Variable frequency-fixed frequency submersible sewage pump set centralized control method based on cooperative control

Abstract

The invention relates to the technical field of water pump control, in particular to a frequency conversion-fixed frequency submersible sewage pump set centralized control method based on cooperative control. According to the historical liquid level information of the regulating reservoir of the sewage plant and the historical starting and stopping working conditions of the fixed-frequency submersible sewage pump, a liquid level threshold value for matched starting and stopping of the fixed-frequency submersible sewage pump and the variable-frequency submersible sewage pump is set; when the water level of the regulating reservoir is higher than the (m + 1) th threshold value and lower than the (m + 2) th threshold value, the m fixed-frequency submersible sewage pumps are started, the variable-frequency submersible sewage pumps are controlled to enable the liquid levels of the variable-frequency submersible sewage pumps to be stabilized at the set value, and when the water level of the regulating reservoir is higher than the (m + 2) th threshold value, an alarm prompt is given; through cooperative control of one variable-frequency submersible sewage pump and a plurality of fixed-frequency submersible sewage pumps, adjustment of the variable-frequency submersible sewage pump is realized in combination with the liquid level difference, stable control of the liquid level of the adjusting tank of the sewage plant is realized, and the problem of energy consumption increase caused by frequent start and stop is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of water pump control, and in particular to a centralized control method of a variable frequency-fixed frequency submersible sewage pump group based on coordinated control. Background Art

[0002] At present, the main measures taken in energy-saving control of submersible sewage pump units in sewage plants are:

[0003] 1) Replace the old submersible sewage pump with a more efficient new submersible sewage pump, which can directly achieve energy saving effect from the perspective of equipment efficiency;

[0004] 2) Replace all old fixed-frequency submersible sewage pumps with new variable-frequency submersible sewage pumps to achieve efficient operation and coordination of submersible sewage pumps.

[0005] The above methods all achieve energy saving from the perspective of the overall pump group hardware, which is costly and does not consider the method of using a variable frequency submersible sewage pump to cooperate with an old fixed frequency submersible sewage pump to achieve energy saving control.

[0006] At present, the main measures taken in sewage treatment plants to control the liquid level in regulating tanks through submersible sewage pump units are:

[0007] The liquid level is adjusted by unilaterally controlling the start and stop of the fixed-frequency submersible sewage pump according to the pool flow and liquid level.

[0008] When the control is based solely on flow or liquid level, the water volume may change rapidly, causing the fixed-frequency submersible sewage pump to start and stop frequently, resulting in increased energy consumption. Summary of the invention

[0009] The present invention provides a centralized control method for a variable frequency-fixed frequency submersible sewage pump group based on collaborative control. Through the collaborative control of a variable frequency submersible sewage pump and multiple fixed frequency submersible sewage pumps, the variable frequency submersible sewage pump is regulated by a PID controller in combination with the liquid level difference, thereby achieving stable control of the liquid level in the sewage treatment plant regulating tank, solving the problem of increased energy consumption due to frequent starting and stopping when all fixed frequency submersible sewage pumps are used to adjust the liquid level, and the manufacturing cost is low.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for centralized control of a variable frequency-fixed frequency submersible sewage pump group based on coordinated control, comprising the following steps:

[0012] S1. Obtain the size information of the regulating tank and the types and quantity of the submersible sewage pumps, and set the liquid level threshold for the start and stop of the fixed-frequency submersible sewage pump and the variable-frequency submersible sewage pump according to the historical liquid level information of the sewage treatment plant regulating tank and the start and stop conditions of the historical fixed-frequency submersible sewage pump;

[0013] S2. When the water level in the regulating tank is lower than the set first threshold, all submersible sewage pumps stop running and alarm;

[0014] S3. When the water level in the regulating tank is higher than the set first threshold value and lower than the second threshold value, the variable frequency submersible sewage pump is started and its liquid level is set to stabilize at the set value;

[0015] S4. When the water level in the regulating tank is higher than the set second threshold value and lower than the third threshold value, another fixed-frequency submersible sewage pump is started, and the variable-frequency submersible sewage pump is controlled to stabilize its liquid level at the set value;

[0016] By analogy, the number of fixed-frequency submersible sewage pumps started is gradually increased;

[0017] S5. When the water level in the regulating tank is higher than the set m+1th threshold and lower than the m+2th threshold, start m fixed-frequency submersible sewage pumps and control the variable-frequency submersible sewage pumps to stabilize their liquid levels at the set value;

[0018] S6. When the water level in the regulating tank is higher than the set m+2th threshold, an alarm will be triggered.

[0019] Furthermore, the size information of the regulating tank includes the height of the regulating tank.

[0020] Furthermore, the types of the submersible sewage pumps include fixed-frequency submersible sewage pumps and variable-frequency submersible sewage pumps. The fixed-frequency submersible sewage pumps are m units, and the variable-frequency submersible sewage pump is 1 unit.

[0021] Furthermore, the liquid level threshold is divided into thresholds by averaging according to the size, depth, and number of submersible sewage pumps in the water pool.

[0022] Furthermore, when dividing the liquid level thresholds, the lowest and highest thresholds of the liquid level meet the needs of actual application, and the liquid level in the regulating tank cannot be allowed to be zero, causing the submersible sewage pump to run idle, or the liquid level cannot reach the highest level and overflow.

[0023] Furthermore, if the water level in the regulating tank drops, the number of fixed-frequency submersible sewage pumps that are started will be shut down one by one, and finally the number of variable-frequency submersible sewage pumps will be shut down.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) Use a variable frequency submersible sewage pump together with multiple fixed frequency submersible sewage pumps to reduce the energy consumption caused by frequent start and stop of fixed frequency submersible sewage pumps due to liquid level fluctuations, and can specifically control the frequency of the variable frequency submersible sewage pumps in the regulating tank to maintain the stability of the liquid level;

[0026] 2) Only one variable frequency submersible sewage pump is used to coordinate control with multiple fixed frequency submersible sewage pumps, achieving continuous liquid level adjustment with low power consumption, which is lower in cost than using variable frequency submersible sewage pumps for all units;

[0027] 3) When facing the energy-saving transformation of the fixed-frequency submersible sewage pump unit, compared with the scheme of completely changing to variable-frequency submersible sewage pumps, it has lower costs and the same effect;

[0028] 4) The required liquid level threshold can be set according to the historical liquid level information and relevant dimensions of the water tank, so as to control the submersible sewage pump, and the implementation of the present invention is simple. Description of the Drawings

[0029] Figure 1 is the flowchart of the method of the present invention.

[0030] Figure 2 is the PID control flowchart of the present invention. Detailed Embodiments

[0031] The following further describes the detailed embodiments of the present invention with reference to the drawings:

[0032] See Figure 1 , which is the flowchart of the method of the present invention. A centralized control method for variable-frequency-fixed-frequency submersible sewage pump groups based on cooperative control according to the present invention includes the following steps:

[0033] S1. Obtain the size information of the regulating tank and the types and quantities of the corresponding submersible sewage pumps. The size information of the regulating tank is the height H of the regulating tank. The types of the corresponding submersible sewage pumps include fixed-frequency submersible sewage pump A and variable-frequency submersible sewage pump B. The number of fixed-frequency submersible sewage pumps is m, which are respectively denoted as A1, A2... A m , one variable-frequency submersible sewage pump, denoted as B1. Set appropriate liquid level thresholds x1, x2... x m , x m+1 , x m+2 , where 0 < x1 < x 2< ... < x m < x m+1 < x m+2 < H, or it can also be evenly divided according to the size depth of the water tank and the number of submersible sewage pumps.

[0034] S2. Denote the mark corresponding to the submersible sewage pump when it stops pumping as 0, and vice versa as 1;

[0035] The control of the submersible sewage pump can be divided into the following working conditions:

[0036] 1) Working condition 1: All water pumps stop running and alarm, as shown in Equation (1):

[0037]

[0038] Among them, h(t) is the real-time liquid level of the regulating tank;

[0039] 2) Operating condition two: Start the variable-frequency submersible sewage pump, as shown in Equation (2):

[0040]

[0041] At this time, use the PID controller to control the variable-frequency submersible sewage pump to keep the water level in the pool stable at the set value y1 (x1 < y1 < x2);

[0042] 3) Operating condition three: Start one variable-frequency submersible sewage pump and one fixed-frequency submersible sewage pump, as shown in Equation (3):

[0043]

[0044] At this time, use the PID controller to control the variable-frequency submersible sewage pump to keep the water level in the pool stable at the set value y2 (x2 < y2 < x3);

[0045] And so on:

[0046] 4) Operating condition m + 2: Start one variable-frequency submersible sewage pump and m fixed-frequency submersible sewage pumps, as shown in Equation (4):

[0047]

[0048] At this time, use the PID controller to control the variable-frequency submersible sewage pump to keep the water level in the pool stable at the set value y m+1 (x m+1 <y m+1 <x m+2 ).

[0049] If the water level drops, gradually close the number of started fixed-frequency submersible sewage pumps, and finally close the number of variable-frequency submersible sewage pumps.

[0050] The PID controller consists of a regulator that performs proportional, integral, and derivative calculations to make the deviation zero. The regulator accepts the difference between the current water level and the set water level value corresponding to the current water level range, thereby controlling the frequency conversion device to adjust the variable-frequency submersible sewage pump, and the variable-frequency submersible sewage pump gradually stabilizes the water level in the regulating pool at the set value.

[0051] The control principle of the PID control system is as follows: See Figure 2 , there is a deviation signal e(t) between the actual output value h(t) and the set input value y(t) of the PID control system. Then, perform proportional, integral, and derivative operations on this signal respectively, and perform a certain linear combination on the results. Finally, apply the generated control signal u(t) to the controlled object.

[0052] Among them, the proportional part of PID is called proportional control. When the error of the system increases, proportional control will increase the output to reduce the error. The proportional constant K pIt is used to control the incremental size of the output. The larger its value, the faster the output changes. The product of the proportional constant and the error is called the proportional term, as shown in formula (5):

[0053] proportion=K p e(t) (5)

[0054] Among them, e(t)=y(t)-h(t); K p is the proportionality constant;

[0055] In the present invention, y(t) is the stable liquid level value set in different liquid level intervals, as shown in formula (6):

[0056]

[0057] The integral part of PID is called integral control: the output is adjusted by accumulating the error, and the integral constant K i It controls the size of the integral. It will gradually increase or decrease the output according to the degree of error accumulation, thereby achieving control of the system. The PID integral term intergration is shown in (7):

[0058]

[0059] Among them, T i is the integration time constant;

[0060] The differential part of PID is called differential control: differential control adjusts the output by detecting the rate of change of error, and the differential constant K d Controls the speed of change of the output. When the error changes rapidly, the differential control will increase or decrease the output to adapt to the changes in the system. The PID differential term is shown in (8):

[0061]

[0062] Among them, T d is the differential time constant;

[0063] Combining the three parts gives the output value of the PID controller:

[0064]

[0065] Simplify the above formula and let:

[0066]

[0067] Finally, the following relationship is obtained between the input and output of the PID controller:

[0068]

[0069] The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The methods used in the following embodiments are all conventional methods unless otherwise specified.

[0070]

Embodiment 1

[0071] Obtain the size information and historical liquid level information of the water tank. According to the information, the liquid level thresholds for starting and stopping the submersible sewage pump can be set to prevent the submersible sewage pump from idling and cavitating due to too low liquid level, thereby damaging the submersible sewage pump, or the situation where the liquid level is too high and the water tank leaks.

[0072] Obtain the types and quantities of the corresponding submersible sewage pumps, m fixed-frequency submersible sewage pumps and 1 variable-frequency submersible sewage pump. In practical applications, the number of variable-frequency submersible sewage pumps can be increased, not limited to 1.

[0073] Design the liquid level threshold for the submersible sewage pump to stop: when the real-time liquid level h(t) of the regulating tank < x1, all submersible sewage pumps stop running, and an alarm prompt should also be issued when the liquid level is lower than this threshold, which is convenient for the staff to check the reasons.

[0074] The liquid level threshold for the first submersible sewage pump to start: when x1 < h(t) < x2, start the only variable-frequency submersible sewage pump. At this time, the control system will control the frequency of the variable-frequency submersible sewage pump according to the liquid level difference between the real-time liquid level and the liquid level set value, so that the water tank liquid level is stabilized at the set value y1 (x1 < y1 < x2). Generally, the stable liquid level value can be taken as the middle value of this interval.

[0075] Design the liquid level threshold for two submersible sewage pumps to start: when x2 < h(t) < x3, start the second submersible sewage pump, which is a fixed-frequency submersible sewage pump at this time. At this time, the control system will control the frequency of the variable-frequency submersible sewage pump according to the liquid level difference between the real-time liquid level and the liquid level set value, so that the water tank liquid level is stabilized at y2 (x2 < y2 < x3).

[0076] And so on, design the liquid level threshold for m + 1 submersible sewage pumps to start: when x m+1 < h(t) < x m+2 When, start the (m + 1)-th fixed-frequency submersible sewage pump. At this time, use the PID controller to control the variable-frequency submersible sewage pump to stabilize the water tank liquid level at y m+1 (x m+1 < y m+1 < x m+2 ) position.

[0077] When the liquid level h(t) > xm+2 At this time, all submersible sewage pumps have been started and an alarm prompt is sent outwards.

[0078] Similarly, if the liquid level starts to drop, the corresponding submersible sewage pumps are stopped in sequence, and the variable-frequency submersible sewage pumps are closed-loop controlled within the corresponding liquid level range to keep the liquid level of the water tank stable.

[0079]

Embodiment 2

[0080] Obtain the size information of the water tank, the historical liquid level information, and the types and quantities of the corresponding submersible sewage pumps (3 fixed-frequency submersible sewage pumps and 1 variable-frequency submersible sewage pump), and determine appropriate liquid level thresholds based on the information.

[0081] Design the liquid level threshold for stopping the submersible sewage pumps: When the liquid level h < 1.72 m, all submersible sewage pumps stop running and an alarm is given.

[0082] Design the liquid level threshold for starting the first submersible sewage pump: When 1.72 m < h < 2.04 m, start the variable-frequency submersible sewage pump. At this time, use the PID controller to control the variable-frequency submersible sewage pump to keep the liquid level of the water tank stable at 1.88 m.

[0083] Design the liquid level threshold for starting two submersible sewage pumps: When 2.04 m < h < 2.35 m, start the second submersible sewage pump, which is a fixed-frequency submersible sewage pump. At this time, use the PID controller to control the variable-frequency submersible sewage pump to keep the liquid level of the water tank stable at 2.21 m.

[0084] Design the liquid level threshold for starting three submersible sewage pumps: When 2.35 m < h < 2.68 m, start the third fixed-frequency submersible sewage pump. At this time, use the PID controller to control the variable-frequency submersible sewage pump to keep the liquid level of the water tank stable at 2.51 m.

[0085] Design the liquid level threshold for starting four submersible sewage pumps: When 2.68 m < h < 3.01 m, start the third fixed-frequency submersible sewage pump. At this time, use the PID controller to control the variable-frequency submersible sewage pump to keep the liquid level of the water tank stable at 2.84 m.

[0086] When the liquid level h > 2.84 m, at this time all submersible sewage pumps have been started and an alarm prompt is sent outwards.

Claims

1. A method for centralized control of variable frequency-fixed frequency submersible sewage pump group based on cooperative control, characterized in that: The steps include: S1. Obtain the size information of the regulating tank and the types and number of submersible sewage pumps. According to the historical liquid level information of the sewage treatment plant regulating tank and the start and stop conditions of the historical fixed-frequency submersible sewage pumps, set the liquid level threshold for the start and stop of the fixed-frequency submersible sewage pumps and the variable-frequency submersible sewage pumps. S2. When the water level in the regulating tank is lower than the set first threshold, all submersible sewage pumps stop running and alarm; S3. When the water level in the regulating tank is higher than the set first threshold value and lower than the second threshold value, the variable frequency submersible sewage pump is started and its liquid level is set to stabilize at the set value; S4. When the water level in the regulating tank is higher than the set second threshold value and lower than the third threshold value, another fixed-frequency submersible sewage pump is started, and the variable-frequency submersible sewage pump is controlled to stabilize its liquid level at the set value; By analogy, the number of fixed-frequency submersible sewage pumps started is gradually increased; S5. When the water level in the regulating tank is higher than the set m+1th threshold and lower than the m+2th threshold, start m fixed-frequency submersible sewage pumps and control the variable-frequency submersible sewage pumps to stabilize their liquid levels at the set value; S6. When the water level in the regulating tank is higher than the set m+2th threshold, an alarm will be triggered.

2. According to the method for centralized control of variable frequency-fixed frequency submersible sewage pump group based on cooperative control according to claim 1, it is characterized in that: The size information of the regulating tank includes the height of the regulating tank.

3. The method for centralized control of variable frequency-fixed frequency submersible sewage pump group based on cooperative control according to claim 1 is characterized in that: The types of the submersible sewage pumps include fixed-frequency submersible sewage pumps and variable-frequency submersible sewage pumps. There are m fixed-frequency submersible sewage pumps and one variable-frequency submersible sewage pump.

4. A method for centralized control of variable frequency-fixed frequency submersible sewage pumps based on cooperative control according to claim 1, characterized in that: The liquid level threshold is divided into thresholds according to the size, depth and number of submersible sewage pumps.

5. The method for centralized control of variable frequency-fixed frequency submersible sewage pump group based on cooperative control according to claim 1 is characterized in that: When dividing the liquid level thresholds, the lowest and highest thresholds of the liquid level meet the needs of actual application, and the liquid level in the regulating tank cannot be allowed to be zero, causing the submersible sewage pump to run idle, or the liquid level cannot reach the highest level and overflow.

6. A method for centralized control of variable frequency-fixed frequency submersible sewage pumps based on cooperative control according to claim 1, characterized in that: If the water level in the regulating pool drops, the number of fixed-frequency submersible sewage pumps that are started will be shut down one by one, and finally the number of variable-frequency submersible sewage pumps will be shut down.

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