JP2010216288A - Parallel-off control method for parallel pump and parallel-off control system for parallel pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a parallel-off control method and system for a parallel pump, in which N(N≥2) units of variable speed pumps driven by a variable voltage and a variable frequency power source are constituted so as to execute parallel operation and which is controlled by delivery pressure constant control or estimated end pressure constant control. <P>SOLUTION: The sum of axial drive force when N units of variable speed pumps are operated in parallel and the sum of axial drive force when N-1 units of pumps are operated in parallel are calculated from a head-flow rate quadratic approximate expression of the pump and a target curve of the delivery pressure constant control or a target curve of the estimated end pressure constant control and a flow rate-efficiency quadratic approximate expression of the pump, and pushing-in head. By comparing the sums of the axial drive forces, a flow rate in which the sum of axial drive force during the operation of the N-1 units becomes equal to the sum of axial drive force during the operation of the N units is computed as an energy efficient parallel off flow rate. The parallel-off flow rate is set in the control device as a parallel-off flow rate set value and compared with an actual flow rate, thereby executing the parallel-off control of the pump. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is configured such that a variable speed pump N (N ≧ 2) driven by a variable voltage, variable frequency power supply is operated in parallel, and is controlled by a constant discharge pressure control or an estimated terminal pressure constant control. The present invention relates to a parallel pump disconnection control method and a parallel pump disconnection control system. When the water supply load decreases, the direct feed water supply system disconnects one pump, and when switching from N unit parallel operation to N-1 unit parallel operation, the parallel pump disconnection control method saves energy compared to the conventional method. The present invention relates to a parallel pump disconnection control system.

  In the conventional parallel pump disconnection control method, when the water supply load is reduced and it is possible to disconnect one pump, the water supply load is below the flow rate that can be supplied by N-1 units. It was detected by the speed, frequency, etc. of the electric motor, and after confirming that the predetermined state had passed, the control was performed so that one pump was disconnected and stopped. The conventional parallel pump disconnection control method has not compared the total shaft power of N units and the total shaft power of N-1 units as proposed by the present invention. For this reason, the conventional parallel pump disconnection control method has a drawback that the total shaft power immediately after the disconnection operation becomes larger than the total shaft power before the disconnection.

  For example, the pump control method described in Japanese Patent Application Laid-Open No. 5-240165 includes a detection unit for low flow rate stop and a pressure detection unit, and in parallel according to signals from these detection units, an optimal state of the parallel flow rate Therefore, a complicated mechanism for adjusting the on / off flow rate of the flow rate detection unit for parallel and disconnection control is not provided.

JP-A-5-240165

  In the present invention, the flow rate at which the total shaft power after the disconnection operation becomes equal to the total shaft power before the disconnection is called an energy saving disconnection flow rate, and the energy saving disconnection flow rate is a set constant, a pump head-flow approximation formula, Provided is a parallel pump disconnection control method that saves energy from the conventional method by calculating from the target curve of pressure control, the pump efficiency approximation formula, the number of parallel pumps, and the detected value of the indentation head, and setting these values.

  The first parallel pump disconnection control method uses the indentation head as a variable, the total shaft power when N pumps are operating in parallel, and the N-1 pumps operating in parallel. Find the shaft power of. The energy saving parallel flow rate is obtained by comparing the shaft power when N pumps and N-1 pumps are operating in parallel, and obtaining a flow rate at which the sum of the former shaft power and the latter shaft power are equal. . The first parallel pump disconnection control method sets this result, and when the actual flow rate is equal to or lower than this set value, the pump is disconnected.

  The second parallel pump disconnection control method executes the energy saving parallel flow rate calculation off-line and installs the result as a linear equation in the control device, thereby simplifying the parallel pump. An object of the present invention is to provide a method for energy saving disconnection control and a parallel pump disconnection control system.

  In the parallel pump disconnection control method of the present invention, as a first means, the total shaft power when N pumps are operating in parallel and the shaft when N-1 pumps are operating in parallel The total power is calculated based on the pump head-flow rate quadratic approximation, target curve for constant discharge pressure control, or target curve for constant terminal pressure constant control, pump flow-efficiency quadratic approximation formula, push head, N units. The total shaft power in the middle and the total shaft power during N-1 unit operation are calculated. By comparing the two, the flow rate at which the sum of the shaft power of the N-1 unit operation becomes equal to the sum of the shaft powers of the N unit operation is calculated as an energy saving parallel flow rate. This disengagement flow rate is set as a disengagement flow rate setting value in the control device, and compared with the actual flow rate, the disengagement control of the pump is executed.

  As a second means, in order to simplify the above-described online calculation, a linear equation for calculating an energy saving parallel flow rate is derived in advance from the pushing head and the number of pumps in parallel operation. The derived linear equation for estimating the energy-saving disconnection flow rate is installed as control software for the water supply system, and the pump disconnection control is executed.

  According to the present invention, when the pumps operating in parallel are disconnected, the total shaft power after disconnection is predicted, and the flow rate at which the total shaft power after disconnection becomes equal to the total shaft power before disconnection is calculated. Since it is calculated and set as the energy-saving disconnection flow rate and controlled to be disconnected at this flow rate, the total shaft power increases temporarily immediately after disconnection as in the conventional method, and the energy saving performance is impaired. Since no problem occurs, the energy saving effect is great.

  According to the present invention, when the indentation head is large, the energy saving disconnection flow rate can be moved to the small flow rate side and is automatically performed. Therefore, the energy saving effect is improved as compared with the conventional method in which the disconnection flow rate is fixed. There is an advantage that it is big.

It is a whole lineblock diagram of a direct feed water supply system of two pumps parallel and presumed terminal pressure constant control to which energy saving disconnection control of the present invention is applied. It is a block diagram explaining the energy-saving disconnection control of this invention. It shows a control flow of energy saving parallel flow calculation. An example of calculating the energy-saving parallel flow rate for two units in parallel operation is shown. The calculation example of the energy saving parallel flow volume in discharge pressure constant control is shown. The example which calculated the linear regression formula of the energy saving parallel flow volume in the case of estimation terminal pressure constant control is shown. An example of calculating a linear regression equation of the energy saving parallel flow rate when h00 = 0.8 (p.u.) under constant discharge pressure control is shown. The example which calculated the coefficient and constant of the linear regression type is shown. The example which calculated the coefficient and constant of the linear regression type is shown. It is a block diagram explaining energy-saving disconnection control by a different method. The calculation flow which performs off-line calculation is shown.

  FIG. 1 is an overall configuration diagram of a direct feed water supply system in which two pumps are connected in parallel, and the estimated terminal pressure is constant, to which the energy saving disconnection control of the present invention is applied. FIG. 2 is a block diagram illustrating the energy saving disconnection control of the present invention. FIG. 3 shows a control flow of energy saving parallel flow rate calculation. FIG. 4 shows a calculation example of the energy-saving disconnection flow rate of two units in parallel operation. FIG. 5 shows a calculation example of the energy saving parallel flow rate in the discharge pressure constant control. FIG. 6 shows an example in which a linear regression equation of an energy saving parallel flow rate for explaining the invention according to another method is calculated. FIG. 7 shows an example in which a linear regression equation of the energy saving parallel flow rate for explaining the invention by another method is calculated. FIG. 8 shows an example in which the coefficients and constants of the linear regression equation are calculated. FIG. 9 shows an example in which the coefficients and constants of the linear regression equation are calculated. FIG. 10 is a block diagram illustrating the energy saving disconnection control by a different method. FIG. 11 shows a calculation flow for performing offline calculation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an estimated end pressure constant control configured to perform parallel and alternate operation by two variable speed pumps driven by a variable voltage and variable frequency power source, applying the method of energy saving parallel flow control of the present invention. It shows the overall configuration of the direct feed water supply system that performs. However, in order to describe the present invention, pump alternate operation sequence control, pump pressure holding operation sequence control, and the like that are not directly related are omitted.

  In FIG. 1, the present invention relates to a pump system (1 to 12), motors 13 and 14 and inverters 21 and 22 for driving the pump system, an estimated terminal pressure constant control circuit 31, and an energy saving disconnection stop control circuit 41. And at least. The energy saving disconnection stop control circuit 41 will be described in detail with reference to FIGS.

  First, the operation of the estimated terminal pressure constant control circuit will be briefly described with reference to FIG. The pressure setters 31 to 4 are minimum lift setters for setting the minimum lift h0 (p.u.) of the estimated terminal pressure constant control, and the output .DELTA.h (p.u.) of the pipe friction loss lift calculators HEAD31 to 6. ) Is added to generate the target head hS (p.u.) for the estimated terminal pressure constant control. The target head hS (p.u.) is compared with the output hI of the pressure detector 11, the deviation is amplified by the PID 31 to 1 or the PI controller, and the output fS * is converted into the D / A converter 31. Through ~ 2 and 31 ~ 3, frequency commands f1S and f2S are given to the inverter 21 and the inverter 22, and the speeds of the pump 1 and the pump 2 are adjusted. That is, the estimated terminal pressure constant control system is configured.

The pipe friction loss lift calculators HEAD31 to 6 receive the square q * ² of the estimated flow rate from the flow rate control circuits FLOW31 to ⁵ and calculate the friction loss lift Δh by Δh = (1−h0) q * ² . The flow rate control circuits FLOW31 to FLOW5 have the pump head hP obtained by subtracting the pushing pressure hSU from the pump discharge pressure hI and the inverter command frequency fS * as input, and the pump head-flow rate approximation quadratic equation The square of flow rate q * ² and its square root q * are calculated. Although details of the sequence circuits SEQ 31 to 7 are not shown in the figure, sequence control such as paralleling, disconnecting control, pump pressure holding control, pump stop control, etc. required for automatic operation of the direct feed water system is performed by software. The control block to perform is shown.

  Signals RUN1 and RUN2 from the sequence circuits SEQ31 to SEQ7 are signals for operating the inverters 21 and 22, respectively. A signal ZERO given to the sequence circuits SEQ 31 to 7 is a FLS signal of the flow switch 10 and indicates a signal for detecting that the feed water flow rate has become a specified value or less. The STPs of the sequence circuits SEQ 31 to 7 indicate signals for stopping the pump when the feed water flow rate becomes equal to or less than the energy saving parallel flow rate.

  As illustrated, the pump 1 and the pump 2 are driven by an electric motor 13 driven by an inverter 21 and an electric motor 14 driven by an inverter 22. As shown in the figure, the pump 1 and the pump 2 are arranged in parallel on the discharge side via check valves 3 and 5 and shut-off valves 4 and 6 and on the suction side by a common suction pipe. It is connected. The backflow prevention valve 7 prevents backflow from the water supply system to the water main when the pump is stopped. The pressure detector 12 is a water main pressure detector placed on the upstream side of the check valve 7.

  In addition, the backflow prevention valve 8 of the bypass pipe is placed so that when the water main pressure is higher than the specified pressure, the pump is stopped and water can be supplied only by the water main pressure. . According to the above explanation, if the energy saving disconnection stop signal can be given from the energy saving disconnection stop control circuit 41 as the STP of the sequence circuits 31 to 7, the configuration shown in FIG. Will be able to.

FIG. 2 is a block diagram illustrating the energy saving disconnection control of the present invention. FIG. 3 shows a control flow of energy saving parallel flow rate calculation. 2 and 3, the method of energy saving disconnection control of the present invention will be described. First, a method for calculating the energy saving separation flow rate qMIN will be described. The head-flow rate characteristic of the water supply system when N pumps having the same characteristic are operating in parallel is expressed by Expression (1).
hPAN = hPPAN + hSU = a f 2 - (b / N 2) q 2 ---- (1)
here,
hPAN = head of water supply system when N pumps are operating in parallel (pu)
= Water supply system head H (m) / Pump rated head HPN (m)
hSU = Indentation head (pu)
= Indentation head HSU (m) / Rated pump head HPN (m)
a = pump head coefficient b = pump flow coefficient f = motor frequency (pu) = motor frequency F (Hz) / rated frequency FN (Hz)
q = Flow rate (pu) = Pump flow rate (m ³ / min) / Pump rated flow rate (m ³ / min)
N = Number of parallel operation pumps (units)

On the other hand, the target curve for the estimated terminal pressure constant control is expressed by Expression (2).
hL N = h0 + ((1−h0) / N ² ) q ² ---- (2)

here,
hL N = Target head of fixed terminal pressure constant control (pu)
＝ Target lift HLN (m) for constant estimated terminal pressure control / Rated pump head lift HPN (m)
h0 ＝ Minimum head (pu) for the estimated terminal pressure constant control
＝ Minimum lift H0 (m) with constant estimated terminal pressure control / Rated pump head HPN (m)
H0 ≥ Actual lift HA (m) + Pipe end lift HE (m)

Therefore, the frequency of the electric motor with respect to the flow rate can be calculated as shown in Equation (3) with (1) = (2).
fN = ((γq ² -hSU + h0) / a) ^1/2 ---- (3)
here,
γ = (b + 1−h0) / N ²

Therefore, since the motor frequency when the estimated terminal pressure constant control is performed can be calculated for an arbitrary flow rate, the variable (q / f) for determining the pu efficiency (= pump efficiency / pump rated efficiency) of the pump is Can be calculated. By substituting this result into the pu efficiency approximate expression (4) of the pump, the operating pump pu can be calculated.
ηN = C1 (q0 / f N) ² + C ₂ (q0 / f N) + C ₃ ---- (4)
here,
ηN = Pump pu efficiency (pu) when the flow is shared by N pumps
q0 = shared flow of one pump = q / N (pu)
C ₁ , C ₂ , C ₃ = coefficients representing the efficiency characteristics of the pump

Therefore, the total LN (pu) of the shaft power at an arbitrary flow rate when the N pumps are operating in parallel can be calculated by Expression (5).
LN = ((q / N) × (hL N −hSU)) × (1 / ηN) × N— (5)
In the same manner, the total shaft power in the case where one parallel pump is disconnected from N units and is operated with N-1 units is obtained by substituting N with N-1 in the above formulas to obtain the formula (6 ).
LN −1 = ((q / (N−1)) × (h _LN−1 −hSU)) × (1 / η _N−1 ) × (N−1) ---- (6)
here,
L _N-1 = Total shaft power (pu) when N-1 pumps are operating in parallel
η _N-1 = Pump pu efficiency (pu) when the flow rate is shared by N-1 pumps
= C ₁ (q ₁ / f _N-1 ) ² + C ₂ (q ₁ / f _N-1 ) + C ₃
q ₁ = q / (N−1)
f _N-1 = ((γ _N-1 −q ² −hSU + h 0) / a) ^1/2
γ _N-1 = (b + 1-h0) / (N-1) ²
_{hL N-1 = h0 + (} (1 -h0) / (N-1) 2) q 2

Therefore, the difference ΔL (pu) between the total shaft power of N units parallel operation and the total shaft power of N−1 units operation can be calculated by Equation (7).
ΔL = L _N -L _N-1 ---- (7)
The total shaft power during the operation of N pumps and the total shaft power of N-1 units can be obtained by detecting the indentation head at that point in time if the target curve of the estimated terminal pressure constant control and the number of pumps to be operated are determined. The flow rate can be calculated by the above formulas (5) and (6).

  Therefore, the flow rate satisfying the equation (7), that is, the energy saving parallel flow rate qMIN can be calculated. This calculation is repeated from the maximum number of parallel pumps NMAX to N = 2 in the water supply system, and the energy saving parallel flow rate qMIN (N) for the number of pumps in parallel is calculated and stored in a table. This calculation process is referred to herein as an energy saving parallel flow rate calculation process.

  This process is started each time a pump parallel input completion signal is received from the sequences SEQ31 to SEQ7. If data from NMAX to N = 2 is acquired and stored in the table, this calculation is terminated by a signal indicating the completion of the energy saving parallel flow rate calculation.

  In the present embodiment, FIG. 1 shows the case of two pumps in parallel operation, but the energy saving parallel flow rate calculation processing is performed with NMAX = 5 as the maximum parallel number of the current water supply system. Is remembered. Each time a parallel input completion signal is issued, the energy saving parallel flow calculation processing is activated to detect the newest indentation head at that time, and the energy saving parallel flow qMIN (N) at this value is calculated. Overwrite the data on the table and update the data.

  Further, in this embodiment, this arithmetic processing is started not only every time when a parallel closing completion signal is issued, but also every time a disconnection completion signal is issued when one pump is disconnected, and data is updated. I am doing so. This is to obtain data of the energy saving flow rate qMIN (N) under the condition of the pushing head as close as possible to the actual.

Control of disconnection operation during parallel operation is performed as follows.
Since the number of parallel pumps in operation is known from the parallel charging completion memory, qMIN (N) data for N parallel pumps is read from the table and this value is compared with the flow rate q *. When two pumps perform parallel operation during parallel operation as in this embodiment, qMIN (2) is read out as an energy saving parallel flow rate, and the value is input to a constant device and output as qMINS. Set the energy saving disconnection flow rate.

  The set value is compared with the actual flow rate q *, and when the water supply load is reduced and q * ≦ qMINS, it is detected that the flow rate is equal to or less than the energy saving flow rate. If this state passes a predetermined time, for example, 3.0 sec, a pump disconnection stop signal STP is given to the sequences SEQ31 to SEQ7 to stop the pump disconnection.

  In the present embodiment, the case where two pumps are operated in parallel is shown, but the energy saving parallel flow rate calculation process stores four qMIN (N) data in a table with NMAX = 5 as described above. . Therefore, even in the case of a system configured with a maximum of five units in parallel, qMIN (N) data for each number can be selected. That is, it is possible to stop the energy-saving disconnection of the water supply system operating in parallel with five pumps.

  This will be described with reference to the block diagram of FIG. The energy saving disconnection stop control circuit 41 is a block diagram for generating an energy saving disconnection flow rate calculation process and a disconnection signal of the present invention. The energy saving disconnection flow rate calculation processing start circuits 41 to 1 receive the parallel input completion signal MUL or the disconnection completion signal IND from the sequences SEQ31 to SEQ7, and the energy saving disconnection flow rate calculators 41 to 2 save energy. Start the computation. When the energy-saving disconnection flow rate calculation processing start-up circuits 41 to 1 receive the signal of MUL or the disconnection completion signal IND, the energy-saving disconnection flow rate calculation command is stored.

The stored signal is given to the energy saving parallel flow rate calculators 41 to 2 and reads the pushing head hSU. At the same time, various setting data are read: pump head coefficient a, flow coefficient b, quadratic approximation coefficients C ₁ , C ₂ , C ₃ representing pump pu efficiency, minimum set head h 0, and maximum pump parallel number NMAX. When reading is complete, subsequent changes in hSU are ignored.

  When reading is completed, energy saving parallel flow rate calculation from NMAX to N = 2 is performed. When the calculation of the energy saving parallel flow rate is completed, the result is stored in the energy saving parallel flow data table nRES of the energy saving parallel flow rate calculators 41 to 2. At the same time, the storage of the energy saving disconnection flow rate calculation command is canceled. The process of energy saving parallel flow rate calculation is shown in the control flow of FIG. This principle has already been shown by the equations (1) to (7).

  The pump operation number selection processing circuits 41 to 3 are block diagrams showing processing for selecting the data of the energy saving parallel flow rate data table of the energy saving parallel flow rate calculators 41 to 2 according to the number of operating pumps. 7 receives the signal of the number N of pumps to be operated, reads the disconnected flow rate qMIN (N) corresponding to the number, and writes it in the constant units of the energy saving disconnected flow rate data tables 41-4. The outputs of ENEQ41-4 are compared with the estimated flow rate signal q * as the parallel flow rate setting qMINS.

  The outputs of the comparators 41 to 5 are “1” when q * ≦ qMINS. For example, the delay timer elements 41 to 6 have their output STP set to “1” when 3.0 seconds elapse after the comparators 41 to 5 become “1”. As described above, the STP signal is given to the sequence SEQ 31 to SEQ 7 to disconnect and stop one of the pumps operating in parallel. In this way, the stored energy-saving disconnection flow rate is selected according to the number of pumps currently in operation, and energy-saving disconnection control is performed.

The flowchart shown in FIG. 3 will be described. A control circuit (not shown) continues to check whether the pump is operating (step 31). Next, the control circuit continues to check until parallel input and disconnection are completed (step 32). The control circuit reads the set values h0, a, b, N _MAX, C ₁ , C ₂ , and C ₃ into the energy saving parallel flow rate calculator 41-2, and detects pushing and hsu (step 33).

The control circuit calculates an energy saving disconnection flow rate from N _MAX to N = 2 (step 34). The control circuit checks whether or not the calculation of the energy saving parallel flow rate is completed (step 35). The control circuit ends the process when determining that the calculation of the energy saving disconnection flow rate is completed. If the control circuit determines that the process has not ended, the control circuit calculates up to the maximum flow rate using the flow rate q as a variable (step 36).

  The control circuit calculates the operating frequency during N-unit operation and N-1 unit operation based on the equations (3) and (3) ′ (steps 37 and 37 ′). The control circuit calculates the pump efficiency and shaft power during N-unit operation and N-1 unit operation based on the equations (5) and (6) (steps 38, 38 '). The control circuit calculates the shaft power ΔL based on equation (7) (step 39). The control circuit checks whether the calculation result of the equation (7) satisfies ΔL ≧ 0 (step 40). When the control circuit determines that ΔL ≧ 0 in the step, the control circuit detects the energy saving disconnection flow rate, stores the value, and returns to step 34. When the control circuit determines that ΔL ≧ 0 is not satisfied in the step, the control circuit returns to step 36.

The energy saving disconnection flow varies greatly depending on the size of the indentation head. 4A and 4B show calculation examples of the energy saving parallel flow rate when two units are operated in parallel when hSU = 0 and hSU = 0.5 (pu). Constant of the example, a = 2.83, b = 1.83 , in h0 = 0.7 (pu), C 1 = -1.521, C 2 = 2.351, hSU = 0 in _{C 3 = 0.1, hSU = 0.5} (pu), parallel The case where the number of pumps N = 2 is shown. As shown in FIGS. 4 (a) and 4 (b), it can be seen that the energy-saving flow rate varies greatly depending on the pushing head.

In the above, the calculation method of the energy saving parallel flow rate in the constant estimated terminal pressure control has been described. The target curve for the constant discharge pressure control is expressed by equation (8) with (1−h0) / N ² ) ≡0 in equation (2).
hL N0 = h00 ---- (8)
here,
hL N0 = Target head (pu) for constant discharge pressure control
= Target head HLN0 (m) for constant discharge pressure control / Rated pump head HPN (m)
h00 = Setting head for constant discharge pressure control (pu) ≥ h0
h0 = Minimum setting head H0 (m) for constant discharge pressure control / Rated pump head HPN (m)
H0 ≥ Actual lift HA (m) + Pipe end lift HE (m)
Therefore, the frequency of the electric motor with respect to an arbitrary flow rate in the discharge pressure constant control can be obtained by Expression (9).
fN0 = ((γ0 q ² -hSU + h00) / a) ^1/2 ---- (9)
here,
γ0 = b / N ²

Therefore, since the pump pu efficiency variable (q / fN0) can be calculated, the pump pu efficiency can be calculated in the same way.
Therefore, the total LN (pu) of the shaft power at an arbitrary flow rate during the operation of N pumps in parallel and N-1 pumps can be calculated by Expressions (10) and (11).
L _N = ((q / N) × (h00−hSU)) × (1 / η _N ) × N ---- (10)
L _N-1 = ((q / (N−1)) × (h00−hSU)) × (1 / η _N−1 ) × (N−1) ---- (11)
Therefore, by calculating the shaft power difference ΔL = L _N -L _N-1 using the flow rate as a variable, the flow rate at which ΔL = 0, that is, the energy saving parallel flow rate is the same as in the case of the estimated terminal pressure constant control. It can be calculated by the method. The control flow in this case conforms to FIG.

  In the constant discharge pressure control, the energy saving disconnection flow varies greatly depending on the value of the set head h00. FIGS. 5 (a) and 5 (b) show calculation examples of the energy saving parallel flow rate in the case of hSU = 1.0 and hSU = 0.8 (p.u.) in the constant discharge pressure control.

  Next, a second method obtained by simplifying the first method of the present invention described above will be described. In the method of the present invention described above, each time the parallel charging completion or the sequence completion signal is received from the sequences SEQ31 to SEQ7, the energy saving sequence flow rate calculation of the energy saving sequence flow rate calculators 41 to 2 is activated to save the energy saving solution. It is configured to update the column flow data. For this purpose, it is necessary to execute a convergence calculation for obtaining the energy-saving disconnection flow rate every time the arithmetic processing is started, based on the set value and the indentation head detection value.

  For this reason, there is a drawback that the calculation load of the control microcomputer increases. A second method for solving this drawback will be described. FIG. 6 shows an example of calculating a linear regression equation of the energy saving parallel flow rate in the case of the estimated terminal pressure constant control. FIG. 7 shows an example of calculating a linear regression equation of the energy saving parallel flow rate when h00 = 0.8 (p.u.) in the discharge pressure constant control. First, in order to examine this simplification method, the relationship between the energy saving parallel flow rate and the pushing head is shown in FIGS. 6 and 7 with the number N of pumps in parallel as a parameter. In any case, it was found that the energy saving parallel flow rate has a substantially linear relationship with the indentation head.

Therefore, the estimation formula of the energy saving parallel flow rate was calculated in the form of equation (12).
qSTP N = AN · hSU + BN ---- (12)
here,
q STP N = Energy saving parallel flow rate (pu) for N pumps in parallel operation
AN = proportional coefficient for N pumps parallel BNN = constant for N pumps parallel
hSU = push head (pu)
As a result, FIGS. 8 and 9 were obtained. FIGS. 8A and 8B show examples in which the coefficients and constants of the linear regression equation are calculated. FIGS. 9A and 9B show examples in which the coefficients and constants of the linear regression equation are calculated.

  FIG. 8 shows a linear equation for estimating the characteristics of FIG. 6 in the estimated terminal pressure constant control, the coefficient AN and the constant BN of the equation (12). Similarly, FIG. 9 shows the coefficient AN and the constant BN of equation (12) for estimating the characteristics of FIG. 7 in the discharge pressure constant control. The calculation accuracy of Equation (12) was verified with several models. For example, in the estimated terminal pressure constant control, when N = 2 units and hSU = 0.3 (p.u.), the result was 6% less than the precise calculation value. Under the same conditions, the result was 4.2% less in the case of constant discharge pressure control. However, this level of error is considered acceptable in practice.

  Therefore, as shown in FIG. 11, the energy saving parallel flow rate calculation is calculated off-line, and from the obtained result, the linear regression equation of the energy saving parallel flow rate that varies the indentation head is calculated, and the coefficient AN of the equation (12), BN can be calculated. By using this result, it is possible to calculate the energy-saving disconnection flow rate more easily than the above-described method by only giving the pushing head hSU with the number N of pumps in parallel.

  FIG. 10 is a block diagram illustrating the energy saving disconnection control by a different method. The energy saving disconnection control when this method is employed and the constant estimated terminal pressure control is performed will be described with reference to FIG. 1 is replaced by reference numeral 41A in FIG. However, the parallel input completion signals MUL and IND signals are not used.

The energy saving parallel flow rate calculation processing start circuits 41A to 41 calculate the coefficient AN and the constant BN of the linear regression equation of the energy saving parallel flow rate from the number of pumps. For example, the calculation is performed as shown in FIG. This result is sent to the energy saving parallel flow rate calculation circuits 41A to 41A-2, and the energy saving parallel flow rate qSTP N is calculated by the equation (12) by reading the pump parallel number N and the pushing head hSU at that time. This value is written in the constant units ENEQ41A to 4, and the output is the estimated flow rate signal q as the parallel flow rate setting qMINS.
Compared with *.

  The comparators 41A to 5 output "1" when q * ≤qMINS. When the set time elapses, the output STP of the delay timer elements 41A to 41 becomes “1”. STP is given in the sequence SEQ 31 to 7, and one pump in parallel operation is disconnected and stopped. In this way, an energy saving parallel flow rate that matches the number of pumps in parallel is automatically set, and energy saving parallel control is performed. The second method has an advantage that the processing load of the microcomputer for energy saving disconnection stop control is reduced as compared with the first method.

The flowchart of FIG. 11 will be described. A control circuit (not shown) reads the set values h0, a, b, N _MAX, C ₁ , C ₂ , and C ₃ into the energy saving parallel flow rate calculator (step 1111). The control circuit calculates an energy saving parallel flow rate from N _MAX to N = 2 (step 1112). The control circuit checks whether or not the calculation of the energy saving parallel flow rate is completed (step 1113). When the control circuit determines that the calculation of the energy saving parallel flow rate has been completed, the control circuit calculates the energy saving parallel flow rate regression linear equation using the indentation head as a variable (step 1119). Next, the control circuit calculates the coefficients A _N and B _N (step 1120).

The control circuit checks whether or not the data of the energy saving parallel flow rate calculation formula and the coefficients A _N and B _N have been acquired (step 1121). The control circuit ends if the process is completed in the step, and returns to step 1119 if the process is not completed.

  If the control circuit determines in step 1113 that the process has not been completed, the control circuit calculates up to the maximum flow rate using the flow rate q as a variable (step 1114). The control circuit calculates N units and N-1 shaft powers (step 1115). The control circuit checks whether the calculation result satisfies ΔL ≧ 0 (step 1116). When the control circuit determines that ΔL ≧ 0 in the step, the control circuit detects the energy-saving disconnection flow rate, stores the value, and returns to step 1112. When the control circuit determines that ΔL ≧ 0 is not satisfied in the step, the control circuit returns to step 1114.

  The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the embodiments, and various designs can be made without departing from the matters described in the claims. It is possible to make changes. The inside of the block in the present embodiment is composed of known or publicly known circuits.

Claims (3)

Two or more variable speed pumps driven by an electric motor controlled by a variable voltage / variable frequency power supply are operated in parallel by N units, and the pressure is controlled by a constant discharge pressure control or an estimated terminal pressure constant control method. In the direct feed water supply method when the water supply load decreases from the N unit parallel operation state, one unit is disconnected from the N pumps, and the operation is switched to the N-1 unit operation.
The flow rate at which the total shaft power during N-1 unit operation becomes smaller than the total pump shaft power during N unit operation is a pump head-flow rate quadratic approximate expression, discharge pressure constant control, or estimated terminal pressure. Energy saving in all cases of disengagement of N pumps for each parallel input completion signal or disengagement completion signal from the target curve of constant control, the quadratic approximation formula of the flow rate-efficiency of the pump and the actual pushing head of the water supply system Calculate and store as disconnected flow rate,
Read the calculated and stored data by the actual number of parallel operation, set as the energy-saving parallel flow rate value,
By configuring the pump water supply load to stop the disconnection of the pump at a flow rate equal to the set value of the energy saving disconnection flow rate value,
A parallel pump disconnection control method characterized by minimizing shaft power during disconnection control. In claim 1, the energy saving parallel flow rate is the result of calculating in advance a linear regression equation representing the relationship between the calculation, the energy saving parallel flow rate and the indentation head,
Linear equation STPN = AN × hSU + BN
The parallel pump disconnection is characterized in that the energy saving disconnection flow rate is calculated by the primary equation only by the pushing head and the number of parallel pumps by mounting the linear equation in the pump disconnection control device. Control method.
Where STPN: energy saving parallel flow rate, AN: coefficient of the parallel calculation estimation formula,
hSU: Indentation head, BN: Constant of estimation formula for disassembly calculation. At least from two or more pumps provided in parallel, a pressure detector that detects pressure when water is supplied from the pump, an estimated terminal pressure constant control circuit, a motor that drives the pump, and a motor control circuit In the parallel pump disconnection control system configured,
An indentation head detecting means for detecting an indentation head hsu from the pump;
A table A in which a proportionality constant A determined by the pump itself is stored;
Table B in which an estimation coefficient B based on the number of parallel pumps is stored;
Table C in which energy-saving disconnection flow rates in the number of pumps based on the indentation head are stored;
An energy saving disconnection control circuit for reading out energy saving disconnection flow rate STPN = AN × hSU + BN from the table C based on the tables A and B;
A parallel pump disconnection control system comprising:

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