CN110953169B - Control method of parallel variable-frequency constant-voltage control system - Google Patents

Control method of parallel variable-frequency constant-voltage control system Download PDF

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CN110953169B
CN110953169B CN201911223859.8A CN201911223859A CN110953169B CN 110953169 B CN110953169 B CN 110953169B CN 201911223859 A CN201911223859 A CN 201911223859A CN 110953169 B CN110953169 B CN 110953169B
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frequency
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pressure
control system
delta
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CN110953169A (en
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陈益丰
潘敏辉
潘晓铭
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Wenzhou University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
    • F04D15/0072—Installation or systems with two or more pumps, wherein the flow path through the stages can be changed, e.g. series-parallel
    • E—FIXED CONSTRUCTIONS
    • E03—WATER SUPPLY; SEWERAGE
    • E03B—INSTALLATIONS OR METHODS FOR OBTAINING, COLLECTING, OR DISTRIBUTING WATER
    • E03B5/00—Use of pumping plants or installations; Layouts thereof
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
    • F04D15/0005—Control, e.g. regulation, of pumps, pumping installations or systems by using valves
    • F04D15/0022—Control, e.g. regulation, of pumps, pumping installations or systems by using valves throttling valves or valves varying the pump inlet opening or the outlet opening
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2260/00—Function
    • F05D2260/81—Modelling or simulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2270/00—Control
    • F05D2270/01—Purpose of the control system
    • F05D2270/20—Purpose of the control system to optimize the performance of a machine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2270/00—Control
    • F05D2270/30—Control parameters, e.g. input parameters
    • F05D2270/306—Mass flow
    • F05D2270/3061—Mass flow of the working fluid
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2270/00—Control
    • F05D2270/30—Control parameters, e.g. input parameters
    • F05D2270/335—Output power or torque

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Public Health (AREA)
  • Water Supply & Treatment (AREA)
  • Control Of Non-Positive-Displacement Pumps (AREA)

Abstract

The invention relates to a control method of a parallel variable frequency constant voltage control system, which comprises the steps of firstly, establishing an output stream of the parallel variable frequency constant voltage control systemThe method comprises the steps of measuring a mathematical model for online detection, calculating the output flow of a pump according to a flow model, and further determining a working point of the pump; secondly, solving the flow Q corresponding to the working point with the maximum inscribed circle area in the high-efficiency interval under the condition of the same lift according to the principle that the stability margin of the high-efficiency interval is maximumopFurther, the optimum number N of pumps to be operated is determinedop(ii) a Finally, dynamically adjusting the number of pumps to make the output flow of each running pump equal to or closest to QopAnd the high-efficiency operation stability margin and the optimal efficiency index of each pump of the parallel variable-frequency constant-voltage control system are ensured.

Description

Control method of parallel variable-frequency constant-voltage control system
Technical Field
The invention relates to the field of electromechanical control, in particular to a control method of a parallel variable-frequency constant-voltage control system.
Background
The constant pressure control of the fluid has wide application in the fields of petroleum, chemical industry, food, medicine, water supply and drainage, urban water supply and the like, and plays an important role in ensuring the normal operation of industrial and agricultural production and daily life. The pump is a core component of a constant pressure control system, and the operation performance of the pump is directly related to the performance index, especially the energy consumption index, of the whole control system. The pump is used as a high-energy-consumption general machine, the electric energy consumed by the pump unit accounts for more than 21% of the total national electricity consumption every year, and accounts for 30% -60% of the production cost in water supply enterprises. The running efficiency of the pump in the constant-pressure control system is improved by only 1 percent, which brings great benefits to the energy conservation and environmental protection of China, and 30 to 50 percent of the electric energy consumed by the pump can be saved. By adopting the variable frequency control technology, the energy consumption of the pump can be effectively reduced, 282 hundred million kWh of electricity can be saved every year, and the aims of energy conservation and emission reduction are fulfilled. However, the variable-frequency constant-pressure control system needs to ensure that the pump operates in a high-efficiency interval to realize high efficiency and energy conservation. Due to the fact that in the process control fields of petroleum, chemical industry, food, medicine and the like and water supply occasions, the demand of the fluid has 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 during the low valley period, the frequency converter and pump operate at a low frequency due to the small flow. At the moment, the heat loss and the low-frequency vibration of the motor are serious, the energy consumption of the whole variable-frequency constant-voltage control system is increased sharply, and the system efficiency is low. 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, adverse effects are generated on the safety reliability and the production cost of the constant-voltage control system, and even more serious safety accidents are caused.
The efficient operation of the variable-frequency constant-voltage control system is a common technical problem which needs to be mainly solved for realizing energy conservation, emission reduction, safety and reliability. In order to realize the efficient operation of the variable-frequency constant-voltage control system, the operation state of each pump which works in the parallel constant-voltage control system needs to be acquired in real time, so that the operation number of the pumps of the parallel constant-voltage control system is optimized and controlled, and the efficient operation stability margin and the efficiency index of the parallel constant-voltage control system are ensured to be optimal.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a control method of a parallel variable-frequency constant-voltage control system.
In order to achieve the purpose, the invention provides the following technical scheme:
a control method of a parallel variable-frequency constant-voltage control system comprises the following steps:
step one, sampling period is adopted
Figure BDA0002299839770000024
Collecting pressure values p for intervalsi(k) While obtaining the output frequency f of the frequency converter ii(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 BDA0002299839770000023
And standard deviation SiK is the current sampling frequency, i is 1, 2, …, U is the number of running frequency converters and pumps, and satisfies that U is more than or equal to 1 and less than or equal to N, j is k-N +1, k-N +2,. k, and N is a preset positive integer which is more than 1;
step two, the centralized control unit uses the period TcTo sample the output pressure value P at intervals,and obtaining all frequency converters
Figure BDA0002299839770000021
And SiAnd obtaining from the acquired data
Figure BDA0002299839770000022
And amount of average frequency adjustment
Figure BDA0002299839770000031
Step three, judging
Figure BDA0002299839770000032
If the judgment condition is not satisfied, increasing the number of the running water pumps, and sampling again until the judgment condition is satisfied, PsetIs a set head;
step four, when the three conditions are met, judging whether the system is in a stable state, if the system is not stable, sending the average frequency regulating quantity sigma to the U frequency converters by the centralized control unitiI 1, 2, …, U, driving the system to stabilize;
marking the current time as t ═ 0 when the system is stable, and applying disturbance delta F to the output frequencies of all frequency converters;
step six, acquiring an actual pressure fluctuation value delta P (m) ═ P (m) — P and a pressure variation estimation value delta P at a corresponding moment according to the applied disturbance delta Fg(m) and using Δ p (m) as a reference sequence, Δ pg(m) obtaining the correlation coefficient of the two as a comparison sequence
Figure BDA0002299839770000033
Wherein Δ (min) is the second-stage minimum difference, Δ (max) is the second-stage maximum difference, γ is the resolution coefficient, γ is 0.5, Δ0(m) is the error sequence, Δ0(m)＝|Δp(m)-Δpg(m)|；
Seventhly, judging whether xi (m) > (0.95) is true, and if yes, obtaining an actual output flow value Q of the parallel variable-frequency constant-voltage control system, wherein Q is Qg[m]；
Step eight, passing
Figure BDA0002299839770000034
By using Q,
Figure BDA0002299839770000035
U and F, flow Q of the ith pump is estimatedi；
Constructing a high-efficiency interval, and acquiring the circle center r (Q) of the maximum inscribed circle with the lift P according to the maximum principle of the inscribed circleopP) and obtaining the flow Q corresponding to the working point with the maximum inscribed circle area in the high-efficiency interval under the condition of the same liftop；
Step ten, judging | Qi-QopIf l is less than or equal to tau, tau is any set value, and if it is not, the optimum number of running pumps is obtained
Figure BDA0002299839770000041
And obtaining the number of pumps needed to be increasedop-U；
And step eleven, switching the delta N water pumps from the standby water pumps to operate according to the service life indexes by the centralized control unit.
In step four, whether max { | σ is satisfied simultaneously or not is determinedi|}≤σrefAnd max { Si}≤SrefTo determine whether the system is in a steady state, wherein: sigmaref，SrefThe positive reference value can be set according to the actual system.
The sixth step comprises:
1) make t equal 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 BDA0002299839770000042
Tdis a predefined observation time length; setting an initial value of the flow rate estimation value to
Figure BDA0002299839770000043
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;
2) judging whether M is more than M, 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;
3) and determining
Figure BDA0002299839770000044
If the alpha is any set value, the requirement of the constant-pressure water supply system on the pressure performance index is determined, and if the alpha is not any set value, the central control unit continuously sends the average frequency regulating quantity sigma to all the frequency converters iiTo make it stand; when it is established, the pressure fluctuation value Δ p is acquiredg(m)；
By passing
Figure BDA0002299839770000051
Using the obtained Qg[m]And P, F, Δ F, β, and t ═ mTcTo obtain Δ pg(m), wherein P is the pressure value of the pressure sensor, F is the average value of the output frequency of the frequency converter, and Delta F is the frequency disturbance increment and satisfies | Delta F | < min { F |i}，i∈[1，n]Beta is a coefficient of mass,
Figure BDA0002299839770000052
k is the spring rate of the spring-loaded energy storage tank, ScThe sectional area of the spring type energy storage tank.
Figure BDA0002299839770000053
The values of (c) include two distribution cases:
1)
Figure BDA0002299839770000054
2)
Figure BDA0002299839770000055
and obtained from two distribution cases
Figure BDA0002299839770000056
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 BDA0002299839770000057
And obtaining the water pressure variation amount delta p (t)
Figure BDA0002299839770000058
The invention has the beneficial effects that:
the high-efficiency control strategy of the parallel variable-frequency constant-voltage control system can realize the online detection of the running section of the pump without a flow sensor, so that the time and cost required by the installation and debugging of the system are saved, the system structure is simpler, and the system cost is lower;
the online detection method for the operation interval of the pump has the advantages of simple algorithm, high detection speed, high practicability, high reliability and the like;
and thirdly, the high-efficiency control strategy of the parallel variable-frequency constant-voltage control system optimizes and controls the number of running pumps on the basis of obtaining the running interval of the pumps, so that the high-efficiency running stability margin and the efficiency index of each pump are optimal.
Drawings
Fig. 1 is a structural diagram of a parallel variable-frequency constant-voltage control system.
Fig. 2a and 2b are schematic diagrams of the operating frequency distribution of the parallel variable-frequency constant-voltage control system.
Fig. 3 is a schematic diagram of the high efficiency operation area of the speed regulating pump.
Fig. 4a and 4b are schematic diagrams of the operation interval of the speed regulating pump.
FIG. 5 is a diagram of the optimal operating conditions of the speed regulating pump.
Detailed Description
Assuming that the parallel variable-frequency constant-voltage control 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.
The invention provides a control method of a parallel variable-frequency constant-voltage control system. Firstly, establishing a mathematical model for online detection of output flow of a parallel variable-frequency constant-pressure control system, calculating the output flow of a pump according to the flow model, and further determining a working point of the pump; secondly, solving the flow Q corresponding to the working point with the maximum inscribed circle area in the high-efficiency interval under the condition of the same lift according to the principle that the stability margin of the high-efficiency interval is maximumopFurther, the optimum number N of pumps to be operated is determinedop(ii) a Finally, dynamically adjusting the number of pumps to make the output flow of each running pump equal to or closest to QopAnd the high-efficiency operation stability margin and the optimal efficiency index of each pump of the parallel variable-frequency constant-voltage control system are ensured.
a) Output flow and output power mathematical model of parallel variable frequency constant voltage control system
The schematic diagram of the parallel variable-frequency constant-pressure control system is shown in fig. 1, and the system mainly comprises a liquid source, a centralized control unit, a frequency converter i, a pump i, a check valve i, a gate valve i, i being 1, 2, …, n, a pressure sensor, a spring-type energy storage tank and the like. The liquid source is mainly a liquid medium which needs constant pressure control and can be water, oil or other liquid; the main functions of the centralized control unit are: firstly, collecting a pressure signal; secondly, the constant-pressure control system is communicated with a frequency converter to realize the flow-equalizing control of the constant-pressure control system and the optimal dispatching control of the pump; the man-machine interface function acquires the input of parameters and the display of the running state; the main functions of the frequency converter are as follows: uploading current running states including starting/stopping states, running frequency values, other voltage and current information and the like; receiving a pressure value and a frequency regulating quantity sent by the centralized control unit, and regulating the rotating speed of the pump to realize constant pressure control and current sharing control functions; the pump i conveys liquid in the liquid source to a pipeline through the high-speed rotation of the impeller blades; the check valve i mainly functions to prevent the reverse flow of liquid; the gate valve i is used for realizing connection and disconnection of the pump and the pipe network; the pressure sensor is used for detecting the pressure of the pipe network; the function of the spring type energy storage tank is to stabilize the pressure of a pipe network and prevent water hammer.
The variables are described as follows: f. ofi(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) the outlet flow of the spring type energy storage tank 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 BDA0002299839770000081
wherein: qi(t)×pi(t) is the actual output power, ηiTo be efficient, siFor slip, R1，R2，X1σ，X2σ，m1，
Figure BDA0002299839770000082
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 constant voltage control system's output lift is greater than the pump far away and pushes away the pipe resistance of the 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;
since the parallel constant voltage control system adopts the uniform frequency control, the control method can be applied to the control of the parallel constant voltage control system
Figure BDA0002299839770000085
Comprises the following steps:
|fi(t)-F(t)|≤σ(t) (3)
wherein: f (t) is the frequency average value
Figure BDA0002299839770000083
And sigma (t) is the average frequency performance index.
Because the frequency converter and the centralized control unit use a control chip with excellent performance and an average frequency control algorithm, the situation that sigma (t) is very small can be ensured. Considering that the AC motor and the frequency converter have the same type and adopt frequency conversion control, the AC motor and the frequency converter have the same mechanical characteristic curve, and the corresponding slip ratio si and efficiency eta thereofiApproximately equal, i.e.:
Figure BDA0002299839770000084
order:
Figure BDA0002299839770000091
then the simultaneous (4) yields:
Ci＝Cj＝C (5)
wherein:
Figure BDA0002299839770000092
therefore, for
Figure BDA0002299839770000097
Comprises the following steps:
Qi(t)×p(t)＝C×fi(t)2 (6)
and because of
Figure BDA0002299839770000093
Therefore, the method comprises the following steps:
Figure BDA0002299839770000094
the parameters of the parallel variable-frequency constant-voltage control system in a relatively steady 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 F, 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-voltage control system relative to the steady state, namely:
Figure BDA0002299839770000095
then there are:
|Fi-F|≤ (9)
Figure BDA0002299839770000096
wherein:
Figure BDA0002299839770000101
suppose to be at (0, T)d]The frequency converter output frequency is regulated to be by the parallel connection frequency conversion constant voltage control system integrated controller in time: 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 a time value greater than 0, and the time value is artificially determined according to different performance indexes of the constant pressure control system; 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 BDA0002299839770000102
unfolding (11) and finishing to obtain:
Figure BDA0002299839770000103
combining (10) and (12), and finishing to obtain:
Figure BDA0002299839770000104
because of the existence of the large inertia damping link of the energy storage tank, 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 BDA0002299839770000111
dividing (15) by (10) yields:
Figure BDA0002299839770000112
will be provided with
Figure BDA0002299839770000113
Substitution (16) can give:
Figure BDA0002299839770000114
at present
Figure BDA0002299839770000115
The values of (a) were analyzed: considering an extreme distribution, as shown in fig. 2(a), there are:
Figure BDA0002299839770000116
wherein: sigmau＝F-Fu，σj＝Fj-F，σu＞0，σjNot less than 0; therefore, the method comprises the following steps:
Figure BDA0002299839770000117
and (3) unfolding and arranging the materials to obtain:
Figure BDA0002299839770000118
the simultaneous (18), (20) can obtain:
Figure BDA0002299839770000119
another extreme distribution case is considered, namely FiEven distribution, as shown in fig. 2(b), there are:
Figure BDA0002299839770000121
wherein: i.e. ik，in-k+1＝{1，2，…，n}；ik≠in-k+1；
Figure BDA0002299839770000122
Then:
Figure BDA0002299839770000123
wherein:
Figure BDA0002299839770000124
finishing (23) to obtain:
Figure BDA0002299839770000125
due to the fact that
Figure BDA0002299839770000126
Therefore:
Figure BDA0002299839770000127
wherein:
Figure BDA0002299839770000128
from the geometrical knowledge, F for any other distributioniWhich is
Figure BDA0002299839770000129
Values lie between the two extreme distributions, so there are:
Figure BDA00022998397700001210
considering that the unbalance degree of the average frequency control system with the most common performance is within 10 percent, namely less than or equal to 0.1F, the unbalance degree is less than or equal to 0.1F2＜＜F2，
Figure BDA00022998397700001211
Thus, there are:
Figure BDA00022998397700001212
the simultaneous formulas (17) and (27) can be obtained:
Figure BDA00022998397700001213
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 BDA0002299839770000131
therefore, T ∈ (0, T)d]The length variation quantity delta l (t) of the energy storage tank spring is as follows:
Figure BDA0002299839770000132
therefore, T ∈ (0, T)d]The water pressure change quantity delta p (t) of the energy storage tank is as follows:
Figure BDA0002299839770000133
combining (28) and (31) and finishing to obtain:
Figure BDA0002299839770000134
order:
Figure BDA0002299839770000135
then there are: y' (t) ═ Δ Qin(t) and y (0) ═ 0, and formula (32) can be collated:
Figure BDA0002299839770000136
equations (28) and (33) are combined and solved to obtain:
Figure BDA0002299839770000137
coefficient of order
Figure BDA0002299839770000138
Then:
Figure BDA0002299839770000141
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)d]The value of the pressure variation delta p (t) can be used for measuring the output flow Q value of the parallel variable-frequency constant-pressure control system in a steady state on line.
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 BDA0002299839770000142
the centrifugal pump and the frequency converter of the parallel connection frequency conversion constant voltage control 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, so that the frequency-equalizing control system has the following functions:
Figure BDA0002299839770000143
wherein:nithe 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 BDA0002299839770000144
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 BDA0002299839770000145
therefore, the method comprises the following steps:
Figure BDA0002299839770000146
wherein: i ═ 1, 2, … n }. Will be provided with
Figure BDA0002299839770000151
Substitution (40) has:
Figure BDA0002299839770000152
therefore, the output flow Q of any ith pump of the parallel variable-frequency constant-voltage control system in a steady state can be measured on line on the basis of obtaining the total flow Qi。
b) Operation interval judgment of parallel variable-frequency constant-voltage control system
According to a formula (41), the flow Q of each pump of the parallel variable-frequency constant-voltage control system at any relative steady-state moment can be obtainedi. Meanwhile, the output lift H of the parallel variable-frequency constant-voltage control system and the operating frequency F of each pumpiThe value of the voltage reference value can be obtained through a pressure sensor and the output frequency of a reading frequency converter, and then the working point of each pump of the parallel variable-frequency constant-voltage control system on a Q-H characteristic curve is obtained.
FIG. 3 shows a pumpHigh-efficiency interval distribution diagram, the high-efficiency interval of the pump being rated frequency FNHead characteristic curve HNLowest frequency FminHead characteristic curve HminParabola l under similar working conditionsi1Parabola l under similar working conditionsi2A fan-shaped annular area ABCD. If the pump is in the region ABCD at the operating point of the Q-H characteristic curve, then efficient operation is in progress; otherwise, the system is in a non-efficient operation state.
The operation section distribution is described in detail below.
(1) The lift P is unchanged, the valve opening is changed:
suppose that the ith pump operates at a frequency Fi 1The lift characteristic curve is H1The lift value of the operating point 1 is P, and the flow rate is Q1. As can be seen from fig. 4(a), the operating point 1 is in the high-efficiency operating interval ABCD. The following two cases were analyzed: firstly, when the flow is reduced due to the reduction of the opening degree of the valve, the operation frequency of the parallel variable-frequency constant-pressure control system is inevitably reduced under the condition of maintaining the output lift P unchanged, and the operation frequency is Fi 2The lift characteristic curve is switched to H2The lift value of the operating point 2 is P and the flow rate is Q2. As can be seen from the third diagram, the operating point 2 is not located in the high-efficiency area ABCD, and the efficiency is lower as it deviates from the high-efficiency operating interval; secondly, when the flow is increased due to the increase of the opening degree of the valve, the operation frequency of the parallel variable-frequency constant-pressure control system is inevitably increased under the condition of keeping the output lift P unchanged, and the operation frequency is Fi 3The lift characteristic curve is switched to H3The lift value of the operating point 3 is P and the flow rate is Q3. As can be seen from fig. three, the operating point 3 is not located in the high-efficiency region ABCD, and the efficiency decreases as it deviates from the high-efficiency operating interval.
(2) The lift P changes, the valve opening is unchanged:
assume that the current pump is operating at a frequency Fi 1The pump head characteristic curve is H1The lift corresponding to the running point 1 is P1At a flow rate of Q1. As can be seen from fig. 4(b), the operating point 1 is in the high-efficiency operating interval ABCD. The following two cases are carried outAnd (3) analysis: setting the lift P1Decrease to P2In the process, the operation frequency of the parallel variable-frequency constant-pressure control system is inevitably reduced under the condition that the opening degree of the valve is unchanged, and the operation frequency is Fi 2The lift characteristic curve is switched to H2The lift value of the operating point 2 is P2At a flow rate of Q2. As can be seen from fig. 4(b), the operating point 2 is not located in the high efficiency area ABCD; ② setting the lift from P1Increase to P3In the process, the operation frequency of the parallel variable-frequency constant-pressure control system is inevitably increased under the condition that the opening degree of the valve is unchanged, and the operation frequency is Fi 3The lift characteristic curve is switched to H3The lift value of the operating point 3 is P3At a flow rate of Q3. As can be seen from fig. 4(b), the operating point 3 is not located in the high efficiency area ABCD;
through the analysis, the operation interval of the parallel variable-frequency constant-voltage control system is not always in the high-efficiency interval operation, and changes along with the change of the output lift and the output flow, and in order to realize the high-efficiency, safe and reliable operation of the parallel variable-frequency constant-voltage control system, the parallel variable-frequency constant-voltage control system needs to be efficiently and optimally controlled.
The invention provides a control method of a parallel variable-frequency constant-voltage control system, which comprises the following steps:
(1) frequency converter i with sampling period
Figure BDA0002299839770000171
For sampling pressure values at intervals, the first sample value is marked as pi(1) (ii) a The current sampling frequency is k, and k is made to be 1; wherein: i is {1, 2, …, U }, U is the number of running frequency converters and pumps, and U is more than or equal to 1 and less than or equal to 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) And (4) dividing. Find { fi(j) Mean value of }
Figure BDA0002299839770000172
And standard deviation of
Figure BDA0002299839770000173
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 sampling output pressure values P at intervals and communicating with frequency converters
Figure BDA0002299839770000174
And Si. Computing
Figure BDA0002299839770000175
And amount of average frequency adjustment
Figure BDA0002299839770000176
(4) Judgment of
Figure BDA0002299839770000177
Whether or not this is true. If yes, the number U of the currently operated water pumps cannot meet the constant pressure control, the variable U is updated to be U +1, namely the number of the water pumps is increased, and the step (20) is carried out; otherwise, entering the step (5);
(5) judging whether the parallel variable-frequency constant-voltage control 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-voltage control system is considered to be in a stable state, and the step (6) is carried out; otherwise, the constant pressure control system is in an unstable state, and the step (19) is carried out;
(6) with the time t being 0, a fixed arbitrary disturbance Δ F is applied to all the converter output frequencies via the communication bus, i.e. this is done
Figure BDA0002299839770000181
(7) Let m be 1, m is defined as,
Figure BDA0002299839770000182
Tdis a predefined observation time length;
(8) definition of Qg[m]Is t ═ mTcEstimate of output flow at time, defining Δ pg(m) is the estimated value of the pressure variation at the corresponding moment; order to
Figure BDA0002299839770000183
Wherein
Figure BDA0002299839770000184
Is the initial value of the output flow estimated 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;
(9) judging whether M is greater than M, if so, entering a step (19); otherwise, at t ═ mTcAt the moment, acquiring a pressure value p (m); to give Δ P (m) ═ P (m) -P;
(10) judgment of
Figure BDA0002299839770000185
Whether the pressure change is established or not (alpha is any set value, but is 0.1, 0.05 or other numbers, and is determined by the requirement of the constant pressure control system on the pressure performance index, and the basis for meeting the expression is that the violent fluctuation of the system pressure cannot be caused when the frequency change delta F operation is carried out, otherwise, the existing premise is lost). If not, the step (19) is carried out; otherwise, the flow estimation value Q is usedg[m]And P, F, Δ F, β, and t ═ mTcSubstituting into a formula:
Figure BDA0002299839770000186
solving to obtain delta pg(m)。
(11) 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 pg(m) phase relationNumber ξ (m):
Figure BDA0002299839770000187
(12) it is judged whether ξ (m) > -0.95 holds (ξ (m) is a correlation coefficient, i.e., the actual pressure change value Δ p (m) and the estimated pressure change value Δ pg(m) proximity, the greater the correlation coefficient ξ (m), indicates that Δ p (m) is related to 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 (13); otherwise, the variable is updated: m is m + 1;
Figure BDA0002299839770000191
and (5) returning to the step (9).
(13) Output flow estimate Qg[m]Namely the actual output flow value of the parallel variable-frequency constant-voltage control system, namely Q is Qg[m]；
(14) Q is added,
Figure BDA0002299839770000192
Substituting U and F into the formula:
Figure BDA0002299839770000193
estimating the flow Q of the ith pumpi；
(15) According to the maximum principle of the inscribed circle of the ABCD, the center r (Q) of the maximum inscribed circle with the lift P is obtainedopP) and calculates the flow Qop；
(16) Determine | Qi-QopWhether the | is less than or equal to gamma (gamma is an artificial arbitrary set value and represents Q)iAnd QopDegree of deviation) of the image. If so, entering step (19); otherwise, entering the step (17);
(17) computing
Figure BDA0002299839770000194
And solving for the number of pumps Δ N-N that need to be addedopU (if Δ N is negative, indicating the number of stations that need to be reduced);
(18) switching the delta N water pumps from the standby water pumps by the centralized control unit according to the service life index to operate, and entering the step (20);
(19) the centralized control unit sends the frequency regulating quantity sigma of the uniform frequency control algorithm to the U-station frequency converter through a communication busi(i＝1，2，…，U)；
(20) Let k be k + 1; carrying out next sampling, and marking the sampling value of the output pressure as pi(k) (ii) a And (4) returning to the 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 (7)

1. A control method of a parallel variable-frequency constant-voltage control system is characterized by comprising the following steps: which comprises the following steps:
step one, sampling period is adopted
Figure FDA0002661760170000011
Collecting pressure values p for intervalsi(k) While obtaining the output frequency f of the frequency converter ii(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 FDA0002661760170000012
And standard deviation SiK is the current sampling frequency, i is 1, 2, …, U is the number of running frequency converters and pumps, and satisfies that U is more than or equal to 1 and less than or equal to N, j is k-N +1, k-N +2,. k, and N is a preset positive integer which is more than 1;
step two, the centralized control unit uses the period TcThe output pressure value P is sampled at intervals, and all frequency converters are obtained
Figure FDA0002661760170000013
And SiAnd obtaining from the acquired data
Figure FDA0002661760170000014
And amount of average frequency adjustment
Figure FDA0002661760170000015
Figure FDA0002661760170000016
The average value of the pressure of an inlet corresponding to the frequency converter i is shown, and F is the average value of the output frequency of the frequency converter;
step three, judging
Figure FDA0002661760170000017
If the judgment condition is not satisfied, increasing the number of the running water pumps, and sampling again until the judgment condition is satisfied, PsetIs a set head;
step four, when the three conditions are met, judging whether the system is in a stable state, if the system is not stable, sending the average frequency regulating quantity sigma to the U frequency converters by the centralized control unitiI 1, 2, …, U, driving the system to stabilize;
marking the current time as t ═ 0 when the system is stable, and applying disturbance delta F to the output frequencies of all frequency converters;
step six, acquiring an actual pressure fluctuation value delta P (m) ═ P (m) — P and a pressure variation estimation value delta P at a corresponding moment according to the applied disturbance delta Fg(m) and using Δ p (m) as a reference sequence, Δ pg(m) obtaining the correlation coefficient of the two as a comparison sequence
Figure FDA0002661760170000021
Wherein Δ (min) is the second-stage minimum difference, Δ (max) is the second-stage maximum difference, γ is the resolution coefficient, γ is 0.5, Δ0(m) is the error sequence, Δ0(m)＝|Δp(m)-Δpg(m) |, p (m) is at t ═ mTcObtaining a pressure value at any moment;
seventhly, judging whether xi (m) > (0.95) is true, and if yes, obtaining an actual output flow value Q of the parallel variable-frequency constant-voltage control system, wherein Q is Qg[m]，Qg[m]As an estimate of flow；
Step eight, passing
Figure FDA0002661760170000022
By using Q,
Figure FDA0002661760170000023
U and F, flow Q of the ith pump is estimatedi；
Constructing a high-efficiency interval, and acquiring the circle center r (Q) of the maximum inscribed circle with the lift P according to the maximum principle of the inscribed circleopP) and obtaining the flow Q corresponding to the working point with the maximum inscribed circle area in the high-efficiency interval under the condition of the same liftop；
Step ten, judging | Qi-QopIf l is less than or equal to tau, tau is any set value, and if it is not, the optimum number of running pumps is obtained
Figure FDA0002661760170000024
And obtaining the number of pumps needed to be increasedop-U；
And step eleven, switching the delta N water pumps from the standby water pumps to operate according to the service life indexes by the centralized control unit.
2. The control method of the parallel variable-frequency constant-voltage control system according to claim 1, characterized in that: in step four, whether max { | σ is satisfied simultaneously or not is determinedi|}≤σrefAnd max { Si}≤SrefTo determine whether the system is in a steady state, wherein: sigmaref，SrefThe positive reference value can be set according to the actual system.
3. The control method of the parallel variable-frequency constant-voltage control system according to claim 1, characterized in that: the sixth step comprises:
1) make t equal 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 FDA0002661760170000031
Tdis a predefined observation time length; setting an initial value of the flow rate estimation value to
Figure FDA0002661760170000032
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;
2) judging whether M is more than M, 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;
3) and determining
Figure FDA0002661760170000033
If the alpha is any set value, the requirement of the constant-pressure water supply system on the pressure performance index is determined, and if the alpha is not any set value, the central control unit continuously sends the average frequency regulating quantity sigma to all the frequency converters iiTo make it stand; when it is established, the pressure variation amount estimated value Δ p is acquiredg(m)。
4. The control method of the parallel variable-frequency constant-voltage control system according to claim 3, characterized in that: by passing
Figure FDA0002661760170000034
Using the obtained Qg[m]And P, F, Δ F, β, and t ═ mTcTo obtain Δ pg(m), wherein P is the pressure value of the pressure sensor, F is the average value of the output frequency of the frequency converter, and Delta F is the frequency disturbance increment and satisfies | Delta F | < min { F |i}，i∈[1，n]Beta is a coefficient of mass,
Figure FDA0002661760170000035
k is spring of spring energy storage tankRigidity, ScIs the sectional area of the spring type energy storage tank, FiIs the output frequency of the frequency converter i.
5. The control method of the parallel variable-frequency constant-voltage control system according to claim 1, characterized in that:
Figure FDA0002661760170000036
the values of (c) include two distribution cases:
1)
Figure FDA0002661760170000041
2)
Figure FDA0002661760170000042
and obtained from two distribution cases
Figure FDA0002661760170000043
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]，ΔQin(t) is the inlet flow fluctuation value caused by delta F, P is the pressure value of the pressure sensor, Q is the inlet and outlet flow of the energy storage tank, F is the average value of the output frequency of the frequency converter, and sigma isj＝Fj-F，FiIs the output frequency of the frequency converter i.
6. The control method of the parallel variable-frequency constant-voltage control system according to claim 5, characterized in that: and obtaining a pressure fluctuation value delta p (t) caused by delta F according to the volume change delta v (t) and the spring length change delta l (t) of the spring type energy storage tank.
7. The control method of the parallel variable-frequency constant-voltage control system according to claim 6, characterized in that: according to
Figure FDA0002661760170000044
And ΔObtaining the value of pressure fluctuation caused by F
Figure FDA0002661760170000045
Beta is a coefficient
Figure FDA0002661760170000046
K is the spring stiffness of the spring energy storage tank; scThe sectional area of the spring type energy storage tank is shown, and t is a time variable.
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