CN112066594A - Ordered power utilization control method for large-scale electric heat pump based on mu PMU device - Google Patents

Ordered power utilization control method for large-scale electric heat pump based on mu PMU device Download PDF

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CN112066594A
CN112066594A CN202010893913.6A CN202010893913A CN112066594A CN 112066594 A CN112066594 A CN 112066594A CN 202010893913 A CN202010893913 A CN 202010893913A CN 112066594 A CN112066594 A CN 112066594A
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余昆
陈星莺
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
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Abstract

The invention discloses a method for orderly controlling the power consumption of a large-scale electric heating pump based on a mu PMU device, which is a method for orderly controlling the power consumption of an electric heating pump load group in three working states by utilizing the rapid and accurate measurement data of the mu PMU, combining an electric heating pump model and starting characteristics to select characteristic quantities and formulating characteristic criteria of the starting state of the electric heating pump according to power constraint coupled by a power distribution network voltage constraint model considering a cluster electric heating pump. The method controls the electric heat pump to stop in order, reduces the steady state power and controls the starting sequence, and avoids the electric heat pump from starting impact superposition out of limit.

Description

Ordered power utilization control method for large-scale electric heat pump based on mu PMU device
Technical Field
The invention relates to an electric control method for an electric heating pump, in particular to a sequential electric control method for a large-scale electric heating pump based on a mu PMU device.
Background
The electric heat pump is a heat pump system which drives a heat pump machine to operate by electric energy, has the advantages of wide application range, low operation cost, stable performance and environmental protection, and is widely used for heating and hot water supply of houses at present, but the electric heat pump has the characteristics of large single-machine power and centralized electricity consumption of users, and has obvious influence on load daily peak-valley difference and seasonal peak-valley difference, and particularly in the heating season with sharply increased load, the irregularity of heating and traveling of residents is added, so that the problems of large load peak-valley difference and three-phase imbalance of the load of a power distribution network are solved. In low-voltage distribution networks, the starting impact caused by the short starting process of the electric heat pump can cause obvious sudden increase type pulse and voltage drop type pulse of current inrush current.
The starting impact influences that the operation of the electric heating pump is irregular and the starting impact influences, the instantaneous fluctuation of three-phase voltage easily exceeds the regulation of electric energy quality, the serious voltage reduction can cause the starting failure of the electric heating pump, the starting impact influences the electric energy quality of a low-voltage power distribution network, the electric heating pump can be possibly started, and the operation and the starting of other electric heating pumps and other electric equipment can be influenced. In the prior art, the power distribution network is widely constructed and modified to ensure power utilization, but the method is not only low in economical efficiency, but also long in construction period and is not suitable for practical application.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a method for orderly controlling the power utilization of a large-scale electric heating pump based on a mu PMU device, which reduces the starting impact of the electric heating pump when the electric heating pump is used in a large scale.
The technical scheme is as follows: the technical scheme adopted by the invention is a method for orderly controlling the electricity utilization of a large-scale electric heat pump based on a mu PMU device, which comprises the following steps:
1) modeling an electric heating pump heating system;
2) identifying the state of the electric heat pump based on the mu PMU measurement;
3) and the electric heating pump orderly power utilization strategy based on measurement identification.
In the heating system of the electric heating pump in the step 1)
Compressor electric power PcmpWith respect to the number of revolutions N and the refrigerant flow rate mrFunctional relationship of (c):
Figure BDA0002657814280000011
in the above formula c1Is the specific volume of the compressor suction gas, n is the polytropic exponent of the compression process, etacmpA ratio of power and consumed power is indicated for the compressor,
Figure BDA0002657814280000021
representing the ratio of exhaust pressure to suction pressure;
the heat exchange model of the condenser is as follows:
Figure BDA0002657814280000022
in the formula, Cr,sh,condIs the specific heat coefficient of the refrigerant; t is2Is the temperature of the refrigerant flowing into the condenser; t iscondIs the superheat temperature of the condenser; t is3Is the temperature of the refrigerant exiting the condenser; r iscondThe structure radius of the plate condenser; a. thei,condThe heat exchange area of the plate condenser; t iswIs the outlet temperature at the hot water side of the condenser; u shapesc,cond、 Ush,cond、Utp,condThe heat exchange comprehensive coefficients of a cold water measuring area, an overheating area and a two-phase area of the condenser are TwThe temperature is the temperature of hot water;
the heat exchange quantity of the evaporator meets the following requirements:
Qeva＝Qtp+Qsh＝Qa (3)
in the above formula QevaFor heat transfer to refrigerant in evaporator, QaAbsorbing heat from the heat source medium for the evaporator.
The d-q coordinate system complex variable model of the asynchronous motor is described as follows:
Figure BDA0002657814280000023
in the above formula, the first and second carbon atoms are,
Figure BDA0002657814280000024
stator voltage, stator current, rotor current, stator magnet, respectivelyPhasors of the chains and rotor flux linkages; rs、Ls、M、Rr、LrRespectively a stator resistor, a stator inductor, a stator-rotor mutual inductance, a rotor resistor and a rotor inductor; ls＝Ls-M and lr＝Lr-M is the stator and rotor leakage inductances, respectively; omegarIs the electrical angular velocity of the rotor, with unit rad/s; j is a complex unit.
The active power P of the starting process of the electric heat pump in the step 1)sThe closed interval function relationship with respect to time t is:
Ps(t)＝-1160(t-0.2)2+Pmax t∈[t0,t1] (5)
in the above formula t0To start the initial moment, t1To complete the moment when the electric heat pump enters a steady state, PmaxThe maximum power is started for the electric heat pump.
Firstly establishing a head end node voltage U in the step 2)iConstraint, platform area head end node voltage UiThe following requirements are met:
Ui≥{max(Ulim.k)|Tek(ωmaxrk,Ulim.k)＝Tm(ωmaxrk),k∈[1,n]} (6)
in the above formula Ulim.kIs a critical value T when the load of the electric heat pump at the node k can be normally startedek(ωmaxrk,Ulim.k) For the electromagnetic torque, omega, acting on the motor rotor in the load of the kth electric heat pumpmaxrkIs TekMaximum rotor speed, U, corresponding to maximum valuelim.kIs the critical start voltage at node k, Tm(ωmaxrk) Is the per unit value omega of the rotating speed of the asynchronous motormaxrkMechanical torque of the electric heat pump.
And then judging the starting state of the electric heat pump according to the power impact and the voltage sag, wherein the power impact criterion is as follows:
Figure BDA0002657814280000031
in the above formula, P (t) is the current timeLoad power at moment t; p (t-1) is the load power at the previous measurement moment; n is the measuring frequency of the moment t, and N measuring data are measured by the power change amount and are sequentially subjected to subtraction and summation to obtain the power change amount; p' (t) is the load power change rate at the current time t; lambda [ alpha ]1、λ2Is a threshold value corresponding to the criterion.
The voltage sag criterion is:
Figure BDA0002657814280000032
in the formula, λ3And λ4For describing Ut-1And Ut-2N is the measurement frequency at time t.
And 2) identifying the number of the electric heating pumps in the starting state by utilizing the number of quadratic functions in the starting impact power of the electric heating pumps in the step 2).
In the step 3), the load voltage is converted into the load power, which specifically comprises the following steps:
the voltage and the injected active power of the head end node n meet:
Un＝kP·[P-P(t0)]+Un(t0) (9)
in the formula of UnThe voltage demanded for the head end node n; p is the injection power, U, demanded by the head-end node nn(t0)、P(t0) Is t0The current node voltage and power, k, measured at any momentpFor the slope, the value of one of the quantities can be calculated in the case that the other quantity is known.
The sequential power utilization strategy comprises the following steps:
1) obtaining load information according to a measuring and identifying method and determining load groups in different states;
2) the electric heat pump loads of the two equipment groups in starting and running states are prioritized;
3) and determining the sequence and the quantity of the controlled electric heating pump equipment.
And in the step 2), the superposition peak value of the starting impact power of the electric heat pump started at the same time exceeds the limit, and the steady-state voltage priority, the different temperature priorities and the current sequence position number are added to obtain the starting sequence number.
And in the step 2), the power caused by the superposed starting power when the load of the distribution transformer in steady-state operation is large is out of limit, and the current sequence position number, the priority of the electric heat pump according to the average value of the applied voltage and the priorities of different temperatures are added to obtain the closing sequence number.
Has the advantages that: the invention provides an electric heat pump ordered electricity utilization control method for optimizing starting impact based on electric heat pump state identification and mu PMU rapid measurement. The method controls the electric heat pump to stop in sequence, reduces the steady-state power and controls the starting sequence, and avoids the electric heat pump from starting impact superposition out of limit.
Drawings
FIG. 1 is a heating cycle diagram of an electric heat pump unit;
FIG. 2 is a schematic heat transfer diagram of an evaporator;
FIG. 3 is a T-shaped equivalent circuit diagram of an asynchronous motor;
FIG. 4 is a mechanical characteristic diagram of an asynchronous machine;
FIG. 5 is an equivalent circuit diagram of a radial low-voltage distribution network;
FIG. 6 is an equivalent circuit diagram of the port of the electric heat pump at node k;
FIG. 7 is a simplified Thevenin equivalent circuit diagram;
fig. 8 is a line equivalent diagram of a low voltage distribution network;
FIG. 9 is a flow chart of an orderly power utilization control method of the electric heat pump;
fig. 10 is a graph of the thermal behavior and power characteristics of an electrothermal pump load.
Detailed Description
Modeling of electric heating pump heating system
The main internal elements of the electric heat pump unit are an evaporator, a compressor, a four-way valve, a condenser and an expansion valve. Wherein compressor, condenser, evaporimeter constitute electric heat pump unit's main heat transfer, power consumption part:
A. a compressor: the mechanical energy is converted into the internal energy of the fluid by continuously doing work in a rotating way, and the internal energy is called the heart of the electric heating pump unit. The compressor is the source of power in the refrigerant cycle, and the rotor rotation of the compressor works to adiabatically compress the refrigerant vapor from the evaporator and to continually push the vapor at a higher pressure into the condenser.
B. Evaporator, condenser: is an important heat exchange component in the electric heating pump unit. The evaporator is a process in which the refrigerant and the heat source medium convectively evaporate to absorb heat, so that the refrigerant obtains heat energy. The condenser is a component for releasing heat from the refrigerant to the cooling water through the condensation heat release process to realize the heat transfer of the refrigerant.
Element 1 in fig. 1 is an evaporator; 2 is a compressor; a four-way valve 3; 4 is a condenser; 5 is a through expansion valve; 6, a water valve is closed; 7 is an indoor radiator; and 8 is a circulating water pump. T isaIs ambient temperature, TwIs the hot water temperature; qoTo output the heating quantity; t iseva,i、Teva,oThe temperature of the refrigerant flowing into and out of the evaporator; t iscond,i、Tcond,oThe temperature of the refrigerant flowing in and out of the condenser; t isw,i、Tw,oThe temperature of cooling water flowing in and out of the condenser; p is a radical ofeva,i、peva,oThe pressure of the inflow medium and the outflow medium of the evaporator; p is a radical ofcond,i、pcond,oThe pressure of the inflow and outflow medium of the condenser.
As shown in fig. 2, a zoning model is generally used to describe the heat exchange process in the evaporator: divided into a two-phase zone and a superheated zone. The refrigerant in the evaporation tube absorbs heat in the two-phase region, and the refrigerant boils and vaporizes into refrigerant vapor after absorbing the heat. Because the heat exchange coefficient of the refrigerant in the overheating zone is low, and the heat exchange amount per unit area of the overheating zone is much smaller than that of the two-phase zone. The heat source medium entering the evaporator therefore performs heat exchange with the refrigerant primarily in the two-phase region.
Heat exchange amount on the heat source medium side of the evaporator:
Qa＝ζ·Cp,a·ma·(Ta-T0) (10)
in the formula, TaThe temperature of the heat source medium flowing in is DEG C; zeta is the moisture separating coefficient; cp,aThe specific heat capacity of the medium can be 1.003 kJ/(kg. multidot.K); m isaIs the mass of the low-level heat source medium flowing into the evaporator, and ma＝ρ·V； T0The temperature of the medium flowing out of the evaporator is given in units of ℃.
Heat exchange amount on refrigerant side of evaporator:
the heat exchange equation of the refrigerant side of the two-phase region of the evaporator is as follows:
Figure BDA0002657814280000051
in the above formula, γiIs the fouling factor in the pipe; a istpThe two-phase heat exchange coefficient of the refrigerant; dinThe cross section of the heat exchange tube is the volume; t isW2Is the wall temperature of the two-phase region; t iseva.iIs the temperature of the liquid refrigerant entering the evaporator; ltpThe two-phase region length.
The heat exchange equation of the refrigerant side of the evaporator superheat zone is as follows:
Figure BDA0002657814280000052
in the formula, aVSingle-phase heat exchange coefficient of the refrigerant; t isW1The wall temperature of the overheating zone; t iseva.oIs the refrigerant vapor temperature; lshIs the length of the superheat zone.
It can be seen that the evaporator absorbs heat Q from the heat source mediumaMainly determined by the temperature and flow rate of the heat source medium. The expressions (11) to (12) show that the heat quantity transferred to the refrigerant by the evaporator is mainly determined by the structural parameters of the two-phase area and the overheating area of the evaporator.
Mathematical model of compressor
In order to ensure the normal operation of the refrigerant cycle, the compressor consumes electric power and inputs mechanical energy to the refrigerant in adiabatic compression, and continuously pushes refrigerant vapor formed in the evaporator to be sent into the condenser after adiabatic compression. The compressor drives the entire refrigerant cycle.
The input power to the compressor is related to the pressure in the refrigerant cycle as follows:
Figure BDA0002657814280000061
in the above formula, PcmpThe electric power consumed by the compressor, kW; the frequency f is 50HZ, and s is the slip ratio of the asynchronous motor; vdFor the theoretical gas (m) delivery of the compressor3)；ηVIs a volume coefficient and takes a value of
Figure BDA0002657814280000062
ηcmpThe ratio of the indicated power and the consumed power of the compressor is taken as 0.64;
Figure BDA0002657814280000063
expressing the ratio of the exhaust pressure to the intake pressure, i.e., the compression ratio; n is the polytropic exponent in the compression process, and n is a constant in the adiabatic compression process.
Refrigerant mass flow mrSatisfies the following conditions:
Figure BDA0002657814280000064
wherein N ═ 60f (1-s) is the compressor speed (rpm); c. C1Is the specific volume (m) of suction gas of the compressor3/kg)。
The compressor electric power P can be established by the above formula (13) and formula (14)cmpRotation speed N and refrigerant flow rate mrFunctional relationship of (c):
Figure BDA0002657814280000065
it can be seen that the compressor consumes electrical energy to participate in the refrigerant cycle, and its operating power and rotational speed directly affect the flow to the refrigerant and the pressure (i.e., internal energy) of the refrigerant vapor.
Mathematical model of condenser
The high-temperature and high-pressure refrigerant steam after adiabatic compression of the compressor is pushed into a condenser, and the condenser is a heat exchange component which can release heat from the refrigerant to cooling water to realize heat energy transfer of the refrigerant. The condenser usually adopts a plate heat exchanger, and according to energy conservation, a heat exchange model of the condenser is as follows:
Figure BDA0002657814280000071
in the formula, Cr,sh,condIs the specific heat coefficient of the refrigerant; t is2Is the temperature of the refrigerant flowing into the condenser; t iscondIs the superheat temperature of the condenser; t is3Is the temperature of the refrigerant exiting the condenser; r iscondThe structure radius of the plate condenser; a. thei,condThe heat exchange area of the plate condenser; t iswIs the outlet temperature at the hot water side of the condenser; u shapesc,cond、 Ush,cond、Utp,condThe heat exchange comprehensive coefficients of a cold water measuring area, a superheat area and a two-phase area of the condenser are respectively.
The mathematical model analysis of each component in the electric heating pump unit obtains the heat converted by the two circulating media in each component. The complete operation condition of the electric heat pump is related through the flow and the temperature of the medium in each link, and the parameters which are important in the aspect of operation control are the heating capacity, the power consumption and the energy efficiency ratio of the electric heat pump.
The low-level heat energy Q gathered by the heat collector can be known from the formula (2-2)cMainly by the ambient temperature T of the heat source mediumoFlow and heat collection efficiency. Assuming that the heat completely enters the evaporator, the heat exchange quantity of the heat source medium of the evaporator is equal to the heat energy gathered by the heat collector, namely Qa＝Qc. To steamHeat Q transferred to refrigerant in generatorevaEqual to heat exchange quantity Q of two phase regions in evaporatortpHeat exchange quantity Q with superheat zoneshAnd (2) when the heat exchange loss of the superheat zone and the two-phase zone is neglected, the heat exchange quantity of the evaporator meets the following requirements from the formula (10) to the formula (12):
Qeva＝Qtp+Qsh＝Qa (3)
besides the heat energy input of the low-level heat source, the electric heat pump unit applies work by means of electric energy and also provides energy for the refrigerant circulation. From the foregoing analysis, the electric heating pump system has power consuming elements such as a compressor, a fan, and a water pump. And the compressor does work and has the largest influence on the heating of the electric heat pump. The compressor electric power P of the electric heat pump can be known from the formula (1)cmpWill directly influence the flow m of the refrigerant in the refrigerant cyclerAnd pressure, equation (2) illustrates the flow rate m of the refrigerantrAnd the temperature T of the refrigerantcondDetermines the heat exchange quantity Q of the condensercond. Therefore, the heating capacity finally output by the electric heating pump should be composed of two parts: the heat energy of the low-level heat source and the electric energy of the electric heat pump compressor do work. The heating quantity Q output by the electric heating pump can be obtainedoHeat exchange quantity Q with evaporatorevaElectric power P consumed by the compressorcmpThe following equation relationship exists:
Qo＝Qeva+Pcmp·ηcmp (15)
the energy conservation equation describes the heating quantity Q of the electric heating pumpoContains two parts of energy of heat absorbed from the outside and electric power doing work. Engineering description of energy saving performance of temperature control equipment is often referred to as energy efficiency ratio, where energy efficiency ratio COP is the ratio of the amount of heat produced by the equipment to the amount of electric power consumed by the equipment:
Figure BDA0002657814280000081
the COP reflects the energy-saving heating capacity of the electric heating pump, and the larger the COP value is, the more heat is generated by the electric heating pump under the unit power consumption. The model analysis of the electric heating pump heating system shows that: COP and outer of electric heat pumpTemperature T of boundary heat source mediumoHeat exchange efficiency of the heat exchanger (evaporator and condenser) and operating power P of the main power consuming element (compressor)cmpIt is related.
The model of each component of the unit of the electric heat pump heating system is analyzed, and the power consumption components of the electric heat pump heating system comprise a compressor, a fan and a water pump, wherein the compressor is a component with larger power consumption in the electric heat pump. The power demand at the start of the electric heat pump comes mainly from the compressor. In addition, the compressor of the electric heating pump almost adopts an asynchronous motor with good speed regulation characteristic, so that the power consumption characteristic of the electric heating pump can be represented by adopting a model of the asynchronous motor.
Due to the existence of high-order nonlinear flux linkage coupling, the mathematical model of the asynchronous motor in a static coordinate system is complex and is often transformed into a d-q two-phase rotating coordinate system. The d-q coordinate system complex variable model of the asynchronous motor is described as follows:
Figure BDA0002657814280000082
in the above formula, the first and second carbon atoms are,
Figure BDA0002657814280000083
respectively stator voltage, stator current, rotor current, stator flux linkage and rotor flux linkage; rs、Ls、M、Rr、LrRespectively a stator resistor, a stator inductor, a stator-rotor mutual inductance, a rotor resistor and a rotor inductor; ls＝Ls-M and lr＝Lr-M is the stator and rotor leakage inductances, respectively; omegarIs the electrical angular velocity of the rotor, with unit rad/s; j is a complex unit.
From the above equation (4), the matrix equation of the T-type transient equivalent circuit of the induction motor can be obtained:
Figure BDA0002657814280000084
in the formula, p is a differential operator;
Figure BDA0002657814280000085
a potential is induced for the speed of the induction motor.
Because of e in T-type transient equivalent modelsThe existence of (2) makes the model become a complex differential equation, and makes the calculation amount of solution and derivation large and difficult. Considering that the speed induction potential of the asynchronous motor with cage rotor is zero[40]I.e. esWhen the value is 0, the analysis can be further simplified by selecting an induction motor without a speed induced electromotive force. Its complex variable model can be described as:
Figure BDA0002657814280000091
as shown in fig. 3, in a simplified T-type transient equivalent circuit. Neglecting the speed-induced potential e in the rotor circuitsInstead, the rotor equivalent resistance is used. When in steady state operation p ═ j ω, factor
Figure BDA0002657814280000092
The T-shaped transient equivalent circuit is degenerated into a T-shaped steady-state equivalent circuit,
it can be seen that the stator resistance and reactance in the transient T-shaped equivalent model are consistent with those of the steady-state model, but the rotor resistance of the transient equivalent model is the equivalent resistance and the differential factor of the steady-state rotor
Figure BDA0002657814280000093
The product of (a). However, the dynamic mathematical model of the motor has the characteristics of nonlinearity and strong coupling, and the existence of unobservable quantities such as a differential operator p and a differential rate s in the starting process makes model solution and parameter identification difficult and inconvenient to research and use.
At the moment of start-up of the asynchronous machine, because the machine rotor has not yet rotated. The slip ratio s of the asynchronous motor is 1, and the motor structure can be equivalent to a transformer with a short-circuited secondary, so that the asynchronous motor has the following structure
Figure BDA0002657814280000094
Substituting the above equation into equation (18) yields:
Figure BDA0002657814280000095
Figure BDA0002657814280000096
in the above formula, LsσIs the leakage inductance coefficient of the stator.
When the asynchronous machine is in idle stable operation, the rotating speed of the rotor is close to the rotating speed of the electromagnet. In this case, the slip s is small (about 0.03), and the approximation s is 0. At the moment, the equivalent model of the motor is similar to the transformer model with the secondary side open circuit, and the equivalent model exists
Figure BDA0002657814280000097
The above formula (18) can be substituted to obtain:
Figure BDA0002657814280000101
Figure BDA0002657814280000102
simplified equations (20) and (22) are port characteristics in two states of the asynchronous motor starting instant and no-load stable operation, and the change process of the differential rate s from 1 to approximately 0 in the transient process from starting to stable operation is difficult to describe.
Based on the above analysis, the following two studies are made on the starting process of the electric heat pump: and fitting a starting power function based on the test, and analyzing the critical starting voltage based on model parameter identification.
In order to solve the problem that a starting power model cannot be established due to the fact that the differential rate s is difficult to describe in the starting process, the test platform enables the electric heat pump to be started under the rated voltage for many times, and measured values of current and voltage are recorded. A plurality of starting power data of the electric heat pump in the starting process can be calculated according to the measured values of the starting current and the voltage and drawn into a curve. The test data with higher test precision can be selected as source data for model identification, and abundant test simulation data can be obtained according to the fact that the starting impact multiple (5.9-7.1) and the starting time (0.22-0.36 s) of the electric heat pump accord with uniform distribution simulation on the basis of the source data. And finally, identifying a starting power model of the electric heat pump by adopting a curve fitting method.
And (3) selecting quadratic function fitting test data, and finding after comparing and observing an active power curve: the starting power and time curve of the electrothermal pump presents a more obvious quadratic function characteristic. Thus, the active power P can be constructedsThe quadratic function with respect to time t is as follows:
Ps(t)＝a(t-b)2+c (23)
in the above formula, a, b, c are parameters to be identified. The starting characteristic of the electric heat pump and the vertex-type characteristic of the quadratic function are combined to obtain: ps(t) vertex coordinates of the curve (t)max,Pmax) Corresponding to the time t when the starting power of the electric heat pump reaches the maximum valuemaxSum peak value Pmax. Identifying model parameters by using test data to obtain:
Figure BDA0002657814280000103
it is worth mentioning that: the t-domain in the formula should be the initial starting time t0To the moment t when the starting of the electric heating pump is finished and the electric heating pump enters the steady state1And b is approximately half the start-up period. So the active power P of the starting process of the electric heat pumpsThe closed interval function relationship with respect to time t is:
Ps(t)＝-1160(t-0.2)2+Pmax t∈[t0,t1] (5)
the similarity and the mean value of the quadratic function at each fitting point are shown in table 1, and the mean similarity of the quadratic function to the fitting of the test power curve of the electrothermal pump reaches 0.931.
TABLE 1
Figure BDA0002657814280000111
The leakage inductance L of the stator in the formulas (20) and (22)sσStator inductance LsStator resistor RsRotor resistor RrIs the unknown parameter to be determined. The parameters can be identified by using test measurement data of two time periods of the start of the asynchronous motor and the entering of the asynchronous motor into no-load stable operation.
In order to simplify the identification complexity, a first-order filter is designed for the differential equations of the formula (20) and the formula (22), and the identification of the differential equations is converted into least square identification by using filtered data. And identifying the resistance and reactance parameters of the stator and the rotor of the T-shaped equivalent model by virtue of test data, as shown in the table 2.
TABLE 2
Figure BDA0002657814280000112
After the impedance parameters of the asynchronous motor are obtained through identification, the electromagnetic torque and the mechanical torque can be analyzed in the starting process of the asynchronous motor by utilizing the T-shaped equivalent circuit. When the rotor of the asynchronous machine rotates, the rotating rotor absorbs electromagnetic power P from the stator sideE. Electromagnetic power is applied to the rotor in the magnetic field by means of electromagnetic torque and causes the rotor to rotate, thereby completing the conversion of electrical energy into mechanical energy of the rotor. Electromagnetic torque TeAnd PEThe following relationships exist:
PE＝△P+Pmec＝f(Us 2,Z) (25)
Figure BDA0002657814280000113
in the formula, PEIs the electromagnetic power of the asynchronous machine; delta P is the rotor resistance copper loss; pmecThe total mechanical power generated on the rotating shaft; u shapesIs the terminal voltage of the asynchronous machine;z is the port equivalent impedance of the asynchronous motor; and omega is the per unit value of the rotating speed of the asynchronous motor.
Electromagnetic torque T of asynchronous machineeMechanical torque T of electrothermal pump load in relation to rotation speed and terminal voltagemProportional to the square of the rotation speed. The mechanical torque of the load of the electric heating pump is composed of a variable part which is in direct proportion to the square of the rotating speed and a fixed part which is determined by friction loss. Mechanical torque T of electric heat pumpmComprises the following steps:
Tm(ω)＝T0+△Tω2 (27)
in the above formula, T0Constant coefficient of the mechanical torque fixed part; Δ T is the mechanical torque with respect to ω2Constant coefficient of proportional variation, taking T0＝0.8471，△T＝0.1875[44]。
When the network impedance is not considered, the mechanical characteristics (the relationship curve between the electromagnetic torque and the rotating speed of the asynchronous motor) of the asynchronous motor under different terminal voltages (the terminal voltages of the motor are 1.0pu, 0.98pu and 0.95pu respectively) can be obtained based on the value of the model parameters as shown in fig. 4.
The electromagnetic torque and mechanical torque curves of the asynchronous motor can be known as follows: when the starting voltage of the motor port is high enough (U is more than or equal to 0.95pu), the electromagnetic torque T iseWith mechanical torque TmThere is an intersection point (equilibrium operating point), in which case the asynchronous machine can be started and accelerated to a stable operating state; when the starting voltage is lower than a certain threshold value (U)<0.95pu), TeAnd TmWithout intersection points, the mechanical torque is always higher than the maximum electromagnetic torque corresponding to the starting voltage, and the motor cannot accelerate to a stable operation state. So that the electromagnetic torque TeWith mechanical torque TmWhether the balanced operating point exists is a condition whether the motor is successfully started or not. The peak value of the electromagnetic torque is determined by the starting voltage, so TeAnd TmWhether a balanced operating point exists depends on the magnitude of the port voltage value when the motor is started.
Defining the electromagnetic torque T enabling an asynchronous machineeWith mechanical torque TmThe voltage value with the only intersection point is the critical starting voltage Ulim. As can be seen from formula (26) and FIG. 4Maximum electromagnetic torque T of asynchronous machinee,maxAnd maximum rotational speed omegamaxOnly with respect to the impedance of the asynchronous machine itself and not with respect to the port voltage. So long as the maximum speed ω is determinedmaxCan pass the electromagnetic torque T of the formula (26)eAnd (27) mechanical torque TmThe critical voltage U of the normal start of the load of the electric heat pump can be obtained by equal calculationlim。
Te(ωmax,Ulim)＝Tm(ωmax) (28)
In fig. 4, when the port voltage is 0.95pu, there is a unique intersection point (T) between the mechanical torque and the electromagnetic torque of the electric heat pumpe,max,ωmax) I.e. its critical starting voltage is 0.95 pu. When considering the impedance of the power distribution network and the voltage fluctuation of the motor starting, whether the asynchronous motor can normally run depends on whether the voltage value of the node is lower than the critical voltage U of the asynchronous motor which can normally startlim。
Second, based on mu PMU measurement to identify the state of the electric heat pump
First, the voltage U of the head end node is determinediOf (3) is performed. According to the existing theory, whether the electric heat pump is started successfully or not depends on whether the compressor is started successfully or not. For the fixed-frequency compressor adopting the single-phase asynchronous motor, whether the fixed-frequency compressor is successfully started or not depends on whether the port voltage reaches the critical starting voltage U of the asynchronous motor or notlim。
In an actual low-voltage distribution network, electric heating pumps are dispersed in all places of a power grid, and the voltages of the electric heating pumps are different due to the fact that voltage drops exist in a distribution line. Therefore, the voltage of the head end node must be high enough to ensure that the voltage of each electric heat pump after being reduced by the circuit is not lower than the critical starting voltage U of the electric heat pumplim。
The structural characteristics of parallel connection of the T-shaped equivalent model of the electric heat pump and the distribution line containing impedance are utilized to obtain a network equivalent circuit containing n electric heat pumps, as shown in figure 5, wherein UiFor power supply access point voltage (taking low voltage distribution transformer outlet voltage), RkAnd XkAnd (k ═ 1, 2.., n) is the resistance and reactance of the kth line. RskAnd RrkStator resistors of the kth electric heat pump loadAnd rotor resistance, XskAnd XrkThe reactance of the stator and the rotor of the kth electric heat pump load respectively; xmkIs an excitation reactance; slip sk＝(ωs-ωrk)/ωs，ωsFor synchronous angular velocity, omegarkIs the rotor angular velocity.
In order to obtain the voltage of the load access point of the kth electric heat pump, the voltage of the load access point of the kth electric heat pump can be calculated by adopting a node voltage method for the network equivalent circuit. The graph contains n nodes, and a node admittance matrix Y of the network can be obtained according to the node admittance matrix definition and the characteristics of an equivalent circuit:
Figure BDA0002657814280000131
in the above formula, YkkThe self-admittance of a node k comprises a line admittance and an electric heat pump equivalent admittance positioned at the node k; y isk+1,kIs the mutual admittance of node k +1 and node k, i.e. the admittance of line k + 1. The node admittance matrix Y is a sparse n × n matrix because only mutual admittance exists between adjacent nodes. From this, a node voltage equation Y · U ═ I in the form of a matrix can be established as follows:
Figure BDA0002657814280000132
in the above formula, the first and second carbon atoms are,
Figure BDA0002657814280000141
is the node voltage of node k;
Figure BDA0002657814280000142
is a current injected into node 1 and
Figure BDA0002657814280000143
Z1is the line impedance from node 1 to the power supply access point and Z1＝R1+jX1. Under the condition that the line impedance and the T-shaped equivalent circuit impedance of the electrothermal pump are known, the node voltage equation is adopted(30) The port voltage of the electric heat pump of the node k can be obtained by solving
Figure BDA0002657814280000144
Is about
Figure BDA0002657814280000145
Linear function of (c):
Figure BDA0002657814280000146
FIG. 6 shows the port voltage is UkThe electric heat pump equivalent circuit. In order to calculate the electromagnetic torque of the rotor with respect to the port voltage and the impedance of the rotor, the circuit parts except the equivalent branch of the rotor impedance are simplified and equivalent. A simplified port equivalent circuit is obtained as shown in fig. 7.
Calculating to obtain simplified series equivalent potential U according to Thevenin circuit equivalent principleekSum equivalent impedance Rek+jXekThe following equation is satisfied:
Figure BDA0002657814280000147
Figure BDA0002657814280000148
the electromagnetic torque T acted on the motor rotor in the kth electric heat pump load can be obtained by a simplified circuit and new equivalent parametersek(ωrk,Ui) Comprises the following steps:
Figure BDA0002657814280000149
in the above formula, skAnd UekRespectively rotor speed omegarkAnd station area head end node voltage UiIs a linear function of (a). Let equation (33) relate to rotor speed ωrkIs 0, T can be obtainedekMaximum rotor speed omega corresponding to maximum valuemaxrk。
Figure BDA00026578142800001410
As can be seen from equation (34): maximum rotor speed omegamaxrkOnly affected by the load rotor impedance, stator impedance and excitation impedance of the electric heating pump and the equivalent impedance of the external network, and not related to the port voltage. Therefore, after the load impedance and the network impedance parameters of each electric heating pump are determined, the maximum rotor speed omega of each electric heating pump load can be calculated by the formula (34)maxrk. Obtaining the maximum rotor speed omega corresponding to the maximum electromagnetic torquemaxrkThen, according to the relation (27) between the mechanical torque and the rotating speed, the mechanical torque of the kth electric heating pump can be obtained as follows:
Figure BDA00026578142800001411
in the above formula, Tm(omega) is the mechanical torque of the electric heat pump under the per unit value omega of the rotating speed of the asynchronous motor, T0Constant coefficient of the mechanical torque fixed part; Δ T is the mechanical torque with respect to ω2Constant coefficient of proportional variation, usually taken as T0＝0.8471，△T＝0.1875。Tk0And Δ TkThe constant coefficient of the fixed and variable part of the mechanical torque of the kth electric heating pump takes the same value as the formula (27). Then, from the equation (28) of the threshold starting voltage, the combined equation (33) and (35) has Tek(ωmaxrk,Ui)＝Tm(ωmaxrk). The voltage U of the node at the head end of the transformer area when the electric heat pump positioned at the node k in the low-voltage distribution network can be normally started can be calculated by the equationiCritical value of Ulim.k。
In summary, when n electric heat pumps are connected in the transformer area of the low-voltage distribution transformer, the node voltage U at the head end of the transformer areaiThe requirements are as follows:
Ui≥{max(Ulim.k)|Tek(ωmaxrk,Ulim.k)＝Tm(ωmaxrk),k∈[1,n]} (6)
in the formula of UiTaking a critical value U when the load of the electric heat pump at a node k (k is 1, 2.., n) can be normally startedlim.kIs measured. When U is turnediWhen the above formula is satisfied, even if the voltage of each node in the network drops due to the existence of line impedance and load impedance, the voltage is not as low as the critical starting voltage U of the electric heating pumplimTherefore, each electric heating pump in the network can be ensured to be started successfully.
The micro phasor measurement unit (mu PMU) has the advantages of precision and high speed. The starting state of the electric heat pump is judged based on the following two criteria:
criterion one, power impact
The starting moment of the electric heat pump is accompanied by larger power impact, because the rotating speed of the compressor is zero at the electrifying moment, in order to obtain enough electromagnetic torque, the starting power peak value of the fixed-frequency electric heat pump is as high as 6 times of rated power, and the impact process duration is about 0.3 s.
The quadratic function model of the starting power of the electrothermal pump can also show that: the starting power has a larger value and a faster increase speed, for Ps(t) the function (equation 5) derives the slope of the curve to each instant, i.e. the rate of change of the starting power:
Ps′(t)＝-2320(t-0.2) (36)
it can be found that: when t is 0.2, the increase rate of the starting power is 0, and the starting power reaches the maximum value. The P in the whole starting process can be known by a starting power quadratic function models' (t) has a value range of [ -464,464]. Accordingly, the power variation and P can be determinedsThe value of' (t) identifies whether there is electrothermal pump starting power at the present time t:
Figure BDA0002657814280000151
in the above formula, p (t) is the load power at the current time t; p (t-1) is the load power at the previous measurement moment; n is the measuring frequency of the moment t, and N measuring data are measured by the power change amount and are sequentially subjected to subtraction and summation to obtain the power change amount; p' (t) is the load power change rate at the current time tRate; lambda [ alpha ]1、λ2Is a threshold value corresponding to the criterion. The approximate calculation of | P' (t) | can be easily achieved in the presence of μ PMU metrology data support:
Figure BDA0002657814280000161
in the formula, P (t)2)、P(t1) Are each t2、t1The load power is calculated by the voltage and current measurement values of the mu PMU device at the moment.
It is worth mentioning that: threshold lambda1、λ2The value of (2) has a large influence on the identification result, if the value is too small, the conventional load fluctuation can be identified by mistake, and if the value is too large, some impact power can be missed. Therefore, reasonable values can be taken, most of conventional load fluctuation can be filtered, misjudgment is prevented, and the impact power of the electric heat pump can be accurately and uninterruptedly identified.
Criterion two, voltage sag
The starting process of the known electric heat pump consumes a large amount of power based on a starting test and a starting power model analysis, and the large current causes obvious voltage sag along with current inrush current. Whereas the voltage sag Δ U is characterized by a distinct peak and transient.
The mu PMU device can monitor the power flow condition of the power distribution network in real time, and a voltage measurement value U at the moment ttVoltage measurement value U far less than t-1 momentt-1And U ist-1Voltage measurement value U at time t-2t-2Very closely, it can be determined that a sag has occurred in the voltage at time t, and therefore the voltage sag criterion is as follows:
Figure BDA0002657814280000162
in the formula, the threshold value lambda3Is a larger positive number and is used for describing UtIs much smaller than Ut-1The degree of (d); threshold lambda4Is a very small positive number and is used to describe Ut-1And Ut-2Degree of closeness of(ii) a N is the measurement frequency at time t.
It is worth mentioning that: the network includes a basic resident load P with small fluctuation and slow changeLAnd when the electric heat pump is loaded, the starting of the single electric heat pump firstly influences the rapid climbing of the network power and then causes the obvious drop of the voltage: based on the starting test, the starting process of the asynchronous motor consumes a large amount of power (delta P ═ eta. P)NAnd eta is 5 to 7), and voltage drop caused by large current is serious along with current inrush current. From voltage sag equation
Figure BDA0002657814280000163
The line resistance R of the low-voltage distribution network is large, so that the active power P has a large influence on the voltage. The node injection power comprises load steady-state power and starting impact power of the electric heat pump, namely P ═ PLAnd a + DeltaP. So the voltage sag satisfies:
Figure BDA0002657814280000171
when k electric heat pumps are started simultaneously, P is equal to PL+. Δ P · k, causing a voltage drop of:
Figure BDA0002657814280000172
the superposition of the starting power enables the network power to climb to a larger amplitude, and the caused voltage drop is more serious. Lambda [ alpha ]1、λ2、λ3、λ4The value of (A) is the key for judging whether the state judgment result is accurate, and the reasonable selection of the threshold value can ensure that the judgment can accurately judge the impact influence of the starting of a single heat pump and the simultaneous starting of a plurality of heat pumps. Therefore, the value of the threshold in the first criterion and the second criterion can be selected according to the network power and voltage change value when a single heat pump is started, and the impact condition of simultaneous starting of a plurality of heat pumps can be more easily judged according to the selected threshold. But in the actual gridIn the network, the power and voltage variation values of the network are subjected to the network load P ═ PLThe influence of the situation of the positive Δ P, so the selection of the threshold needs to be analyzed according to the actual measured data and determined by an enumeration method.
And then further identifying the number of the electric heating pumps which are in the starting state at the current moment. A certain tnThe measured value at the time is P (t)n) If there is a criterion determined at tnAt the moment, the starting impact power of the electric heat pump exists, namely, the load power contains instantaneous sudden pulse fluctuation. The starting impact power P of the electrothermal pump at the current moment can be obtained by comparing the load power before the electrothermal pump is startedimp(tn) (pulse fluctuations) can be separated by:
Pimp(tn)＝P(tn)-P(tm) (41)
in the formula, P (t)n) Is tnA power measurement value at a time; p (t)m) Is a distance tnT without impulse power at very close timemThe power measurement at that time. If the measurement result does not meet the starting state characteristic criterion, the moment without impact power is regarded as the moment, and the distance t is selectednTime t at a relatively close timemThe calculation result of the equation (41) is prevented from being subjected to an error due to normal fluctuation of the load. Thus tmThe time is taken as the previous moment of non-impact power judged by the characteristic judgment of the starting state of the electric heat pump.
The starting of the electrothermal pump is usually random, then at tnAt the moment, a plurality of electric heat pumps may exist in the starting process at the same time, so that the starting impact power at the current moment is obtained by the superposition of the starting power of the plurality of electric heat pumps, and P can be obtained based on a quadratic function model of the starting impact powerimp(tn) Is the sum of the superposition of several quadratic functions:
Pimp(tn)＝Ps.1(tn)+Ps.2(tn)+…+Ps.i(tn) (42)
in the above formula, Ps.i(tn) The starting power of the ith electrothermal pump in the starting state is provided.
Therefore, the number of the electrothermal pumps in the starting state at the present moment is identified as Pimp(tn) Is formed by overlapping how many quadratic functions. Setting a startup state coefficient k (n) ═ k1,k2,...,kN) To sum the start delay coefficient Deltat (n) ═ t1,t2,...,tN)TStarting power function P of the electric heating pumps(t) carrying out discrete value taking to obtain starting power function values P at different momentss(ti) Based on K (n), (Δ t (n), and Ps(ti) The combination can describe the superposition condition of all the impact powers of the electric heat pump:
S(n)＝K(n)·Ps[△t(n)]＝k1·Ps(t1)+k2·Ps(t2)+…+kN·Ps(tN) (43)
wherein S (n) is a quadratic function Ps(t) superimposing the obtained impact power of the electric heat pump; n is the starting power function P of the electric heating pumps(t) the number of sampling points can be determined by combining the data acquisition frequency of the mu PMU; t is tNTo start power Ps(t) starting time corresponding to the sampling point; ps(tN) To be at a starting time tNThe starting power function value of (1); k is a radical ofNTo be at the starting time tNThe number of the electric heating pumps. When k isNWhen 0, it indicates that there is no on-time tNWhen k isNWhen k is equal, k electric heat pumps are in starting time tNThe starting power is k.Ps(tN)。
To identify the number of the starting electric heat pumps, the fitted superimposed power S (n) and the impact power measurement value P are solvedimp(tn) The starting state coefficient k (n) ═ k corresponding to the values of the two1,k2,...,kN)T. To describe the measured power Pimp(tn) And the proximity of the superimposed power S (n), P being usedimp(tn) And the Pearson's correlation coefficient γ of S (n) as the identified objective function, which is defined by the equation:
γ＝cov[Pimp(tn),S(n)]/[μPimp(tn)·μS(n)] (43)
in the formula, cov [ P ]imp(tn),S(n)]For impact power P of electric heat pumpimp(tn) Covariance of the fitted superposition power S (n), μ Pimp(tn) And μ S (n) is the standard deviation of the measured power and the superimposed power.
The closer the value of gamma is to 1, the more similar the values are, i.e. the measured power Pimp(tn) And the superimposed power S (n) has a better fit, approximately Pimp(tn) (n). At the moment, the number of the electrothermal pumps in starting and the corresponding starting time can be determined according to the identified starting state coefficient A (n) and the starting delay coefficient Deltat (n).
In the above identification process using the pearson correlation coefficient γ as the objective function, the on-state coefficient k (n) ═ k (k) needs to be determined1,k2,...,kN) The optimization is performed, and the value of N is larger because the measured data of mu PMU has higher density, and the element kNAre discrete non-negative integers. Therefore, the function problem is a discrete combined optimization problem, and the solution can be quickly completed by means of mathematical optimization software (such as CPLEX).
Third, orderly electricity utilization method of electric heat pump based on measurement identification
From a direct load control perspective, it is often necessary to translate the voltage problem into a load power problem. Therefore, all nodes with electrothermal pump loads in the platform area are equivalent to a generalized node m, as shown in fig. 8. The radial low-voltage distribution network can be regarded as a two-node network after equivalent, a first node is connected with the network, and a second node is connected with a platform area load.
Analyzing the current relation between a head end node n of the transformer area and a load generalized node m, wherein the value of the current relation satisfies the following conditions:
Figure BDA0002657814280000181
where the phase angle difference between the m-node voltage and the n-node voltage is given. The complex power of node n may be expressed as:
Figure BDA0002657814280000191
in the formula (I), the compound is shown in the specification,
Figure BDA0002657814280000192
is a current phasor
Figure BDA0002657814280000196
Conjugation of (1);
Figure BDA0002657814280000193
is the impedance angle. The active power P and the voltage U can be simplified by the equations (44) and (45) because the low-voltage distribution network has shorter lines, larger line impedance R and smaller phase angle differencenThe relationship between them is as follows:
Figure BDA0002657814280000194
it can be seen that the injected power P of the head end node n and its node voltage UnApproximately satisfies a linear variation relation therebetween. The active power regulation voltage can be taken when the voltage is out of limit. The linear variation coefficient k can be conveniently calculated through the measured data of the mu PMUp：
Figure BDA0002657814280000195
In the formula of Un(t0)、P(t0) Is t0The current node voltage and power measured at any moment; p (t)1)、Un(t1) Is t1The measured current node power and voltage at that time. Different from the identification criterion: t is t0Time and t1The time of day should have a longer time interval. The ratio of the difference of the measured values can be approximated as the slope k of the linear relationshippThus obtaining a head-end nodeThe voltage and the injected active power of n meet the following conditions:
Un＝kP·[P-P(t0)]+Un(t0) (9)
in the formula of UnThe voltage demanded for the head end node n; p is the injection power demanded by the head-end node n. In case one of the quantities is known, the value of the other quantity can be calculated. For the node connected to the electric heating pump, the node voltage U is used for meeting the starting voltage requirement of the electric heating pumpnIs lined by the critical starting voltage, i.e. is determined by UnAnd (5) solving the P.
To ensure voltage constraint U of the head end node of the transformer arealimI.e. the injection power is required not to exceed Plim＝f(Ulim). Therefore, the running power and the shortage of the power limit of the electric heat pump are the power reduction amount which is adjusted to meet the requirement of the starting of the electric heat pump, and the problem of the starting voltage of the electric heat pump is converted into the problem of the load power restriction of the transformer area.
Combining the above steps, considering the starting impact power of the electric heat pump, a strategy flow for identifying the starting state of the electric heat pump by using PMU measurement and ensuring the critical voltage of each node by limiting the load of the transformer area is shown in fig. 9. In practical applications, there are two different off-limit situations of the load power of the cell: (1) the superposition peak value of the starting impact power of the electric heat pump started at the same time exceeds the limit; (2) when the load of the steady-state operation of the distribution transformer is large, the power caused by the overlapped part of the starting power is out of limit. The sequential electricity utilization method of the electric heat pump under the two different conditions is as follows:
the required power reduction amount P is obtained by solving the limit of the measurement criterion and the critical voltagecatThen, a corresponding control strategy can be formulated for response. The operation characteristic of the electric heat pump mainly depends on a compressor, and the power consumption in the starting process is several times that in normal operation, so that the following starting strategy divides the whole operation process of the electric heat pump into three states of starting, operating and closing, which is different from the steady-state operation strategy of the electric heat pump. Therefore, the relationship between the power characteristics of the operation of the electric heat pump at the time of starting the impact power and the room temperature is considered as shown in fig. 10.
T in FIG. 10maxAnd TminThe temperature upper and lower limit values of the indoor temperature interval can meet the requirement of the comfort degree of a user as long as the strategy of controlling the electric heating pump is ensured to ensure that the room temperature of the electric heating pump does not exceed the temperature limit value. Under the condition that the load ratio of the electric heat pump is large, a large number of users are started randomly for use, the operation condition of each electric heat pump is changed along with the external environment and the requirements of the users, if the temperature change curve in the graph in fig. 6 is subdivided into a plurality of operation sections, each electric heat pump can be in any section of a control period at any one moment, and consumed power comprises two conditions of steady-state operation power and starting impact power. Therefore, the electric heating pump orderly power utilization strategy not only considers the steady-state operation power but also considers the starting impact power. Namely, the electric heat pump in the starting state and the running state is regulated and controlled at the same time.
Based on the above consideration, the electric heat pumps are grouped into load groups of corresponding states according to the operating state. The whole operation power of the load state group can be changed by mutually converting the electric heat pumps in different working states through setting a control strategy. The electric heat pumps in three different states of starting, running and closing exist in the power distribution network at any time, and the electric heat pumps are grouped by using the following load state groups:
Figure BDA0002657814280000201
Figure BDA0002657814280000202
Figure BDA0002657814280000203
in the formula, t is the current moment of strategy execution; st、RtAnd BtThe corresponding load number is n for the current electric heat pump load group working on starting, running and closing1、n2And n3The total load n of the electric heating pump is n1+n2+n3. It can be seen that the working state of the load of the electric heating pump and S are carried out along with the working of the load of the electric heating pumpt、RtAnd BtNumber n of (2)1、n2And n3Will change. The set of electric heat pumps in all states in the system can thus be expressed as:
Figure BDA0002657814280000211
the electric powers consumed by different electric heat pump loads in different working states at the current moment t are different, and an equipment group power set is defined according to a load group set method:
Figure BDA0002657814280000212
in the formula (I), the compound is shown in the specification,
Figure BDA0002657814280000213
for the electric power consumed by the electric heat pump at the moment t, the electric heat pump in different working states corresponds to different load powers (starting power P)s(t) rated power PNAnd zero); dtThe power drawn by the internal device from the grid at time t may be represented as:
Figure BDA0002657814280000214
in the formula (I), the compound is shown in the specification,
Figure BDA0002657814280000215
starting power for the kth electric heat pump in a starting state at the moment t;
Figure BDA0002657814280000216
the rated power of the jth electrothermal pump in the running state at the moment t. Therefore, the electric heat pumps in the response group are subjected to temperature setting by the ordered power utilization control strategyThe load running power of the electric heating pumps is further changed by constant value adjustment or switch operation, and the whole running power of the load group of the electric heating pumps can be influenced by responding to the power change of each electric heating pump in the group.
The operation power condition and the load power limit P of the electric heat pump are obtained in the strategy flow chart 9limIs used as the power reduction amount PcatAnd then, the key of the establishment of the control strategy is to select the number and which working state the electric heat pump in is converted into another working state to change the whole operating power of the load state group. The process of the power change caused by the change of the working state of the electric heat pump comprises the following steps: the operation is changed into a closed state, and the closing is changed into an starting state. The change in the parameters for the state change is shown in table 3.
TABLE 3
Figure BDA0002657814280000221
When an orderly power utilization strategy is established, the electric heating pumps in different working states are mutually converted according to the two state conversion processes to change the integral operation power of the load state group, and the power regulation of the system can be responded. The method comprises the following steps of:
1) and obtaining load information according to the measuring and identifying methods and determining load groups in different states.
2) The electric heat pump loads of the two equipment groups in starting and running states are prioritized.
Aiming at the two different district load power out-of-limit situations, different orderly electricity utilization methods of an electric heating pump are specifically adopted:
the first situation is as follows: controlling the start-up sequence to limit the start-up power
When a plurality of electric heat pumps are started simultaneously, the superposed starting power impact of the electric heat pumps possibly exceeds the platform area load power limit Plim. Under the condition of no heavy load of a distribution network, the start impact power of part of the heat pumps does not cause the load of the transformer area to exceed the limit, so the serious power is avoided by artificially controlling the starting sequence of the electric heat pumps to avoid the simultaneous start of the electric heat pumpsOne way of impacting. In order to determine the starting sequence of the electric heating pump, priority arrangement is carried out according to the critical starting voltage of the electric heating pump and the voltage level of an access node of the electric heating pump, and the number of the starting units is determined according to the priority and the searching condition.
Firstly, according to the voltage average value U of the node where the electric heat pump is located in historical operation timekThe electric heat pumps which are started and are about to be started are sequenced from small to large, and the connected voltage U is enabled according to the principle of 'difficult starting, first starting' (namely the electric heat pump with the external voltage lower than the starting critical voltage is started preferentially)kLarger electric heat pumps have a more backward sequence. Then each electric heat pump is according to UkTo rated voltage UNAnd its critical starting voltage UlimDeviation of (2) generating a steady state voltage priority FuAs follows. FuThe larger the value of (A) is, the higher the priority is, the same applies hereinafter.
Figure BDA0002657814280000222
According to the electric heat pump NkIndoor temperature T ofkFor the electric heat pumps with different levels of room temperature, different temperature priorities F are generated according to the principle of 'low temperature and first start' (namely the electric heat pump with the room temperature close to the lower limit of the temperature interval is started preferentially)TThe following were used:
Figure BDA0002657814280000231
combining the above sorting and priority calculation methods, the voltage average U in historical operation time is calculatedkAnd updating the sequenced electric heat pump starting sequence. The updating method adds corresponding priority to the current sequence position number if the electric heat pump N is usedkAccording to the voltage mean value U in historical operation timekIf the sequence is located at k bits, the starting sequence number after considering the priority is:
K′＝k+Fu+FT (56)
case two: controlling orderly shutdown to reduce steady state power
When the load of the distribution transformer in steady state operation is large, the overlapped part of the starting power can cause the off-limit of the load power of the transformer area. Similar to the control of the turn-on sequence of the electric heat pump, the number and sequence of the turn-off stages need to be reasonably arranged in order to reasonably reduce the load of the steady-state operation to reduce the total load of the power station region. And carrying out priority arrangement according to the critical starting voltage of the electric heating pump and the indoor temperature level of the electric heating pump, and determining the number of the closed units according to the priority and the searching condition.
Firstly according to the indoor temperature T of the electric heating pumpinIn the relationship from large to small, the electric heat pumps in stable operation are sorted according to the principle of 'high temperature and first off' (namely the electric heat pumps with the room temperature close to the upper limit of the temperature interval are preferentially turned off), so that the electric heat pumps with the room temperature close to the lower limit of the temperature interval have a more backward sequence. Then according to the electric heat pump NjIndoor temperature T ofjGenerating different temperature priorities F 'for electric heating pumps with different grades of room temperature'TThe following were used:
Figure BDA0002657814280000241
then according to the principle of easy starting and first closing (i.e. the electric heat pump whose external voltage is higher than starting critical voltage is closed preferentially), according to the electric heat pump NjAverage value U of applied voltage in long-time running statejAnd its critical starting voltage UlimDeviation generation voltage priority of F'UThe following were used:
Figure BDA0002657814280000242
the method for updating the turn-off sequence of the electric heating pump is similar to the method for updating the turn-on sequence of the electric heating pump, the current sequence position number is added with the corresponding priority, if the electric heating pump N is usedjPress UjIf the sequence is at j, the closing sequence after considering the priority is numbered as: j '═ j + F'T+F′U。
3) Determining the receiverThe sequence and the number of the controlled electric heating pump devices. When the system is about to limit the load starting power, the load group S istControlling to limit the number of starting devices; when the system is to reduce the load to ensure the completion of the start-up, the load group R is selectedtControl is performed to reduce the steady-state load. By the amount of power reduction P required by the systemcutThe number of the electric heating pumps to be controlled is determined, and the determination method of the number of the response devices is shown in table 4.
TABLE 4
Figure BDA0002657814280000251
For two different cases of the start-up power surge problem, the load group S is started up based on the table ruletAnd an operating load group RtAnd (5) performing condition search. From the search direction and the search condition, a population R 'which participates in the load control at the end of time t can be obtained'tAnd S'tAs follows.
Figure BDA0002657814280000252
Figure BDA0002657814280000253
R 'are turned off in turn as required'tInternal equipment or start S'tInternal device, wherein for the boot sequence S'tThe starting time of the medium electric heat pump unit is subjected to time delay intervention, so that the starting time is ensured to be staggered as much as possible, and impact superposition is avoided. The delay time of the heat pump to be started in the ith station is delta t-i.t' (i-1, 21) And t' the maximum starting time of the electricity-taking heat pump. The running state of the devices is directly changed through the on-off control of the electric heating pump. The purpose of limiting the number of the starting stations, avoiding the starting power superposition out-of-limit and reducing the steady-state load to preferentially meet the starting requirement is achieved.

Claims (10)

1. A large-scale electric heat pump orderly power utilization control method based on a mu PMU device is characterized by comprising the following steps:
1) modeling an electric heating pump heating system;
2) identifying the state of the electric heat pump based on the mu PMU measurement;
3) and the electric heating pump orderly power utilization strategy based on measurement identification.
2. The PMU-based large-scale electric heat pump orderly power utilization control method according to claim 1, wherein the step 1) is performed in an electric heat pump heating system
Compressor electric power PcmpWith respect to the number of revolutions N and the refrigerant flow rate mrFunctional relationship of (c):
Figure FDA0002657814270000011
in the above formula c1Is the specific volume of the compressor suction gas, n is the polytropic exponent of the compression process, etacmpA ratio of power to consumed power is indicated for the compressor,
Figure FDA0002657814270000012
representing the ratio of exhaust pressure to suction pressure;
the heat exchange model of the condenser is as follows:
Figure FDA0002657814270000013
in the formula, Cr,sh,condIs the specific heat coefficient of the refrigerant; t is2Is the temperature of the refrigerant flowing into the condenser; t iscondIs the superheat temperature of the condenser; t is3Is the temperature of the refrigerant exiting the condenser; r iscondThe radius of the plate condenser; a. thei,condThe heat exchange area of the plate condenser; t iswIs the outlet temperature at the hot water side of the condenser; u shapesc,cond、Ush,cond、Utp,condRespectively a cold water measuring area and an overheating area of the condenser,Comprehensive coefficient of heat transfer in two-phase region, TwIs the hot water temperature;
the heat exchange quantity of the evaporator meets the following requirements:
Qeva＝Qtp+Qsh＝Qa
in the above formula QevaFor heat transfer to refrigerant in evaporator, QaAbsorbing heat from the heat source medium for the evaporator.
The d-q coordinate system complex variable model of the asynchronous motor is described as follows:
Figure FDA0002657814270000021
in the above formula, the first and second carbon atoms are,
Figure FDA0002657814270000022
Figure FDA0002657814270000023
respectively stator voltage, stator current, rotor current, stator flux linkage and rotor flux linkage; rs、Ls、M、Rr、LrRespectively a stator resistor, a stator inductor, a stator-rotor mutual inductance, a rotor resistor and a rotor inductor; ls＝Ls-M and lr＝Lr-M is the stator and rotor leakage inductances, respectively; omegarIs the electrical angular velocity of the rotor, with unit rad/s; j is a complex unit.
3. The mu PMU device-based large-scale electrothermal pump orderly power utilization control method according to claim 1, characterized in that the active power P in the starting process of the electrothermal pump heating system in step 1) is PsThe closed interval function relationship with respect to time t is:
Ps(t)＝-1160(t-0.2)2+Pmax t∈[t0,t1]
in the above formula t0To start the initial moment, t1To complete the moment when the electric heat pump enters a steady state, PmaxAnd starting the maximum power value for the electric heating pump.
4. The method according to claim 1, wherein the step 2) is to first establish a head end node voltage UiConstraint, platform area head end node voltage UiThe requirements are as follows:
Ui≥{max(Ulim.k)|Tek(ωmaxrk,Ulim.k)＝Tm(ωmaxrk),k∈[1,n]}
in the above formula Ulim.kIs a critical value T when the load of the electric heat pump at the node k can be normally startedek(ωmaxrk,Ulim.k) For the electromagnetic torque, omega, acting on the motor rotor in the load of the kth electric heat pumpmaxrkIs TekMaximum rotor speed, U, corresponding to maximum valuelim.kIs the critical start voltage at node k, Tm(ωmaxrk) Is the per unit value omega of the rotating speed of the asynchronous motormaxrkMechanical torque of the electric heat pump.
5. The mu PMU device-based large-scale electrothermal pump orderly power utilization control method according to claim 4, characterized in that the starting state of the electrothermal pump is judged according to power surge and voltage sag, wherein the power surge criterion is as follows:
Figure FDA0002657814270000024
in the above formula, p (t) is the load power at the current time t; p (t-1) is the load power at the previous measurement moment; n is the measuring frequency of the moment t, and N measuring data are measured by the power change amount and are sequentially subjected to subtraction and summation to obtain the power change amount; p' (t) is the load power change rate at the current time t; lambda [ alpha ]1、λ2Is a threshold value corresponding to the criterion.
The voltage sag criterion is:
Figure FDA0002657814270000031
in the formula, λ3And λ4For describing Ut-1And Ut-2N is the measurement frequency at time t.
6. The mu PMU device-based large-scale electrothermal pump order power control method according to claim 1, wherein the number of electrothermal pumps in an activated state is identified by using the number of quadratic functions in the starting impact power of the electrothermal pumps in step 2).
7. The method for orderly controlling the power consumption of the large-scale electrothermal pump based on the mu PMU device according to claim 1, wherein the load voltage is converted into the load power in step 3), and the method comprises the following steps:
the voltage and the injected active power of the head end node n meet:
Un＝kP·[P-P(t0)]+Un(t0)
in the formula of UnThe voltage demanded for the head end node n; p is the injection power, U, demanded by the head-end node nn(t0)、P(t0) Is t0The current node voltage and power, k, measured at any momentpIn the case where one of the quantities is known, the value of the other quantity can be calculated as a slope.
8. The mu PMU device-based large-scale electrothermal pump orderly power utilization control method according to claim 7, characterized in that the orderly power utilization strategy is implemented by the following steps:
1) obtaining load information according to a measuring and identifying method and determining load groups in different states;
2) the electric heat pump loads of the two equipment groups in starting and running states are prioritized;
3) and determining the sequence and the quantity of the controlled electric heating pump equipment.
9. The mu PMU device-based large-scale electrothermal pump orderly power utilization control method according to claim 8, characterized in that in step 2), for the overlapped peak value of the starting impact power of the electrothermal pumps started at the same time exceeding the limit, the steady-state voltage priority, the different temperature priorities and the current sequence position number are added to obtain the starting sequence number.
10. The mu PMU device-based orderly power utilization control method for large-scale electrothermal pumps according to claim 8, characterized in that, in step 2), for the power overrun caused by overlapping part of the start power when the load of the steady-state operation of the distribution transformer is large, the current sequence position number, the priority of the electrothermal pumps sorted according to the mean value of the applied voltage, and the priority of different temperatures are added to obtain the closing sequence number.
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