Water supply system

Abstract

The water supply system comprises a control module, wherein the following three sub-conditions are set in the control module: the system output pressure is less than or equal to the sum of the set pressure and the dormancy detection pressure difference; the frequency converter outputs frequency lt; hibernation detection frequency; the frequency converter outputs frequency change amplitude lt; and detecting the frequency difference value in a dormancy manner. Executing frequency injection operation when the three sub-conditions are met: adding the current output frequency of the frequency converter and the injection frequency to serve as the frequency converter output frequency to drive the motor to run for continuous frequency injection time; and then the output frequency of the frequency converter is controlled to be zero, so that the water supply system enters a dormant state.

Description

Technical Field

[0001] This invention relates to a water supply system that enables reliable and stable sleep control. Background Technology

[0002] In water supply systems, PID controllers are commonly used to control system pressure. One scenario in water supply system applications is that when a valve is closed, the water flow through the valve decreases to zero. In this scenario, it's desirable to control the water pump to reduce its speed until it stops operating. In an existing constant-pressure water supply system, a traditional PID controller controls the pump speed based on system pressure feedback. In the above scenario, the system pressure is essentially constant, and the PID controller does not control the pump speed to decrease. In another existing constant-pressure water supply system, after detecting the above scenario (i.e., the system output flow becomes very small or even zero), the pump speed is reduced, but the pump always runs at a low speed, which can easily cause system pressure instability. In yet another existing constant-pressure water supply system, the pump is put into sleep mode when both of the following conditions are met: actual output pressure ≥ set pressure, and output frequency ≤ sleep frequency within a specific time period. According to this sleep control scheme, the pump may enter sleep mode when the valve opening is very small, i.e., the output flow is very small; then, when the output pressure drops to the wake-up pressure, the pump is awakened. This leads to dynamic sleep-wake control that repeats repeatedly under low flow conditions. Summary of the Invention

[0003] The purpose of this invention is to provide a water supply system that can provide reliable and stable pump hibernation control when the valve is closed.

[0004] Therefore, in one aspect, the present invention provides a water supply system comprising:

[0005] A water pump driven by an electric motor, with a valve installed on the pump's output pipeline;

[0006] A frequency converter transmits an output frequency to a motor to control its operation.

[0007] A PID controller collects the output pressure of the water pump and performs closed-loop control on the frequency converter based on the set pressure and the output pressure to adjust the output frequency of the frequency converter.

[0008] The control module acquires the set pressure and output pressure, and includes the following preset parameters:

[0009] hibernation detection time;

[0010] Differential pressure detection during hibernation;

[0011] Sleep detection frequency;

[0012] Difference in sleep detection frequency;

[0013] Frequency injection time;

[0014] Injection frequency;

[0015] The control module includes a sleep condition, which comprises the following three sub-conditions:

[0016] Sub-condition (1): The output pressure ≤ set pressure + sleep detection pressure difference;

[0017] Sub-condition (2): The output frequency < sleep detection frequency;

[0018] Sub-condition (3): The output frequency change amplitude is less than the difference in sleep detection frequency;

[0019] The control module is configured to determine that the sleep condition is met when all three sub-conditions are met, and to perform a frequency injection operation after determining that the sleep condition is met: to make the PID regulator drive the motor to run for the duration of the frequency injection time by adding the current output frequency of the inverter to the injected frequency as the output frequency.

[0020] Then, the PID controller is set to zero to control the output frequency of the frequency converter, so that the water supply system enters a sleep state.

[0021] According to the water supply system of the present invention, a sleep condition is set based on feedback pressure and the output frequency of the frequency converter. This sleep condition includes three judgment criteria: an upper limit for output pressure, an upper limit for output frequency, and an upper limit for output frequency variation. This allows for more reliable detection of the conditions requiring the water pump to enter sleep mode, avoiding output pressure fluctuations and accidental sleep mode entry during normal low-flow water supply. Furthermore, after the sleep condition is met, a frequency injection operation is performed to increase the output pressure before initiating sleep mode, thereby ensuring that the sleep state is maintained during valve closure and preventing accidental awakening. The control scheme of the present invention can prevent the water supply system from being accidentally put into sleep mode and accidentally awakened, thus improving the reliability and accuracy of the sleep control of the water supply system. Attached Figure Description

[0022] The foregoing and other aspects of the present invention will be more fully understood and appreciated through the following detailed description with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a schematic diagram of a water supply system according to the present invention;

[0024] Figure 2 This is a schematic diagram of the control flow of the water supply system according to the present invention. Detailed Implementation

[0025] This invention relates generally to water supply systems, which are applicable to various water supply scenarios, such as municipal and industrial water supply, domestic water supply, and equipment water supply.

[0026] An exemplary layout of the water supply system of the present invention is as follows: Figure 1 As shown in the figure, the water supply system includes a water pump 1, which pressurizes and outputs water from a water source. The water pump 1 is driven by a motor 2, which is equipped with a frequency converter 3 to control the frequency and voltage of the drive current supplied to the motor 2.

[0027] The water supply system also includes a PID controller 4, which can acquire the actual output pressure Pout of the water pump 1 collected by the pressure transmitter 5.

[0028] The water supply system also includes a PLC (Programmable Logic Controller) 6, which is connected to the motor 2, frequency converter 3, and PID controller 4 to interact with them. Operators can set the parameters of the motor 2, frequency converter 3, and PID controller 4 via the PLC 6, and the PLC 6 can also collect the operating status signals of the motor 2, frequency converter 3, and PID controller 4 (such as the output frequency signal of the frequency converter 3). A system start button 7 is connected to the PLC 6. The PLC 6 can also receive detection signals from other sensors (such as a water source level sensor).

[0029] The operator can set the set pressure Pset of the water supply system via PLC 6. PLC 6 transmits the set pressure Pset to PID controller 4. PID controller 4 performs PID closed-loop control on frequency converter 3 based on the set pressure Pset and the actual output pressure Pout to adjust the output frequency of frequency converter 3 to motor 2.

[0030] A valve 8 is installed on the output pipeline of water pump 1. The output pipeline of water pump 1 can be opened and closed via valve 8, and the opening degree of valve 8 determines the flow area and output water volume of the output pipeline. A pressure transmitter 5 detects the actual output pressure Pout between the output port of water pump 1 and valve 8. This actual output pressure Pout is also called the feedback pressure.

[0031] In normal water supply operation, valve 8 opens to a certain degree, and motor 2 drives water pump 1 to operate. PID controller 4 receives the actual output pressure Pout detected by pressure transmitter 5. Based on the difference between the output pressure Pout and the set pressure Pset, PID controller 4 adjusts the output frequency of frequency converter 3 to change the speed of motor 2, thereby adjusting the output flow rate of water pump 1, so that the output pressure Pout is kept as close as possible to the set pressure Pset. In reality, the output pressure Pout may not be strictly equal to the set pressure Pset, but may fluctuate within a small range relative to the set pressure Pset. This invention achieves closed-loop control of the water supply system's output pressure through PID controller 4; therefore, this water supply system is a constant pressure water supply system.

[0032] When valve 8 is closed, its opening decreases, causing the output flow of pump 1 to decrease and the output pressure to increase. The PID controller 4 detects that the output pressure Pout is greater than the set pressure Pset, thereby reducing the output frequency of the frequency converter 3 to reduce the change in the speed of motor 2 and lower the output pressure Pout.

[0033] If valve 8 is completely closed, the output flow of pump 1 decreases to zero. It is desirable to put pump 1 (the water supply system) into a sleep state after a certain time window (for which a sleep detection time will be set). Specifically, the output frequency of the control inverter 3 slowly decreases to zero, causing pump 1 to stop running and enter sleep mode. In sleep mode, due to the closure of valve 8, the output pressure Pout remains essentially constant above the set pressure Pset. When valve 8 is reopened, the output pressure Pout drops to the wake-up pressure, and the output drive frequency of the control inverter 3 is adjusted to drive motor 2 to operate pump 1, thus waking pump 1 (the water supply system). The wake-up pressure can be set by the operator in PLC 6 and transmitted to the PID controller 4.

[0034] To achieve the aforementioned hibernation function, a control module (not shown in the figure) is provided in the water supply system of this invention. This control module is capable of acquiring the set pressure Pset and the output pressure Pout, and the following parameters are set within this control module:

[0035] Hibernation detection time T1;

[0036] The differential pressure ΔP is detected during hibernation.

[0037] Sleep detection frequency F1;

[0038] The difference in sleep detection frequency ΔF;

[0039] Frequency injection time T2;

[0040] Injection frequency F2.

[0041] These parameters can all be set or adjusted using PLC 6.

[0042] In addition, a hibernation condition is established in the control module. This hibernation condition contains three sub-conditions, and the hibernation condition is determined to be valid only if all three sub-conditions are met. These three sub-conditions are:

[0043] Subcondition (1): Feedback pressure Pout ≤ Set pressure Pset + Sleep detection pressure difference ΔP;

[0044] Subcondition (2): The output frequency of inverter 3 is less than the sleep detection frequency F1;

[0045] Subcondition (3): The output frequency change of inverter 3 is less than the difference ΔF between the sleep detection frequency and the frequency change.

[0046] After the above-mentioned sleep conditions are maintained for a period of time up to the sleep detection time T1, the control module performs a frequency injection operation.

[0047] Regarding the aforementioned sub-condition (1), it serves as the basic criterion for determining the sleep condition. During the closing of valve 8, due to a certain lag in the frequency adjustment of the PID controller 4 (this lag is actually beneficial for suppressing output pressure fluctuations), the feedback pressure Pout will definitely become higher than the set pressure Pset. However, unlike the prior art, this invention does not use the feedback pressure Pout becoming higher than the set pressure Pset as the basic criterion for determining the sleep condition. Instead, it uses the feedback pressure Pout being equal to or lower than (set pressure Pset + sleep detection pressure difference ΔP) as the basic criterion for determining the sleep condition. This avoids the accidental activation of the sleep operation when valve 8 is switched to a very small opening. Therefore, in setting the basic criterion, this invention is completely opposite to the prior art. The sleep detection pressure difference ΔP is a manually set and adjustable value, which can be set as a proportion of the set pressure Pset, for example, 0.2 to 0.4 times.

[0048] Regarding the aforementioned sub-condition (2), setting it can reliably prevent accidental activation of the sleep operation during normal operation of the water supply system (such as during periods of low flow output), thereby avoiding output pressure oscillations. The sleep detection frequency F1 is a manually set and adjustable value, which can be set to a value lower than the rated output frequency output by the PID controller 4 to the motor 2 during normal operation, for example, 0.1 to 0.5 times the rated output frequency. The sleep detection frequency F1 can be set based on a lower limit of the output frequency (equal to or slightly higher than this lower limit). When the output frequency is lower than this lower limit, due to internal leakage, backflow, and other problems of the water pump 2 itself, it can hardly output any flow. Therefore, this lower limit can be regarded as the output frequency required to maintain the minimum output flow of the water pump 1 to the motor 2. Below this lower limit, the present invention can directly shut down the water pump 2 to save energy.

[0049] Regarding the above sub-condition (3), by limiting the output frequency variation of inverter 3, the sleep operation can be avoided from being accidentally started during dynamic adjustment of the water supply system (i.e., when the output flow rate changes significantly during water supply operation). The sleep detection frequency difference ΔF is a manually set and adjustable value, which can be set to a ratio of the rated output frequency, for example, 0.1 to 0.3 times.

[0050] To ensure the accuracy of hibernation condition judgment, the hibernation detection time T1 should not be too short, for example, it can be set in the range of 5 to 10 seconds.

[0051] By setting these three sub-conditions in the hibernation conditions of this invention, the scenario in which hibernation needs to be initiated can be accurately determined, avoiding misjudgment and accidental initiation of hibernation. Compared with the prior art, which uses actual output pressure ≥ set pressure and output frequency ≤ hibernation frequency within a specific time as hibernation conditions, the accuracy of the scenario determination for initiating hibernation in this invention is greatly improved, and it can avoid accidental initiation of hibernation in situations such as low flow output or large changes in output flow.

[0052] Furthermore, after determining that the sleep condition is met, the control module of the present invention performs the following frequency injection operation: the PID regulator 4 controls the motor 2 to run by adding the injection frequency F2 to the current output frequency of the inverter 3, and the frequency injection time is T2.

[0053] After the frequency injection operation is sustained for a frequency injection time T2, the PID controller 4 controls the frequency converter 3 to stop outputting frequency, the motor 2 stops rotating, and the water pump 2 stops running, thus putting the water supply system into a dormant state.

[0054] Since the sleep condition remains in effect for a period of time equal to the sleep detection time T1, the output frequency of the inverter 3 of the PID controller 4 drops to a value that is essentially equal to the lower limit of the output frequency, and the output flow of the water pump 1 becomes very small or even zero. In this situation, before the PID controller 4 controls the inverter 3 to stop the output frequency, the PID controller 4 first controls the inverter 3 to drive the motor 2 at the current output frequency plus the injection frequency F2, which can increase the output pressure Pout of the water pump 1 slightly. Since the output pressure Pout will gradually decrease during the sleep period, increasing the output pressure Pout by frequency injection can more reliably maintain the sleep state and avoid or suppress the accidental awakening of the water supply system due to the natural decrease of the output pressure Pout (due to natural leakage of the system, etc.) to the wake-up pressure while the valve 8 is closed.

[0055] The injection frequency F2 and injection time T2 can be manually set, for example, to increase the output pressure Pout by a set value. It should be noted that during frequency injection operation, even if the output pressure Pout increases above the set pressure Pset + sleep detection pressure difference ΔP by setting the injection frequency F2 and injection time T2, it does not affect the water supply system entering sleep mode or maintaining sleep mode during valve 8 closure. This further improves the reliability of the sleep control of this invention.

[0056] The frequency injection time T2 can be set in the range of 1 to 5 seconds, for example, 1 to 2 seconds.

[0057] In the dormant state, when valve 8 is reopened, the output pressure Pout drops rapidly to the wake-up pressure, causing the PID controller 4 to control the frequency converter 3 to output the drive frequency to the motor 2 to drive the water pump 1 to run, thus waking up the water supply system.

[0058] The control module of this application can execute... Figure 2 The exemplary control flow is shown.

[0059] See Figure 2 In step S1, the feedback pressure, i.e. the water pump output pressure, is detected.

[0060] Next, in step S2, it is determined whether the sub-condition (1) of the hibernation condition is satisfied; if the result is no, proceed to step S5; if the result is yes, proceed to step S3.

[0061] In step S3, it is determined whether the sub-condition (2) of the hibernation condition is satisfied; if the result is no, proceed to step S5; if the result is yes, proceed to step S4.

[0062] In step S4, it is determined whether the sub-condition (3) of the hibernation condition is satisfied; if the result is no, proceed to step S5; if the result is yes, proceed to step S6.

[0063] In step S5, the timer is cleared, and the process returns to step S1.

[0064] In step S6, the timer increments by one timing unit (usually in the form of the counter incrementing by 1), and then proceeds to step S7.

[0065] In step S7, it is determined whether the timer has reached the sleep detection time T1; if the result is no, return to step S1; if the result is yes, proceed to step S8.

[0066] In step S8, during the frequency injection time T2, the PID controller 4 performs a frequency injection operation to increase the output pressure, and then stops the output frequency and enters a sleep state.

[0067] In the hibernation control flow described above, step S2, which determines whether sub-condition (1) of the hibernation condition is true, should be performed before steps S3 and S4, which determine whether sub-conditions (2) and (3) are true. If sub-condition (1) is false, there is no need to determine sub-conditions (2) and (3). Sub-condition (2) is determined only when sub-condition (1) is true, and then sub-condition (3) is determined only when sub-condition (2) is also true. This saves computation in the program and ensures the reliability of the determination results.

[0068] Based on the principles of this invention, those skilled in the art can make adaptive modifications to various details of the water supply system sleep control scheme according to specific application scenarios. In particular, the various parameters used in this invention can be set and adjusted (e.g., input to the control module via PLC 6). This control module can be integrated into the PID controller 4 in software form, or into the PLC 6, or even into the controller inside the frequency converter 3. This improves the adaptability of the control module.

[0069] According to the water supply system of the present invention, a sleep condition is set based on feedback pressure and the output frequency of the frequency converter. This sleep condition includes three judgment criteria: an upper limit for output pressure (set pressure Pset + sleep detection pressure difference ΔP), an upper limit for output frequency (sleep detection frequency F1), and an upper limit for output frequency variation (sleep detection frequency difference ΔF). This allows for more reliable detection of the conditions requiring the water pump to enter sleep mode, avoiding output pressure fluctuations and accidental sleep mode entry during normal low-flow water supply. Furthermore, after the sleep condition is met, a frequency injection operation is performed to increase the output pressure before initiating sleep mode, thereby ensuring the sleep state is maintained while valve 8 is closed and preventing accidental awakening. The control scheme of the present invention can prevent the water supply system from being accidentally put into sleep mode and accidentally awakened, thus improving the reliability and accuracy of the sleep control of the water supply system.

[0070] Although the invention has been described herein with reference to specific embodiments, the scope of the invention is not limited to the details shown. Various modifications may be made to these details without departing from the basic principles of the invention.

Claims

1. A water supply system, comprising: A water pump (1) is driven by a motor (2), and a valve (8) is provided on the output pipeline of the water pump (1); The frequency converter (3) transmits the output frequency to the motor (2) to control the operation of the motor (2); The PID controller (4) collects the output pressure (Pout) of the water pump (1) and performs closed-loop control on the frequency converter (3) based on the set pressure (Pset) and the output pressure (Pout) to adjust the output frequency of the frequency converter (3). The control module acquires the set pressure (Pset) and output pressure (Pout), and includes the following preset parameters: Sleep detection time (T1); Dormant detection pressure difference (ΔP); Sleep detection frequency (F1); Sleep detection frequency difference (ΔF); Frequency injection time (T2); Injection frequency (F2); The control module includes a sleep condition, which comprises the following three sub-conditions: Sub-condition (1): The output pressure (Pout) ≤ set pressure (Pset) + sleep detection pressure difference (ΔP); Sub-condition (2): The output frequency < sleep detection frequency (F1); Sub-condition (3): The output frequency change amplitude is less than the sleep detection frequency difference (ΔF); The control module is configured to determine that the sleep condition is met when all three sub-conditions are met, and to perform a frequency injection operation after determining that the sleep condition is met: the PID regulator (4) uses the current output frequency of the inverter (3) plus the injection frequency (F2) as the output frequency to drive the motor (2) to run for the frequency injection time (T2). Then, the PID controller (4) controls the output frequency of the frequency converter (3) to zero so that the water supply system enters a dormant state.

2. The water supply system as described in claim 1, wherein, When determining the sleep condition, the control module first determines whether sub-condition (1) is true, then determines sub-condition (2) only when sub-condition (1) is true, and then determines sub-condition (3) only when sub-condition (2) is also true.

3. The water supply system as described in claim 1 or 2, wherein, The injection frequency (F2) and injection time (T2) are set to control the output pressure (Pout) to increase by a set value.

4. The water supply system as described in claim 3, wherein, The injection frequency (F2) and frequency injection time (T2) are set to control the output pressure (Pout) to rise above the set pressure (Pset) + sleep detection pressure difference (ΔP).

5. The water supply system as described in any one of claims 1-4, wherein, The sleep detection pressure difference (ΔP) is a manually set and adjustable value, for example, it can be set to 0.2 to 0.4 times the set pressure (Pset).

6. The water supply system as described in any one of claims 1-5, wherein, The sleep detection frequency (F1) is a manually set and adjustable value, for example, based on the lower limit of the output frequency, which is the output frequency required to maintain the minimum output flow of the water pump (1) to the motor (2).

7. The water supply system as described in any one of claims 1-6, wherein, The sleep detection frequency difference (ΔF) is a manually set and adjustable value, for example, set to 0.1 to 0.3 times the rated output frequency of the inverter (3).

8. The water supply system as described in any one of claims 1-7, wherein, The sleep detection time (T1) is set in the range of 5 to 10 seconds; the frequency injection time (T2) is set in the range of 1 to 5 seconds, for example, 1 to 2 seconds.

9. The water supply system according to any one of claims 1-8 further includes a programmable logic controller (6) configured to be at least operable to input the parameters to or adjust the parameters of the PID controller (4).

10. The water supply system as described in claim 9, wherein, The control module is integrated into any one of the PID regulator (4), programmable logic controller (6), and inverter (3) internal controller.

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