests in the same direction, the PLC reads the actual active power of the other actuators before the start of the substitution output and accumulates the actual active energy during the substitution output period. The actual active energy during the substitution output period is subtracted from the product of the actual active power before the substitution output and the duration of the substitution output to obtain the actual directional control quantity completed by the other actuators. The smaller of this actual completed control quantity and the remaining unexecuted control quantity is used to deduct the unexecuted control quantity, thus preventing historical requests already completed by other actuators from being released again.

[0105] The PLC checks each unexecuted control increment from earliest to latest according to its creation time. When 300 seconds have passed between the current time and the creation time of a certain unexecuted control increment, that unexecuted control increment is removed from the remaining unexecuted control increments and will no longer participate in subsequent releases; unexecuted control increments that have not yet reached 300 seconds are retained. Thus, historical requirements that were formed earlier and have lost their timeliness can be invalidated independently without affecting subsequently formed unexecuted control increments that are still within their validity period.

[0106] Furthermore, the PLC performs trend correction on the basic safety margin obtained in the aforementioned manner to reflect the changing state of the controlled parameters of the second control loop as they approach or move away from the preset unsafe boundary.

[0107] The PLC reads the controlled parameters of the second control loop in the current control cycle and the previous control cycle.

[0108] The time interval between two readings is the aforementioned 5 seconds. The rate of change of the controlled parameter in the current time period is obtained by subtracting the controlled parameter from the controlled parameter of the previous control cycle and then dividing by 5 seconds. This rate of change is directly obtained from two consecutive measured values, without setting change weights, trend coefficients, or manual correction factors.

[0109] When the second control loop is a wastewater treatment control loop, a dissolved oxygen rate of change less than 0 indicates that the dissolved oxygen is decreasing, i.e., moving towards the unsafe boundary of 1.8 mg / L; a dissolved oxygen rate of change greater than 0 indicates that the dissolved oxygen is increasing, i.e., moving away from the unsafe boundary. The current measured dissolved oxygen value is added to the change in dissolved oxygen over the next 5-second control cycle to obtain the predicted dissolved oxygen value for the next control cycle. Then, 1.8 mg / L is subtracted from the predicted value to obtain the corrected safety margin.

[0110] When the second control loop is a flue gas desulfurization control loop, a rate of change of sulfur dioxide concentration in the outlet flue gas greater than 0 indicates that the concentration is rising, i.e., moving towards the unsafe boundary of 35 mg / m³; a rate of change of concentration less than 0 indicates that the concentration is falling, i.e., moving away from the unsafe boundary. The current measured sulfur dioxide concentration in the outlet flue gas is added to the change in concentration generated by this rate of change in the next 5-second control cycle to obtain the predicted concentration value for the next control cycle. Then, the predicted value is subtracted from 35 mg / m³ to obtain the corrected safety margin.

[0111] The trend prediction span is fixed at one control cycle, i.e., 5 seconds. A prediction span of 1 to 3 control cycles can be used; this implementation uses 1 control cycle. When the prediction span exceeds 3 control cycles, the possibility of changes in the actuator status and process load during the prediction period increases; using 1 control cycle can reflect the latest trend and avoid introducing additional prediction coefficients. When the controlled parameter changes towards the unsafe boundary, the corrected safety margin is less than the basic safety margin; when the controlled parameter changes away from the unsafe boundary, the corrected safety margin is greater than the basic safety margin.

[0112] If the corrected safety margin is less than or equal to 0, the second control loop has reached the unsafe boundary or will reach the unsafe boundary in the next control cycle according to the current trend. In this release cycle, the unexecuted control quantity will not be released. If the corrected safety margin is greater than 0, it will be used as the input for the subsequent calculation of the first release upper limit.

[0113] Furthermore, the minimum guaranteed resource quantity of the second control loop is the positive value obtained by subtracting its current actual active power from the current requested active power of the second control loop; when the difference is less than or equal to 0, the minimum guaranteed resource quantity is recorded as 0.

[0114] In the aforementioned resource reserve calculation, deducting the larger of the current requested active power and the actual active power of the second control loop is equivalent to deducting the current actual occupied power of the second control loop and its minimum guaranteed resource quantity.

[0115] The minimum guaranteed resource quantity is not a fixed percentage because the current requested power and actual power of the second control loop can be directly read, and the difference can accurately represent the resource demand that has not yet been obtained. Using the actual difference can avoid the resource idleness caused by an excessively large fixed reservation ratio, or the resource idleness caused by an excessively small fixed reservation ratio, which would result in the current demand of the second control loop being squeezed out by historical demand.

[0116] Furthermore, the revised safety margin needs to be converted into a first release limit with the same dimension as the unexecuted control quantity. Therefore, before the system is put into coordinated control, safety margin correspondence tables are established for the wastewater treatment control loop as the second control loop and for the flue gas desulfurization control loop as the second control loop, respectively.

[0117] When establishing the correspondence table, the second control loop is kept in a stable operating state, and the additional output of the first control loop is increased incrementally in increments of 5% of the maximum continuous operating power of its actuator. The calibration step size of the additional output can be 2% to 10% of the maximum continuous operating power of the actuator; in this embodiment, 5% is used. When the calibration step size is less than 2%, the power change of the actuator may be close to the measurement fluctuation; when the calibration step size is greater than 10%, a single test may have an excessively large instantaneous impact on the second control loop. A calibration step size of 5% can identify parameter changes caused by different additional outputs and maintain sufficient resolution between adjacent calibration levels.

[0118] Each additional output lasts for 20 seconds, then returns to the output before the test, and the controlled parameters of the second control loop are continuously recorded within the maximum transmission time of the aforementioned controlled parameters (150 seconds). When the second control loop is a wastewater treatment control loop, the maximum decrease in dissolved oxygen relative to the start of the test is recorded; when the second control loop is a flue gas desulfurization control loop, the maximum increase in the outlet flue gas sulfur dioxide concentration relative to the start of the test is recorded. Both the maximum decrease and the maximum increase are the maximum adverse changes towards the unsafe boundary.

[0119] Each additional output for each level is tested three times, and the largest adverse change among the three test results is recorded in the corresponding table. The number of repetitions can be 2 to 5 times; this implementation uses 3 times. Fewer than 2 repetitions are insufficient to eliminate single-condition fluctuations, and more than 5 repetitions will significantly increase the field testing time; using 3 repetitions and taking the maximum value can preserve a relatively conservative response result without introducing statistical weights.

[0120] During actual release, the PLC calls the corresponding safety margin table based on the type of the second control loop, and looks up the maximum additional power in the table whose maximum adverse change does not exceed the current corrected safety margin. This maximum additional power is multiplied by the 20-second release cycle to obtain the first release upper limit. If the maximum adverse change corresponding to all additional powers in the table is greater than the current corrected safety margin, the first release upper limit is recorded as 0.

[0121] This conversion process ensures that the first release upper limit is derived from the correspondence between the additional output of the first control loop measured on-site and the adverse changes in the second control loop, rather than being obtained through manually set weights or safety factors. The first release upper limit is expressed in kW·s, having the same dimensions as the unexecuted control quantity.

[0122] Resource reserves are expressed in kW. Multiplying the resource reserves by a 20s release cycle yields the second release limit. When the resource reserves are 0, the second release limit is 0. The second release limit represents the maximum historical release volume that the shared power supply resources can handle within this release cycle without occupying the current minimum guaranteed resources of the second control loop.

[0123] The PLC reads the maximum continuous operating power of the actuator in the first control loop and subtracts the requested active power corresponding to the current normal closed-loop control output of the first control loop from this maximum continuous operating power to obtain the active power that the actuator can currently increase. If the result is less than 0, it is treated as 0. Then, the active power that the actuator can currently increase is multiplied by a 20-second release cycle to obtain the third release upper limit. The third release upper limit represents the maximum control quantity that can actually be increased in this release cycle without exceeding the continuous operating capacity of the actuator.

[0124] Before the start of the next release cycle, the PLC re-acquires the corrected safety margin of the second control loop, the resource margin of the shared power supply, and the increaseable power of the actuators in the first control loop, and regenerates three release limits. The safety margin, resource margin, and allowable release amount of the previous release cycle are not directly used for the next release cycle. Therefore, when unexecuted control quantities are allocated to multiple release cycles, each release cycle is constrained by the actual safety and resource status at that time.

[0125] Furthermore, the following safety margin threshold, resource threshold, and execution feedback judgment rules are applied to the aforementioned suspension and recovery conditions.

[0126] When the second control loop is a wastewater treatment control loop, the pause threshold for the corrected safety margin is set to 0.2 mg / L. This threshold can be set to 0.1–0.3 mg / L; in this embodiment, 0.2 mg / L is used. When the pause threshold is below 0.1 mg / L, the release stops only after the safety margin approaches the minimum allowable dissolved oxygen value, leaving less time for the actuator to respond and update measurements; when it is above 0.3 mg / L, the release will pause prematurely while the wastewater treatment control loop still has a significant safety margin. Using 0.2 mg / L allows for an early stop margin above the minimum allowable value of 1.8 mg / L and is greater than the minimum resolution of the dissolved oxygen detection device of 0.01 mg / L.

[0127] When the second control loop is a flue gas desulfurization control loop, the pause threshold for the corrected safety margin is set to 2 mg / m³. This threshold can be set to 1–3 mg / m³, but in this embodiment, 2 mg / m³ is used. When the pause threshold is below 1 mg / m³, the release will stop only after the sulfur dioxide concentration in the outlet flue gas approaches the maximum allowable concentration of 35 mg / m³; when it is above 3 mg / m³, the safe range available for coordinated release will be narrowed. Using 2 mg / m³ is higher than the resolution of 1 mg / m³ for the continuous flue gas monitoring device and stops additional release before approaching the unsafe boundary.

[0128] Anomalies in execution feedback include failure to return valid control command feedback within one 5-second control cycle after the target control output is sent, interruption of actual active power feedback, the feedback status being marked as invalid by the measuring device, and the actual active power exceeding the range from 0 to the maximum continuous operating power of the actuator for two consecutive control cycles. The control command feedback, the valid status of the power feedback, and the maximum continuous operating power are obtained from the inverter communication status, the valid measurement status of the power measuring device, and the equipment technical parameters, respectively, without manual judgment.

[0129] The allowable measurement deviation for actual active power exceeding the maximum continuous operating power is set to 2% of the maximum continuous operating power. This deviation can be set to 1% to 3%, and in this implementation, it is set to 2%. A deviation below 1% may identify normal measurement errors as abnormalities, while a deviation above 3% may mask obvious over-limit feedback. If the actual active power exceeds 102% of the maximum continuous operating power, or if negative power feedback occurs and the actuator does not have energy feedback functionality, the feedback is recorded as invalid.

[0130] Furthermore, the recovery process after the pause uses a recovery threshold higher than the pause threshold to form a hysteresis interval.

[0131] The hysteresis range is the numerical range between the pause threshold and the recovery threshold. Its function is to prevent the additional release output from repeatedly starting and stopping when the safety margin fluctuates slightly near the pause boundary.

[0132] The aforementioned hysteresis interval adopts a state-maintaining rule related to the current release state. When the first control loop is currently in the release state, the safety margin is greater than the pause threshold but less than the recovery threshold, and the PLC maintains the current release state. When the first control loop is currently in the pause state, the safety margin is greater than the pause threshold but less than the recovery threshold, and the PLC maintains the pause state. Only when the safety margin is less than or equal to the pause threshold will the PLC switch from the release state to the pause state. Only when the safety margin is greater than or equal to the recovery threshold and other recovery conditions are met simultaneously will the PLC switch from the pause state to the release state.

[0133] When the second control loop is a wastewater treatment control loop, the recovery threshold can be set to 0.3–0.6 mg / L; in this embodiment, 0.4 mg / L is used. 0.4 mg / L is higher than the 0.2 mg / L pause threshold, creating a hysteresis range of 0.2 mg / L between the two. This range is greater than the measurement resolution of the dissolved oxygen detection device and the normal short-term fluctuations, allowing dissolved oxygen to recover to a stable and safe level before continuing to be released.

[0134] When the second control loop is a flue gas desulfurization control loop, the recovery threshold can be set to 3-6 mg / m³, and in this embodiment, 4 mg / m³ is used. 4 mg / m³ is higher than the 2 mg / m³ suspension threshold, creating a hysteresis range of 2 mg / m³ between the two. This range can eliminate small fluctuations in the outlet flue gas sulfur dioxide concentration near the suspension boundary and ensures that there is still a safety margin to accommodate a minimum additional output during recovery.

[0135] In addition to ensuring the safety margin reaches the recovery threshold, the resource margin of the shared power supply must also be no less than the power required for the aforementioned minimum additional output. The minimum additional output is 5% of the maximum continuous operating power of the first control loop actuator, and its source is consistent with the minimum calibration level in the aforementioned safety margin correspondence table. If the resource margin is lower than the power required for this minimum additional output, even if the resource margin is greater than 0, it is insufficient to execute a complete minimum release unit, therefore release is not restored.

[0136] Normal feedback recovery means that the control command feedback is effective, the actual active power feedback is effective, and there is no feedback interruption or value exceeding the limit for three consecutive control cycles. The recovery confirmation time can be set to 10-20 seconds; this implementation uses 15 seconds, corresponding to three 5-second control cycles. A time lower than 10 seconds is easily affected by single communication recovery, while a time higher than 20 seconds will delay normal connection continuation. Using 15 seconds balances feedback stability and recovery timeliness.

[0137] When the safety margin reaches the recovery threshold, the resource margin meets the minimum additional output requirement, the execution feedback is normal for 15 consecutive seconds, and the current adjustment demand direction of the first control loop is consistent with the control direction of the remaining unexecuted control quantity, the PLC restarts and releases according to the aforementioned recovery processing method.

[0138] When restarting the release, the target control output before the pause is not restored, nor is the allowable release amount before the pause used. The PLC uses the remaining unexecuted control quantities retained during the pause as input, rereads the corrected safety margin, resource margin, and actuator increase output at that time, and regenerates the allowable release amount. The portion issued before the pause but not actually completed is still retained in the unexecuted control quantities and is not directly deducted upon resumption.

[0139] When the current adjustment demand of the first control loop has disappeared or the control direction is opposite to the control direction of the remaining unexecuted control quantities, the additional release output in the original direction is not restored, and it is deducted or cleared according to the aforementioned handling of unexecuted control quantity direction and failure management method. After the remaining unexecuted control quantities are reduced to 0, the additional release output is canceled and the current historical demand release process ends.

[0140] Operating conditions In this operating condition, the aeration blower in the wastewater treatment control loop is limited by the shared power supply capacity. Therefore, the wastewater treatment control loop is used as the first control loop, and the flue gas desulfurization control loop is used as the second control loop. The available active power of the power supply bus is 810kW, the PLC control cycle is 5s, and the release cycle of unexecuted control quantities is 20s.

[0141] Before the wastewater treatment control loop enters the restricted state, the measured dissolved oxygen value in the biological treatment tank is 2.08 mg / L, which is lower than the dissolved oxygen control setpoint of 2.50 mg / L. Therefore, the aeration blower needs to run in the direction of increasing output.

[0142] Based on the current control commands of the aerator and the pre-established correspondence table between control commands and active power, the requested active power of the aerator is 220kW. Since the actual active power of the power supply bus reaches 810kW, the actual active power of the aerator is limited to 180kW, resulting in a 40kW unfulfilled power gap between the requested and actual active power.

[0143] The restricted state lasts for 60 seconds, corresponding to 12 control cycles. Within each 5-second control cycle, the 40kW of unfulfilled power corresponds to a 200kW·s unexecuted control increment. The PLC sequentially accumulates the unexecuted control increments formed by the 12 control cycles to obtain a 2400kW·s unexecuted control quantity, and stores this unexecuted control quantity independently of the closed-loop control integral quantity of the wastewater treatment control loop, while recording its control direction as increasing the output of the aeration blower.

[0144] After other loads on the power supply bus decreased, the actual active power of the bus remained below 810kW for three consecutive control cycles. The aeration blower was in automatic control mode and there were no faults, local control, or output limiting signals. The wastewater treatment control loop exited the restricted state. At this time, the measured dissolved oxygen value in the biological treatment tank was 2.10mg / L, which was still lower than the dissolved oxygen control setpoint of 2.50mg / L. Therefore, the increased aeration demand corresponding to the 2400kW·s unexecuted control quantity still existed.

[0145] At the start of the first release cycle, the measured sulfur dioxide concentration in the flue gas at the current outlet of the flue gas desulfurization control loop was 26.0 mg / m³, while the measured concentration in the previous control cycle was 25.5 mg / m³. Based on the changes between the two adjacent control cycles, the predicted sulfur dioxide concentration in the outlet flue gas for the next control cycle is 26.5 mg / m³. Subtracting 26.5 mg / m³ from the maximum allowable sulfur dioxide concentration of 35 mg / m³ in the outlet flue gas yields a corrected safety margin of 8.5 mg / m³.

[0146] According to the aforementioned table of correspondence between safety margin and permissible release control, the maximum additional power allowed by the corrected safety margin of 8.5 mg / m³ is 30 kW. Multiplying 30 kW by the 20 s release period, we obtain the first release limit as 600 kW·s.

[0147] Before the first release cycle begins, the actual total power of the power supply bus is 735kW, the requested active power of the flue gas desulfurization control loop is 170kW, and the actual active power is 160kW. The current unmet power demand of the flue gas desulfurization control loop is 10kW. Therefore, subtracting 735kW from 810kW and then subtracting 10kW yields a resource margin of 65kW available for releasing the historical demand of the wastewater treatment control loop. Multiplying 65kW by the 20s release cycle, we obtain the second release limit of 1300kW·s.

[0148] The maximum continuous operating power of the aeration blower is 250kW, and the requested active power corresponding to its current normal closed-loop control output is 210kW. Therefore, the power that the aeration blower can currently increase is 40kW. Multiplying 40kW by the 20s release cycle, we get the third release limit as 800kW·s.

[0149] The PLC compares the remaining unexecuted control quantity of 2400 kW·s, the first release limit of 600 kW·s, the second release limit of 1300 kW·s, and the third release limit of 800 kW·s, and takes the minimum value of 600 kW·s as the allowable release quantity for the first release cycle. Dividing 600 kW·s by 20s yields an additional release power of 30 kW. This 30 kW is added to the current normal requested active power of 210 kW to form a target active power of 240 kW. This target active power is then converted into a target control command according to the control command-active power correspondence table and sent to the aeration blower.

[0150] Before sending the target control command, the pre-release baseline power of the aerator blower is 210kW. During the 20s feedback sampling period, the normal closed-loop control output, excluding additional release power, remains unchanged. The actual active power consumed by the aerator blower during this feedback sampling period is converted to 4760kW·s, and the baseline execution quantity corresponding to the pre-release baseline power within 20s is 4200kW·s, with a difference of 560kW·s. Since 560kW·s is less than the allowable release quantity of 600kW·s for this cycle, the PLC determines 560kW·s as the actual execution increment and reduces the unexecuted control quantity from 2400kW·s to 1840kW·s. The 40kW·s that was allowed to be released but not actually completed by the aerator blower is still retained in the unexecuted control quantity.

[0151] Upon entering the second release cycle, the measured concentration of sulfur dioxide in the outlet flue gas decreased from 26.0 mg / m³ in the previous control cycle to 25.8 mg / m³, and the predicted concentration for the next control cycle was 25.6 mg / m³, resulting in a corrected safety margin of 9.4 mg / m³. According to the table corresponding to safety margins and permissible release control values, the maximum additional power corresponding to this safety margin is 35 kW, and the first release limit is 700 kW·s.

[0152] Before the start of the second release cycle, the actual total power of the power supply bus was 740kW, the requested active power of the flue gas desulfurization control circuit was 168kW, the actual active power was 163kW, and the unmet current power demand of the flue gas desulfurization control circuit was 5kW. Therefore, the resource margin was 65kW, and the upper limit of the second release was 1300kW·s. The current power that the aeration blower can add is still 40kW, and the upper limit of the third release is 800kW·s.

[0153] The PLC compares the remaining unexecuted control quantity of 1840 kW·s, the first release limit of 700 kW·s, the second release limit of 1300 kW·s, and the third release limit of 800 kW·s, and takes 700 kW·s as the allowable release quantity for the second release cycle, corresponding to an additional release power of 35 kW and a target active power of 245 kW.

[0154] The actual active power consumed by the aeration blower during the second release cycle is converted to 4880 kW·s. After deducting the baseline execution amount of 4200 kW·s, the actual increase in execution amount in the same direction is 680 kW·s. The PLC deducts the unexecuted control amount according to 680 kW·s, and the remaining unexecuted control amount is reduced from 1840 kW·s to 1160 kW·s.

[0155] Entering the third release cycle, the measured concentration of sulfur dioxide in the flue gas increased from 25.8 mg / m³ to 26.2 mg / m³, and the predicted concentration for the next control cycle was 26.6 mg / m³, resulting in a corrected safety margin of 8.4 mg / m³. According to the table corresponding to safety margins and permissible release control values, the maximum additional power corresponding to this safety margin is 30 kW, and the first release limit is 600 kW·s.

[0156] Before the start of the third release cycle, the actual total power of the power supply bus was 745kW, the requested active power of the flue gas desulfurization control circuit was 170kW, the actual active power was 165kW, the minimum guaranteed resource was 5kW, the resource margin was 60kW, and the second release limit was 1200kW·s. The aeration blower can currently increase its power by 40kW, and the third release limit is 800kW·s.

[0157] The PLC compares the remaining unexecuted control quantity of 1160 kW·s, the first release limit of 600 kW·s, the second release limit of 1200 kW·s, and the third release limit of 800 kW·s, and takes 600 kW·s as the allowable release quantity for the third release cycle, with an additional release power of 30 kW and a target active power of 240 kW.

[0158] The actual active power consumed by the aeration blower in the third release cycle is converted to 4790 kW·s. After deducting the baseline execution amount of 4200 kW·s, the actual execution increment is 590 kW·s. The PLC deducts the unexecuted control amount according to 590 kW·s, and the remaining unexecuted control amount is reduced from 1160 kW·s to 570 kW·s.

[0159] Entering the fourth release cycle, the measured concentration of sulfur dioxide in the flue gas decreased from 26.2 mg / m³ to 25.9 mg / m³, and the predicted concentration for the next control cycle was 25.6 mg / m³, resulting in a corrected safety margin of 9.4 mg / m³. Based on the table corresponding to safety margins and permissible release control levels, the first release limit is 700 kW·s.

[0160] Before the start of the fourth release cycle, the actual total power of the power supply bus is 750kW. The requested active power and actual active power of the flue gas desulfurization control loop are both 170kW. There is no need to reserve additional unmet current power demand for it, and the resource margin is 60kW. The second release limit is 1200kW·s. The aeration blower can currently increase its power by 40kW, and the third release limit is 800kW·s.

[0161] The remaining unexecuted control quantity is 570 kW·s, which is less than the first release limit, the second release limit, and the third release limit. Therefore, the PLC uses 570 kW·s as the allowable release quantity for the fourth release cycle. Dividing 570 kW·s by 20s yields an additional release power of 28.5 kW, forming a target active power of 238.5 kW.

[0162] The actual active power consumed by the aeration blower in the fourth release cycle is converted to 4770 kW·s. After deducting the baseline execution amount of 4200 kW·s, the actual execution increment is 570 kW·s. The PLC deducts the unexecuted control amount according to 570 kW·s, reducing the remaining unexecuted control amount from 570 kW·s to 0.

[0163] During the four release cycles, the corrected safety margin of the flue gas desulfurization control loop remained greater than zero, the resource margin of the power supply bus remained greater than zero, and the execution feedback of the aeration blower remained effective, thus preventing the triggering of a release suspension. The actual reduction in unexecuted control quantities for the four release cycles was 560 kW·s, 680 kW·s, 590 kW·s, and 570 kW·s, respectively, totaling 2400 kW·s, consistent with the unexecuted control quantities generated during the restricted period.

[0164] After the unexecuted control quantity is reduced to 0, the PLC cancels the additional release output, and the aeration blower reverts to only executing the current normal closed-loop control output of the wastewater treatment control loop. Throughout the release process, the historical unfulfilled demands of the aeration blower are not output all at once, the sulfur dioxide concentration in the flue gas at the outlet of the flue gas desulfurization control loop remains below the unsafe boundary of 35 mg / m³, the actual power of the power supply bus does not exceed the available upper limit of 810 kW, and in each release cycle, the unexecuted control quantity is reduced only according to the additional execution quantity actually completed by the aeration blower.

[0165] It should be noted that the other control loop works similarly.

[0166] Control effect comparison and verification To verify the release effect of unexecuted control quantities formed during the restricted period after the restrictions are lifted, comparative verification was carried out in the same wastewater treatment and flue gas desulfurization co-control system using Comparative Example 1, Comparative Example 2, Comparative Example 3 and the present invention example, respectively. In each group, the flue gas desulfurization control loop was used as the first control loop, the wastewater treatment control loop was used as the second control loop, and a common power supply bus with an active power allowable continuous operation limit of 810kW, a control cycle of 5s, and a release cycle of 20s were used.

[0167] Before the start of the verification for each group, the sulfur dioxide concentration in the flue gas at the outlet was 30.5 mg / m³, the dissolved oxygen concentration in the biochemical tank was 2.35 mg / L, the requested active power of the flue gas desulfurization control loop was 200 kW, and the actual active power of the slurry circulation pump was 160 kW. The restricted state lasted for 50 seconds, and the initial unexecuted control quantity of 2000 kW·s was formed from the uncompleted power of 40 kW.

[0168] Each group will put on a 45kW auxiliary power load for 30 seconds after the release begins and continue for 10 seconds. At the same time, the current aeration demand of the sewage treatment control loop will be increased, so that the dissolved oxygen safety margin of the second control loop and the shared power supply resource margin will decrease simultaneously. After the auxiliary power load is removed, the same sewage treatment influent conditions, flue gas flow rate, inlet flue gas sulfur dioxide concentration, equipment operating status and data acquisition cycle will continue to be maintained.

[0169] In Comparative Example 1, after the flue gas desulfurization control loop exits the restricted state, all unexecuted control quantities are added to the current control output at once, and the unexecuted control quantities are deducted according to the historical release quantities that have been issued. The safety margin of the second control loop, the resource margin of the shared power supply resources, and the actual execution feedback of the slurry circulation pump are not used to limit the release process.

[0170] Comparative Example 2 releases the unexecuted control quantity in cycles according to a fixed additional power of 20kW, and stops increasing the additional power when the power supply bus reaches the allowable continuous operation limit of 810kW. At the same time, the unexecuted control quantity is reduced according to the actual execution increment of the slurry circulation pump, and the release is paused and resumed without using the safety margin of dissolved oxygen in the biological treatment tank.

[0171] Comparative Example 3 determines the allowable release amount based on the corrected safety margin of the second control loop, the resource margin of the shared power supply, and the increaseable power of the slurry circulation pump. The unexecuted control amount is directly deducted according to the allowable release amount, without correcting the deduction result based on the actual execution increment of the slurry circulation pump corresponding to the allowable release amount.

[0172] In this invention, three release limits are generated based on the corrected safety margin of the second control loop, the resource margin of the shared power supply, and the increaseable power of the slurry circulation pump. The minimum value among the remaining unexecuted control quantity and the three release limits is taken as the allowable release quantity. Release is suspended when the safety margin is insufficient or the power supply is restricted again. The unexecuted control quantity is deducted only according to the actual unidirectional execution increment completed by the slurry circulation pump.

[0173] The technical differences between the various verification methods are shown in Table 1.

[0174] Table 1 Control conditions for each verification method Comparative Example 1 Released in one go after restrictions are lifted Not adopted Not adopted Not adopted Historical release volume Comparative Example 2 Released in stages at a fixed additional power of 20kW. Not adopted use Pause only when resources are insufficient Actual execution increment Comparative Example 3 Released in phases based on safety margin and resource margin. use use use Permissible release amount Example of the present invention Released in phases based on three release limits. use use use Actual execution increment During the verification process, the actual active power of the power supply bus is recorded by the bus power measurement device, the dissolved oxygen concentration of the biochemical tank is recorded by the dissolved oxygen detection device, the sulfur dioxide concentration of the flue gas at the outlet is recorded by the flue gas continuous monitoring device, and the actual active power and cumulative active energy are recorded by the frequency converter or power measurement device corresponding to the slurry circulation pump. The actual completed release amount is obtained based on the actual increase in active energy in each release cycle.

[0175] To uniformly evaluate the impact of each verification method on the safety status of the second control loop, all groups used the same safety margin correction method to process dissolved oxygen records. The corrected safety margins of Comparative Example 1 and Comparative Example 2 were only used for verification result analysis and did not participate in the corresponding control process.

[0176] The cumulative release amount is accumulated by multiplying the additional release power and the actual duration in each release cycle. The same unfulfilled demand is included in the cumulative release amount again when it is re-released in a subsequent release cycle. Therefore, the cumulative release amount can be greater than the initial unexecuted control amount of 2000 kW·s.

[0177] The system records the deduction amount as the value deducted from the unexecuted control quantity during the control process for the corresponding control mode. The actual completed release amount is the same-direction execution amount that the slurry circulation pump actually increases relative to the basic execution quantity. The positive value obtained by subtracting the actual completed release amount from the system records the deduction amount as the error deduction amount.

[0178] The results, shown in Table 2, were obtained by verifying the above conditions.

[0179] Table 2. Comparison and Verification Results of Control Effect Initial unexecuted control quantity (kW·s) 2000 2000 2000 2000 Cumulative allocation, including re-allocated portions (kW·s) 2000 2118 2000 2090 Actual discharge capacity of slurry circulation pump (kW·s) 768 2000 1716 2000 The system records the amount deducted (kW·s). 2000 2000 2000 2000 Error reduction (kW·s) 1232 0 284 0 Actual remaining unexecuted control quantity (kW·s) at the end of verification 1232 0 284 0 Maximum actual active power of the power supply bus (kW) 823.1 808.9 799.4 800.2 Cumulative time (s) exceeding the maximum allowable continuous operation limit of 810kW 12 0 0 0 Minimum dissolved oxygen concentration (mg / L) in the biological treatment tank 1.73 1.78 2.01 2.05 Minimum safety margin after correction (mg / L) -0.13 -0.06 0.14 0.15 Is it below the unsafe threshold of 1.80 mg / L? yes yes no no Number of times historical demand release has been paused 0 0 1 1 Time (s) required for the unexecuted control quantity to actually decrease to 0 More than 240 118 More than 240 120 Time (s) required for sulfur dioxide concentration in flue gas at the outlet to decrease to 25 mg / m³ More than 240 126 More than 240 132 The system records the status when the verification is completed. Completed Completed Completed Completed Actual completion status at the end of verification Incomplete Completed Incomplete Completed Comparative Example 1: After the flue gas desulfurization control loop exited the restricted state, it released 2000 kW·s of historical demand at once, causing the maximum actual active power of the power supply bus to reach 823.1 kW, and exceeding the allowable continuous operation limit of 810 kW within 12 seconds. After the shared power supply resources were concentratedly occupied by historical demand, the ability of the sewage treatment control loop to obtain current aeration resources was weakened, causing the minimum dissolved oxygen concentration in the biological treatment tank to drop to 1.73 mg / L, which is below the unsafe boundary of 1.80 mg / L.

[0180] In Comparative Example 1, after the historical release command was issued, the 2000 kW·s of unexecuted control quantity was deducted. Due to the influence of power supply capacity, maximum continuous operating power and equipment response process, the slurry circulation pump only actually completed 768 kW·s. The system recorded a deduction of 1232 kW·s between the deduction and the actual completed release quantity, resulting in the system recording the status as completed when there was still an uncompleted demand of 1232 kW·s.

[0181] Comparative Example 2 uses a fixed additional power and deducts the unexecuted control quantity according to the actual execution increment, so that the maximum actual active power of the power supply bus is maintained at 808.9kW, and the system records the deduction quantity is consistent with the actual completed release quantity. Since the dissolved oxygen safety margin of the biological treatment tank is not used as a suspension condition during the fixed release process, the historical demand for flue gas desulfurization is still continuously released during the period of auxiliary power load input and current aeration demand of sewage treatment, so that the minimum dissolved oxygen concentration in the biological treatment tank drops to 1.78mg / L and is below the unsafe boundary.

[0182] The verification results of Comparative Example 2 show that using only fixed periodic release and actual execution feedback reduction can reduce resource peaks and eliminate erroneous reductions, but it cannot control the release eligibility of historical demands based on the real-time safety status of another control loop, and therefore cannot avoid the secondary impact caused by insufficient safety margin across loops.

[0183] Comparative Example 3 restricts the release of historical demand based on the revised safety margin and resource margin, and suspends the release when the revised safety margin decreases, so that the maximum actual active power of the power supply bus is kept at 799.4kW and the minimum dissolved oxygen concentration in the biochemical pool is kept at 2.01mg / L, thereby avoiding exceeding the unsafe boundary of 1.80mg / L.

[0184] Comparative Example 3 directly deducts the unexecuted control quantity based on the allowable release quantity generated for each release cycle. Under the influence of equipment response and power fluctuations, the slurry circulation pump only actually completes 1716 kW·s. The system still deducts all 2000 kW·s of unexecuted control quantity, resulting in an erroneous deduction of 284 kW·s, and causing the system to stop subsequent releases before the actual historical demand has been met.

[0185] In this invention, during the period of auxiliary power load input and dissolved oxygen decrease in the biological treatment tank, the historical demand release is paused once based on the corrected safety margin. This keeps the maximum actual active power of the power supply bus at 800.2kW, the minimum dissolved oxygen concentration in the biological treatment tank at 2.05mg / L, and the minimum corrected safety margin at 0.15mg / L. The entire release process does not exceed the upper limit of the continuous operation of the power supply bus and the unsafe boundary of the sewage treatment control loop.

[0186] In this invention, a total of 2090 kW·s of historical release volume has been issued. Among them, 90 kW·s is the portion that the slurry circulation pump did not actually complete after receiving the target control output and was reissued in subsequent cycles. The PLC only deducts the unexecuted control volume according to the 2000 kW·s actually completed by the slurry circulation pump, so that the system records the deducted volume, the actual completed release volume and the initial unexecuted control volume are consistent.

[0187] This invention reduces the uncontrolled amount to 0 within 120s and reduces the sulfur dioxide concentration in the flue gas to 25mg / m³ in 132s. Compared with Comparative Example 2, it only increases the sulfur dioxide recovery time in the flue gas by 6s. At the same time, it avoids the dissolved oxygen in the biological treatment tank from falling below the unsafe boundary. Compared with Comparative Example 3, it eliminates the erroneous reduction of 284kW·s and completes the release of all historical demand.

[0188] The results shown in Table 2 indicate that directly restoring historical demand after the restrictions are lifted can easily lead to peak shared resources and distortion of command reduction. Fixed additional power release can control resource peaks but cannot respond to the safety status of the second control loop. Reducing only according to the allowed release amount can protect the second control loop but cannot guarantee that historical demand has been actually completed. The present invention forms a complete control closed loop through cross-loop security authorization, shared resource restriction, periodic release, actual execution feedback reduction, and pause continuation.

[0189] The requested active power, actual active power, total power of the power supply bus, dissolved oxygen concentration in the biochemical tank, sulfur dioxide concentration in the outlet flue gas, actuator status, and cumulative active power used in this invention can all be directly obtained from existing closed-loop controllers, frequency converters, power measurement devices, and online detection devices. The allowable release amount, actual execution increment, and remaining unexecuted control amount are all generated from the obtained data according to the aforementioned processing relationship. Therefore, this invention can be implemented in a system where the wastewater treatment control loop and the flue gas desulfurization control loop share limited power supply resources.

[0190] This embodiment also provides a PLC-based wastewater and flue gas desulfurization coordinated control system, including: The control loop determination module, the non-execution management module, the release condition acquisition module, the release output generation module, the execution increment decrement module, and the pause recovery module are all implemented by program function blocks in the PLC.

[0191] The control loop determination module receives the current control commands of the wastewater treatment control loop and the flue gas desulfurization control loop, the actual execution feedback of the actuator, the operating status of the actuator and the status of the shared power supply resources. Based on the difference between the requested control quantity and the actual execution quantity and the restricted status signal, it determines the first control loop and the second control loop, and sends the first control loop identifier and the second control loop identifier to the non-execution management module and the release condition acquisition module.

[0192] The unexecuted control management module obtains the requested control quantity and the actual executed representation quantity of the first control loop based on the first control loop identifier, converts the actual executed representation quantity into the actual executed quantity, and updates the unexecuted control quantity according to the uncompleted difference between the requested control quantity and the actual executed quantity. The unexecuted control management module stores the unexecuted control quantity independently of the closed-loop control integral quantity of the first control loop, and records the control loop identifier, formation time, and control direction. The unexecuted control management module sends the remaining unexecuted control quantity and its control direction to the release output generation module, the execution increment deduction module, and the pause recovery module.

[0193] The release condition acquisition module obtains the controlled parameters of the second control loop based on the second control loop identifier, determines the safety margin based on the difference between the controlled parameters and the preset unsafe boundary, and obtains the available upper limit and current occupancy of the shared power supply resources to determine the resource margin.

[0194] The release condition acquisition module sends the safety margin and resource margin to the release output generation module and the pause recovery module.

[0195] The release output generation module receives the remaining unexecuted control quantity, safety margin, and resource margin. Based on the above data, it determines the allowable release quantity for the current release cycle, converts the allowable release quantity into an additional control output, and superimposes the additional control output onto the current control output of the first control loop to form the target control output.

[0196] The release output generation module sends the target control output to the actuator of the first control loop and sends the allowable release amount to the execution increment decrement module.

[0197] The incremental deduction module receives the actual execution feedback from the first control loop actuator, determines the actual execution increment based on the baseline execution amount before the target control output is sent and the actual execution amount after the target control output is sent, takes the smaller value between the actual execution increment and the current allowable release amount as the deduction amount, and feeds back the remaining unexecuted control amount after deduction to the unexecuted management module.

[0198] The pause / recovery module receives the safety margin, resource margin, execution feedback status of the first control loop, remaining unexecuted control quantities, and their control directions. When the safety margin or resource margin does not meet the release conditions, or when an anomaly occurs in the execution feedback of the first control loop, the pause / recovery module sends a pause signal to the release output generation module, setting the additional control output to zero and retaining the remaining unexecuted control quantities. When the safety margin and resource margin meet the release conditions again, the execution feedback returns to normal, and the control requirements corresponding to the remaining unexecuted control quantities still exist and the control directions are consistent, the pause / recovery module sends a recovery signal to the release output generation module, causing the release output generation module to recalculate the allowable release quantity and continue releasing.

[0199] In the above module connection relationship, the control loop determination module first determines the first and second control loops in this collaborative control; the unexecuted management module generates historical uncompleted requirements based on the uncompleted difference of the first control loop; the release condition acquisition module generates release constraints based on the safety status of the second control loop and the shared power supply resource status; the release output generation module generates the target control output under the historical uncompleted requirements and release constraints; the execution incremental reduction module updates the historical uncompleted requirements based on the actual completion status; and the pause and recovery module controls the pause and resumption of the release process based on the real-time safety status, resource status, and execution feedback status, thereby forming a closed-loop processing process of unexecuted control quantity generation, condition judgment, release, feedback reduction, and pause and recovery.

[0200] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A PLC-based method for coordinated control of wastewater and flue gas desulfurization, wherein the wastewater treatment control loop and the flue gas desulfurization control loop share a power supply resource with an available upper limit, characterized in that, include: The control loop in the restricted state is designated as the first control loop, and the other control loop is designated as the second control loop. The system obtains the requested control quantity of the first control loop and the actual execution representation quantity fed back by the actuator. It converts the actual execution representation quantity into an actual execution quantity with the same dimension as the requested control quantity. It updates the unexecuted control quantity based on the uncompleted difference between the requested control quantity and the actual execution quantity, and stores the unexecuted control quantity independently of the closed-loop control integral quantity of the first control loop. When the restricted state of the first control loop is lifted and the control requirement corresponding to the unexecuted control quantity still exists, obtain the safety margin of the second control loop relative to the preset unsafe boundary and the resource margin of the power supply resources. The allowable release amount is determined based on the unexecuted control amount, safety margin, and resource margin. The allowable release amount is then superimposed on the current control output of the first control loop to form the target control output, which is then sent to the actuator of the first control loop. Obtain the actual execution increment of the first control loop actuator corresponding to the allowable release quantity, and deduct the unexecuted control quantity according to the actual execution increment; When the safety margin or resource margin does not meet the release conditions, the release of the remaining unexecuted control quantities is suspended, and the release continues after the safety margin and resource margin meet the release conditions again.

2. The PLC-based coordinated control method for wastewater and flue gas desulfurization as described in claim 1, characterized in that, The power supply resources are the available active power capacity of the power supply bus shared by the sewage treatment control loop and the flue gas desulfurization control loop. The occupancy of the power supply resources by the two control loops is represented by the actual active power of the corresponding actuators. The restricted state includes at least one of the following: actuator failure, manual control, local control, output limiting, limited output rate of change, and insufficient power supply resources.

3. The PLC-based coordinated control method for wastewater and flue gas desulfurization as described in claim 1, characterized in that, When the control direction of the unfulfilled difference is consistent with the current adjustment demand direction of the first control loop, the unexecuted control increment corresponding to the unfulfilled difference is accumulated into the unexecuted control quantity; When the control direction is opposite to the current adjustment demand direction, the accumulation stops, and the unexecuted control quantity is reduced according to the control quantity corresponding to the current adjustment demand in the opposite direction, and the reduction amount does not exceed the remaining unexecuted control quantity.

4. The PLC-based wastewater and flue gas desulfurization synergistic control method as described in claim 3, characterized in that, Set storage limits and expiration periods for unexecuted control variables; When the amount of unexecuted control reaches the storage limit, stop accumulating new unexecuted control increments and maintain the amount of unexecuted control at the storage limit. When the controlled parameter of the first control loop is within the preset stable range for N consecutive control cycles, release is stopped and the unexecuted control quantity corresponding to the disappeared control requirement is cleared. When the corresponding control requirements are fulfilled by other implementing agencies, the amount of unexecuted control shall be reduced according to the amount of control actually completed by the other implementing agencies. When the validity period expires, any remaining unexecuted control quantities will be cleared.

5. The PLC-based coordinated control method for wastewater and flue gas desulfurization as described in claim 1, characterized in that, When the second control loop is a wastewater treatment control loop, the safety margin is determined based on the difference between the measured dissolved oxygen value in the biological treatment tank and the minimum allowable dissolved oxygen value. When the second control loop is a flue gas desulfurization control loop, the safety margin is determined based on the difference between the maximum allowable concentration of sulfur dioxide in the outlet flue gas and the actual measured concentration of sulfur dioxide in the outlet flue gas.

6. The PLC-based coordinated control method for wastewater and flue gas desulfurization as described in claim 5, characterized in that, The safety margin is corrected according to the direction and rate of change of the controlled parameter of the second control loop relative to the preset unsafe boundary. Specifically, when the controlled parameter changes toward the preset unsafe boundary, the safety margin is reduced according to the rate of change, and when the controlled parameter changes away from the preset unsafe boundary, the safety margin is increased according to the rate of change. The larger of the current resource occupancy of other loads, the current basic requested resource occupancy of the first control loop, and the actual resource occupancy, and the current requested resource occupancy of the second control loop, is subtracted from the available upper limit of power supply resources. The resulting non-negative result is determined as the resource reserve.

7. The PLC-based coordinated control method for wastewater and flue gas desulfurization as described in claim 6, characterized in that, According to the preset conversion relationship, the safety margin and resource margin are converted into the first release limit and the second release limit with the same dimension as the unexecuted control quantity, respectively. The third release limit is determined according to the execution quantity that the first control loop actuator can increase in a single release cycle. The minimum value among the remaining unexecuted control quantity, the first release limit, the second release limit and the third release limit is determined as the allowable release quantity, and the unexecuted control quantity is allocated to multiple release cycles for release.

8. The PLC-based coordinated control method for wastewater and flue gas desulfurization as described in claim 1, characterized in that, During the feedback sampling period to determine the actual execution increment, the basic control output of the first control loop without superimposed additional control output remains unchanged; Before the target control output is sent, the reference execution rate of the first control loop actuator is obtained, and the reference execution amount is determined based on the reference execution rate and the feedback sampling duration. The actual cumulative execution amount of the first control loop actuator is obtained during the feedback sampling period. The smaller of the non-negative difference value that is consistent with the direction of the additional control output and the allowable release value obtained by subtracting the reference execution amount from the actual cumulative execution amount is determined as the actual execution increment. The unexecuted control quantity is deducted based on the actual executed increment. When no actual executed increment is generated, the unexecuted control quantity is not deducted.

9. The PLC-based coordinated control method for wastewater and flue gas desulfurization as described in claim 8, characterized in that, Set a pause threshold and a resume threshold that exceeds the pause threshold; When the first control loop is in the unexecuted control quantity release state, if the safety margin of the second control loop is greater than the pause threshold, and the resource margin and execution feedback meet the release conditions, the current release state is maintained. When the safety margin of the second control loop is less than or equal to the pause threshold, the resource margin is lower than the preset resource pause threshold, or the execution feedback of the first control loop is abnormal, the additional control output is canceled and the remaining unexecuted control quantity is retained, so that the first control loop enters the pause state. When the first control loop is in a paused state, the paused state is maintained when the safety margin of the second control loop is lower than the recovery threshold. When the safety margin of the second control loop is greater than or equal to the recovery threshold, the resource margin meets the release conditions again, the execution feedback returns to normal, and it is reconfirmed that the control demand corresponding to the remaining unexecuted control quantity still exists and its control direction is consistent with the current adjustment demand direction of the first control loop, the allowable release quantity is re-determined based on the safety margin, resource margin and remaining unexecuted control quantity at that time, and the remaining unexecuted control quantity continues to be released.

10. A PLC-based wastewater and flue gas desulfurization co-control system, based on the PLC-based wastewater and flue gas desulfurization co-control method according to any one of claims 1 to 9, characterized in that, include: The control loop determination module is used to determine a control loop in a restricted state as the first control loop and another control loop as the second control loop. The unexecuted management module is used to obtain the requested control quantity of the first control loop and the actual execution representation quantity fed back by the actuator, convert the actual execution representation quantity into an actual execution quantity with the same dimension as the requested control quantity, update the unexecuted control quantity according to the unfinished difference between the requested control quantity and the actual execution quantity, and store the unexecuted control quantity independently of the closed-loop control integral quantity of the first control loop. The release condition acquisition module is used to acquire the safety margin of the second control loop relative to the preset unsafe boundary and the resource margin of the power supply resources when the restricted state of the first control loop is released and the control requirement corresponding to the unexecuted control quantity still exists. The release output generation module is used to determine the allowable release amount based on the unexecuted control amount, safety margin and resource margin, convert the allowable release amount into an additional control output with the same dimension as the current control output of the first control loop, superimpose the additional control output onto the current control output of the first control loop to form the target control output, and send the target control output to the actuator of the first control loop. The incremental deduction module is used to obtain the actual execution increment of the first control loop actuator corresponding to the additional control output, and deduct the unexecuted control quantity according to the actual execution increment; The pause and recovery module is used to control the release output generation module to pause the release of the remaining unexecuted control quantities when the safety margin or resource margin does not meet the release conditions, and to control the release output generation module to continue releasing the remaining unexecuted control quantities after the safety margin and resource margin meet the release conditions again.

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