CN103487099B - A kind of low discharge online test method based on parameter reverse method - Google Patents

Abstract

The invention provides a kind of low discharge online test method based on parameter reverse 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 frequency small-signal under steady state operating conditions, the force value of sampling water system pipe network, according to flow calculated with mathematical model, and with standard deviation scope for foundation obtains 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

Small flow online detection method based on parameter inverse solution method

Technical Field

The invention belongs to the field of electromechanical integration measurement and control, particularly relates to a small-flow online detection method based on a parameter inversion method, and is particularly suitable for small-flow operation detection and protection of a water pump of a variable-frequency constant-pressure water supply device of an air pressure tank.

Background

The lift characteristic and the pipe resistance characteristic have important influence on the performance of the water supply system in the constant-pressure variable-frequency water supply system, when the water valve is not completely closed or the water supply system operates at a small flow rate due to leakage of the pipeline valve, the pipe resistance and the lift loss of the water supply system are increased, the energy consumption of the system is increased, and the efficiency is low. The small flow refers to the situation that when the opening degree of the water tap is small or the water tap is not completely closed and the water consumption is small or close to zero due to pipeline leakage, the situation is called as the small flow situation of the variable-frequency water supply system. At the moment, the water pump runs at a small flow, so that the efficiency of the water pump is greatly reduced, the energy-saving purpose cannot be achieved, and the power of the water pump is increased more and more.

Meanwhile, the water pump motor and the frequency converter are in a low-frequency operation state due to low-flow operation, so that the low-frequency noise of the motor and the frequency converter is serious, the service life and the performance of the motor and the frequency converter are reduced, and the safety reliability and the production cost of water supply are adversely affected.

The small flow detection of the water pump constant-pressure water supply system is one of key technical problems which need to be solved in key aspects for realizing energy-saving, high-efficiency, safe and reliable water supply of the water pump variable-frequency constant-pressure water supply system. At present, there are two main ways related to the detection of the small flow of the water pump:

firstly, a flow sensor scheme: namely, a flow sensor is arranged at the water outlet of the water pump, so that small flow detection is realized; the commonly used flow sensor detection mechanisms are mainly of impeller type and float type.

The impeller type detection has the following three conditions, which can lead to low flow detection precision and reliability performance indexes: under the condition of high water supply flow rate, solid impurities in water quality impact an impeller, so that the impeller is deformed and damaged, the rotational inertia of the whole mechanism is unbalanced, and the flow detection is invalid or the precision and the data reliability are greatly reduced; secondly, when water quality is polluted and acidic or alkaline, the impeller mechanism can be seriously corroded, the rotational inertia of the whole mechanism is unbalanced, and the flow detection is invalid or the precision and the data reliability are greatly reduced; and thirdly, the impeller type flow detection drives the impeller blades to rotate through flowing liquid, so that a related electromagnetic mechanism is driven to act, and a rotation signal of the impeller blades is converted into an electric signal with different frequencies. Under the condition that the cross section of the pipeline is constant, the flow of the liquid can be measured by sampling the frequency of the electric signal. Since inertia of a rotating member such as an impeller cannot be small in consideration of constraints such as mechanical strength, machining accuracy, and machining cost, there is a small flow measurement dead zone range, and therefore, a small flow state such as dripping, water leakage, or the like cannot be detected. Meanwhile, the detection mechanism has certain inertia and a time delay exists in the process of carrying out conversion conditioning and program processing on signals, so that the mathematical model can be understood as a first-order inertia system with a hysteresis link, and the flow detection response speed is low.

When the floater type flow rate detection device is used for detecting whether flow rate exists or not, the mechanical structure of the device mainly comprises a cavity body formed by an outer wall and an inner wall and a floating ball linkage device. The stroke of the floating ball in the cavity is a key factor influencing the accuracy and reliability of the flow detection. The overlarge stroke can cause the mechanism to have large volume, high material cost, complex installation, large measurement inertia and time delay and low sensitivity, thus causing detection failure; the over-small stroke can cause the defects of high machining precision and machining cost of the mechanism, high precision requirement of the magnetic cylinder, high integral assembly precision, poor interference resistance and the like.

II, a scheme of a special controller and a special water pump motor is as follows: the characteristic curve of the water pump working under the condition of small flow is obtained by repeatedly testing the lift characteristic curve of a special water pump motor, the curve is used as a reference value of the system detection flow, and the system small flow is detected by detecting whether the current operation characteristic of the water pump motor is in a small flow characteristic interval.

The scheme of the special controller and the special water pump motor is to repeatedly test a lift characteristic curve and a water pressure response characteristic curve, and the characteristic quantity of the water pump working under various small flow conditions is obtained and is used as a reference value of the system detection flow. And then obtaining the actual characteristic quantity of the system in the current running state through a large amount of data online acquisition and program processing, and carrying out similarity analysis on the actual characteristic quantity and the reference characteristic quantity so as to obtain the current flow value of the system and further judge whether the system runs in a small-flow working condition. However, this method has serious problems that:

the requirements for hardware and software of a control system are high. The controller needs to acquire a large amount of data, process signals, solve characteristic quantities of the system and analyze similarity with reference characteristic quantities stored in a memory, so that the requirement on the controller is high;

secondly, a large amount of characteristic quantities of the data acquisition, processing and solving system are required, and similarity analysis is carried out on the characteristic quantities and reference characteristic quantities, so that the method is large in program quantity, long in processing time and low in detection speed;

in the long-term operation process of the system, motor parameters, frequency converter parameters and the like are influenced by environmental factors and change due to aging, so that the operation characteristic quantity of the system is changed greatly, the measurement precision and reliability are poor, and the control system has misjudgment action;

since the water supply system continuously runs for a long time, once a water pump breaks down, only a motor strictly matched with the controller can be adopted, and other types of water pump motors cannot be used, so that the running and maintenance cost of the system is high, and the practicability and the applicability are poor.

Disclosure of Invention

The invention aims to overcome the defects and provides the small flow online detection method based on the parameter inversion method, which is simple in structure and good in applicability.

A small flow online detection method based on a parameter inversion method is characterized by comprising the following steps:

(1) with a sampling period T_sSampling the water pressure value of a water supply system pipe network and the output frequency of a frequency converter at intervals, and marking the first sampling values as p (1) and f (1); the current sampling frequency is k, and k = 1;

(2) establishing a water pressure value array { p (i) } formed by M elements and a frequency converter output frequency array { f (i) }, wherein i ═ k-M +1, k-M +2,. k }, M is a preset positive integer larger than 1, and k is the current sampling time; p (i) leucotrichia_i＜＝0＝0，f(i)|_i＜＝0＝0；

(3) Judging whether the water supply system is in a stable state; if yes, entering the step (4); otherwise, the water supply system is in an unstable state, and the step (15) is carried out;

(4) solving the mean value of the water pressure valuesAnd average value of output frequency of frequency converter $\stackrel{\‾}{F}=\frac{1}{M}\underset{i=k-M+1}{\overset{k}{\mathrm{\Σ}}}f\left(i\right);$

(5) Let n = 1;wherein, T_dIs a predefined observation time length;

(6) marking the current moment as t =0 moment, and giving a fixed arbitrary disturbance △ F to the output frequency of the frequency converter_n；

(7) Let m = 1;

(8) determine mT_s＞T_dWhether the information is established or not is judged, if so, the step (11) is carried out; otherwise, at t ═ mT_sSampling the pressure value p of the water supply system pipe network at any moment_n(m) is calculated to obtain

$\mathrm{\Δ}{p}_n\left(m\right)=p_n\left(m\right)-\stackrel{\‾}{P};$

(9) Judgment ofIf the judgment result is not true, the step (15) is carried out; otherwise, will Δ p_n(m)、 ΔF_n、T_b、P_b、V_bT and T ═ mT_sSubstitution formulaSolving to obtain Q_n[m](ii) a Wherein, P_bFor the rated pressure value, V, of the pressure tank of the water supply system_bRated volume of air chamber of air pressure tank for water supply system, T_bRated temperature for the water supply system air pressure tank; t is the ambient temperature;

(10) updating the variable, and enabling m to be m +1;

(11) calculating the mean value

(12) Updating the variable, let n = n +1;

judging whether n is more than 5, if so, entering the step (13); otherwise, turning to the step (6);

(13) calculating the standard deviationDetermine sigma_QIf yes, go to step (14); otherwise, go to step (15);

(14) calculating the mean valueJudgment ofWhether or not, if so, thenNamely the system flow value, and quitting; otherwise, go to step (15); wherein,the flow rate is a maximum flow rate value corresponding to a preset small-flow-rate running state;

(15) let k = k +1; after the current sampling period is finished, sampling for the next time, and marking the sampling values of the water pressure value and the output frequency of the frequency converter as p (k) and f (k); and (4) returning to the step (2).

The invention is further arranged in that said steady state is defined as:

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

Judging whether the following conditions are met simultaneously: sigma_p＜_pAnd σ_f＜_fWherein:_pand_fis a preset positive value; if the condition is met, the water supply system is considered to be in a stable state, otherwise, the water supply system is considered to be in an unstable state.

The small flow online detection method based on the parameter inversion method has the following beneficial effects:

compared with the existing scheme of installing the flow sensor, the invention can realize small-flow detection without the flow detection sensor and an auxiliary circuit, saves the time and cost for installing and debugging the flow sensor and the auxiliary processing circuit, and has simpler system structure and lower system cost;

compared with the scheme of the existing special controller and the special water pump motor, the invention is suitable for small-flow detection of water supply of three-phase alternating-current water pump motors of various models and has wide universality. Because the system operates under the working condition of low flow, the flow mathematical model isWherein: p is the water pressure value when the water supply system operates stably, delta P (t) is the water pressure variation when the water supply system operates in disturbance, F is the motor frequency value when the water supply system operates stably, delta F is the frequency variation when the water supply system operates stably, Q is the flow value when the water supply system operates stably, P is_b、V_bAnd T_bThe pressure value, the volume value and the temperature value of the air chamber under the rated working condition of the air pressure tank are shown, T is the current temperature value of the system, and T is the time quantum. According to the formula, to detect the flow rate of the current system in stable operation, only the water pressure value P of the water supply system in stable operation, the motor frequency value F in stable operation, the frequency variation delta F in disturbance operation, the water pressure variation delta P (t) in disturbance operation and the air pressure tank parameter P are required to be obtained_b、V_b、T_bThe flow Q in stable operation can be measured according to the parameters such as the current environment temperature T, and the model and the specific parameters of the water pump motor do not need to be known. Therefore, the method can be widely applied to connection of various types of three-phase alternating-current water pump motors meeting voltage and power indexes with the controller, and small-flow online detection is realized.

Thirdly, the small-flow online detection method has the characteristics of high detection speed, high reliability, strong practicability and the like; the low-efficiency fault caused by low-frequency operation under the low-flow working condition of the motor and the frequency converter can be effectively protected, the service life and the reliability of the system are improved, and reliable guarantee is provided for safe and efficient operation of the water pump motor.

Drawings

FIG. 1 is a schematic diagram of a water supply system;

fig. 2 is a water supply system head-pipe resistance characteristic diagram.

Detailed Description

The small flow threshold (i.e. the maximum flow value corresponding to the small flow operation state) is different according to the rated flow of the supplied water, for example, two families have 10 taps and 2 taps respectively, which all have water leakage and water dripping, and obviously all belong to the small flow. But the small flow value of 10 taps is greater than the small flow value of 2 taps. At the same time, the threshold value for the low flow value is also related to the head, the low flow threshold value being generally larger in the case of high head than in the case of low head. For example, if the same two types of faucets are closed and the same opening is used, the flow value with the set head of 20m is definitely larger than the flow value with the set head of 10 m. Therefore, the size of the small flow threshold is limited by many factors, and cannot be determined in a general way, and can be set by a person as needed. For example, a resident who has 10 taps and a head of 20m may set: the water consumption Q is less than or equal to 10L/min, which is a small flow threshold value. Also, a resident who has 2 taps and a head of 10m can set: the water consumption Q is less than or equal to 1L/min, which is a small flow threshold value.

The invention provides a small flow online detection method based on a parameter inversion method, which is mainly based on a mathematical model of a water supply system. The water supply system is schematically shown in fig. 1, and mainly comprises a water intake source, a check valve 2, a water pump motor M, an air pressure tank 4, a water pressure detection device 5, an ambient temperature detection device 6, a water outlet control valve 3, a frequency converter 7, a controller 8 and the like. The water taking source is mainly a tap water pipe network or a deep well, a pond, a river, a lake and the like; the check valve 2 has the main function of preventing water in a user network management from flowing back to a water source when the water pump stops running; the water pump motor M conveys water in a water source to a user through high-speed rotation of the impeller blades; the air pressure tank 4 mainly has the function of stabilizing water pressure, and prevents the damage of water hammer accidents to a pipe network; the water pressure detection device 5 is used for detecting the water pressure of the water supply system; the environment temperature detection device 6 is used for detecting the current temperature of the system; the water outlet control valve 3 is used for starting or stopping water supply to a user; the controller 8 mainly realizes the input of relevant parameters, the display of running states and the running of a system control program; the frequency converter 7 mainly realizes the frequency conversion speed regulation control of the water pump motor by receiving the control quantity sent by the controller.

The variables are described as follows: q. q.s₁(t) is the water inflow; q. q.s₂(t) water yield; p (t) is the water pressure value of the pipe network; f (t) is the frequency converter output frequency; the volume of the air chamber of the air pressure tank is v₁(t); pressure p of air chamber of air pressure tank_a(t) the volume of the water chamber of the air pressure tank is v₂(t) the sectional area of the pressure tank is S, and the total volume of the pressure tank is V_zPressure value P of air pressure tank_bRated volume V of air chamber of air pressure tank_bRated temperature T of air pressure tank_bThe environmental temperature is T (t), t is a time variable, rho is the liquid density, and g is the gravity acceleration. When the water supply system is in a steady state: the pressure value is P, the output frequency of the frequency converter is F, the water inlet and outlet flow is Q, the ambient temperature is T, and the volume of the air chamber of the air pressure tank is V₁Volume of the water chamber is V₂All quantities mentioned above are in international units. Defining the time t =0 as the last time the system is operating stably at the frequency F, i.e. there are:

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

assume at [0, T_d]The running frequency of the water pump in time is as follows: f (T) F + Δ F, Δ F being the frequency perturbation increment, T_dThe time value is greater than 0 and is artificially determined in advance according to different power of the water supply system; the water pressure value is P (t), P + Δ P (t), and Δ P (t) is a water pressure fluctuation value caused by Δ F; the water inlet of the water pump is q₁(t)＝Q+Δq₁(t)，Δq₁(t) is the inlet water flow fluctuation value caused by delta F; the water outlet quantity of the water pump is q₂(t)＝Q+Δq₂(t)，Δq₂(t) is the fluctuation value of the effluent flow caused by delta F; it can be known from the study and design of the constant-pressure sprinkling irrigation control system based on the PLC tea garden in the Master thesis of Chongqing university that the relationship between the water inlet flow rate and the water pressure of the water pump and the operation frequency of the motor is as follows:

$\frac{q_1\left(t\right)p\left(t\right)}{\mathrm{\η}}=\frac{m_1{k}_u^2\frac{R_2}{S}f{\left(t\right)}^2}{{(R_1+\frac{R_2}{S})}^2+{(X_{1\mathrm{\σ}}+X_{2\mathrm{\σ}})}^2}---\left(1\right)$

wherein: eta is the efficiency of the water pump, namely the ratio of the effective power of the motor to the output power of the shaft;

s is slip;

R₁,R₂,X_1σ,X_2σ,m₁,the parameters are inherent parameters of a water pump motor;

because the water pump motor adopts frequency conversion speed regulation control, s basically keeps unchanged. Order:

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

k is only related to the structural parameters of the motor, and is not related to flow and pressure. The formula can be simplified as:

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

let k ═ η k. Then at t =0, there is:

QP＝k′F²(4)

at T ∈ [0, T_d]Q is prepared by₁(t)＝Q+Δq₁(t), F (t) ═ F + Δ F and P (t) ═ P + Δ P (t) are substituted into formula (3):

(Q+Δq₁(t))(P+Δp(t))=k′(F+ΔF)²(5)

unfolding (5) and finishing to obtain:

PQ+QΔp(t)+PΔq₁(t)+Δq₁(t)Δp(t)＝k′(F²+2FΔF+ΔF²)(6)

substituting (4) into (6) can obtain:

QΔp(t)+PΔq₁(t)+Δq₁(t)Δp(t)＝k′(2FΔF+ΔF²)(7)

fig. 2 is a head-pipe resistance characteristic curve of the system, wherein: flow rate Q on the abscissa and pressure P, n on the ordinate_i(i ═ 1,2,3,4,5,6) represents the rotational speed of the water pump; r_i(i-1, 2,3,4,5,6,7,8) denotes a valveThe pipe network resistance under the different aperture circumstances, the aperture is less, and the resistance is bigger.

When the water yield q is₂(t) is very small, i.e. when Q is small at steady state, it can be known from fig. 2 that when the valve opening is very small, the pipe resistance of the system is very large, and the influence of the pressure and the rotation speed change of the water pump motor on the water outlet flow is very small. Thus, it can be said that Δ q₂(t) 0, i.e. q₂(t) ═ Q. Thus at time [0, T_d]In addition, since the value of Δ p (t) by Δ F is small, there are:

|Δp(t)|＜＜P(8)

so finishing (7) to obtain:

QΔp(t)+PΔq₁(t)＝k′(2FΔF+ΔF²)(9)

dividing equation (9) by (4) yields:

$\frac{\mathrm{\Δ}{q}_1\left(t\right)}{Q}+\frac{\mathrm{\Δp}\left(t\right)}{P}=\frac{2F\×\mathrm{\ΔF}+\mathrm{\Δ}{F}^2}{F^2}---\left(10\right)$

the pressure tank kinetic equation is at T ∈ [0, T_d]Of the water chamber of the pressure tankThe volume change is:

$\mathrm{\Δ}{v}_2\left(t\right)={\∫}_0^t(q_1\left(t\right)-q_2\left(t\right))\mathrm{dt}$

$={\∫}_0^t(Q+\mathrm{\Δ}{q}_1\left(t\right)-Q)\mathrm{dt}---\left(11\right)$

$={\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}$

therefore, T ∈ [0, T_d]The water chamber volume is:

$v_2\left(t\right)=V_2+{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}---\left(12\right)$

because V remains constant, the chamber volume is:

$v_1\left(t\right)=V_1-{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}---\left(13\right)$

assume T ∈ [0, T_d]And (3) keeping the ambient temperature constant in time, and then obtaining the following by an ideal gas equation:

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

substituting (13) into (14) to obtain:

$\frac{p_a\left(t\right)-p_a\left(0\right)}{p_a\left(0\right)}=\frac{{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}}{V_1-{\∫}_0^t{q}_1\left(t\right)\mathrm{dt}}---\left(15\right)$

let Δ p_a(t)＝p_a(t)-p_a(0) The pressure variation of the air chamber of the air pressure tank is as follows:

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

and the pressure variation caused by the volume change of the water chamber is as follows:

$\mathrm{\Δ}{p}_s\left(t\right)=\frac{\mathrm{\ρg}{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}}{S}---\left(17\right)$

therefore, the amount of change in the water pressure

Δp(t)＝Δp_a(t)+Δp_s(t)

$=\frac{p_a\left(0\right){\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}}{V_1-{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}}+\frac{\mathrm{\ρg}{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}}{S}---\left(18\right)$

If the parameter T_dIs reasonably selected to meetThen:

$\mathrm{\Δp}\left(t\right)=\frac{p_a\left(0\right)+\mathrm{\ρg}\frac{V_1}{S}}{V_1}{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}---\left(19\right)$

will be provided withSubstituting into formula (19), and arranging to obtain:

$\mathrm{\Δp}\left(t\right)=\frac{P-\mathrm{\ρg}\frac{V_2}{S}+\mathrm{\ρg}\frac{V_1}{S}}{V_1}{\∫}_0^t\mathrm{\Δ}{q}_1\left(t\right)\mathrm{dt}---\left(20\right)$

from equation (20) we can derive:

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

wherein: v is V₁+V₂. Due to the fact thatThe water pressure generated corresponding to the vertical height of the air pressure tank is usually much smaller than the actual lift (the constant pressure water supply lift is generally more than 14 m), so thatTherefore, the method comprises the following steps:

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

substituting (22) into (10) and arranging to 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 for Δ q₁(t) linear constant coefficient differential equation, solvable:

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

simultaneous equations (24) and (10) can be found:

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

assuming that the pressure tank has no gas leakage, the ideal gas equation shows that:

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

equations (25) and (26) are combined, and are arranged as follows:

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

due to the parameters P, F, Δ F, P_b、V_b、T_bT and T are all observable and known quantities, and thus are measured at T ∈ [0, T_d]The flow Q value of the system in a steady state can be calculated. And (3) carrying out Taylor series expansion on the formula (27) at t =0 and finishing:

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

since Q is small, equation (28) is approximated as:

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

at T ∈ [0, T_d]If equation (29) is satisfied, the following constraint must be satisfied:

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

the invention provides a small flow online detection method based on a parameter inversion method, which comprises the following steps:

(1) with a sampling period T_sSampling the water pressure value of a water supply system pipe network and the output frequency of a frequency converter at intervals, and marking the first sampling values as p (1) and f (1); the current sampling frequency is k, and k = 1;

(2) establishing a water pressure value array { p (i) } formed by M elements and a frequency converter output frequency array { f (i) }, wherein i ═ k-M +1, k-M +2,. k }, M is a preset positive integer larger than 1, and k is the current sampling time; p (i) leucotrichia_i＜＝0＝0，f(i)|_i＜＝0＝0；

(3) And judging whether the water supply system is in a stable state. The steady state is defined as: calculating the standard deviation of M sampling pressure values p (t)And the standard deviation of the output frequency f (t) of the frequency converterJudging whether to useSimultaneously, the following requirements are met: sigma_p＜_pAnd σ_f＜_f(wherein:_p，_fto set the positive value, the setting may be made according to the actual system, and may be, for example, 0.1 or 0.2). If yes, the water supply system is considered to be in a stable state, and the step (4) is carried out; otherwise, the water supply system is in an unstable state, and the step (15) is carried out.

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

(5) Let n = 1;wherein, T_dIs a predefined observation time length;

(6) at the time marked as t =0, a fixed arbitrary disturbance Δ F is given to the output frequency_nI.e. by $f\left(m{T}_s\right)=\stackrel{\&OverBar;}{F}+\mathrm{\&Delta;}{F}_n.$

(7) Let m = 1;

(8) determine mT_s＞T_dIf yes, entering the step (11); otherwise, at t ═ mT_sAt any moment, sampling pipe network pressure value p_n(m); to obtain Δ p_n(m)＝p_n(m)-P；

(9) Judgment ofWhether or not this is true. If not, turning to the step (15); otherwise, will Δ p_n(m)、 ΔF_n、T_b、P_b、V_bT and T ═ mT_sSubstitution formula $\frac{\mathrm{\&Delta;}{p}_n\left(m\right)}{\stackrel{\&OverBar;}{P}}=\frac{2F\&times;\mathrm{\&Delta;}{F}_n+\mathrm{\&Delta;}{F_n}^2}{{\stackrel{\&OverBar;}{F}}^2}\frac{Q_n\left[m\right]P{T}_b}{P_b{V}_{b}T}m{T}_s,$ Solving to obtain Q_n[m]。

(10) Updating variables:

and (5) enabling m to be m +1, and returning to the step (8).

(11) Calculating the mean valueStep (12) is entered.

(12) Updating variables:

let n = n +1;

and judging whether n is more than 5. If yes, entering the step (13); otherwise, go to step (6).

(13) Calculating the standard deviationDetermine sigma_QWhether or not 0.5 is true. If yes, entering step (14); otherwise, go to step (15).

(14) Calculating the mean valueJudgment ofWhether or not this is true. Wherein:the maximum flow value corresponding to the small-flow operation state is set by the user according to the minimum water consumption. If so, thenNamely the system flow value, and quitting; otherwise, go to step (15).

(15) Let k = k +1; after the current sampling period is finished, sampling for the next time, and marking the sampling values of the water pressure value and the output frequency of the frequency converter as p (k) and f (k); and (4) returning to the step (2).

Claims (1)

1. A small flow online detection method based on a parameter inversion method is characterized by comprising the following steps:

(1) with a sampling period T_sSampling the water pressure value of a water supply system pipe network and the output frequency of a frequency converter at intervals, and marking the first sampling values as p (1) and f (1); the current sampling frequency is k, and k is made to be 1;

(2) establishing a water pressure value array { p (i) } formed by M elements and a frequency converter output frequency array { f (i) }, wherein i ═ k-M +1, k-M +2,. k }, M is a preset positive integer larger than 1, and k is the currently-sampled integerSampling times; p (i) leucotrichia_i＜＝0＝0，f(i)|_i＜＝0＝0；

(3) Judging whether the water supply system is in a stable state; if yes, entering the step (4); otherwise, the water supply system is in an unstable state, and the step (15) is carried out;

the steady state is defined as:

calculate the standard deviation of the array { p (i) }And the standard deviation of the array { f (i) }Judging whether the following conditions are met simultaneously: sigma_p＜_pAnd σ_f＜_fWherein:_pand_fis a preset positive value; if so, the water supply system is considered to be in a stable state, otherwise, the water supply system is considered to be in an unstable state;

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

(5) Let n equal to 1;wherein, T_dIs a predefined observation time length;

(6) marking the moment when the current moment is t-0, and giving a fixed arbitrary disturbance delta F to the output frequency of the frequency converter_n；

(7) Let m equal to 1;

(8) determine mT_s＞T_dWhether the information is established or not is judged, if so, the step (11) is carried out; otherwise, at t ═ mT_sAt any moment, the pressure value of the sampling water supply system pipe network is p_n(m) is calculated to obtain ${\mathrm{\&Delta;p}}_n\left(m\right)=p_n\left(m\right)-\stackrel{\&OverBar;}{P};$

(9) Judgment ofIf the judgment result is not true, the step (15) is carried out; otherwise, will Δ p_n(m)、ΔF_n、T_b、P_b、V_bT and T ═ mT_sSubstitution formula $\frac{{\mathrm{\&Delta;p}}_n\left(m\right)}{\stackrel{\&OverBar;}{P}}=\frac{2\stackrel{\&OverBar;}{F}\&times;{\mathrm{\&Delta;F}}_n+{{\mathrm{\&Delta;F}}_n}^2}{{\stackrel{\&OverBar;}{F}}^2}\frac{Q_n\&lsqb;m\&rsqb;\stackrel{\&OverBar;}{P}{T}_b}{P_b{V}_{b}T}{\mathrm{mT}}_s,$ Solving to obtain Q_n[m](ii) a Wherein, P_bFor the rated pressure value, V, of the pressure tank of the water supply system_bRated volume of air chamber of air pressure tank for water supply system, T_bRated temperature for the water supply system air pressure tank; t is the ambient temperature;

(10) updating a variable, and enabling m to be m +1; returning to the step (8);

(11) calculating the mean value

(12) Updating the variable, and enabling n to be n +1;

judging whether n is more than 5, if so, entering the step (13); otherwise, turning to the step (6);

(13) calculating the standard deviationDetermine sigma_QIf yes, go to step (14); otherwise, go to step (15);

(14) calculating the mean valueJudgment ofWhether or not, if so, thenNamely the system flow value, and quitting; otherwise, go to step (15); wherein,the flow rate is a maximum flow rate value corresponding to a preset small-flow-rate running state;

(15) let k be k +1; after the current sampling period is finished, sampling for the next time, and marking the sampling values of the water pressure value and the output frequency of the frequency converter as p (k) and f (k); and (4) returning to the step (2).