PLC control system for building direct drinking water station

Abstract

This invention relates to the field of programmable logic control technology and discloses a PLC control system for a building direct drinking water station, comprising: a signal acquisition input module, a drive control output module, a data storage register module, and a PLC main control module. The PLC main control module reads pulse signals and writes them into the displacement register unit during the scanning cycle, calculates the water usage gradient index to adjust the pressure dead zone half-width, outputs a feedforward reference frequency when the pressure change rate is lower than the water hammer threshold, and calculates an initial integral value based on the pressure deviation and the dead zone half-width during the feedforward period, writing it into the integral storage register unit. After the feedforward ends, the initial integral value is loaded to restore the closed loop. This invention utilizes low-computing-power bitwise operations to sense the water usage gradient and adaptively adjust the dead zone, suppressing frequent pump start-stops; by presetting the initial integral value while outputting the feedforward reference frequency, it mitigates water hammer impact, reduces computational overhead, and decreases flushing water consumption.

Description

Technical Field

[0001] This invention relates to a PLC control system for building direct drinking water stations, belonging to the field of programmable logic control technology. Background Technology

[0002] Building-based direct drinking water stations typically integrate filtration components, reverse osmosis membrane units, disinfection pipelines, and variable frequency booster pumps. Water demand varies significantly at different times. Existing systems generally use programmable logic controllers (PLCs) as the main control unit, refreshing input and output states according to a fixed scanning cycle, triggering reverse osmosis membrane flushing through a periodic timer, and using a proportional-integral-derivative (PID) regulator with a fixed dead zone to control the output frequency of the inverter and the start and stop of the water pump. Within each scanning cycle, the controller collects sensor signals and controls the actuators to maintain the pressure of the main water supply pipe.

[0003] In office buildings and similar locations, the morning rush hour for water usage alternates with periods of no water use at night. The flow rate in the water supply network can fluctuate rapidly or only slightly. Given a fixed system hardware configuration, the stability and response speed of the network depend on the scheduling strategy of the control algorithm. For example, Chinese invention patent application CN101050636A discloses a digital constant-pressure water supply energy-saving device that uses a conventional discrete PID algorithm, employing a pressure sensor to collect network pressure for closed-loop regulation. However, when water consumption at building drinking water stations changes rapidly, this type of PID control cannot adjust according to flow rate. Adjusting control parameters in advance to reflect changing trends can lead to water hammer in the pipeline network when a large flow terminal is suddenly turned on, causing a sharp drop in water pressure. In contrast, under low flow conditions with slight fluctuations, fixed control parameters can cause the frequency converter to repeatedly start and stop at the edge of the dead zone, which not only accelerates mechanical wear but also increases the cycle calculation burden on the PLC due to complex calculations, making it difficult to meet the real-time control requirements of the system. Furthermore, flushing at fixed intervals is difficult to match with the actual settling conditions of the water: water stagnation is likely to occur when the water usage frequency is low, while forced flushing when the water usage frequency is high will cause a drop in water supply pressure and waste of water resources.

[0004] Therefore, how to accurately sense the real-time water gradient, dynamically adjust the pressure control dead zone, and suppress water hammer impact through feedforward control by utilizing the programmable logic controller's own scan cycle and bit registers without significantly increasing the computational burden has become a technical problem that needs to be solved. Summary of the Invention

[0005] To address the problems in the background art, the technical solution of the present invention is as follows: A PLC control system for a building direct drinking water station, comprising:

[0006] The signal acquisition input module includes an inlet water pressure acquisition module, an outlet water pressure acquisition module, a water temperature acquisition module, and a flow pulse acquisition module;

[0007] The drive control output module includes a frequency converter drive module, an inlet valve control module, a flushing valve control module, a circulation drive module, and a sterilization control module;

[0008] The data storage register module includes a displacement register unit and an integral storage register unit;

[0009] The PLC main control module is used to read the pulse signal from the flow pulse acquisition module within a fixed scan cycle. At the end of each fixed scan cycle, it writes the pulse Boolean flag to the least significant bit of the displacement register unit and shifts the displacement register unit to the left. It calculates the total number of logic 1s in the displacement register unit through bit statistics instructions to obtain the dimensionless real-time water use gradient index. Based on the real-time water use gradient index, it dynamically adjusts the pressure control dead zone half-width and controls the system to switch between sleep mode, variable frequency boosting water supply mode, circulating antibacterial mode, and membrane flushing mode. It calculates the sampling change rate of the outlet water pressure acquisition module. When the sampling change rate is lower than the negative water hammer trigger threshold, it pauses the closed-loop operation and outputs the feedforward reference frequency to the variable frequency drive module. During the feedforward control period, it calculates the initial integral value based on the outlet water pressure deviation and the pressure control dead zone half-width and writes it to the integral storage register unit. After the feedforward control ends, it loads the initial integral value to resume the closed-loop operation.

[0010] Preferably, at the end of each fixed scan cycle, the PLC main control module detects the pulse increment of the flow pulse acquisition module. When the pulse increment is greater than a predetermined threshold and a pulse signal exists for a consecutive predetermined number of fixed scan cycles, the pulse Boolean flag is set to logic 1; otherwise, it is set to logic 0. The displacement register unit is a 32-bit displacement register unit, the bit statistics instruction is the Popcount instruction, and the real-time water gradient index ranges from 0 to 32.

[0011] Preferably, in the variable frequency boosting water supply mode, the PLC main control module calculates the pressure control dead zone half-width according to the formula: ,in, For pressure control dead zone half width, Given a basic pressure hysteresis half-width, The dead zone compression factor is... For real-time water use gradient index, The total number of bits for the 32-bit displacement register unit; when the pressure of the water supply main pipe sampled by the outlet pressure acquisition module is lower than the difference between the set pressure and half the pressure control dead zone width, the PLC main control module controls the system to switch to the frequency conversion booster water supply state.

[0012] Preferably, the PLC main control module divides the difference between the water supply main pipe pressure collected in the current fixed scanning cycle and the previous fixed scanning cycle by the time length of the fixed scanning cycle to calculate the sampling change rate. When the sampling change rate is lower than the negative water hammer trigger threshold, the PLC main control module cuts off the output of the proportional-integral-derivative controller, maintains the feedforward reference frequency output for a predetermined feedforward duration, and multiplies the ratio of the current outlet pressure deviation to the half-width of the pressure control dead zone by a predetermined scaling factor within the feedforward duration. The calculation result is then written into the integral storage register unit as the initial integral value.

[0013] Preferably, when the control system switches from the frequency conversion boost water supply state to the sleep state, the PLC main control module keeps the flushing valve control module closed and drives the frequency conversion drive module to reduce the output frequency to the intermediate transition frequency according to the first frequency reduction slope; when the outlet water pressure rises back to the set pressure, the frequency reduction rate is switched to the second frequency reduction slope which is less than the first frequency reduction slope, the frequency is reduced to the predetermined lower limit frequency, and after a predetermined valve closing time, the inlet valve control module is closed and the output of the frequency conversion drive module is cut off.

[0014] Preferably, the data storage register module also includes a flushing weight accumulator unit; in the variable frequency boosting water supply state, at the end of each fixed scan cycle, the PLC main control module multiplies the real-time water use gradient index by a predetermined weight ratio coefficient to obtain the periodic weight increment, and accumulates the periodic weight increment to the flushing weight accumulator unit; when the stored value of the flushing weight accumulator unit reaches the predetermined weight threshold, and the real-time water use gradient index is less than the predetermined low threshold, the PLC main control module controls the system to switch to the membrane flushing state, opens the flushing valve control module and drives the variable frequency drive module to run at the predetermined high frequency flushing for the predetermined flushing time, and clears the flushing weight accumulator unit to zero after the flushing is completed.

[0015] Preferably, the data storage register module also includes a static timer unit; when the system is in sleep mode, the PLC main control module accumulates the timing value of the static timer unit. When the timing value of the static timer unit reaches the predetermined static time threshold, or when the water temperature of the circulating return water pipeline sampled by the water temperature acquisition module exceeds the predetermined temperature threshold, the PLC main control module controls the system to switch to the circulating antibacterial state, connects the circulating drive module and turns on the sterilization control module, drives the circulating water body to perform pipeline disinfection for a predetermined circulation time, and clears the static timer unit to zero after the circulation ends.

[0016] Preferably, the signal acquisition input module also includes a liquid level detection module; when the liquid level detection module detects that the inlet water tank is short of water, or when the pressure sampled by the outlet water pressure acquisition module is continuously lower than the predetermined safety lower limit for a predetermined fault timeout period, the PLC main control module switches the control system to the fault-safe state, cuts off the control signals of the frequency converter drive module, the inlet valve control module, the flushing valve control module and the circulation drive module, and latches the fault code in the status flag register unit in the data storage register module.

[0017] Preferably, when the pressure of the water supply main pipe sampled by the outlet pressure acquisition module is higher than the sum of the set pressure and the pressure control dead zone half-width, and the duration reaches the predetermined maintenance time, the PLC main control module controls the system to switch out of the frequency conversion boost water supply state and enter the sleep state; the dead zone compression coefficient is greater than 0 and less than 1. When the real-time water use gradient index increases, the PLC main control module automatically reduces the pressure control dead zone half-width; when the real-time water use gradient index decreases, the PLC main control module automatically increases the pressure control dead zone half-width.

[0018] Preferably, the fixed scanning cycle of the PLC main control module is 10ms; the flow pulse acquisition module is connected to the pulse flow sensor installed on the main water supply pipeline to receive high-speed pulses; the inlet pressure acquisition module and the outlet pressure acquisition module are respectively connected to the inlet pressure sensor and the outlet pressure sensor to receive standard current signals of 4mA to 20mA; the frequency conversion drive module is used to output 0V to 10V analog voltage signals to the water supply frequency converter to adjust the operating frequency of the frequency conversion booster pump; the water temperature acquisition module is connected to the temperature sensor located in the circulating return water pipeline.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. In the PLC control of building direct drinking water stations, the real-time water consumption gradient index is obtained by using a fixed scan cycle, displacement register unit, and bit statistics instructions. Based on this, the pressure control dead zone half-width is adjusted so that the water supply control can change with the water consumption status. When the water consumption is small or the pipeline pressure fluctuates only slightly, the pressure control dead zone half-width can be appropriately widened to reduce the frequency converter and booster pump from repeatedly starting and stopping near the critical pressure, thereby reducing the workload of electrical components and the mechanical wear of the pump. When the water consumption increases rapidly, the pressure control dead zone half-width can be narrowed in time to improve the system's response speed to pressure drop, so as to balance stable operation at low flow and timely water supply at high flow.

[0021] 2. By identifying the rapid drop in water supply main pipe pressure based on the rate of change of water pressure in adjacent fixed scanning cycles and outputting the feedforward reference frequency in a timely manner, the variable frequency booster pump can increase the water supply capacity in advance before the closed-loop regulation responds, reducing pressure drop and water hammer impact caused by sudden water use. During the feedforward control period, the initial integral value is pre-calculated and written into the integral storage register unit, so that after the closed-loop operation is restored, it can start adjusting from the integral value that matches the current pressure state, reducing abrupt changes in control output and improving the smoothness of switching between feedforward control and closed-loop control.

[0022] 3. The flushing weight accumulator unit can accumulate the operating load of the reverse osmosis membrane according to the actual water usage and trigger membrane flushing when the water usage drops, thereby reducing the problem of mismatch between fixed timed flushing and actual operating conditions, and avoiding water pressure drop and water supply interruption caused by flushing during peak water usage periods. At the same time, the settling timer unit and return water temperature conditions can trigger circulating antibacterial based on the settling time and water temperature of the pipeline network, making membrane flushing and pipeline disinfection more in line with the actual operating conditions of the direct drinking water station, reducing unnecessary flushing water and circulation operation while ensuring water quality safety. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating the control system module architecture and signal interaction of the present invention.

[0024] Figure 2 This is a logic diagram of the system's working state transition in this invention.

[0025] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0027] A PLC control system for a building-based direct drinking water station includes:

[0028] The signal acquisition input module includes an inlet water pressure acquisition module, an outlet water pressure acquisition module, a water temperature acquisition module, and a flow pulse acquisition module;

[0029] The drive control output module includes a frequency converter drive module, an inlet valve control module, a flushing valve control module, a circulation drive module, and a sterilization control module;

[0030] The data storage register module includes a displacement register unit and an integral storage register unit;

[0031] The PLC main control module is used to read the pulse signal from the flow pulse acquisition module within a fixed scan cycle. At the end of each fixed scan cycle, it writes the pulse Boolean flag to the least significant bit of the displacement register unit and shifts the displacement register unit to the left. It calculates the total number of logic 1s in the displacement register unit through bit statistics instructions to obtain the dimensionless real-time water use gradient index. Based on the real-time water use gradient index, it dynamically adjusts the pressure control dead zone half-width and controls the system to switch between sleep mode, variable frequency boosting water supply mode, circulating antibacterial mode, and membrane flushing mode. It calculates the sampling change rate of the outlet water pressure acquisition module. When the sampling change rate is lower than the negative water hammer trigger threshold, it pauses the closed-loop operation and outputs the feedforward reference frequency to the variable frequency drive module. During the feedforward control period, it calculates the initial integral value based on the outlet water pressure deviation and the pressure control dead zone half-width and writes it to the integral storage register unit. After the feedforward control ends, it loads the initial integral value to resume the closed-loop operation.

[0032] Preferably, at the end of each fixed scan cycle, the PLC main control module detects the pulse increment of the flow pulse acquisition module. When the pulse increment is greater than a predetermined threshold and a pulse signal exists for a consecutive predetermined number of fixed scan cycles, the pulse Boolean flag is set to logic 1; otherwise, it is set to logic 0. The displacement register unit is a 32-bit displacement register unit, the bit statistics instruction is the Popcount instruction, and the real-time water gradient index ranges from 0 to 32.

[0033] Preferably, in the variable frequency boosting water supply mode, the PLC main control module calculates the pressure control dead zone half-width according to the formula: ,in, For pressure control dead zone half width, Given a basic pressure hysteresis half-width, The dead zone compression factor is... For real-time water use gradient index, The total number of bits for the 32-bit displacement register unit; when the pressure of the water supply main pipe sampled by the outlet pressure acquisition module is lower than the difference between the set pressure and half the pressure control dead zone width, the PLC main control module controls the system to switch to the frequency conversion booster water supply state.

[0034] Preferably, the PLC main control module divides the difference between the water supply main pipe pressure collected in the current fixed scanning cycle and the previous fixed scanning cycle by the time length of the fixed scanning cycle to calculate the sampling change rate. When the sampling change rate is lower than the negative water hammer trigger threshold, the PLC main control module cuts off the output of the proportional-integral-derivative controller, maintains the feedforward reference frequency output for a predetermined feedforward duration, and multiplies the ratio of the current outlet pressure deviation to the half-width of the pressure control dead zone by a predetermined scaling factor within the feedforward duration. The calculation result is then written into the integral storage register unit as the initial integral value.

[0035] Preferably, when the control system switches from the frequency conversion boost water supply state to the sleep state, the PLC main control module keeps the flushing valve control module closed and drives the frequency conversion drive module to reduce the output frequency to the intermediate transition frequency according to the first frequency reduction slope; when the outlet water pressure rises back to the set pressure, the frequency reduction rate is switched to the second frequency reduction slope which is less than the first frequency reduction slope, the frequency is reduced to the predetermined lower limit frequency, and after a predetermined valve closing time, the inlet valve control module is closed and the output of the frequency conversion drive module is cut off.

[0036] Preferably, the data storage register module also includes a flushing weight accumulator unit; in the variable frequency boosting water supply state, at the end of each fixed scan cycle, the PLC main control module multiplies the real-time water use gradient index by a predetermined weight ratio coefficient to obtain the periodic weight increment, and accumulates the periodic weight increment to the flushing weight accumulator unit; when the stored value of the flushing weight accumulator unit reaches the predetermined weight threshold, and the real-time water use gradient index is less than the predetermined low threshold, the PLC main control module controls the system to switch to the membrane flushing state, opens the flushing valve control module and drives the variable frequency drive module to run at the predetermined high frequency flushing for the predetermined flushing time, and clears the flushing weight accumulator unit to zero after the flushing is completed.

[0037] Preferably, the data storage register module also includes a static timer unit; when the system is in sleep mode, the PLC main control module accumulates the timing value of the static timer unit. When the timing value of the static timer unit reaches the predetermined static time threshold, or when the water temperature of the circulating return water pipeline sampled by the water temperature acquisition module exceeds the predetermined temperature threshold, the PLC main control module controls the system to switch to the circulating antibacterial state, connects the circulating drive module and turns on the sterilization control module, drives the circulating water body to perform pipeline disinfection for a predetermined circulation time, and clears the static timer unit to zero after the circulation ends.

[0038] Preferably, the signal acquisition input module also includes a liquid level detection module; when the liquid level detection module detects that the inlet water tank is short of water, or when the pressure sampled by the outlet water pressure acquisition module is continuously lower than the predetermined safety lower limit for a predetermined fault timeout period, the PLC main control module switches the control system to the fault-safe state, cuts off the control signals of the frequency converter drive module, the inlet valve control module, the flushing valve control module and the circulation drive module, and latches the fault code in the status flag register unit in the data storage register module.

[0039] Preferably, when the pressure of the water supply main pipe sampled by the outlet pressure acquisition module is higher than the sum of the set pressure and the pressure control dead zone half-width, and the duration reaches the predetermined maintenance time, the PLC main control module controls the system to switch out of the frequency conversion boost water supply state and enter the sleep state; the dead zone compression coefficient is greater than 0 and less than 1. When the real-time water use gradient index increases, the PLC main control module automatically reduces the pressure control dead zone half-width; when the real-time water use gradient index decreases, the PLC main control module automatically increases the pressure control dead zone half-width.

[0040] Preferably, the fixed scanning cycle of the PLC main control module is 10ms; the flow pulse acquisition module is connected to the pulse flow sensor installed on the main water supply pipeline to receive high-speed pulses; the inlet pressure acquisition module and the outlet pressure acquisition module are respectively connected to the inlet pressure sensor and the outlet pressure sensor to receive standard current signals of 4mA to 20mA; the frequency conversion drive module is used to output 0V to 10V analog voltage signals to the water supply frequency converter to adjust the operating frequency of the frequency conversion booster pump; the water temperature acquisition module is connected to the temperature sensor located in the circulating return water pipeline.

[0041] Example 1: In this example, the building-level drinking water station is installed in a 30-story office building. The PLC main control module scans at a fixed cycle of 10ms. In cyclic operation, the signal acquisition input module receives high-speed pulse signals through a pulse flow sensor installed on the main water supply pipeline. When the increase in flow pulse detected within the current fixed scanning cycle exceeds a predetermined threshold, and pulse signals are present for a consecutive predetermined number of fixed scanning cycles, the PLC main control module sets the pulse Boolean flag. Set to logic 1 if necessary, otherwise set to logic 0. At the end of each fixed scan cycle, Write to 32-bit shift register The least significant bit is then used to perform a left shift on the 32-bit shift register. The update logic is as follows: ,in, and These are the 32-bit shift register units for the current fixed scan cycle and the previous fixed scan cycle, respectively. The value, As a pulse Boolean flag, after the shift is complete, the PLC main control module calculates the total number of logic 1s in the 32-bit shift register unit using the Popcount bit statistics instruction, obtaining the dimensionless real-time water use gradient index with a value range of 0 to 32. This is used to characterize the density and variability of water demand within the past 32 fixed scanning cycles, i.e., the 320ms sampling window. When the flow rate of the building's direct drinking water station changes abruptly, the flow pulse sequence will correspondingly become denser or sparser. Within the 320ms sampling window, when the pipeline changes from static zero flow to high flow, the pulse input will rapidly change from zero pulse state to high density input within 30ms, and the number of logic 1s will increase from 0 to more than 28. Under continuous high flow conditions, the pulse density remains high, and the value obtained by the Popcount bit statistics instruction can remain at 32. The PLC main control module adjusts the pressure control dead zone half-width according to this value, so that the control parameters change with the water use status of the pipeline.

[0042] The system is in variable frequency booster water supply mode. At that time, the PLC main control module dynamically adjusts the pressure control dead zone half-width according to the following formula: ,in, For pressure control dead zone half width, The half-width of the hysteresis loop is the base pressure, which is taken as 0.05 MPa in this embodiment; The dead zone compression factor is set to 0.4. This is a real-time water use gradient index; The total number of bits in the 32-bit shift register is set to 32. At 02:00 AM, when the flow rate is extremely low, the pulse signal is continuously missing, and the pulse Boolean flag is... Maintain logic 0, 32-bit shift register unit The data gradually changes to all zeros, and the real-time water use gradient index satisfies... Pressure control dead zone half width Increase to 0.05 MPa and set the pressure. When the pressure is 0.35 MPa, the control range of the water supply header pressure is 0.30 MPa to 0.40 MPa; the outlet pressure The system remains in hibernation mode when the pressure is 0.34 MPa. The variable frequency drive module and the variable frequency booster pump do not repeatedly start and stop near the critical pressure point.

[0043] After the user stops receiving water, the pulse Boolean flag is set. The water gradient index changes to logic 0 cycle by cycle. As the pressure decreases, the PLC main control module adjusts the pressure control dead zone half-width cycle by cycle according to the above formula; when When the pressure drops to 0, the pressure control dead zone half-width is updated to 0.05MPa. The outlet water pressure is higher than the sum of the set pressure and the current pressure control dead zone half-width, i.e., higher than 0.40MPa. After this pressure is maintained for a predetermined time, the PLC main control module switches out of the frequency conversion booster water supply state and enters the sleep state. After entering the centralized water collection period at 08:30 in the morning, multiple water terminals are turned on at the same time, and the flow pulse high-frequency input is used. The pulse Boolean flag is continuously set to logic 1. The real-time water gradient index rises to 28 within several fixed scanning cycles. At this time, the pressure control dead zone half-width is compressed to 0.0325MPa, and the control range of the water supply main pipe pressure becomes 0.3175MPa to 0.3825MPa.

[0044] During a sudden surge in water flow, the pressure in the main water supply pipe drops rapidly. The PLC main control module calculates the rate of change of water pressure sampling within each fixed scanning cycle. The calculation formula is as follows: ,in, The rate of change of outlet water pressure is denoted as . The water pressure at the outlet of the main water supply pipe is collected during the current fixed scanning cycle. The water pressure at the outlet of the main water supply pipe was collected in the previous fixed scanning cycle. With a fixed scan period of 10ms (0.01s), when the outlet water pressure drops from 0.34MPa in the previous fixed scan period to 0.31MPa in the current fixed scan period, the outlet water pressure sampling change rate is -3MPa / s, which is lower than the negative water hammer trigger threshold. In this embodiment, the threshold is set to -0.15 MPa / s. The PLC main control module suspends the closed-loop operation of the proportional-integral-derivative controller and outputs a 38 Hz feedforward reference frequency to the frequency converter drive module. and maintain a feedforward duration of 200ms. .

[0045] During feedforward control, the PLC main control module will compare the current outlet pressure deviation with the pressure control dead zone half-width. Multiplying the ratio by a predetermined scaling factor yields the initial integral value, and the calculation result is written into the integral storage register. The feedforward duration is... When the operation ends and the outlet water pressure rises back to around 0.33MPa, the PLC main control module resumes closed-loop operation. The proportional-integral-derivative regulator loads the initial integral value in the integral storage register unit, so that the closed-loop output is continuously connected with the feedforward reference frequency. The fixed scanning cycle of 10ms, together with the water supply frequency converter and variable frequency booster pump with a response time of 50ms, is used to handle the pipeline pressure drop process that lasts from 100ms to 500ms after the water terminal is quickly turned on. This process is the pressure drop process caused by the inertia of water flow in the pipeline. The PLC main control module outputs a 38Hz feedforward reference frequency before the pressure drop forms the lowest trough, so as to increase the pump output in advance and reduce the secondary pressure impact caused by local cavitation interruption and the back impact after the water column breaks.

[0046] When water demand decreases, the PLC main control module activates the variable frequency booster water supply mode. Towards dormancy During the switching control process, the flushing valve control module remains closed. The variable frequency drive module first reduces the output frequency at a first frequency reduction slope of 5Hz / s until the intermediate transition frequency of 20Hz. After the water terminal is closed, the pipeline flow decreases, but the variable frequency booster pump continues to output, and the outlet pressure rises accordingly. When the outlet pressure rises to the set pressure of 0.35MPa, the PLC main control module switches the frequency reduction rate to a second frequency reduction slope of 2Hz / s, and continues to reduce it to the predetermined lower limit frequency of 15Hz. After reaching the predetermined lower limit frequency, the predetermined valve closing time is delayed by 100ms before the inlet valve control module is closed and the output of the variable frequency drive module is cut off. The first frequency reduction slope is used to quickly reduce the pump head, the second frequency reduction slope is used to slow down the pressure change before the pump stops, and the delayed valve closing is used to reduce the back pressure flush generated when the pump stops and the valve closes at the same time.

[0047] In variable frequency booster water supply mode During operation, the flushing weight accumulator unit in the data storage register module accumulates weights according to the following formula for each fixed scan cycle: ,in, and These are the cumulative flushing weights for the current fixed scan cycle and the previous fixed scan cycle, respectively. The weighting ratio is set to 0.01. For the real-time water usage gradient index, when the stored value of the flushing weight accumulator unit reaches the predetermined weight threshold of 1000, and the real-time water usage gradient index is less than the predetermined low threshold of 4, the system transitions to the membrane flushing state. The PLC main control module starts the flushing valve control module and controls the frequency converter drive module to run at a predetermined high-frequency flushing frequency of 45Hz for 30 seconds to flush the reverse osmosis membrane; after flushing, the flushing weight accumulator unit is cleared to zero.

[0048] Under standard drinking water quality, for every 1000L of purified water treated by the reverse osmosis membrane module, micron-level inorganic salt scaling and colloidal adsorption layer form on the membrane surface, reducing the membrane permeate flux by 3.2%. Each pulse output by the pulse flow sensor represents 0.01L of water flowing through. Within a fixed scanning cycle of 10ms, the real-time water use gradient index is multiplied by 0.01 and accumulated cycle by cycle. When the accumulated value reaches the predetermined weight threshold of 1000, the corresponding reverse osmosis membrane has produced 1000L of water. When the real-time water use gradient index is lower than the predetermined low threshold, flushing is performed. After flushing, the membrane permeate flux recovers to 99.2% of its initial state.

[0049] When the system is in hibernation At that time, the PLC main control module accumulates the static timer unit. The system will switch to a circulating antibacterial state when the timing value reaches 7200s, or when the water temperature in the circulating return water pipeline sampled by the water temperature acquisition module exceeds the predetermined temperature threshold of 298.15K. The circulation drive module is connected and the sterilization control module is turned on, driving the circulating water to run for 300 seconds. After the circulation ends, the PLC main control module clears the static timer unit. The process parameter storage unit simultaneously saves the winter antifreeze monitoring lower limit of 280K and the predetermined temperature threshold of 298.15K. Among them, the over-temperature trigger of the circulation sterilization state uses 298.15K, and 280K is used to identify the low temperature state in winter. Within the daily water temperature range of 288K to 293K, the water temperature of the circulating return water pipe does not exceed 298.15K, and the system remains in a dormant state.

[0050] This embodiment also collects the water shortage signal of the inlet water tank through the liquid level detection module. The PLC main control module reads the signal in each fixed scanning cycle. When the water shortage of the inlet water tank is detected, the control system switches to the fault-safe state. If the pressure sampled by the outlet water pressure acquisition module is continuously lower than the predetermined limit safety lower limit, the PLC main control module accumulates the low pressure duration according to the fixed scanning cycle. After reaching the predetermined fault timeout duration, it switches to the fault-safe state. After entering the fault-safe state, the PLC main control module cuts off the control signals of the frequency conversion drive module, the inlet water valve control module, the flushing valve control module, and the circulation drive module, and writes the fault code corresponding to the fault triggering cause into the status flag register unit in the data storage register module for latching.

[0051] The above control process utilizes a fixed scan cycle, a 32-bit displacement register unit, Popcount bit statistical instructions, basic integer operations, and a status flag register unit to complete real-time water gradient index calculation, pressure control dead zone half-width adjustment, feedforward control, integral initial value writing, segmented frequency reduction, membrane flushing, circulating sterilization, and fault safety control. The PLC main control module completes various logic operations and input / output refreshes within a fixed scan cycle of 10ms, enabling each control state to switch according to the corresponding trigger conditions and execution order.

[0052] Example 2: This example constructs a hardware test platform for a building-based direct drinking water station, including a 30-layer simulated pipe network and a variable frequency booster pump. This platform is used to test control stability, water hammer suppression effectiveness, equipment start-up and shutdown frequency, and the fixed scan cycle of the PLC main control module. The 10ms response time is used for the water pressure sensor, which has a range of 0 to 1.0 MPa, an accuracy of 0.1%FS, and a sampling frequency of 100Hz. The high-speed pulse flow sensor has a resolution of 0.01L / pulse. The variable frequency drive module connects the water supply frequency converter with a response time of 50ms to the variable frequency booster pump. The test signal source is superimposed with the hydraulic vibration noise of the pipeline network with a signal-to-noise ratio of 25dB and the 50Hz power frequency harmonic interference.

[0053] Fixed scan cycle We will still use 10ms to account for the rate of change in effluent pressure sampling. The sampling rate and the computational load of the PLC main control module affect the detection time of pressure surges as the fixed scan period increases; conversely, as the fixed scan period decreases, the impact of high-frequency noise from the sensor on the rate of change calculation increases, affecting the 32-bit displacement register unit. Total number of digits Taking 32 corresponds to a 320ms pulse statistics window. This time window covers the mechanical jitter period of the flow pulse sensor and the micro-pulse range of water flow. The PLC main control module directly uses the Popcount bit statistics result as the real-time water usage gradient index. To avoid phase lag caused by multi-cycle floating-point filtering, the base pressure hysteresis half-width is... Take 0.05 MPa as the dead zone compressibility factor. Set the pressure to 0.4. Take 0.35MPa; these parameters are determined based on the allowable pressure fluctuation range of the water supply main pipe and the switching frequency of the frequency converter.

[0054] The test setup included the sample group of this invention, control group one, control group two, and control group three. The sample group of this invention performed Popcount bit statistics, adaptive adjustment of pressure control dead zone half-width, and negative water hammer trigger threshold. Judgment, feedforward control, integral initial value preset, and flushing weight accumulation; Control group 1 uses a fixed pressure of 0.05MPa to control the dead zone half-width and a conventional proportional-integral-derivative controller; Control group 2 retains the real-time water gradient index. The pressure control dead zone half-width adjustment is performed, but feedforward control and integral initial value preset are not executed; the control group three executes the control process of the sample group of this invention, and adjusts the dead zone compression coefficient. The test conditions were set to 0.85, including the following conditions: nighttime static micro-leakage condition 1 (00:00 to 05:00), morning peak sudden large flow water intake condition 2 (08:00 to 09:00), off-peak slight fluctuation condition 3 (10:00 to 17:00), and cumulative load and membrane flushing condition 4 (24 hours of continuous operation).

[0055] In operating condition one, the initial flow pulse increment for each test group was 0, and the real-time water gradient index was... All recorded values ​​were 0, and the rate of change of effluent pressure was 0. Both are -0.01 MPa / s, feedforward reference frequency. Both are 0Hz. The pressure control dead zone half-width of the sample group and control group II of this invention is 0.0500MPa. The water supply header pressure can vary from 0.3000MPa to 0.4000MPa. The water pump start-stop frequency of the sample group of this invention is 0 times / hour, and the minimum water supply pressure is 0. The pressure recovery time was 0ms, and the peak water hammer impact was 0.003MPa. The pump start-stop frequency of control group 2 was also 0 times / hour, the minimum water supply pressure was 0.341MPa, the pressure recovery time was 0ms, and the peak water hammer impact was 0.003MPa. The pressure control dead zone half-width of control group 1 was also 0.0500MPa, but it used a fixed dead zone and a conventional proportional-integral-derivative controller. The pump start-stop frequency was 14 times / hour, the minimum water supply pressure was 0.298MPa, the pressure recovery time was 850ms, and the peak water hammer impact was 0.042MPa.

[0056] In operating condition two, the initial flow pulse increment for each test group was 28, and the effluent pressure sampling change rate was... All values ​​are -3.00 MPa / s. The real-time water use gradient index of the sample group in this invention is obtained by Popcount digit statistics. The pressure control dead zone half-width is adjusted to 0.0325 MPa, as the value is 28. Since -3.00 MPa / s is lower than the negative water hammer trigger threshold of -0.15 MPa / s, this is necessary. The PLC main control module outputs a 38Hz feedforward reference frequency. During this input and control process, the water pump starts and stops once per hour, the minimum water supply pressure is 0.328 MPa, the pressure recovery time is 115 ms, and the peak water hammer impact is 0.012 MPa.

[0057] Control group 1 did not calculate the real-time water use gradient index when the initial flow pulse increment was 28, and the recorded value was 0. The pressure control dead zone half-width was maintained at 0.0500 MPa, and the feedforward reference frequency was 0 Hz. Its pump start-stop frequency was 1 time / hour, the minimum water supply pressure was 0.245 MPa, the pressure recovery time was 1420 ms, and the water hammer impact peak was 0.085 MPa. Control group 2 obtained the real-time water use gradient index 28 from 28 initial flow pulse increments, and the pressure control dead zone half-width was 0.0325 MPa, but the feedforward reference frequency was 0 Hz. Its pump start-stop frequency was 1 time / hour, the minimum water supply pressure was 0.262 MPa, the pressure recovery time was 980 ms, and the water hammer impact peak was 0.068 MPa. Under the same pressure control dead zone half-width condition, after the sample group of this invention outputs the feedforward reference frequency, its minimum water supply pressure, pressure recovery time, and water hammer impact peak showed corresponding differences from control group 2, which did not implement feedforward control.

[0058] Control group 3 uses a real-time water gradient index of 28 obtained from 28 raw flow pulse increments, with an outlet pressure sampling change rate of -3.00 MPa / s, a feedforward reference frequency of 38 Hz, and a dead zone compressibility coefficient. After setting it to 0.85, the pressure control dead zone half-width decreased to 0.0128 MPa, and the pump start-stop frequency increased to 8 times / hour; the minimum water supply pressure was 0.315 MPa, the pressure recovery time was 340 ms, the water hammer impact peak was 0.038 MPa, and the dead zone compressibility coefficient... When the coefficient of pressure control is 0.4, the half-width of the pressure control dead zone in the sample group of this invention is 0.0325 MPa, the pump start-stop frequency is 1 time / hour, and the pressure recovery time is 115 ms. After the dead zone compressibility coefficient is increased to 0.85, the half-width of the pressure control dead zone further decreases, while the pump start-stop frequency increases. This set of data shows that when the dead zone compressibility coefficient is around 0.4, the pressure response speed and the equipment start-stop frequency are relatively balanced; after increasing to 0.85, the control stability decreases.

[0059] In operating condition three, the initial flow pulse increments of both the sample group and control group one were 5, and the effluent pressure sampling change rate was... All values ​​were -0.08 MPa / s, not lower than the negative water hammer trigger threshold, and the feedforward reference frequency was 0 Hz. The real-time water use gradient index was obtained from the sample group of this invention through Popcount digit statistics. The control group's real-time water gradient index was 0, with a pressure control dead zone half-width of 0.0469 MPa, a pump start-stop frequency of 0 times / hour, a minimum water supply pressure of 0.345 MPa, a pressure recovery time of 45 ms, and a water hammer impact peak value of 0.005 MPa. The control group's real-time water use gradient index was 0, with a pressure control dead zone half-width of 0.0500 MPa, a pump start-stop frequency of 22 times / hour, a minimum water supply pressure of 0.312 MPa, a pressure recovery time of 620 ms, and a water hammer impact peak value of 0.031 MPa.

[0060] During the continuous 24-hour test under operating condition four, the sample group of this invention was tested by flushing the weight accumulator unit. Accumulate the real-time water gradient index for each fixed scan cycle The corresponding periodic weight, when the accumulated value reaches a predetermined weight threshold, water usage decreases and... At that time, the system avoids the morning and afternoon peak water usage periods and migrates to the membrane flushing state. Compared with the control group that uses fixed-time flushing, the flushing water consumption of the present invention was reduced by 36.2%, and the static timer unit... When the time reaches 7200s, the system migrates to a cyclic antibacterial state. During the test, the water temperature at the end of the pipeline did not exceed 280K, the bacterial colony index met the standard, the actual processing time of the PLC main control module within a single fixed scan cycle remained within 1.2ms, and the resource utilization rate of the main control processor was less than 15%. The above processing time and resource utilization indicate that the PLC main control module can complete displacement register statistics, feedforward control, and integral initial value preset within a fixed scan cycle.

[0061] Example 3: In this example, the building-level drinking water station is installed in a 30-story office building. The PLC main control module performs a fixed scan cycle of 10ms. The PLC main control module reads the pulse increment from the internal flow pulse acquisition module. To filter out false pulses caused by sensor mechanical jitter and pipeline fluid pulsation, a continuous cycle counter is set. and continuous periodicity determination threshold ,in, Choose 3. When the pulse increment detected within a fixed scan period exceeds a predetermined threshold, Increment by 1; otherwise, Reset to zero, when Only then will the pulse Boolean flag be set. Set to logic 1, otherwise set to logic 0.

[0062] At the end of each fixed scan cycle, the PLC main control module will Write to 32-bit shift register The least significant bit is then shifted left in the 32-bit shift register, and the update logic is maintained as follows. ,in, and These are the 32-bit shift register units for the current fixed scan cycle and the previous fixed scan cycle, respectively. The value, As the pulse Boolean flag, after the shift is complete, the PLC main control module calls the Popcount bit statistics instruction to calculate the total number of logic 1s in the 32-bit shift register unit, thus obtaining the real-time water use gradient index. This filters out random pulses that do not appear consecutively from the pulse sequence.

[0063] Continuous period counter The variable data storage area of ​​the PLC main control module is configured as a 16-bit unsigned integer register. When refreshing in each fixed scan cycle, if the pulse increment is greater than the predetermined threshold, the PLC main control module executes an increment instruction on the register. After incrementing, the register value is compared with the continuous cycle judgment threshold 3. When the count value reaches 3, subsequent increment instructions are blocked and the count value is latched at 3. When the pulse increment detected in any fixed scan cycle is less than or equal to the predetermined threshold, the PLC main control module writes 0 to the register through a transmission instruction, so that the continuous cycle counter is cleared and reset, avoiding register value overflow caused by long-term operation.

[0064] The system is in variable frequency booster water supply mode. At that time, the outlet water pressure acquisition module samples the pressure of the water supply main pipe in real time, and the PLC main control module performs the corresponding sampling in each fixed scanning cycle. The rate of change of water pressure sampling was calculated, where, The rate of change of outlet water pressure is denoted as . The water pressure at the outlet of the main water supply pipe is collected during the current fixed scanning cycle. The fixed scanning cycle is the water pressure collected from the water supply main pipe outlet during the previous fixed scanning cycle. Take 10ms, which is 0.01s.

[0065] When multiple valves at the user end are opened simultaneously, causing the rate of change in the outlet water pressure sampling to fall below the negative water hammer trigger threshold... At this time, the PLC main control module pauses the closed-loop operation of the proportional-integral-derivative controller and outputs a 38Hz feedforward reference frequency to the frequency converter drive module. and maintain a feedforward duration of 200ms. The negative water hammer triggering threshold in this embodiment Take -0.15MPa / s.

[0066] During feedforward control, the PLC main control module follows... Calculate the current outlet pressure deviation, where the set pressure is... Take 0.35 MPa, The current outlet water pressure is then used to calculate the deviation from the current outlet water pressure. Divide by the current pressure control dead zone half width Then multiply by a predetermined scaling factor of 120. ,according to Calculate the initial value of the integral. The initial integral value is then written to the integral storage register unit, and the feedforward duration is... Upon expiration, the PLC main control module resumes closed-loop operation and stores the initial integral value in the integral storage register unit. Loaded into the integral state variable of the proportional-integral-derivative controller.

[0067] The proportional-integral-derivative (PID) controller is constructed using a standard ladder diagram instruction block. During feedforward control, the PLC main control module sets the manual disturbance-free switching flag of this instruction block to 1, pausing the accumulation iteration of the closed-loop feedback algorithm. Simultaneously, through a data transmission instruction, the initial integral value is written to the address of the double-word register used to store the integral accumulation state variable in the PLD controller's data storage area. After the feedforward duration expires, the manual disturbance-free switching flag is reset to 0, the closed-loop operation is restarted, and the preset initial integral value in the register is used as the integral term base for the current fixed scan cycle, ensuring a continuous connection between the controller's output frequency and the feedforward reference frequency, thus preventing a jump in the control quantity during closed-loop recovery.

[0068] When user water consumption decreases and the pressure in the main water supply pipe increases, the system switches to variable frequency booster water supply mode. Enter sleep mode At this time, the PLC main control module keeps the flushing valve control module closed and starts segmented frequency reduction control. The variable frequency drive module first reduces the frequency by a first frequency reduction slope of 5Hz / s. Reduce the output frequency until an intermediate transition frequency of 20Hz is reached. During this process, the PLC main control module continuously reads the outlet water pressure sampled by the outlet water pressure acquisition module. When the outlet water pressure rises back to the set pressure of 0.35 MPa At that time, the down-frequency rate is switched to the second down-frequency slope of 2Hz / s. Continue to reduce the frequency to the predetermined lower limit of 15Hz. .

[0069] Once the output frequency reaches the predetermined lower limit, the PLC main control module starts the valve closing delay timer. ,when The count value reaches the predetermined valve closing time of 100ms. When the inlet valve control module is closed, the control signal output of the variable frequency drive module is cut off. The segmented frequency reduction and valve closing delay are executed in sequence to gradually reduce the water pump output and reduce the back pressure backflow caused when the water pump stops and the valve closes at the same time.

[0070] Example 4: This example combines Figures 1 to 2 This document describes a PLC control system for a building-based direct drinking water station, such as... Figure 1 As shown, the signal acquisition input module includes a flow pulse acquisition module, an inlet water pressure acquisition module, an outlet water pressure acquisition module, and a water temperature acquisition module. The drive control output module includes a frequency converter drive module, an inlet valve control module, a flushing valve control module, a circulation drive module, and a sterilization control module. The data storage register module includes a displacement register unit and an integral storage register unit. The PLC main control module schedules the control logic within a fixed scan cycle and dynamically adjusts the pressure control dead zone half-width. The flow pulse acquisition module receives high-speed pulse signals and writes pulses to the PLC main control module. The inlet water pressure acquisition module receives standard current signals. The outlet water pressure acquisition module evaluates the sampling change rate and water hammer status and feeds back the outlet water pressure to the PLC main control module. The water temperature acquisition module monitors the circulation... The PLC main control module calculates the initial integral value and writes it into the integral storage register unit. The integral storage register unit is used to write and load the initial integral value to restore the closed loop. The displacement register unit is used to calculate the water gradient index. The PLC main control module reads the real-time water gradient index from the displacement register unit. The PLC main control module outputs a control signal to switch the membrane flushing state to the flushing valve control module. The flushing valve control module cooperates with the membrane flushing state switching. The PLC main control module outputs a feedforward reference frequency to the frequency converter drive module. The frequency converter drive module receives the feedforward reference frequency to smooth water hammer impact. The inlet valve control module is used to control the opening and closing of the water supply valve. The circulation drive module is used to activate the disinfection of the circulating water network. The sterilization control module is used to activate synchronously in the circulation sterilization state.

[0071] like Figure 2As shown, when a water shortage is detected in the inlet tank, or when the pressure sampled by the outlet pressure acquisition module remains below the predetermined safety lower limit for a predetermined fault timeout period, the control system switches to a fault-safe state. When no water shortage is detected in the inlet tank and the pressure sampled by the outlet pressure acquisition module does not remain below the predetermined safety lower limit for a predetermined fault timeout period, it is determined that the pressure of the water supply header sampled by the outlet pressure acquisition module is lower than the difference between the set pressure and the half-width of the pressure control dead zone. When the pressure of the water supply header sampled by the outlet pressure acquisition module is lower than the difference between the set pressure and the half-width of the pressure control dead zone, the control system switches to a fault-safe state. Upon entering the variable frequency boosted water supply state, the system determines whether the stored value of the flushing weight accumulator unit reaches a predetermined weight threshold and whether the real-time water usage gradient index is less than a predetermined low threshold. When the stored value of the flushing weight accumulator unit reaches the predetermined weight threshold and the real-time water usage gradient index is less than the predetermined low threshold, the control system transitions to the membrane flushing state and resets back to the variable frequency boosted water supply state after flushing. Conversely, if the stored value of the flushing weight accumulator unit does not reach the predetermined weight threshold or the real-time water usage gradient index is not less than the predetermined low threshold, the system determines that the water supply header pressure is higher than the set pressure and the pressure control system is dead. When the pressure in the water supply header is higher than the sum of the set pressure and the pressure control dead zone half-width, and the duration reaches the predetermined maintenance time, the system switches out of the variable frequency booster water supply mode and enters a dormant state. When the pressure in the water supply header is not higher than the sum of the set pressure and the pressure control dead zone half-width, or the duration does not reach the predetermined maintenance time, the control system remains in the variable frequency booster water supply mode. When the water supply header pressure sampled by the outlet pressure acquisition module is not lower than the difference between the set pressure and the pressure control dead zone half-width, the system enters a dormant state. The system determines whether the timing value of the static timer unit reaches the predetermined static time threshold, or whether the water temperature of the circulating return water pipe sampled by the water temperature acquisition module exceeds the predetermined temperature threshold. When the timing value of the static timer unit reaches the predetermined static time threshold, or the water temperature of the circulating return water pipe sampled by the water temperature acquisition module exceeds the predetermined temperature threshold, the control system transitions to a circulating antibacterial state and returns to a dormant state after circulation. When the timing value of the static timer unit does not reach the predetermined static time threshold and the water temperature of the circulating return water pipe sampled by the water temperature acquisition module does not exceed the predetermined temperature threshold, the system remains in a dormant state.

[0072] Example 5: Before the building's direct drinking water station goes online, the PLC main control module performs signal endpoint calibration on the inlet pressure acquisition module, outlet pressure acquisition module, water temperature acquisition module, and flow pulse acquisition module. When calibrating the analog input channel, the standard current signal generator is adjusted to 4mA and 20mA in sequence to perform endpoint calibration on each AI channel, and the full-scale linear conversion calibration is completed on the outlet pressure of the water supply main pipe received by the outlet pressure acquisition module.

[0073] After completing the endpoint calibration, a high-precision standard pressure gauge is connected to the water supply header. Pressure is gradually increased in increments of 0.05 MPa within the range of 0.10 MPa to 0.60 MPa. The PLC main control module records the sampled conversion value from the outlet water pressure acquisition module at each calibration point, calculates the pressure conversion deviation between the sampled conversion value and the standard pressure gauge reading, and writes the corresponding deviation correction increment into the process parameter storage unit of the data storage register module for subsequent outlet water pressure sampling change rate. Calculation call.

[0074] When calibrating the flow pulse acquisition module, connect a standard high-speed pulse generator to the pulse input terminal and input continuous square wave pulses with frequencies ranging from 10Hz to 1kHz. The PLC main control module scans at a fixed period of 10ms. Run and check the continuous cycle counter. The accumulation process and the 32-bit shift register unit The left-shift refresh process continues for 320ms after the pulse input stops to confirm the real-time water use gradient index obtained from the Popcount bit statistics command. The data acquisition channel is calibrated to zero within the sampling window, thus completing the on-site calibration.

[0075] Dynamic control parameters were determined through closed-loop response tests. During the tests, the system switched to variable frequency booster water supply mode. Set pressure Using 0.35 MPa, maintaining a static zero flow rate at the user end, and real-time water gradient index. When the value is 0, different pressure control dead zone half-widths are set respectively. Record the start-up and shutdown status of the variable frequency drive module and the variable frequency booster pump, and the base pressure hysteresis half-width. When the pressure is 0.05 MPa, the pressure of the water supply main pipe changes slowly between 0.30 MPa and 0.40 MPa, and the variable frequency booster pump does not start erroneously. Based on this, the half-width of the hysteresis loop of the base pressure is determined to be 0.05 MPa.

[0076] Subsequently, a sudden surge in water flow was simulated to establish a real-time water usage gradient index. The coefficient of performance was increased to 28, and the dead zone compression factor was adjusted in increments of 0.05. When the dead zone compressibility coefficient increases from 0.1 to 0.4, the pressure control dead zone half-width decreases from 0.0456MPa to 0.0325MPa, and the pressure recovery time of the water supply main pipe is shortened from 850ms to 120ms. When the dead zone compressibility coefficient continues to increase to 0.6, the inverter output frequency oscillates at the critical pressure point. Based on the test results, the dead zone compressibility coefficient is determined to be 0.4, and the basic pressure hysteresis half-width and the dead zone compressibility coefficient are written into the process parameter storage unit of the data storage register module.

[0077] The parameter relationship of the pressure control dead zone half-width adopts a linear mapping between the pressure fluctuation of the water supply main pipe and the real-time water consumption gradient index. The basic pressure hysteresis half-width of 0.05MPa is equivalent to 14.3% of the set pressure of 0.35MPa. Its value is determined based on the allowable static pressure fluctuation range of the building's water supply network. The dead zone compressibility coefficient of 0.4 is determined based on the step response and stability test of a 30-story simulated network: When the dead zone compressibility coefficient is less than 0.2, the pressure control dead zone half-width contraction during peak water supply is insufficient, and the water supply main pipe pressure recovery time exceeds 850ms; when the dead zone compressibility coefficient is greater than 0.6, the inverter output frequency generates high-frequency oscillation under slight pressure disturbance, and the start-stop frequency of the variable frequency booster pump exceeds 8 times / hour; when the dead zone compressibility coefficient is 0.4, the pressure control dead zone half-width corresponding to the highest real-time water consumption gradient index is 0.0325MPa, the pressure recovery time is kept within 120ms, and the control loop damping ratio is 0.707.

[0078] Example 6: This example illustrates the fault safety control process of a building direct drinking water station. The PLC main control module reads the input signals of the liquid level detection module and the outlet pressure acquisition module at a fixed scanning cycle of 10ms, and controls the system status according to the detection results.

[0079] When the level detection module detects that the inlet water tank is low on water, the PLC main control module switches the control system to a fail-safe state within the current fixed scanning cycle, cuts off the control signals of the frequency converter drive module, the inlet water valve control module, the flushing valve control module, and the circulation drive module, and stops the frequency converter booster water supply, water inlet, membrane flushing, and circulation water supply actions. At the same time, it writes the fault code indicating that the inlet water tank is low on water into the status flag register unit in the data storage register module and keeps the fault code latched.

[0080] When the level detection module does not detect a water shortage in the inlet tank, the PLC main control module continues to read the water supply main pipe pressure sampled by the outlet pressure acquisition module. When the water supply main pipe pressure is lower than the predetermined safety lower limit, the low pressure duration is accumulated according to a fixed scanning cycle. If the water supply main pipe pressure recovers to above the predetermined safety lower limit before the predetermined fault timeout duration is reached, the accumulated low pressure duration is cleared to zero. If the water supply main pipe pressure continues to be lower than the predetermined safety lower limit and the accumulated time reaches the predetermined fault timeout duration, the PLC main control module switches the control system to a fault-safe state and cuts off the control signals of the frequency converter drive module, the inlet valve control module, the flushing valve control module, and the circulation drive module.

[0081] When the water supply main pipe pressure remains too low and enters a fail-safe state, the PLC main control module writes the corresponding low-pressure fault code into the status flag register unit. The status flag register unit latches the fault code, so that the water shortage fault in the inlet tank and the continuous low pressure fault in the water supply main pipe have different recording results. This makes it easier to determine the source of the fault based on the latched content. In the fail-safe state, the PLC main control module keeps the above control signals in the cut-off state to prevent the variable frequency booster pump, inlet valve, flushing valve and circulation drive device from continuing to operate under water shortage or continuous low pressure conditions.

[0082] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0083] Finally, 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.

Claims

1. A PLC control system for a building-based direct drinking water station, characterized in that, include: The signal acquisition input module includes an inlet water pressure acquisition module, an outlet water pressure acquisition module, a water temperature acquisition module, and a flow pulse acquisition module; The drive control output module includes a frequency converter drive module, an inlet valve control module, a flushing valve control module, a circulation drive module, and a sterilization control module; The data storage register module includes a displacement register unit and an integral storage register unit; The PLC main control module is used to read the pulse signal from the flow pulse acquisition module within a fixed scan cycle. At the end of each fixed scan cycle, it writes the pulse Boolean flag to the least significant bit of the displacement register unit and shifts the displacement register unit to the left. It calculates the total number of logic 1s in the displacement register unit through bit statistics instructions to obtain the dimensionless real-time water use gradient index. Based on the real-time water use gradient index, it dynamically adjusts the pressure control dead zone half-width and controls the system to switch between sleep mode, variable frequency boosting water supply mode, circulating antibacterial mode, and membrane flushing mode. It calculates the sampling change rate of the outlet water pressure acquisition module. When the sampling change rate is lower than the negative water hammer trigger threshold, it pauses the closed-loop operation and outputs the feedforward reference frequency to the variable frequency drive module. During the feedforward control period, it calculates the initial integral value based on the outlet water pressure deviation and the pressure control dead zone half-width and writes it to the integral storage register unit. After the feedforward control ends, it loads the initial integral value to resume the closed-loop operation.

2. The PLC control system for a building direct drinking water station according to claim 1, characterized in that, At the end of each fixed scan cycle, the PLC main control module detects the pulse increment of the flow pulse acquisition module. When the pulse increment is greater than a predetermined threshold and a pulse signal exists for a predetermined number of consecutive fixed scan cycles, the pulse Boolean flag is set to logic 1; otherwise, it is set to logic 0. The displacement register unit is a 32-bit displacement register unit, and the bit statistics instruction is the Popcount instruction. The real-time water gradient index ranges from 0 to 32.

3. A PLC control system for a building direct drinking water station according to claim 2, characterized in that, Under variable frequency boosted water supply conditions, the PLC main control module calculates the pressure control dead zone half-width according to the formula: ,in, For pressure control dead zone half width, Given a basic pressure hysteresis half-width, The dead zone compression factor is... For real-time water use gradient index, The total number of bits for the 32-bit displacement register unit; when the pressure of the water supply main pipe sampled by the outlet pressure acquisition module is lower than the difference between the set pressure and half the pressure control dead zone width, the PLC main control module controls the system to switch to the frequency conversion booster water supply state.

4. A PLC control system for a building direct drinking water station according to claim 1, characterized in that, The PLC main control module calculates the sampling change rate by dividing the difference between the water supply main pipe pressure collected in the current fixed scanning cycle and the previous fixed scanning cycle by the time length of the fixed scanning cycle. When the sampling change rate is lower than the negative water hammer trigger threshold, the PLC main control module cuts off the output of the proportional-integral-derivative controller, maintains the feedforward reference frequency output for a predetermined feedforward duration, and multiplies the ratio of the current outlet pressure deviation to the half-width of the pressure control dead zone by a predetermined scaling factor within the feedforward duration. The calculation result is written into the integral storage register unit as the initial integral value.

5. A PLC control system for a building direct drinking water station according to claim 3, characterized in that, When the control system switches from variable frequency boosting water supply mode to sleep mode, the PLC main control module keeps the flushing valve control module closed and drives the variable frequency drive module to reduce the output frequency to the intermediate transition frequency according to the first frequency reduction slope. When the outlet water pressure rises back to the set pressure, the frequency reduction rate is switched to the second frequency reduction slope, which is less than the first frequency reduction slope, and the frequency is reduced to the predetermined lower limit frequency. After a predetermined valve closing time, the inlet valve control module is closed and the output of the variable frequency drive module is cut off.

6. A PLC control system for a building direct drinking water station according to claim 1, characterized in that, The data storage register module also includes a flushing weight accumulator unit. In the variable frequency boosting water supply state, at the end of each fixed scan cycle, the PLC main control module multiplies the real-time water use gradient index by a predetermined weight ratio coefficient to obtain the periodic weight increment, and accumulates the periodic weight increment to the flushing weight accumulator unit. When the stored value of the flushing weight accumulator unit reaches the predetermined weight threshold and the real-time water use gradient index is less than the predetermined low threshold, the PLC main control module controls the system to switch to the membrane flushing state, opens the flushing valve control module and drives the variable frequency drive module to run at the predetermined high frequency flushing for the predetermined flushing duration, and clears the flushing weight accumulator unit to zero after the flushing is completed.

7. A PLC control system for a building direct drinking water station according to claim 1, characterized in that, The data storage register module also includes a static timer unit. When the system is in sleep mode, the PLC main control module accumulates the timing value of the static timer unit. When the timing value of the static timer unit reaches the predetermined static time threshold, or when the water temperature of the circulating return water pipeline sampled by the water temperature acquisition module exceeds the predetermined temperature threshold, the PLC main control module controls the system to switch to the circulating antibacterial state, connects the circulating drive module and turns on the sterilization control module, drives the circulating water to perform pipeline disinfection for a predetermined circulation time, and clears the static timer unit to zero after the circulation ends.

8. A PLC control system for a building direct drinking water station according to claim 1, characterized in that, The signal acquisition input module also includes a liquid level detection module. When the liquid level detection module detects that the inlet water tank is short of water, or when the pressure sampled by the outlet water pressure acquisition module is continuously lower than the predetermined safety limit for a predetermined fault timeout period, the PLC main control module switches the control system to the fault-safe state, cuts off the control signals of the frequency converter drive module, the inlet valve control module, the flushing valve control module and the circulation drive module, and latches the fault code in the status flag register unit in the data storage register module.

9. A PLC control system for a building direct drinking water station according to claim 3, characterized in that, When the pressure of the main water supply pipe sampled by the outlet pressure acquisition module is higher than the sum of the set pressure and the pressure control dead zone half-width, and the duration reaches the predetermined maintenance time, the PLC main control module controls the system to switch out of the frequency conversion boost water supply state and enter the sleep state; the dead zone compression coefficient is greater than 0 and less than 1. When the real-time water use gradient index increases, the PLC main control module automatically reduces the pressure control dead zone half-width; when the real-time water use gradient index decreases, the PLC main control module automatically increases the pressure control dead zone half-width.

10. A PLC control system for a building direct drinking water station according to claim 1, characterized in that, The fixed scan cycle of the PLC main control module is 10ms; the flow pulse acquisition module is connected to the pulse flow sensor installed on the main water supply pipeline to receive high-speed pulses; the inlet pressure acquisition module and the outlet pressure acquisition module are respectively connected to the inlet pressure sensor and the outlet pressure sensor to receive standard current signals from 4mA to 20mA; the frequency conversion drive module is used to output 0V to 10V analog voltage signals to the water supply frequency converter to adjust the operating frequency of the frequency conversion booster pump; The water temperature acquisition module is connected to the temperature sensor located in the circulating return water pipeline.

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