Power-saving optimization operation method and switching point determining method for water pump unit

Abstract

A power-saving optimization operation method and switching point determining method for a water pump unit. In the parallel water pump units, k water pumps converters form a sub-pump unit A. The water output Q.sub.1 of a first water pump in the sub-pump unit A, the input power P.sub.1 of the frequency converter corresponding to Q.sub.1 and the operating frequency f.sub.1 of the frequency converter corresponding to Q.sub.1 are recorded, where Q.sub.A=Q.sub.1, P.sub.A=P.sub.1. The Q.sub.A-P.sub.A curve of an operating water pump serves as the working curve w.sub.1, where Q.sub.A=mQ.sub.1 and P.sub.A=mP.sub.1, and k≥m≥2. The working curve w.sub.m of m operating water pumps operating at the same frequency is obtained, where f.sub.1=f.sub.2= . . . =f.sub.m. The intersection point of the working curve w.sub.m-1 and the working curve w.sub.m is the optimal switching point between m-1 operating water pumps and m operating water pumps under the constant pressure H.sub.s.

Claims

1. A power-saving operation method for a water pump unit, comprising: connecting, in parallel, all water pumps in the water pump unit, wherein the water pump unit comprises a sub-pump unit A having k water pumps with an identical model and other sub-pump units having k1 water pumps with other models, each water pump is equipped with a frequency converter, k is an integer greater than 1, and k1 is an integer greater than or equal to 0; setting the water pump unit to operate at a constant pressure, wherein a constant pressure value is H.sub.s, the constant pressure value H.sub.s is a value equivalent to a total head of the water pump unit, density of delivered liquid is ρ, a total water output of the sub-pump unit A is Q.sub.A, a total input power of frequency converters in the sub-pump unit A is P.sub.A, a water output of an i.sup.th water pump in the sub-pump unit A is Q.sub.i, where 1≤i≤k, an input power of a frequency converter of the i.sup.th water pump is P.sub.i, an operating frequency of the frequency converter of the i.sup.th water pump is f.sub.i, then Q.sub.A=Q.sub.1+Q.sub.2+ . . . +Q.sub.k, P.sub.A=P.sub.1+P.sub.2+ . . . +P.sub.k, for the sub-pump unit A; obtaining working curves w.sub.1, w.sub.2, . . . , w.sub.k based on two coordinate variables of ρ.sup.αQ.sub.A.sup.φH.sub.s.sup.λP.sub.A.sup.μ and βρ.sup.ωQ.sub.A.sup.δH.sub.s.sup.ξP.sub.A.sup.σ for the sub-pump unit A using the density of the delivered liquid, different total water outputs under different number of operating water pumps in the sub-pump unit A, the constant pressure value, different total input powers of frequency converters under different number of operating water pumps in the sub-pump unit A, wherein α, φ, λ, μ, β, ω, δ, ξ and α are coefficients, β≠0, φ and μ cannot be equal to 0 at the same time, φ and δ cannot be equal to 0 at the same time, σ and δ cannot be equal to 0 at the same time, σ and μ cannot be equal to 0 at the same time; increasing or decreasing a number of operating water pumps in the water pump sub-pump unit A based on the working curves.

2. The method according to claim 1, wherein, obtaining the working curves w.sub.1, w.sub.2, . . . , w.sub.k based on two coordinate variables of ρ.sup.αQ.sub.A.sup.φH.sub.s.sup.λP.sub.A.sup.μ−βρ.sup.ωQ.sub.A.sup.δH.sub.s.sup.ξP.sub.A.sup.σ for the sub-pump unit A using the density of the delivered liquid, different total water outputs under different number of operating water pumps in the sub-pump unit A, the constant pressure value, different total input powers of the frequency converters under different number of operating water pumps in the sub-pump unit A, comprises: acquiring a water output Q.sub.1 of only one operating water pump in the sub-pump unit A and an input power P.sub.1 of a frequency converter corresponding to the one water pump, where Q.sub.A=Q.sub.1, P.sub.A=P.sub.1, and obtaining a working curve w.sub.1 of the one operating water pump, acquiring a total water output of m-1 operating water pumps in the sub-pump unit A and a total input power of frequency converters of m-1 operating water pumps, wherein Q.sub.A=(m-1) Q.sub.1 and P.sub.A=(m-1) P.sub.1, where m is a positive integer, and 2≤m≤k, and obtaining a working curve w.sub.m-1 of m-1 operating water pumps operating at the same frequency, where f.sub.1=f.sub.2= . . . =f.sub.m-1; acquiring a total water output of m operating water pumps in the sub-pump unit A and a total input power of frequency converters of m operating water pumps, wherein Q.sub.A=mQ.sub.1 and P.sub.A=mP.sub.1, where m is a positive integer, and 2≤m≤k, and obtaining a working curve w.sub.m of m operating water pumps operating at the same frequency, where f.sub.1=f.sub.2= . . . =f.sub.m; obtaining an intersection point of the working curve w.sub.m-1 and the working curve w.sub.m as an optimal switching point for switching between m-1 operating water pumps and m operating water pumps under the constant pressure H.sub.s, where Q.sub.A=Q.sub.m-1, m, P.sub.A=P.sub.m-1, m; at the intersection point, H.sub.s is the same, Q.sub.A is the same and P.sub.A is the same, so that efficiency of m-1 operating water pumps is the same as that of m operating water pumps, which is referred to as “equivalent switching”; Q.sub.m-1, m is an optimal switching point expressed by a total water output of the sub-pump unit A, P.sub.m-1, m is an optimal switching point expressed by a total input power of the frequency converters in the sub-pump unit A; f.sub.1=f.sub.2= . . . =f.sub.m-1 when the m-1 water pumps operate, f.sub.1=f.sub.2= . . . =f.sub.m when the m water pumps operate, and frequency converters corresponding to operating water pumps in the sub-pump unit A at the same output frequency, which is referred to as “same pump with same frequency”, such that Q.sub.i, P.sub.i, H.sub.s and operating efficiency of each operating water pump are the same.

3. The method according to claim 2, after obtaining the intersection point of the working curve w.sub.m-1 and the working curve w.sub.m as the optimal switching point for switching between m-1 operating water pumps and m operating water pumps under the constant pressure H.sub.s, the method further comprising: acquiring a value of any one of Q.sub.m-1, m and P.sub.m-1, m; acquiring an optimal value of the value of any one of Q.sub.m-1, m and P.sub.m-1, m multiplied by (1−θ.sub.1) when the number of operating water pumps increases from m-1 to m, where 0≤θ.sub.1≤0.15, and an optimal value of the value of any one of Q.sub.m-1, m and P.sub.m-1, m multiplied by (1−ε.sub.1) when the number of operating water pumps is reduced from m to m-1, where 0≤ε.sub.1≤0.15.

4. The method according to claim 2, after obtaining the intersection point of the working curve w.sub.m-1 and the working curve w.sub.m as the optimal switching point for switching between m-1 operating water pumps and m operating water pumps under the constant pressure H.sub.s, the method further comprising: obtaining frequency curves y on different number of operating water pumps in the sub-pump unit A using two coordinate variables of ρ.sup.αQ.sub.A.sup.φH.sub.s.sup.λf.sub.A.sup.γ and νρ.sub.ωQ.sub.A.sup.δH.sub.s.sup.ξf.sub.A.sup.ψ, where α, φ, λ, γ, ν, ω, δ, ξ, ψ are coefficients, ν≠0, φ and γ cannot be equal to 0 at the same time, φ and δ cannot be equal to 0 at the same time, ψ and δ cannot be equal to 0 at the same time, and ψ and γ cannot be equal to 0 at the same time; obtaining optimal frequency switching points, on the frequency curves y when setting α=0, φ=1, λ=0, γ=0, ν=1, ω=0, δ=0, ξ=0, ψ=1, using Q.sub.m-1, m obtained by the working.

5. The method according to claim 4, wherein obtaining the optimal frequency switching point, on the frequency curves y when setting α=0, φ=1, λ=0, γ=0, ν=1, ω=0, δ=0, ξ=0, ψ=1, using Q.sub.m-1, m obtained by the working curves, comprises: acquiring the water output Q.sub.1 of only one operating water pump in the sub-pump unit A and the frequency f.sub.1 of a corresponding frequency converter of the one operating water pump, where Q.sub.A=Q.sub.1, f.sub.A=f.sub.1, f.sub.A represents a frequency value when output frequencies of all operating frequency converters in the sub-pump unit A are the same; and obtaining a frequency curve y.sub.1 of the one operating water pump based on two coordinate variables of Q.sub.A and f.sub.A; obtaining a frequency curve y.sub.m-1 of m-1 operating water pumps operating at the same frequency based on two coordinate variables of Q.sub.A and f.sub.A, wherein Q.sub.A=(m-1) Q.sub.1, where m is a positive integer and 2≤m≤k, and f.sub.A=f.sub.1=f.sub.2= . . . =f.sub.m-1; obtaining a frequency curve y.sub.m of m operating water pumps operating at the same frequency based on two coordinate variables of Q.sub.A and f.sub.A, wherein Q.sub.A=mQ.sub.1, and f.sub.A=f.sub.1=f.sub.2==f.sub.m; obtaining a frequency switching point f.sub.m-1, m on the frequency curve y.sub.m-1 corresponding to Q.sub.m-1, m, and a frequency switching point f.sub.m, m-1 on the frequency curve y.sub.m corresponding to Q.sub.m-1, m, wherein f.sub.m-1, m is an operating frequency of the frequency converters of m-1 operating water pumps at the optimal switching point Q.sub.m-1, m obtained by the working curve w.sub.m-1 and the working curve w.sub.m, and f.sub.m, m-1 is an operating frequency of the frequency converters of m operating water pumps at the optimal switching point Q.sub.m-1, m, where f.sub.m-1, m>f.sub.m, m-1.

6. The method according to claim 5, after obtaining the frequency switching point f.sub.m-1, m on the frequency curve y.sub.m-1 corresponding to Q.sub.m-1, m, and the frequency switching point f.sub.m, m-1 on the frequency curve y.sub.m corresponding to Q.sub.m-1, m, the method further comprising: obtaining an optimal frequency switching point where a frequency value is a frequency value of f.sub.m-1, m multiplied by (1+θ.sub.2) when the number of operating water pumps increases from m-1 to m, where 0≤θ.sub.2≤0.15, and an optimal frequency switching point where a frequency value is a frequency value of f.sub.m, m-1 multiplied by (1−ε.sub.2) when the number of operating water pumps is reduced from m to m-1, where 0≤ε.sub.2≤0.15.

7. The method according to claim 2, wherein, the variable βρ.sup.ωQ.sub.A.sup.δH.sub.s.sup.ξP.sub.A.sup.σ is β.sub.1ρQ.sub.AH.sub.s/P.sub.A when ω=1, δ=1, ξ=1, σ=−1 and β=β.sub.1, wherein β.sub.1ρQ.sub.AH.sub.s/P.sub.A represents operating efficiency η(H.sub.s) of the sub-pump unit A, β.sub.1 is a coefficient, and when Q.sub.A≥Q.sub.1,2, the operating efficiency of the sub-pump unit A is η(H.sub.s)≥β.sub.1ρQ.sub.1,2H.sub.s/P.sub.1,2.

8. The method according to claim 2, wherein, a control of the “same pump with same frequency” is implemented by sending a frequency value to all frequency converters at one time via a bus communication signal and an analog output signal of a controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to explain the embodiments of the present disclosure or the technical scheme in the prior art more clearly, the drawings needed in the embodiments will be briefly introduced hereinafter. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those skilled in the art, other drawings can be obtained according to these drawings without paying creative labor.

(2) FIG. 1 is an embodiment of using Q.sub.A-P.sub.A curve as a working curve to obtain the optimal switching point and the optimal speed controlling method when k=3.

(3) FIG. 2 is an embodiment of using Q.sub.A-Q.sub.A/P.sub.A curve as a working curve to obtain the optimal switching point and the optimal speed controlling method when k=3.

(4) FIG. 3 is an embodiment of using Q.sub.A-P.sub.A curve and Q.sub.A-f.sub.A curve to obtain the optimal switching point and the optimal speed controlling method when k=3.

(5) FIG. 4 is a flow chart of another power-saving optimization operation method and switching point determining method for a water pump unit according to the present disclosure.

(6) FIG. 5 is a schematic structural view of a water pump unit according to the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) The technical scheme in the embodiments of the present disclosure will be described clearly and completely hereinafter with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without paying creative labor belong to the scope of protection of the present disclosure.

(8) The purpose of the present disclosure is to provide a power-saving optimization operation method and switching point determining method for a water pump unit, so as to find and determine the power-saving optimal switching point and the optimal operation method for a water pump unit in engineering.

(9) Referring to FIG. 5, all water pumps in the water pump unit are connected in parallel. The water pump unit comprises a sub-pump unit A having k water pumps with an identical model and other sub-pump units having k1 water pumps with other models, each water pump is equipped with a frequency converter, k is an integer greater than 1, and k1 is an integer greater than or equal to 0. In the sub-pump unit A, all frequency converters are connected to a controller.

(10) In order to make the above objects, features and advantages of the present disclosure more obvious and understandable, the present disclosure will be further explained in detail hereinafter with reference to the drawings and specific embodiments.

(11) In FIG. 1, in the parallel water pump units, three water pumps of the same model equipped with frequency converters form a sub-pump unit A, k=3. No water pumps of other models are provided, k1=0. The parallel water pump units use a constant pressure operation mode with the constant pressure value H.sub.s=17 (meters). The constant pressure value is the constant pressure value of the total head of the water pump unit. The water pump unit delivers clean water, and any water pump in the sub-pump unit A is designated as the first water pump. The water output of the i-th water pump in the sub-pump unit A is Q.sub.i, the input power of the frequency converter is P.sub.i, the operating frequency is f.sub.i, the total water output of the sub-pump unit A is Q.sub.A, and the total input power of the frequency converter in the sub-pump unit A is P.sub.A, Q.sub.A=Q.sub.1+Q.sub.2+Q.sub.3, P.sub.A=P.sub.1+P.sub.2+P.sub.3. α=0, φ=1, λ=0, μ=0, β=1, ω=0, δ=0, ξ=0, σ=1. ρ.sup.αQ.sub.A.sup.φH.sub.s.sup.λP.sub.A.sup.μ−βρ.sup.ωQ.sub.A.sup.δH.sub.s.sup.ξP.sub.A.sup.σ becomes Q.sub.A−P.sub.A. Q.sub.A-P.sub.A is used as the working curve w. While keeping the operating status of the constant pressure H.sub.s=17 (meters), the water output Q.sub.1 of a first water pump in the sub-pump unit A and the input power P.sub.1 of the frequency converter corresponding to Q.sub.1 are recorded, where Q.sub.A=Q.sub.1, P.sub.A=P.sub.1. The Q.sub.A-P.sub.A curve of an operating water pump is taken as the working curve w.sub.1, where Q.sub.A=2Q.sub.1 and P.sub.A=2P.sub.1. The working curve w.sub.2 of two operating water pumps is obtained, where Q.sub.A=3Q.sub.1 and P.sub.A=3P.sub.1. The working curve w.sub.3 of three operating water pumps is obtained. The working curve w.sub.1 and the working curve w.sub.2 intersect at point C, which is the optimal switching point between an operating water pump and two operating water pumps under the constant pressure H.sub.s=17 (meters), where Q.sub.A=Q.sub.1, 2, P.sub.A=P.sub.1, 2; P.sub.1, 2 is selected as the optimal switching point. At the intersection point, H.sub.s is the same, Q.sub.A is the same and P.sub.A is the same, so that the efficiency of an operating water pump is the same as that of two operating water pumps, which is referred to as “equivalent switching”. When P.sub.A>P.sub.1, 2, an operating water pump is switched to two operating water pumps. When two water pumps are operating, f.sub.1=f.sub.2 is kept. The frequency converters corresponding to the operating water pumps of the same model operate at the same output frequency, which is referred to as “the same pump with the same frequency”, where Q.sub.1=Q.sub.2, P.sub.1=P.sub.2. H.sub.s is the same. When P.sub.A<P.sub.1, 2, two operating water pumps are switched to one operating water pump. The working curve w.sub.2 and the working curve w.sub.3 intersect at point D, which is the optimal switching point between two operating water pumps and three operating water pumps under the constant pressure H.sub.s=17 (meters), where Q.sub.A=Q.sub.2, 3, P.sub.A=P.sub.2, 3; P.sub.2, 3 is selected as the optimal switching point. When P.sub.A>P.sub.2, 3, two operating water pumps are switched to three operating water pumps. When three water pumps are operating, f.sub.1=f.sub.2=f.sub.3 is kept. When P.sub.A<P.sub.2, 3, three operating water pumps are switched to two operating water pumps, and f.sub.1=f.sub.2 is kept. The process requirements have time limits on the start-stop interval of water pumps. In order to avoid frequent switching of the number of operating water pumps near the optimal switching point, the value of the actual switching point is within a range near the optimal switching point. When the number of operating water pumps increases from 1 to 2, the actual switching point is P.sub.1, 2 (1+0.08), and when the number of operating water pumps decreases from 2 to 1, the actual switching point is P.sub.1, 2 (1−0.08). When the number of operating water pumps increases from 2 to 3, the actual switching point is P.sub.2, 3 (1+0.08), and when the number of operating water pumps decreases from 3 to 2, the actual switching point is P.sub.2, 3 (1−0.08). The value near the optimal switching point is used as the actual switching point value. The number of operating water pumps is maintained at the switching point, the number of operating water pumps is increased when it is greater than the switching point value, and the number of operating water pumps is decreased when it is less than the switching point value. These actual switching points are approximately optimal switching points. For different constant voltage operating values H.sub.s, different optimal switching points and different actual switching points are obtained by the same method.

(12) In FIG. 2, in the parallel water pump units, three water pumps of the same model equipped with frequency converters form a sub-pump unit A, k=3. No water pumps of other models are provided, k1=0. The parallel water pump units use a constant pressure operation mode with the constant pressure value H.sub.s=17 (meters). The constant pressure value is the constant pressure value of the total head of the water pump unit. The water pump unit delivers clean water, and any water pump in the sub-pump unit A is designated as the first water pump. The water output of the i-th water pump in the sub-pump unit A is Q.sub.i, the input power of the frequency converter is P.sub.i, the operating frequency is f.sub.1, the total water output of the sub-pump unit A is Q.sub.A, and the total input power of the frequency converter in the sub-pump unit A is P.sub.A, Q.sub.A=Q.sub.1+Q.sub.2+Q.sub.3, P.sub.A=P.sub.1+P.sub.2+P.sub.3. α=0, φ=1, λ=0, μ=0, β=1, ω=0, δ=0, ξ=0, σ=1. ρ.sup.αQ.sub.A.sup.φH.sub.s.sup.λP.sub.A.sup.μ−βρ.sup.ωQ.sub.A.sup.δH.sub.s.sup.ξP.sub.A.sup.σ becomes Q.sub.A−Q.sub.A/P.sub.A. Q.sub.A−Q.sub.A/P.sub.A is used as the working curve w. While keeping the operating status of the constant pressure H.sub.s=17 (meters), the water output Q.sub.1 of a first water pump in the sub-pump unit A and the input power P.sub.1 of the frequency converter corresponding to Q.sub.1 are recorded, where Q.sub.A=Q.sub.1, P.sub.A=P.sub.1. The Q.sub.A−Q.sub.A/P.sub.A curve of an operating water pump is taken as the working curve w.sub.1, where Q.sub.A=2Q.sub.1 and P.sub.A=2P.sub.1. The working curve w.sub.2 of two operating water pumps is obtained, where Q.sub.A=3Q.sub.1 and P.sub.A=3P.sub.1. The working curve w.sub.3 of three operating water pumps is obtained. The working curve w.sub.1 and the working curve w.sub.2 intersect at point C, which is the optimal switching point between an operating water pump and two operating water pumps under the constant pressure H.sub.s=17 (meters), where Q.sub.A=Q.sub.1, 2; Q.sub.1, 2 is selected as the optimal switching point. When Q.sub.A>Q.sub.1, 2, an operating water pump is switched to two operating water pumps. When two water pumps are operating, f.sub.1=f.sub.2 is kept. When Q.sub.A<Q.sub.1, 2, two operating water pumps are switched to one operating water pump. The working curve w.sub.2 and the working curve w.sub.3 intersect at point D, which is the optimal switching point between two operating water pumps and three operating water pumps under the constant pressure H.sub.s=17 (meters), where Q.sub.A=Q.sub.2, 3; Q.sub.2, 3 is selected as the optimal switching point. When Q.sub.A≥Q.sub.2, 3, two operating water pumps are switched to three operating water pumps. When three water pumps are operating, f.sub.1=f.sub.2=f.sub.3 is kept. When Q.sub.A<Q.sub.2, 3, three operating water pumps are switched to two operating water pumps, and f.sub.1=f.sub.2 is kept. The process requirements have time limits on the start-stop interval of water pumps. In order to avoid frequent switching of the number of operating water pumps near the optimal switching point, the value of the actual switching point is within a range near the optimal switching point. When the number of operating water pumps increases from 1 to 2, the actual switching point is Q.sub.1, 2 (1+0.04), and when the number of operating water pumps decreases from 2 to 1, the actual switching point is Q.sub.1, 2 (1−0.04). When the number of operating water pumps increases from 2 to 3, the actual switching point is Q.sub.2, 3 (1+0.04), and when the number of operating water pumps decreases from 3 to 2, the actual switching point is Q.sub.2, 3 (1−0.04). That is to say, the value near the optimal switching point is used as the actual switching point value. The number of operating water pumps is maintained at the switching point, the number of operating water pumps is increased when it is greater than the switching point value, and the number of operating water pumps is decreased when it is less than the switching point value. These actual switching points are approximately optimal switching points. For different constant voltage operating values H.sub.s, different optimal switching points and different actual switching points are obtained by the same method.

(13) In FIG. 3(a) and FIG. 3(b), in the parallel water pump units, three water pumps of the same model equipped with frequency converters form a sub-pump unit A, k=3. No water pumps of other models are provided, k1=0. The parallel water pump units use a constant pressure operation mode with the constant pressure value H.sub.s=17 (meters). The constant pressure value is the constant pressure value of the total head of the water pump unit. The water pump unit delivers clean water, and any water pump in the sub-pump unit A is designated as the first water pump. The water output of the i-th water pump in the sub-pump unit A is Q.sub.1, the input power of the frequency converter is P.sub.i, the operating frequency is f.sub.1, the total water output of the sub-pump unit A is Q.sub.A, and the total input power of the frequency converter in the sub-pump unit A is P.sub.A, Q.sub.A=Q.sub.1+Q.sub.2+Q.sub.3, P.sub.A=P.sub.1+P.sub.2+P.sub.3. α=0, φ=1, λ=0, μ=0, β=1, ω=0, δ=0, ξ=0, σ=1. ρ.sup.αQ.sub.A.sup.φH.sub.s.sup.λf.sub.A.sup.γ−νρ.sup.ωQ.sub.A.sup.δH.sub.s.sup.ξf.sub.A.sup.ψ becomes Q.sub.A−f.sub.A. Q.sub.A−f.sub.A is used as the working curve y. While keeping the operating status of the constant pressure H.sub.s=17 (meters), the water output Q.sub.1 of a first water pump in the sub-pump unit A, the input power P.sub.i of the frequency converter corresponding to Q.sub.1 and the operating frequency f.sub.1 of the frequency converter corresponding to Q.sub.1 are recorded, where Q.sub.A=Q.sub.1, P.sub.A=P.sub.i. The working curve w.sub.1 of an operating water pump is obtained, where Q.sub.A=2Q.sub.1 and P.sub.A=2P.sub.1. The working curve w.sub.2 of two operating water pumps is obtained, where Q.sub.A=3Q.sub.1 and P.sub.A=3P.sub.1. The working curve w.sub.3 of three operating water pumps is obtained. The working curve w.sub.1 and the working curve w.sub.2 intersect at point C, which is the optimal switching point between an operating water pump and two operating water pumps under the constant pressure H.sub.s=17 (meters), where Q.sub.A=Q.sub.1, 2. The working curve w.sub.2 and the working curve w.sub.3 intersect at point D, which is the optimal switching point between two operating water pumps and three operating water pumps under the constant pressure H.sub.s=17 (meters), where Q.sub.A=Q.sub.2, 3. f.sub.max is the power supply frequency corresponding to the rated speed ne of the first water pump, where Q.sub.A=Q.sub.1, f.sub.A=f.sub.1. According to the data records, the frequency curve y.sub.1 of an operating water pump is obtained, Q.sub.A=2Q.sub.1 and f.sub.A=f.sub.1; the frequency curve y.sub.2 of two operating water pumps operating at the same frequency is obtained, Q.sub.A=3Q.sub.1 and f.sub.A=f.sub.1; the frequency curve y.sub.3 of three operating water pumps operating at the same frequency is obtained. The switching point on the frequency curve y.sub.1 corresponding to Q.sub.1, 2 is f.sub.1, 2. The switching point on the frequency curve y.sub.2 corresponding to Q.sub.1, 2 is f.sub.2, 1. f.sub.1, 2 is the operating frequency of the frequency converter of an operating water pump at the optimal switching point. f.sub.2, 1 is the operating frequency of the frequency converter of two operating water pumps at the optimal switching point, where f.sub.1, 2>f.sub.2, 1. The switching point on the frequency curve y.sub.2 corresponding to Q.sub.2, 3 is f.sub.2, 3. The switching point on the frequency curve y.sub.3 corresponding to Q.sub.2, 3 is f.sub.3, 2. f.sub.2, 3 is the operating frequency of the frequency converter of two operating water pumps at the optimal switching point. f.sub.3, 2 is the operating frequency of the frequency converter of three operating water pumps at the optimal switching point, where f.sub.2, 3>f.sub.3, 2. When one water pump is operating, if f.sub.A>f.sub.1, 2, one operating water pump is switched to two operating water pumps and f.sub.1>f.sub.2 is kept. When two water pumps are operating, if f.sub.A<f.sub.2, 1, two operating water pumps are switched to one operating water pump. When two water pumps are operating, if f.sub.A>f.sub.2, 3, two operating water pumps are switched to three operating water pumps and f.sub.1=f.sub.2=f.sub.3 is kept. When three water pumps are operating, if f.sub.A<f.sub.2, 3, three operating water pumps are switched to two operating water pumps, and f.sub.1=f.sub.2 is kept. The process requirements have time limits on the start-stop interval of water pumps. In order to avoid frequent switching of the number of operating water pumps near the optimal switching point, the value of the actual switching point is within a range near the optimal switching point. When the number of operating water pumps increases from 1 to 2, the actual switching point is f.sub.1, 2 (1+0.02), and when the number of operating water pumps decreases from 2 to 1, the actual switching point is f.sub.2, 1 (1−0.02). When the number of operating water pumps increases from 2 to 3, the actual switching point is f.sub.2, 3 (1+0.02), and when the number of operating water pumps decreases from 3 to 2, the actual switching point is f.sub.3, 2(1−0.02). That is to say, the value near the optimal switching point is used as the actual switching point value. The number of operating water pumps is maintained at the switching point, the number of operating water pumps is increased when it is greater than the actual switching point, and the number of operating water pumps is decreased when it is less than the actual switching point. These actual switching points are approximately optimal switching points. For different constant voltage operating values H.sub.s, different optimal switching points and different actual switching points are obtained by the same method.

(14) In addition, corresponding to the technical scheme provided above, the present disclosure further correspondingly provides another power-saving optimization operation method and switching point determining method for a water pump unit. As shown in FIG. 4, the power-saving optimization operation method and switching point determining method for a water pump unit comprise:

(15) Step 100: acquiring the water output of each water pump in the water pump unit, the constant pressure value of the water pump unit, the input power of each frequency converter and the density of liquid delivered by the water pump unit;

(16) Step 101: determining the total water output for a water pump unit according to the water output of each water pump, and determining the total input power of a frequency converter in the water pump unit according to the input power of each frequency converter;

(17) Step 102: acquiring a first specific coefficient set; wherein the first coefficient set comprises α, φ, λ, γ, ν, ω, δ, ξ, γψ, where ν≠0, φ and γ cannot be equal to 0 at the same time, φ and δ cannot be equal to 0 at the same time, ψ and δ cannot be equal to 0 at the same time, ψ and δ cannot be equal to 0 at the same time, and ψ and γ cannot be equal to 0 at the same time;

(18) Step 103: determining and obtaining the working curve in the constant pressure operation mode according to the total water output, the constant pressure value of the water pump unit, the total input power of the frequency converter, the density of the liquid delivered by the water pump unit and the first specific coefficient set;

(19) Step 104: determining the optimal switching point and the optimal operation method of each water pump in the water pump unit according to the working curve;

(20) Further, the power-saving optimization operation method and switching point determining method for a water pump unit further comprise:

(21) Step 105: acquiring the operating frequency and a second specific coefficient set of each water pump in the water pump unit; wherein the second specific coefficient set comprises α, φ, λ, γ, ν, ω, δ, ξ, γψ, where ν≠0, φ and γ cannot be equal to 0 at the same time, φ and δ cannot be equal to 0 at the same time, φ and δ cannot be equal to 0 at the same time, ψ and δ cannot be equal to 0 at the same time, and ψ and γ cannot be equal to 0 at the same time;

(22) Step 106: determining and obtaining the frequency curve in the constant pressure operation mode according to the total water output, the constant pressure value of the water pump unit, the operating frequency and the second specific coefficient set;

(23) Step 107: determining the optimal switching point and the optimal operation method of each water pump in the water pump unit according to the frequency curve and the first power-saving optimization operation method and switching point determining method described above.

(24) In the technical scheme of another water pump unit power-saving optimization operation method and switching point determining method provided, refer to the first water pump unit power-saving optimization operation method and switching point determining method for its substantive implementation process. Because their implementation methods are basically the same, they will not be described in detail here.

(25) In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. It is sufficient to refer to the same and similar parts among each embodiment.

(26) In the present disclosure, a specific example is applied to illustrate the principle and implementation of the present disclosure, and the explanation of the above embodiments is only used to help understand the method and its core idea of the present disclosure. At the same time, according to the idea of the present disclosure, there will be some changes in the specific implementation and application scope for those skilled in the art. To sum up, the contents of this specification should not be construed as limiting the present disclosure.