CN103487095B - A kind of detection method of small flow based on parameter association - Google Patents

Abstract

The invention provides a kind of low discharge online test method based on Newton method, comprising: set up flow, mathematical model between frequency disturbance amount and variation in water pressure amount and constraint condition, form the mathematical model being suitable for low discharge on-line checkingi and needing; Carry out the disturbance of twice frequency small-signal under steady state operating conditions, obtain two pressure histories, the flow value that the intersection point of two curves is corresponding is system flow value.The invention has the advantages that without the need to flow detector and motor structure of water pump parameter, whether on-line detecting system is in low flow rate condition is run.This method detection speed is fast, and reliability is high, practical, can low-frequency operation causes under available protecting motor and frequency converter low flow rate condition inefficiency fault, improves system lifetim and reliability, for pump motor safety, Effec-tive Function provide Reliable guarantee.

Description

A kind of detection method of small flow based on parameter association

Technical field

The invention belongs to electromechanical integration measurement and control area, be specifically related to a kind of low discharge based on parameter association and operate in line detecting method, be particularly useful for air pressure tank constant pressure water supply device water pump low discharge and run detection and protection.

Background technology

In constant pressure frequency conversion water system, lift characteristic and the performance of pipe resistance characteristic on water system have important impact, when not closing completely with penstock or causing water system to run on low discharge due to pipeline valve leakage, now the pipe of water system hinders and headloss increase, system energy consumption is caused to increase, inefficiency.Wherein, " low discharge " refers to when water swivel aperture is very little or water swivel is not closed completely and pipeline water clock causes that its water consumption is very little or close to zero, this situation is called frequency-conversion water supply system low discharge situation.Now, water pump runs under low discharge, and pump efficiency can be caused greatly to reduce, can not reach energy-conservation object, the larger electricity consumption of pump power is more.

Meanwhile, low discharge runs and causes pump motor and frequency converter to be in low-frequency operation state, causes motor and converter low-frequency noise seriously, reduces serviceable life and the performance of motor and frequency converter, has a negative impact to the safe reliability supplied water and production cost.

It is one of key technical problem that pump variable frequency constant pressure water supply system realizes efficient energy-saving, safe and reliable water supply needs emphasis to solve that the low discharge of water pump constant pressure water supply system detects.At present, the low discharge that cuts out the pump detects and mainly contains two kinds of modes:

One, flow sensor scheme: namely install flow sensor by the water outlet at water pump, realizes low discharge and detects; Normally used flow sensor testing agency is mainly vane type and float-type structure.

(1) the following three kinds of situations of vane type detection existence can cause flow detection precision and Reliability performance measure not high: under 1. supplying the larger situation of water flow velocity, the solid sundries existed in water quality can clash into impeller, impeller is out of shape and defect, cause whole mechanism moment of inertia uneven, cause flow detection inefficacy or precision and data reliability greatly to reduce; 2. water quality is subject to pollution when presenting acidity or alkalescence, can heavy corrosion impeller mechanism, causes whole mechanism moment of inertia uneven equally, and flow detection lost efficacy or precision and data reliability reduce greatly; 3. vane type flow detection is rotated by the liquid transmission impeller blade of flowing, thus drives relevant electromagnetic mechanism action, the turn signal of impeller blade is converted into the electric signal of different frequency.When pipeline section amasss constant, the flow of liquid just can be measured by the frequency of electric signal of sampling.Owing to will consider laser intensity and the restraint condition such as machining precision and processing cost, the inertia of the rotatable parts such as impeller can not be very little, thus there is a Small flowrate measurement dead zone range, so can not detect low discharge states such as such as dripping, leak.Simultaneously because testing agency has certain inertia and signal carrying out in conversion conditioning and routine processes process, there is a time delay, thus mathematical model can be understood as the one order inertia system of band delay component, so flow detection response speed is slow.

(2), when float-type detects flow, the cavity formed primarily of outer wall and inwall due to its physical construction and float link device detect whether have flow.The stroke size of ball float in cavity is the key factor affecting the type flow detection precision and reliability.Stroke is crossed conference and is caused the bulky of mechanism, and material cost is high, installs complicated, and greatly, sensitivity is low for measurement inertia and time delay, causes detecting and loses efficacy; Stroke is too small, can cause the machining precision of mechanism and processing cost high, the accuracy requirement of magnetic cylinder is high and overall assembly precision is high, the defects such as poor anti jamming capability.

Two, nonshared control unit+Special water pump motor scheme: namely by carrying out the test repeatedly of heat-capacity curve to special pump motor, draw the family curve of pump working in low discharge situation, and the reference value using this curve as systems axiol-ogy flow, whether be in low discharge property interval by detection pump motor current operating characteristics and carry out detection system low discharge.

Nonshared control unit+Special water pump motor scheme, owing to will carry out the test repeatedly of heat-capacity curve and hydraulic pressure resonse characteristic, show that the characteristic quantity of pump working in various low discharge situation is the reference value of systems axiol-ogy flow.Then by a large amount of online data collections and routine processes, draw the actual characteristic amount under system current operating conditions, by carrying out similarity analysis with reference characteristic quantity, thus the flow value that the system that draws is current, and then judge whether system runs on low flow rate condition.But there is serious problem in this method:

(1) high to the requirement of the hardware and software of control system.Because controller will gather a large amount of data and carry out the characteristic quantity of signal transacting and solving system, and carry out similarity analysis with the reference characteristic amount be stored in internal memory, thus require high to controller;

(2) owing to will carry out a large amount of data sampling and processings and the characteristic quantity of solving system, and carry out similarity analysis with reference characteristic quantity, its procedure quantity is large, and the processing time is long, and detection speed is slow;

(3) because system is in During Process of Long-term Operation, the parameter of electric machine, converter parameter etc. are subject to such environmental effects and senile cause changes, causing the operation characteristic amount of system to change greatly, cause precision and the poor reliability of measurement, there is erroneous judgement action in control system;

(4) because water system is that long-time continuous is run, thus water pump is once break down, and can only adopt the motor strictly mated with controller, and can not use the pump motor of other types, thus cause the operation expense of system high, practicality and poor for applicability.

Summary of the invention

The object of the invention is to overcome above-mentioned weak point, propose the low discharge online test method based on parameter association that a kind of structure is simple, applicability is good.

Based on a low discharge online test method for parameter association, comprise the steps:

(1) with sampling period T _sfor sampling to the hydraulic pressure value of water system pipe network and frequency converter output frequency in interval, first time sampled value is labeled as p (l) and f (1); Present sample number of times is k, makes k=1;

(2) the hydraulic pressure value array { p (i) } be made up of M element is set up, and frequency converter output frequency array { f (i) }, wherein i={k-M+1, k-M+2, ... k}, M be preset be greater than 1 positive integer, k is present sample number of times; P (i) | _{i <=0}=0, f (i) | _{i <=0}=0;

(3) judge whether water system is in steady state (SS); If so, step (4) is entered; Otherwise water system plays pendulum, proceed to step (17);

(4) mean value of hydraulic pressure value is solved and the mean value of frequency converter output frequency $\stackrel{\&OverBar;}{F}=\frac{1}{M}\underset{i=k-M+1}{\overset{k}{\mathrm{\&Sigma;}}}f\left(i\right);$

(5) marking current time is the t=0 moment, to the Arbitrary Perturbation Δ F that frequency converter output frequency one is fixing ₁;

(6) m=1 is made;

(7) mT is judged _s> T _dwhether set up, if set up, then proceed to step (9); Otherwise, at t=mT _smoment, sampling pipe network force value p ₁m (), calculates wherein, T _dfor predefined observation interval;

(8) judge whether set up, if be false, proceed to step (17); Otherwise more new variables, makes m=m+1; Return step (7);

(9) at t ∈ [0, T _d] in the time, draw water system and exist under pressure history Δ p ₁(t);

(10) marking current time is the t=0 moment, to the Arbitrary Perturbation Δ F that frequency converter output frequency one is fixing ₂;

(11) m=1 is made;

(12) mT is judged _s> T _dwhether set up, if set up, then enter step (14); Otherwise, at t=mT _smoment, sampling pipe network force value p ₂m (), calculates

(13) judge whether set up, if be false, proceed to step (17); Otherwise more new variables, makes m=m+1, return step (12);

(14) at t ∈ [0, T _d] in the time, draw water system and exist under pressure history Δ p ₂(t);

(15) Δ p is calculated ₁(t) and Δ p ₂(t) joining Δ p ₀, according to formula

$\frac{\mathrm{\&Delta;}{p}_0}{\stackrel{\&OverBar;}{P}}=\frac{2\stackrel{\&OverBar;}{F}\&times;\mathrm{\&Delta;}{F}_2+\mathrm{\&Delta;}{F_2}^2}{{\stackrel{\&OverBar;}{F}}^2}\frac{Q_0\stackrel{\&OverBar;}{P}{T}_b}{P_b{V}_{b}T}m{T}_s,$ Calculate and p ₀corresponding flow Q ₀;

Wherein, P _bfor water system air pressure tank rated pressure value, V _bfor water system air pressure tank air chamber nominal volume, T _bfor water system air pressure tank rated temperature; T is environment temperature;

(16) judge whether set up, wherein, for the peak flow values that the low discharge running status preset is corresponding; If set up, then Q ₀be exactly system flow value, exit; Otherwise, enter step (17);

(17) k=k+1 is made; After this sampling period terminates, sample, and the sampled value marking hydraulic pressure value and frequency converter output frequency is p (k) and f (k) next time; Return step (2).

The further setting of the present invention is, described steady state (SS) is defined as:

Calculate the standard deviation of array { p (i) } ${\mathrm{\&sigma;}}_p=\sqrt{\frac{M\underset{i=k-M+1}{\overset{k}{\mathrm{\&Sigma;}}}p{\left(i\right)}^2-{\left(\underset{i=k-M+1}{\overset{k}{\mathrm{\&Sigma;}}}p\left(i\right)\right)}^2}{M^2}},$ And the standard deviation of array { f (i) } ${\mathrm{\&sigma;}}_f=\sqrt{\frac{M\underset{i=k-M+1}{\overset{k}{\mathrm{\&Sigma;}}}f{\left(i\right)}^2-{\left(\underset{i=k-M+1}{\overset{k}{\mathrm{\&Sigma;}}}f\left(i\right)\right)}^2}{M^2}},$ Judge whether to meet: σ simultaneously _p< ε _pand σ _f< ε _f, wherein: ε _pand ε _ffor preset on the occasion of; If meet, then think that water system is in steady state (SS), otherwise, think that water system plays pendulum.

Low discharge online test method of the present invention has following beneficial effect:

One, with existing by installing compared with flow sensor scheme, the present invention can realize low discharge without the need to flow detection sensor and auxiliary circuit and detect, eliminate Installation and Debugging required time and the cost of flow sensor and additional processing circuitry, make system architecture more simple, system cost is lower;

Two, compared with existing nonshared control unit+Special water pump motor scheme, the low discharge that the three-phase alternating current pump motor that the present invention is applicable to various model supplies water detects, and has versatility widely.Because when system is run under low flow rate condition, its flow mathematical model is $\frac{\mathrm{\&Delta;p}\left(t\right)}{P}=\frac{2F\&times;\mathrm{\&Delta;F}+\mathrm{\&Delta;}{F}^2}{F^2}\frac{{\mathrm{QPT}}_b}{P_b{V}_{b}T}t(1-\frac{{\mathrm{QPT}}_b}{P_b{V}_{b}T}t).$ Wherein: hydraulic pressure value when P is water system stable operation, Δ p (t) is variation in water pressure amount when disturbance runs, electric machine frequency value when F is water system stable operation, frequency variation when Δ F is for running, flow value when Q is water system stable operation, P _b, V _band T _bfor air pressure tank nominal working conditions press down force value, chamber volume value and temperature value, T is system current temperature value, and t is time quantum.As shown from the above formula, for detecting flow during current system stable operation, variation in water pressure amount Δ p (t), air pressure tank parameter P when when when only needing to obtain water system stable operation, when hydraulic pressure value P, stable operation, electric machine frequency value F, disturbance run, frequency variation delta F, disturbance run _b, V _b, T _bflow Q when can measure stable operation with parameters such as current environmental temperature T, and without the need to the model of knowing pump motor and design parameter.Thus, the method can be widely used in meeting being connected with controller of the three-phase alternating current pump motor of voltage and the various models of power index, realizes low discharge on-line checkingi.

Three, low discharge online test method of the present invention has detection speed soon, the features such as reliability is high, practical; Can low-frequency operation causes under available protecting motor and frequency converter low flow rate condition inefficiency fault, improve system lifetim and reliability, for pump motor safety, Effec-tive Function provide Reliable guarantee.

Accompanying drawing explanation

Fig. 1 is the structure diagram of water system;

Fig. 2 is water system lift-pipe resistance characteristic figure.

Embodiment

The size of low discharge threshold value (peak flow values that namely low discharge running status is corresponding) is different because of varying in size of water supply rated flow, 10 water swivels and 2 water swivels are had respectively in such as two family resident families, its situation of dripping of all leaking, obviously this situation all belongs to low discharge.But the low discharge threshold value of 10 water swivels is greater than the low discharge threshold value of 2 water swivels.Simultaneously, the threshold value of small flow rate values is also relevant with lift, and in high-lift situation, low discharge threshold value is usually large than the threshold value in little lift situation.Such as, the water swivel of same two models is and shuts, and its aperture is the same, then setting lift is that the flow value of 20m is greater than the flow value that lift is 10m certainly.Thus, the size of low discharge threshold value restricts by several factors, can not determine without exception, can artificially set as required.Such as, certain resident its have 10 water swivels, and lift is 20m, can set: water consumption Q≤10L/min is low discharge threshold value.Equally, certain resident its have 2 water swivels, and lift is 10m, can set: water consumption Q≤1L/min is low discharge threshold value.

The invention provides a kind of low discharge online test method based on parameter association, mainly based on following water system mathematical model.Water system sketch as shown in Figure 1, mainly comprises water sources, non-return valve 2, pump motor M, air pressure tank 4, device for detecting water pressure 5, ambient temperature detection device 6, outlet water control valve 3, frequency converter 7 and controller 8 etc.Water sources is mainly tap water pipe network or deep-well, pool, rivers and lakes etc.; Non-return valve 2 major function is when preventing water pump out of service, the aqueous reflux backwater source in user's webmaster; Water in water source is carried to user by impeller blade High Rotation Speed by pump motor M; Air pressure tank 4 mainly stablizes the function of hydraulic pressure, prevents water hammer accident to the harm of pipe network; Device for detecting water pressure 5 is for detecting the hydraulic pressure of water system; Ambient temperature detection device 6 is for the current temperature of detection system; Outlet water control valve 3 is for opening or stopping supplying water to user; Controller 8 mainly realizes the operation of the input of correlation parameter, the display of running status and system control program; The controlled quentity controlled variable that frequency converter 7 sends mainly through receiving controller, realizes pump motor variable frequency regulating speed control.

Variable declaration is as follows: q ₁t () is inflow; q ₂t () is aquifer yield; The hydraulic pressure value that p (t) is pipe network; F (t) is frequency converter output frequency; Air pressure tank chamber volume is v ₁(t); Air pressure tank air chamber pressure p _at (), air pressure tank hydroecium volume is v ₂t (), air pressure tank sectional area is S, and air pressure tank cumulative volume is V _z, air pressure tank rated pressure value P _b, air pressure tank air chamber nominal volume V _b, air pressure tank rated temperature T _b, environment temperature is T (t), t is time variable, and ρ is fluid density, and g is acceleration of gravity.During water system stable state: force value is P, frequency converter output frequency is F, and Inlet and outlet water flow is Q, and environment temperature is T, and air pressure tank chamber volume is V ₁, hydroecium volume is V ₂, the unit of above-mentioned all amounts is international unit.Definition the t=0 moment be system with the last moment of frequency F stable operation, namely exist:

$\left\{\begin{array}{c}{q}_1\left(0\right)=Q\\ q_2\left(0\right)=Q\\ f\left(0\right)=F\\ p_a\left(0\right)=P-\mathrm{\&rho;g}\frac{V_2}{S}\\ T\left(0\right)=T\\ p\left(0\right)=P\\ v_1\left(0\right)=V_1\\ v_2\left(0\right)=V_2\end{array}\right.$

Suppose at [0, T _d] running frequency of water pump is in the time: f (t)=F+ Δ F, Δ F is frequency disturbance increment, T _dfor being greater than the time value of 0, varying in size and artificially determining in advance according to water system power; Then hydraulic pressure value is p (t)=P+ Δ p (t), the water pressure fluctuations value that Δ p (t) causes for Δ F; The inflow of water pump is q ₁(t)=Q+ Δ q ₁(t), Δ q ₁t flow of inlet water undulating quantity that () causes for Δ F; The aquifer yield of water pump is q ₂(t)=Q+ Δ q ₂(t), Δ q ₂t water flow undulating quantity that () causes for Δ F; From University Of Chongqing's Master's thesis " research & design based on PLC tea place constant pressure spriukler irrigation control system ", water feeding of water pump flow, pass between hydraulic pressure and motor running frequency are:

$\frac{q_1\left(t\right)p\left(t\right)}{\mathrm{\&eta;}}=\frac{m_1{k}_u^2\frac{R_2}{s}f{\left(t\right)}^2}{{(R_1+\frac{R_2}{s})}^2+{(X_{1\mathrm{\&sigma;}}+X_{2\mathrm{\&sigma;}})}^2}---\left(1\right)$

Wherein: η is the efficiency of water pump, i.e. the ratio of motor useful power and shaft power;

S is revolutional slip;

R ₁, R ₂, X _{1 σ}, X _{2 σ}, m ₁, for the intrinsic parameter of pump motor;

Because pump motor adopts variable frequency regulating speed control, so s remains unchanged substantially.Order:

$\frac{m_1{k}_u^2\frac{R_2}{s}}{{(R_1+\frac{R_2}{s})}^2+{(X_{1\mathrm{\&sigma;}}+X_{2\mathrm{\&sigma;}})}^2}=k---\left(2\right)$

K is only relevant with the structural parameters of motor own, has nothing to do with flow, pressure.Institute can be reduced to the formula:

$\frac{q_1\left(t\right)p\left(t\right)}{\mathrm{\&eta;}}=\mathrm{kf}{\left(t\right)}^2---\left(3\right)$

Make k '=η k.Then when t=0, have:

QP=k′F ²(4)

At t ∈ [0, T _d], by q ₁(t)=Q+ Δ q ₁(t), f (t)=F+ Δ F and p (t)=P+ Δ p (t) substitutes into formula (3):

(Q+Δq ₁(t))(P+Δp(t))=k′(F+ΔF) ²(5)

Launch (5), and arrange:

PQ+QΔp(t)+PΔq ₁(t)+Δq ₁(t)Δp(t)=k′(F ²+2FΔF+ΔF ²)(6)

(4) are substituted into (6) can obtain:

QΔp(t)+PΔq ₁(t)+Δq ₁(t)Δp(t)=k′(2FΔF+ΔF ²)(7)

Fig. 2 is the lift-pipe resistance characteristic curve of system, and wherein: horizontal ordinate is flow Q, ordinate is pressure P, n _i(i=1,2,3,4,5,6) represent the velocity of rotation of water pump; R _i(i=1,2,3,4,5,6,7,8) represent the resistance of pipe system in valve different opening situation, and aperture is less, and resistance is larger.

As aquifer yield q ₂t () is very little, when namely during stable state, Q is less, as shown in Figure 2, when valve opening is very little, the pipe resistance of system is very large, and the rotation speed change of pressure and pump motor is very little for the impact of water flow.Thus Δ q can be thought ₂(t)=0, i.e. q ₂(t)=Q.Thus at time [0, T _d] in, the value of Δ p (t) that Δ F causes is less, so exist:

|Δp(t)|＜＜P(8)

Obtain so arrange (7):

QΔp(t)+PΔq ₁(t)=k′(2FΔF+ΔF ²)(9)

Formula (9) can be obtained divided by (4):

$\frac{{\mathrm{\&Delta;q}}_1\left(t\right)}{Q}+\frac{\mathrm{\&Delta;p}\left(t\right)}{P}=\frac{2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2}{F^2}---\left(10\right)$

Air pressure tank kinetics equation: at t ∈ [0, T _d], the volume change of air pressure tank hydroecium is:

$\begin{array}{c}{\mathrm{\&Delta;v}}_2\left(t\right)={\&Integral;}_0^t(q_1\left(t\right)-q_2\left(t\right))\mathrm{dt}\\ ={\&Integral;}_0^t(Q+{\mathrm{\&Delta;q}}_1\left(t\right)-Q)\mathrm{dt}\\ ={\&Integral;}_0^t{\mathrm{\&Delta;q}}_1\left(t\right)\mathrm{dt}\end{array}---\left(11\right)$

So, t ∈ [0, T _d] hydroecium volume is:

$v_2\left(t\right)=V_2+{\&Integral;}_0^t{\mathrm{\&Delta;q}}_1\left(t\right)\mathrm{dt}---\left(12\right)$

Because V remains unchanged, thus chamber volume is:

$v_1\left(t\right)=V_1-{\&Integral;}_0^t{\mathrm{\&Delta;q}}_1\left(t\right)\mathrm{dt}---\left(13\right)$

Suppose at t ∈ [0, T _d] in the time, environment temperature remains unchanged, then from equation for ideal gases:

$\frac{p_a\left(t\right)}{p_a\left(0\right)}=\frac{V_1}{v_1\left(t\right)}---\left(14\right)$

(13) are substituted into (14) obtain:

$\frac{p_a\left(t\right)-p_a\left(0\right)}{p_a\left(0\right)}=\frac{{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}{V_1-{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}---\left(15\right)$

Make Δ p _a(t)=p _a(t)-p _a(0) be air pressure tank air chamber pressure variable quantity, then:

$\mathrm{\&Delta;}{p}_a\left(t\right)=\frac{p_a\left(0\right){\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}{V_1-{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}---\left(16\right)$

And the pressure variety caused by hydroecium volume change is:

$\mathrm{\&Delta;}{p}_s\left(t\right)=\frac{\mathrm{\&rho;g}{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}{S}---\left(17\right)$

So, variation in water pressure amount

$\begin{array}{c}\mathrm{\&Delta;p}\left(t\right)=\mathrm{\&Delta;}{p}_a\left(t\right)+\mathrm{\&Delta;}{p}_s\left(t\right)\\ =\frac{p_a\left(0\right){\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}{V_1-{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}+\frac{\mathrm{\&rho;g}{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}{S}\end{array}---\left(18\right)$

If parameter T _dchoose rationally, meet then:

$\mathrm{\&Delta;p}\left(t\right)=\frac{p_a\left(0\right)+\mathrm{\&rho;g}\frac{V_1}{S}}{V_1}{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}---\left(19\right)$

Will substitute into formula (19), and arrange:

$\mathrm{\&Delta;p}\left(t\right)=\frac{P-\mathrm{\&rho;g}\frac{V_2}{S}+\mathrm{\&rho;g}\frac{V_1}{S}}{V_1}{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}---\left(20\right)$

Can be obtained by formula (20):

$\frac{P-\mathrm{\&rho;g}\frac{V}{S}}{V_1}{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}<\mathrm{\&Delta;p}\left(t\right)<\frac{P+\mathrm{\&rho;g}\frac{V}{S}}{V_1}{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}---\left(21\right)$

Wherein: V=V ₁+ V ₂.Due to corresponding to the hydraulic pressure that air pressure tank vertical height produces, normally much smaller than actual lift (constant pressure water supply lift is generally at more than 14m), so so have:

$\mathrm{\&Delta;p}\left(t\right)\&ap;\frac{P}{V_1}{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}---\left(22\right)$

(22) are substituted into (10) and arrange and can obtain:

$\frac{\mathrm{\&Delta;}{q}_1\left(t\right)}{Q}+\frac{{\&Integral;}_0^t\mathrm{\&Delta;}{q}_1\left(t\right)\mathrm{dt}}{V_1}=\frac{2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2}{F^2}---\left(23\right)$

So equation (23) is about Δ q ₁a Differential Equation with Constant Coefficients of (t), can separate:

$\mathrm{\&Delta;}{q}_1\left(t\right)=\frac{Q(2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2)}{F^2}{e}^{-\frac{Q}{V_1}t}---\left(24\right)$

Simultaneous formula (24) and (10) can obtain:

$\mathrm{\&Delta;p}\left(t\right)=\frac{P(2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2)}{F^2}(1-e^{-\frac{Q}{V_1}t})---\left(25\right)$

Suppose air pressure tank gas-tight, then from equation for ideal gases:

$\frac{P_b\&times;V_b}{T_b}=\frac{P\&times;V_1}{T}---\left(26\right)$

Simultaneous formula (25) and (26), and arrange:

$\mathrm{\&Delta;p}\left(t\right)=\frac{P(2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2)}{F^2}(1-e^{-\frac{{\mathrm{QPT}}_b}{P_b{V}_{b}T}t})---\left(27\right)$

Due to parameter P, F, Δ F, P _b, V _b, T _b, T and t be observable quantity and known quantity, thus by test pressure disturbance quantity Δ p (t) at t ∈ [0, T _d] value just can calculate the size of the flow Q value of system when stable state.At t=0 place, Taylor series expansion is carried out to formula (27) and arranges:

$\mathrm{\&Delta;p}\left(t\right)=\frac{P(2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2)}{F^2}\underset{n=0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{(-1)}^{n-1}{\left(\frac{{\mathrm{QPT}}_b}{P_b{V}_{b}T}t\right)}^n---\left(28\right)$

Because Q is very little, institute with the formula (28) is approximately:

$\frac{\mathrm{\&Delta;p}\left(t\right)}{P}=\frac{2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2}{F^2}\frac{{\mathrm{QPT}}_b}{P_b{V}_{b}T}t(1-\frac{{\mathrm{QPT}}_b}{P_b{V}_{b}T}t)---\left(29\right)$

At t ∈ [0, T _d], formula (29) is set up must meet following constraint condition:

$\left|\frac{(2F\&times;\mathrm{\&Delta;F}+{\mathrm{\&Delta;F}}^2)}{F^2}\right|\frac{{\mathrm{QPT}}_b}{P_b{V}_{b}T}t<<1---\left(30\right)$

The invention provides a kind of low discharge online test method based on parameter association, comprise the steps:

(1) with sampling period T _sfor sampling to the hydraulic pressure value of water system pipe network and frequency converter output frequency in interval, first time sampled value is labeled as p (1) and f (1); Present sample number of times is k, makes k=1;

(2) the hydraulic pressure value array { p (i) } be made up of M element is set up, and frequency converter output frequency array { f (i) }, wherein i={k-M+1, k-M+2, ... k}, M be preset be greater than 1 positive integer, k is present sample number of times; P (i) | _{i <=0}=0, f (i) | _{i <=0}=0;

(3) judge whether water system is in steady state (SS).Steady state (SS) is defined as: the standard deviation calculating M sampled pressure value p (t) and the standard deviation of frequency converter output frequency f (t) judge whether to meet: σ simultaneously _p< ε _pand σ _f< ε _f(wherein: ε _p, ε _ffor setting on the occasion of, can set according to real system, such as can get 0.1 or 0.2).If met, then think that water system is in steady state (SS), enter step (4); Otherwise water system plays pendulum, proceed to step (17).

(4) mean value of hydraulic pressure value is solved with the mean value of frequency converter output frequency $\stackrel{\&OverBar;}{F}=\frac{1}{M}\underset{i=k-M+1}{\overset{k}{\mathrm{\&Sigma;}}}f\left(i\right).$

(5) t=0 is designated as, to the Arbitrary Perturbation Δ F that output frequency one is fixing with now blaze ₁, namely $f\left(m{T}_s\right)=\stackrel{\&OverBar;}{F}+{\mathrm{\&Delta;F}}_1;$

(6) m=1 is made;

(7) mT is judged _s> T _dwhether set up, if set up, then enter step (9); Otherwise, at t=mT _smoment, sampling pipe network force value p ₁(m); Calculate

(8) judge whether set up, if be false, proceed to step (17); Otherwise,

More new variables: make m=m+1; Return step (7).

(9) at t ∈ [0, T _d] in the time, system of obtaining exists under pressure history Δ p ₁(t);

(10) t=0 is designated as, to the Arbitrary Perturbation Δ F that output frequency one is fixing with now blaze ₂, namely $f\left(m{T}_s\right)=\stackrel{\&OverBar;}{F}+{\mathrm{\&Delta;F}}_2;$

(11) m=1 is made;

(12) mT is judged _s> T _dwhether set up, if set up, then enter step (14); Otherwise, at t=mT _smoment, sampling pipe network force value p ₂m (), calculates

(13) judge whether set up, if be false, proceed to step (17); Otherwise,

More new variables: make m=m+1; Return step (12).

(14) at t ∈ [0, T _d] in the time, system of obtaining exists under pressure history Δ p ₂(t);

(15) Δ p is calculated ₁(t) and Δ p ₂(t) joining Δ p ₀, according to formula

$\frac{{\mathrm{\&Delta;p}}_0}{\stackrel{\&OverBar;}{P}}=\frac{2\stackrel{\&OverBar;}{F}\&times;{\mathrm{\&Delta;F}}_2+{{\mathrm{\&Delta;F}}_2}^2}{{\stackrel{\&OverBar;}{F}}^2}\frac{Q_0\stackrel{\&OverBar;}{P}{T}_b}{P_b{V}_{b}T}m{T}_s,$ Calculate and p ₀corresponding flow Q ₀;

Wherein, P _bfor water system air pressure tank rated pressure value, V _bfor water system air pressure tank air chamber nominal volume, T _bfor water system air pressure tank rated temperature; T is environment temperature;

(16) judge whether set up.Wherein: for the peak flow values that low discharge running status is corresponding, set according to the size of minimum water consumption by user.If set up, then Q ₀be exactly system flow value, and exit; Otherwise, proceed to step (17).

(17) k=k+1 is made; After this sampling period terminates, sample, and the sampled value marking hydraulic pressure value and frequency converter output frequency is p (k) and f (k) next time; Return step (2).

Claims (1)

1., based on a low discharge online test method for parameter association, it is characterized in that, comprise the steps:

(1) with sampling period T _sfor sampling to the hydraulic pressure value of water system pipe network and frequency converter output frequency in interval, first time sampled value is labeled as p (1) and f (1); Present sample number of times is k, makes k=1;

(2) the hydraulic pressure value array { p (i) } be made up of M element is set up, and frequency converter output frequency array { f (i) }, wherein i={k-M+1, k-M+2, ... k}, M be preset be greater than 1 positive integer, k is present sample number of times; P (i) | _{i <=0}=0, f (i) | _{i <=0}=0;

(3) judge whether water system is in steady state (SS); If so, step (4) is entered; Otherwise water system plays pendulum, proceed to step (17);

Described steady state (SS) is defined as:

Calculate the standard deviation of array { p (i) } ${\mathrm{\&sigma;}}_p=\sqrt{\frac{M\underset{i=k-M+1}{\overset{k}{\&Sigma;}}p{\left(i\right)}^2-{\left(\underset{i=k-M+1}{\overset{k}{\&Sigma;}}p\right(i\left)\right)}^2}{M^2}},$ And the standard deviation of array { f (i) } ${\mathrm{\&sigma;}}_f=\sqrt{\frac{M\underset{i=k-M+1}{\overset{k}{\&Sigma;}}f{\left(i\right)}^2-{\left(\underset{i=k-M+1}{\overset{k}{\&Sigma;}}f\right(i\left)\right)}^2}{M^2}},$

Judge whether to meet: σ simultaneously _p< ε _pand σ _f< ε _f, wherein: ε _pand ε _ffor preset on the occasion of; If meet, then think that water system is in steady state (SS), otherwise, think that water system plays pendulum;

(4) mean value of hydraulic pressure value is solved and the mean value of frequency converter output frequency $\stackrel{\&OverBar;}{F}=\frac{1}{M}\underset{i=k-M+1}{\overset{k}{\&Sigma;}}f\left(i\right);$

(5) marking current time is the t=0 moment, to the Arbitrary Perturbation Δ F that frequency converter output frequency one is fixing ₁;

(6) m=1 is made;

(7) mT is judged _s> T _dwhether set up, if set up, then proceed to step (9); Otherwise, at t=mT _sin the moment, sampling pipe network force value is p ₁m (), calculates wherein, T _dfor predefined observation interval;

(8) judge whether set up, if be false, proceed to step (17); Otherwise more new variables, makes m=m+1; Return step (7);

(9) at t ∈ [0, T _d] in the time, draw water system and exist under pressure history Δ p ₁(t);

(10) marking current time is the t=0 moment, to the Arbitrary Perturbation Δ F that frequency converter output frequency one is fixing ₂;

(11) m=1 is made;

(12) mT is judged _s> T _dwhether set up, if set up, then enter step (14); Otherwise, at t=mT _sin the moment, sampling pipe network force value is p ₂m (), calculates

(13) judge whether set up, if be false, proceed to step (17); Otherwise more new variables, makes m=m+1, return step (12);

(14) at t ∈ [0, T _d] in the time, draw water system and exist under pressure history Δ p ₂(t);

(15) Δ p is calculated ₁(t) and Δ p ₂(t) joining Δ p ₀, according to formula

$\frac{{\mathrm{\&Delta;p}}_0}{\stackrel{\&OverBar;}{P}}=\frac{2\stackrel{\&OverBar;}{F}\&times;{\mathrm{\&Delta;F}}_2+{{\mathrm{\&Delta;F}}_2}^2}{{\stackrel{\&OverBar;}{F}}^2}\frac{Q_0\stackrel{\&OverBar;}{P}{T}_b}{P_b{V}_{b}T}{\mathrm{mT}}_s,$ Calculate and Δ p ₀corresponding flow Q ₀;

Wherein, P _bfor water system air pressure tank rated pressure value, V _bfor water system air pressure tank air chamber nominal volume, T _bfor water system air pressure tank rated temperature; T is environment temperature;

(16) judge whether set up, wherein, for the peak flow values that the low discharge running status preset is corresponding; If set up, then Q ₀be exactly system flow value, exit; Otherwise, enter step (17);

(17) k=k+1 is made; After this sampling period terminates, sample, and the sampled value marking hydraulic pressure value and frequency converter output frequency is p (k) and f (k) next time; Return step (2).