CN110954172A - Flow detection method for parallel variable-frequency constant-pressure water supply system - Google Patents

Flow detection method for parallel variable-frequency constant-pressure water supply system Download PDF

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CN110954172A
CN110954172A CN201911223950.XA CN201911223950A CN110954172A CN 110954172 A CN110954172 A CN 110954172A CN 201911223950 A CN201911223950 A CN 201911223950A CN 110954172 A CN110954172 A CN 110954172A
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frequency
pressure
value
flow
water supply
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CN110954172B (en
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潘晓铭
陈益丰
潘敏辉
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Wenzhou University
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Wenzhou University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
    • G01F1/34—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure
    • E—FIXED CONSTRUCTIONS
    • E03—WATER SUPPLY; SEWERAGE
    • E03B—INSTALLATIONS OR METHODS FOR OBTAINING, COLLECTING, OR DISTRIBUTING WATER
    • E03B1/00—Methods or layout of installations for water supply

Abstract

The invention relates to a flow detection method of a parallel variable-frequency constant-pressure water supply system, which adopts a sampling period
Figure DDA0002299831830000012
Obtaining pressure values p for intervalsi(k) And an output frequency fi(k) Constructing a mathematical model for online detection of output flow of the parallel variable-frequency constant-voltage control system, acquiring total flow, and obtaining the total flow according to the mathematical model
Figure DDA0002299831830000011
Obtaining the flow Q of the ith pumpiThe invention can realize the flow measurement of the parallel variable-frequency constant-pressure water supply system without a flow sensor, and saves the time and cost for installing and debugging the flow sensor and an auxiliary processing circuit, thereby leading the system structure to be simpler and the system cost to be lower.

Description

Flow detection method for parallel variable-frequency constant-pressure water supply system
Technical Field
The invention relates to the field of electromechanical energy-saving control, in particular to a flow detection method for a parallel variable-frequency constant-pressure water supply system.
Background
The parallel connection variable-frequency constant-pressure water supply plays an important role in guaranteeing the normal operation of industrial and agricultural production and daily life. The operation performance of the pump in the water supply system is directly related to the energy consumption index and the operation cost, and the operation performance accounts for 30-60% of the production cost. The running efficiency of the pump in the parallel connection variable-frequency constant-pressure water supply is even improved by 1 percent, and great benefits are brought to social energy conservation and enterprise cost. 30-50% of electric energy consumed by the pump can be saved, and the energy consumption of the pump can be effectively reduced by adopting a variable frequency control technology, so that the aims of energy conservation and emission reduction are fulfilled. However, due to the supply water demand, there is randomness and uncertainty in time. The number of pumps which are operated in parallel is required to be increased during the peak period so as to increase the supply amount to meet the requirements of production and living; in the valley, the number of pumps running in parallel is required to be reduced so as to achieve the purpose of energy conservation. Especially in the low ebb time period, because the flow is little, the converter is in the low frequency state, and motor heat loss and low frequency vibration are serious, and whole water supply system energy consumption sharply increases, and system is inefficient. Under the working condition, energy conservation and emission reduction can not be realized, mechanical vibration and serious heating of a motor stator winding are caused by long-term low-frequency operation of the motor, the safety reliability and the service life of the system are reduced, the safety reliability and the production cost of a water supply system are adversely affected, and even more serious safety accidents are caused.
The efficient operation of the parallel variable-frequency constant-pressure water supply system is a common technical problem for realizing energy conservation and emission reduction. Based on this, it is necessary to ensure that the output flow of each pump is within the range corresponding to the efficient operation interval. Therefore, the system needs to acquire the total output flow and the output flow of each pump in real time, so as to optimally control the operation number and the operation parameters of the pumps and ensure that each pump can operate efficiently. In order to realize the high-efficiency operation of the parallel variable-frequency constant-pressure water supply system, a flow sensor is required to be additionally arranged in a pipe network and used for detecting the flow of the pipe network in real time. However, the scheme needs to add a flow sensor, which increases the complexity of the pipe network and the hardware cost on one hand, and adds corresponding functional modules such as a signal conditioning circuit, a sampling circuit, a software processing program and the like on the other hand, in terms of software and hardware, to the water supply system on the other hand.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a flow detection method for a parallel variable-frequency constant-pressure water supply system.
In order to achieve the purpose, the invention provides the following technical scheme:
a flow detection method for a parallel variable-frequency constant-pressure water supply system comprises the following steps:
step one, a frequency converter i samples a period Ts iObtaining pressure values p for intervalsi(k) K is the sampling frequency, and the output frequency f of the frequency converter i is obtained simultaneouslyi(k) And establishing an output frequency array { f) of the frequency converter i consisting of N elementsi(j) And get { f }i(j) Mean value of }
Figure BDA0002299831810000021
And standard deviation of
Figure BDA0002299831810000022
K, N is a preset positive integer greater than 1, fi(j)|j＜＝0＝0；
Step two, the centralized control unit uses the period TcFor obtaining all frequency converters at intervals
Figure BDA0002299831810000023
And SiAnd obtaining the average frequency adjustment
Figure BDA0002299831810000024
Wherein
Figure BDA0002299831810000025
Step three, whether max { | sigma is met simultaneously or not is judgedi|}≤σrefAnd max { Si}≤SrefTo judge whether the system is in a stable state, if not, the centralized control unit sends the average frequency adjustment quantity sigma to all frequency converters iiAnd stabilizing the system, where σref，SrefThe positive reference value can be set according to an actual system;
step four, when the system is in stability, acquiring a pressure value P of the system, marking the current moment as t as 0, and then applying fixed disturbance delta F to the output frequencies of all frequency converters i by the centralized control unit;
step five, changing t to mTcThe estimated flow at that time is defined as Qg[m]The estimated value of the amount of pressure change at the corresponding time is Δ pg(M), wherein M is 1, 2, …, M,
Figure BDA0002299831810000031
Tdis a predefined observation time length; setting an initial value of the flow rate estimation value to
Figure BDA0002299831810000032
Let m be 1, the second-stage minimum difference Δ (min) be 0, the second-stage maximum difference Δ (max) be 1, and the resolution factor γ be 0.5;
step six, judging whether M is greater than M or not, if so, sending the average frequency adjustment quantity sigma to all frequency converters i by the centralized control unitiThe decision is driven to be false, and in the case where it is false, t ═ mT is acquiredcPressure value p (m) at the moment of time, and obtaining deltap(m)＝p(m)-P；
Step seven, judgment
Figure BDA0002299831810000033
If the frequency is not satisfied, α is an artificial arbitrary set value and is determined by the requirement of the constant-pressure water supply system on the pressure performance index, and if the frequency is not satisfied, the central control unit continues to send the average frequency adjustment quantity sigma to all the frequency converters iiTo make it stand; when it is established, utilize
Figure BDA0002299831810000034
And flow rate estimation value Qg[m]And P, F, Δ F, β and t ═ mTcObtaining Δ pg(m)；
Step eight, taking the delta p (m) as a reference sequence, delta pg(m) calculating the error sequence Δ as a comparison sequence0(m)＝|Δp(m)-Δpg(m) and obtaining Δ p (m) and Δ pg(m) correlation coefficient
Figure BDA0002299831810000035
Step nine, judging whether ξ (m) > -0.95 is true, and if true, acquiring an actual flow value Q ═ Q of the parallel variable-frequency constant-pressure water supply systemg[m]On the contrary, the number of the pumps in the working state is increased, namely m is m + 1;
Figure BDA0002299831810000041
and repeating the step six;
step ten, according to
Figure BDA0002299831810000042
And
Figure BDA0002299831810000043
to obtain
Figure BDA0002299831810000044
And obtaining by operation
Figure BDA0002299831810000045
Wherein: n isiThe rotating speed of the ith centrifugal pump is set; n isjThe rotating speed of the jth centrifugal pump is shown, and f is the output frequency of the frequency converter; s is the slip ratio; p is the pole pair number of the centrifugal pump;
step eleven, when Qg[m]For the actual flow rate value of the system, i.e. Q ═ Qg[m]When it is, Q, FiIs composed of
Figure BDA0002299831810000046
Substituting n and F into those obtained in the step ten
Figure BDA0002299831810000047
Obtaining the flow Q of the ith pumpi。
Figure BDA0002299831810000048
The values of (c) include two distribution cases:
1)
Figure BDA0002299831810000049
2)
Figure BDA00022998318100000410
and obtained from two distribution cases
Figure BDA00022998318100000411
Δ p (t) is the pressure fluctuation value caused by Δ F, Δ F is the frequency disturbance increment, and | Δ F | < min { F |)i}，i∈[1，n]，ΔQinAnd (t) is an inlet flow fluctuation value caused by delta F, P is a pressure value of the pressure sensor, Q is the inlet and outlet flow of the energy storage tank, and F is an average value of the output frequency of the frequency converter.
And acquiring the water pressure change amount delta p (t) according to the volume change amount delta v (t) and the spring length change amount delta l (t) of the spring type energy storage tank.
According to
Figure BDA00022998318100000412
And obtaining the water pressure variation amount delta p (t)
Figure BDA0002299831810000051
The invention has the beneficial effects that:
the flow measurement of the parallel variable-frequency constant-pressure water supply system can be realized without a flow sensor, so that the time and cost for installing and debugging the flow sensor and an auxiliary processing circuit are saved, the system structure is simpler, and the system cost is lower;
the invention can measure the total output flow, can also measure the output flow of each pump, and provides a basis for the high-efficiency operation of the parallel variable-frequency constant-pressure water supply system;
thirdly, the flow measurement method has the characteristics of high reliability, strong practicability and the like; the pump and the frequency converter can be effectively prevented from being in overload and light-load operation, and the efficiency, the service life and the reliability of the water supply system are improved.
Drawings
FIG. 1 is a structural diagram of a parallel connection variable frequency constant pressure water supply system;
FIGS. 2a and 2b are schematic diagrams illustrating the distribution of the operating frequency of the parallel variable-frequency constant-pressure water supply system;
Detailed Description
Assuming that the parallel variable-frequency constant-pressure water supply system adopts the pumps and the frequency converters with the same model, the invention uses the ith pump (i is more than or equal to 1 and less than or equal to n) and the frequency converter as the exposition objects without losing generality. The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A simplified diagram of a parallel connection variable-frequency constant-pressure water supply system is shown in figure 1 and mainly comprises a water source, a centralized control unit, a frequency converter i, a pump i, a check valve i, a gate valve i, a pressure sensor, a spring type energy storage tank and the like, wherein the centralized control unit mainly has the functions of ① pressure signal acquisition, ② communication with the frequency converter to achieve flow-equalizing control of the water supply system and optimal dispatching control of the pump, ③ human-computer interface function to obtain parameter input and operation state display, the frequency converter mainly has the functions of ① uploading current operation state including start/stop state, operation frequency value and other voltage and current information and the like, ② receiving pressure value and frequency adjustment amount sent by the centralized control unit and adjusting the rotating speed of the pump to achieve water supply and flow-equalizing control functions, the pump i conveys water to a pipeline through high-speed rotation of an impeller blade, the check valve i mainly has the function of preventing water, the gate valve i is used for achieving connection and disconnection of the pump and a pipe network, the pressure sensor is used for detecting pressure of a backflow pipe network, and the function of the energy storage.
fi(t) is the output frequency of the frequency converter i; qi(t) is the outlet flow rate of pump i, i ═ 1, 2, …, n; qin(t) is the inlet flow of the spring type energy storage tank; qout(t) is a spring-type energy storage tank outletThe port flow is also the output flow; p (t) is the pressure value of the pipe network; the spring stiffness of the spring type energy storage tank is K; the sectional area of the spring type energy storage tank is Sc(ii) a t is a time variable.
As known from knowledge of centrifugal pumps and alternating current motors, the output power of the ith pump is in the following relation:
Figure BDA0002299831810000061
wherein: qi(t)×pi(t) actual output Power, ηiTo be efficient, siFor slip, R1，R2，X1σ，X2σ，m1，
Figure BDA0002299831810000062
As a parameter inherent to the AC motor, fiAnd (t) is the output frequency of the ith frequency converter.
Consider that every pump export the model of the pipeline and the valve of energy storage jar water inlet department the same, there is less difference only to the distance between the energy storage jar water inlet to the output lift of constant pressure water supply system is greater than the pump far away and pumps the pipe resistance of mouthful department of water inlet of energy storage jar, so can obtain:
pi(t)＝pj(t)≈p(t) (2)
wherein: i, j ≠ j {1, 2, 3, …, n }, i ≠ j; p (t) is the pressure sensor pressure value;
because the parallel connection variable frequency constant pressure water supply adopts the uniform frequency control, the water supply device can realize the control of the water supply pressure in the water supply system
Figure BDA0002299831810000077
Comprises the following steps:
|fi(t)-F(t)|≤σ(t) (3)
wherein: f (t) is the frequency average value
Figure BDA0002299831810000071
And sigma (t) is the average frequency performance index.
Due to superior use performance of frequency converter and centralized control unitThe control chip and the average frequency control algorithm can ensure that sigma (t) is far less than F (t). Considering that the AC motor and the frequency converter are of the same type and adopt frequency conversion control, the AC motor and the frequency converter have the same mechanical characteristic curve and corresponding slip ratio siAnd efficiency ηiApproximately equal, i.e.:
Figure BDA0002299831810000072
order:
Figure BDA0002299831810000073
then the simultaneous (4) yields:
Ci＝Cj＝C (5)
wherein:
Figure BDA0002299831810000074
therefore, for
Figure BDA0002299831810000075
Comprises the following steps:
Qi(t)×p(t)＝C×fi(t)2(6)
and because of
Figure BDA0002299831810000076
Therefore, the method comprises the following steps:
Figure BDA0002299831810000081
the parameters of the parallel variable-frequency constant-pressure water supply system in a relatively stable state are defined as follows: the pressure value of the pressure sensor is P, the flow of the inlet and the outlet of the energy storage tank is Q, the average value of the output frequency of the frequency converter is F, the average frequency performance parameter is delta, and the output frequency of the frequency converter i is FiAll quantities mentioned above are in international units. Defining the moment when t is 0 as the last moment of the parallel variable-frequency constant-pressure water supply system relative to the steady state, namely:
Figure BDA0002299831810000082
then there are:
|Fi-F|≤δ (9)
Figure BDA0002299831810000083
wherein:
Figure BDA0002299831810000084
suppose to be at (0, T)d]The frequency converter output frequency is adjusted to be within the time by the centralized control unit of the parallel connection variable-frequency constant-pressure water supply system: f. ofi(t)＝Fi+ Δ F, Δ F is the frequency perturbation increment and satisfies | Δ F | < min { F |i}，i∈[1，n]；TdThe time value is a predefined observation time length and is greater than 0, and the time value is artificially determined according to different constant-pressure water supply performance indexes; the pressure sensor value is P (t) ═ P + Δ P (t), and Δ P (t) is the pressure fluctuation value caused by Δ F; inlet flow of the energy storage tank is Qin(t)＝Q+ΔQin(t)，ΔQin(t) is the inlet flow fluctuation caused by Δ F; the outlet flow of the energy storage tank is Qout(t)＝Q+ΔQout(t)，ΔQout(t) is the outlet flow fluctuation value caused by delta F;
in T ∈ (0, T)d]Is mixing Q within(t)＝Q+ΔQin(t)，fi(t)＝FiThe expression (7) is substituted with + Δ F and P (t) ═ P + Δ P (t):
Figure BDA0002299831810000091
unfolding (11) and finishing to obtain:
Figure BDA0002299831810000092
combining (10) and (12), and finishing to obtain:
Figure BDA0002299831810000093
because the energy storage tank is a large inertia damping link, and | delta F | < min { F |)i}，i∈[1，n]Then at T e (0, T)d]The pressure variation delta p (t) caused by the flow change of the inlet and the outlet of the energy storage tank in a short time is very small, and the requirements are as follows:
|Δp(t)|＜＜P (14)
since | Δ F | < min { F |)iP, | Δ P (t) | < P, so equation (13) can be approximated as:
Figure BDA0002299831810000094
dividing (15) by (10) yields:
Figure BDA0002299831810000095
will be provided with
Figure BDA0002299831810000096
Substitution (16) can give:
Figure BDA0002299831810000097
at present
Figure BDA0002299831810000101
Figure BDA0002299831810000101
① consider an extreme distribution, as shown in FIG. 2(a), with:
Figure BDA0002299831810000102
wherein: sigmau＝F-Fu，σj＝Fj-F，σu＞0，σjNot less than 0; therefore, the method comprises the following steps:
Figure BDA0002299831810000103
and (3) unfolding and arranging the materials to obtain:
Figure BDA0002299831810000104
the simultaneous (18), (20) can obtain:
Figure BDA0002299831810000105
② consider the other extreme distribution case, namely FiEven distribution, as shown in fig. 2(b), there are:
Figure BDA0002299831810000106
wherein: i.e. ik，in-k+1＝{1，2，…，n}；ik≠in-k+1；
Figure BDA0002299831810000107
Then:
Figure BDA0002299831810000108
wherein:
Figure BDA0002299831810000109
finishing (24) to obtain:
Figure BDA00022998318100001010
therefore:
Figure BDA0002299831810000111
wherein:
Figure BDA0002299831810000112
from the geometrical knowledge, F for any other distributioniWhich is
Figure BDA0002299831810000113
Values lie between the two extreme distributions, so there are:
Figure BDA0002299831810000114
considering that the unbalance degree of the average frequency control system with the most common performance is below 10 percent, namely delta is less than or equal to 0.1F, the delta is less than or equal to 0.1F2＜＜F2，
Figure BDA0002299831810000115
Thus, there are:
Figure BDA0002299831810000116
the simultaneous formulas (17) and (27) can be obtained:
Figure BDA0002299831810000117
since at T ∈ (0, T)d]The pressure of a pipe network is almost kept unchanged, and the outlet flow variation delta Q of the energy storage tank is not changed under the condition that the pipe resistance characteristic is not changedout(t) ≈ 0, i.e. Qout(t) ≈ Q. In T ∈ (0, T)d]The volume change of the liquid in the energy storage tank is as follows:
Figure BDA0002299831810000118
therefore, T ∈ (0, T)d]The length variation quantity delta l (t) of the energy storage tank spring is as follows:
Figure BDA0002299831810000119
therefore, T ∈ (0, T)d]The water pressure change quantity delta p (t) of the energy storage tank is as follows:
Figure BDA0002299831810000121
combining (28) and (31) and finishing to obtain:
Figure BDA0002299831810000122
order:
Figure BDA0002299831810000123
then there are: y' (t) ═ Δ Qin(t) and y (0) ═ 0, and formula (32) can be collated:
Figure BDA0002299831810000124
equations (28) and (33) are combined and solved to obtain:
Figure BDA0002299831810000125
coefficient of order
Figure BDA0002299831810000126
Then:
Figure BDA0002299831810000127
since the parameters Δ P (T), P, Δ F, F, β, and T are all observable and known quantities, by taking the value at T ∈ (0, T ∈ (T))d]The value of the pressure variation delta p (t) can measure the output flow value Q of the parallel variable-frequency constant-pressure water supply in a steady state.
Meanwhile, from a similar theorem of pumps, it can be known that: when the pumps with similar geometry operate under similar working conditions, the flow Q and the operating speed n of the pumps meet the following conditions:
Figure BDA0002299831810000128
the centrifugal pump and the frequency converter of the parallel connection frequency conversion constant-pressure water supply system have the same model, are in the same pipe network and the centralized control unit performs frequency-equalizing control on the running frequency converter, so that the ith centrifugal pump and the jth centrifugal pump meet the similar law, and therefore the frequency-equalizing control system has the following advantages:
Figure BDA0002299831810000131
wherein: n isiThe rotating speed of the ith centrifugal pump is set; n isjThe rotating speed of the jth centrifugal pump;
the rotating speed n of the centrifugal pump meets the following conditions:
Figure BDA0002299831810000132
wherein: f is the output frequency of the frequency converter; s is the slip ratio; p is the pole pair number of the centrifugal pump; the simultaneous (4), (37) and (38) can obtain:
Figure BDA0002299831810000133
therefore, the method comprises the following steps:
Figure BDA0002299831810000134
wherein: i ═ 1, 2, … n }. Will be provided with
Figure BDA0002299831810000135
Substitution (40) has:
Figure BDA0002299831810000136
therefore, the output flow Q of any ith pump of the parallel variable-frequency constant-pressure water supply system in a steady state can be measured on the basis of obtaining the total flow Qi。
The invention provides a flow detection method of a parallel variable-frequency constant-pressure water supply system, which comprises the following steps of:
(1) frequency converter i with sampling period
Figure BDA0002299831810000137
For sampling pressure values at intervals, the first sampling will beThe samples being denoted pi(1) (ii) a The current sampling frequency is k, and k is made to be 1; wherein: i ═ {1, 2, …, n };
(2) the frequency converter i executes a frequency conversion constant voltage control algorithm and an average frequency control algorithm to obtain an output frequency fi(k) And establishing an output frequency array { f) of the frequency converter i consisting of N elementsi(j) Get { f }i(j) Mean value of }
Figure BDA0002299831810000141
And standard deviation of
Figure BDA0002299831810000142
Wherein: j is { k-N +1, k-N +2,. k }, N is a preset positive integer greater than 1, and k is the current sampling frequency; f. ofi(j)|j＜＝0＝0；
(3) The central control unit is controlled with a period TcFor communication with frequency converters at intervals, all frequency converters being acquired
Figure BDA0002299831810000143
And Si. Calculating the average frequency adjustment
Figure BDA0002299831810000144
Wherein:
Figure BDA0002299831810000145
(4) judging whether the parallel variable-frequency constant-pressure water supply system is in a stable state, wherein the stable state is defined as: judging whether max { | sigma is satisfied at the same timei|}≤σrefAnd max { Si}≤Sref. Wherein: sigmaref，SrefThe positive reference value can be set according to the actual system, and can be 0.1 or 0.2, for example. If so, the parallel variable-frequency constant-pressure water supply system is considered to be in a stable state, and the step (5) is carried out; otherwise, the constant pressure water supply system is in an unstable state, and the step (14) is carried out;
(5) acquiring a pressure value P of a parallel variable-frequency constant-pressure water supply system;
(6) with the time scale t being 0,and applying a fixed arbitrary disturbance deltaF to all frequency converter output frequencies via the communication bus, i.e.
Figure BDA0002299831810000146
(7) Definition of Qg[m]Is t ═ mTcFlow estimate at time, defined as Δ pg(m) is the estimated value of the pressure variation at the corresponding moment; wherein M is 1, 2, …, M,
Figure BDA0002299831810000147
Tdis a predefined observation time length; order to
Figure BDA0002299831810000148
Wherein
Figure BDA0002299831810000149
Setting the initial value of the flow estimation value;
let m be 1, the second-stage minimum difference Δ (min) be 0, the second-stage maximum difference Δ (max) be 1, and the resolution factor γ be 0.5;
(8) judging whether M is greater than M, and if so, entering the step (14); otherwise, at t ═ mTcAt the moment, acquiring a pressure value p (m); to give Δ P (m) ═ P (m) -P;
(9) judgment of
Figure BDA0002299831810000151
Whether the pressure performance index is satisfied or not (α is any set value, but 0.1, 0.05 or other number, and is determined by the pressure performance index requirement of the constant-pressure water supply system). The basis for satisfying the expression is that the drastic fluctuation of the system pressure cannot be caused when the frequency change DeltaF operation is carried out, otherwise, the precondition that the system pressure is not present is lost). if the frequency change DeltaF operation is not performed, the step (14) is carried out, otherwise, the flow estimated value Q is carried outg[m]And P, F, Δ F, β and t ═ mTcSubstituting into a formula:
Figure BDA0002299831810000152
solving to obtain delta pg(m)。
(10) Taking Δ p (m) as a reference sequence, Δ pg(m) calculating the error sequence Δ as a comparison sequence0(m)＝|Δp(m)-Δpg(m) |. Solving for Δ p (m) and Δ pgCorrelation coefficient ξ (m) of (m):
Figure BDA0002299831810000153
(11) it is determined ξ (m) > -0.95 if true (ξ (m) is a gray correlation coefficient, i.e., the actual pressure change value Δ p (m) and the estimated pressure change value Δ pg(m) the greater the correlation ξ (m), indicating Δ p (m) and Δ pg(m) is closer to Δ p (m) and Δ p when ξ (m) is 1g(m) are completely identical). If yes, entering step (12); otherwise, the variable is updated: m is m + 1;
Figure BDA0002299831810000154
and (5) returning to the step (8).
(12) Estimated value Qg[m]Namely the actual flow value of the parallel variable-frequency constant-pressure water supply system, namely Q is Qg[m]。
(13) Q is added,
Figure BDA0002299831810000155
Substituting n and F into the formula:
Figure BDA0002299831810000156
solving the flow Q of the ith pumpi；
(14) The centralized control unit sends the frequency regulating quantity sigma of the uniform frequency control algorithm to the n frequency converters through the communication busi(i＝1，2，…，n)；
(15) Let k be k + 1; carrying out next sampling, and marking the sampling value of the output pressure as pi(k) (ii) a Returning to step (2)
The examples should not be construed as limiting the present invention, but any modifications made based on the spirit of the present invention should be within the scope of protection of the present invention.

Claims (4)

1. A flow detection method for a parallel variable-frequency constant-pressure water supply system is characterized by comprising the following steps: which comprises the following steps:
step one, a frequency converter i samples a period Ts iObtaining pressure values p for intervalsi(k) K is the sampling frequency, and the output frequency f of the frequency converter i is obtained simultaneouslyi(k) And establishing an output frequency array { f) of the frequency converter i consisting of N elementsi(j) And get { f }i(j) Mean value of }
Figure FDA0002299831800000011
And standard deviation of
Figure FDA0002299831800000012
K, N is a preset positive integer greater than 1, fi(j)|j＜＝0＝0；
Step two, the centralized control unit uses the period TcFor obtaining all frequency converters at intervals
Figure FDA0002299831800000013
And SiAnd obtaining the average frequency adjustment
Figure FDA0002299831800000014
Wherein
Figure FDA0002299831800000015
Step three, whether max { | sigma is met simultaneously or not is judgedi|}≤σrefAnd max { Si}≤SrefTo judge whether the system is in a stable state, if not, the centralized control unit sends the average frequency adjustment quantity sigma to all frequency converters iiAnd stabilizing the system, where σref，SrefThe positive reference value can be set according to an actual system;
step four, when the system is in stability, acquiring a pressure value P of the system, marking the current moment as t as 0, and then applying fixed disturbance delta F to the output frequencies of all frequency converters i by the centralized control unit;
step five, changing t to mTcThe estimated flow at that time is defined as Qg[m]The estimated value of the amount of pressure change at the corresponding time is Δ pg(M), wherein M is 1, 2, …, M,
Figure FDA0002299831800000016
Tdis a predefined observation time length; setting an initial value of the flow rate estimation value to
Figure FDA0002299831800000017
Let m be 1, second-stage minimum difference a (min) be 0, second-stage maximum difference Δ (max) be 1, and resolution coefficient γ be 0.5;
step six, judging whether M is greater than M or not, if so, sending the average frequency adjustment quantity sigma to all frequency converters i by the centralized control unitiThe decision is driven to be false, and in the case where it is false, t ═ mT is acquiredcA pressure value P (m) at the time point, and Δ P (m) ═ P (m) — P;
step seven, judgment
Figure FDA0002299831800000021
If the frequency is not satisfied, α is an artificial arbitrary set value and is determined by the requirement of the constant-pressure water supply system on the pressure performance index, and if the frequency is not satisfied, the central control unit continues to send the average frequency adjustment quantity sigma to all the frequency converters iiTo make it stand; when it is established, utilize
Figure FDA0002299831800000022
And flow rate estimation value Qg[m]And P, F, Δ F, β and t ═ mTcObtaining Δ pg(m)；
Step eight, taking the delta p (m) as a reference sequence, delta pg(m) calculating the error sequence Δ as a comparison sequence0(m)＝|Δp(m)-Δpg(m) and obtaining Δ p (m) and Δ pg(m) correlation coefficient
Figure FDA0002299831800000023
Step nine, judging whether ξ (m) > -0.95 is true, and if true, acquiring an actual flow value Q ═ Q of the parallel variable-frequency constant-pressure water supply systemg[m]On the contrary, the number of the pumps in the working state is increased, namely m is m + 1;
Figure FDA0002299831800000024
and repeating the step six;
step ten, according to
Figure FDA0002299831800000025
And
Figure FDA0002299831800000026
to obtain
Figure FDA0002299831800000027
And obtaining by operation
Figure FDA0002299831800000028
Wherein: n isiThe rotating speed of the ith centrifugal pump is set; n isjThe rotating speed of the jth centrifugal pump is shown, and f is the output frequency of the frequency converter; s is the slip ratio; p is the pole pair number of the centrifugal pump;
step eleven, when Qg[m]For the actual flow rate value of the system, i.e. Q ═ Qg[m]When it is, Q, FiIs composed of
Figure FDA0002299831800000029
Substituting n and F into those obtained in the step ten
Figure FDA0002299831800000031
Obtaining the flow Q of the ith pumpi。
2. The flow detection method of the parallel variable-frequency constant-pressure water supply system according to claim 1, characterized in that:
Figure FDA0002299831800000032
the values of (c) include two distribution cases:
1)
Figure FDA0002299831800000033
2)
Figure FDA0002299831800000034
and obtained from two distribution cases
Figure FDA0002299831800000035
Δ p (t) is the pressure fluctuation value caused by AF, AF is the frequency disturbance increment, and | Δ F | < min { F |i}，i∈[1，n]，ΔQinAnd (t) is an inlet flow fluctuation value caused by delta F, P is a pressure value of the pressure sensor, Q is the inlet and outlet flow of the energy storage tank, and F is an average value of the output frequency of the frequency converter.
3. The flow detection method of the parallel variable-frequency constant-pressure water supply system according to claim 2, characterized in that: and acquiring the water pressure change amount delta p (t) according to the volume change amount delta v (t) and the spring length change amount delta l (t) of the spring type energy storage tank.
4. The flow detection method of the parallel variable-frequency constant-pressure water supply system according to claim 3, characterized in that: according to
Figure FDA0002299831800000036
And obtaining the water pressure variation amount delta p (t)
Figure FDA0002299831800000037
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