CN110334409B - Method for establishing energy efficiency evaluation model of asynchronous motor under voltage fluctuation and flicker - Google Patents

Method for establishing energy efficiency evaluation model of asynchronous motor under voltage fluctuation and flicker Download PDF

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CN110334409B
CN110334409B CN201910512503.XA CN201910512503A CN110334409B CN 110334409 B CN110334409 B CN 110334409B CN 201910512503 A CN201910512503 A CN 201910512503A CN 110334409 B CN110334409 B CN 110334409B
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energy efficiency
voltage fluctuation
asynchronous motor
flicker
amplitude
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CN110334409A (en
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陈子辉
吴智影
刘勇浩
刘贺
李辰盟
麦荣焕
殷江
汤铭华
周锟
刘恒
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Guangdong Power Grid Co Ltd
Jiangmen Power Supply Bureau of Guangdong Power Grid Co Ltd
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Guangdong Power Grid Co Ltd
Jiangmen Power Supply Bureau of Guangdong Power Grid Co Ltd
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
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    • G06Q50/06—Electricity, gas or water supply
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

Abstract

The invention relates to the technical field of energy efficiency evaluation of electric equipment under the influence of power quality in a power system, in particular to a method for establishing an energy efficiency evaluation model of an asynchronous motor under voltage fluctuation and flicker, which comprises the following steps of S1: setting disturbance sources of simulated voltage fluctuation and flicker; s2: establishing an equivalent circuit of the asynchronous motor; s3: determining the inter-harmonic current fundamental magnetomotive force steering; s4: calculating the energy efficiency of the asynchronous motor; s5: determining the model parameters of the simulated motor, and the value ranges of the fluctuation frequency and the amplitude; s6: compiling simulation codes of the MATLAB file according to the simulation flow and running; s7: and according to the simulation data, obtaining an energy efficiency evaluation formula of the three-phase asynchronous motor along with the voltage fluctuation amplitude and frequency change by utilizing a curve fitting toolbox of MATLAB. The influence of the power quality problem of voltage fluctuation and flicker on the energy efficiency of the asynchronous motor can be qualitatively and quantitatively analyzed.

Description

Method for establishing energy efficiency evaluation model of asynchronous motor under voltage fluctuation and flicker
Technical Field
The invention relates to the technical field of energy efficiency evaluation of electric equipment under the influence of power quality in a power system, in particular to a method for establishing an energy efficiency evaluation model of an asynchronous motor under voltage fluctuation and flicker.
Background
High-power and nonlinear power electronic equipment is widely applied to a power distribution network, and the consequent power quality problem arouses high attention of people. The electric motor drives production machinery with various industrial purposes, and the electricity consumption accounts for about 50% of the total electricity consumption in China. And the inter-harmonic waves generated by voltage fluctuation and flicker increase the extra heating loss of the motor, endanger the normal operation of the motor and reduce the efficiency of energy utilization. Therefore, the method has great and profound guiding significance for researching the energy efficiency influence of voltage fluctuation and flicker on the three-phase asynchronous motor, establishing an energy efficiency evaluation model and evaluating the efficiency of the motor on line, reducing the loss of electric energy in the power distribution process and ensuring the normal operation of a system.
At present, related researches are carried out on the loss characteristics of a three-phase asynchronous motor in the aspects of the problems of three-phase imbalance, harmonic waves, voltage deviation and other electric energy quality. For example: the characteristics of the magnetic densities and the current densities of different positions of stator and rotor iron cores and rotor conducting bars under the condition of three-phase voltage unbalance and the influence of the characteristics on loss along with time are calculated and analyzed by using a time-step finite element method; by utilizing a field-circuit coupling time step finite element method, the change rule of each loss of the motor with light load and rated load is quantitatively analyzed within the range of +/-10% of rated voltage; the method of the equivalent circuit is utilized to research the calculation of the loss, efficiency and power factors of harmonic components contained in the cage type asynchronous motor under the condition of power supply of the inverter; the loss characteristic of the induction motor when harmonic waves and three-phase imbalance coexist in the power supply is analyzed by combining a time step finite element method. Meanwhile, detection and suppression devices of voltage fluctuation and flicker in the power grid are developed in the market successively.
However, the research on the power quality problem of voltage fluctuation and flicker mostly remains in the monitoring stage, and the qualitative and quantitative analysis on the energy efficiency influence of the voltage fluctuation and flicker on specific electric equipment is not performed: or discussing a detection method and a suppression measure of voltage fluctuation and flicker in the generator set under the new energy grid connection, and not considering the influence of the voltage fluctuation and the flicker on the energy efficiency of the motor; or through a series of tests, the influence of the voltage fluctuation of the power grid on the performance of the three-phase asynchronous motor in the agricultural machinery is analyzed, but the voltage fluctuation in the text is the voltage deviation for a long time; or the running process of restarting the motor under the condition of power grid interference for a short time and the relation between the power grid voltage and the electromagnetic torque and the rotating speed are analyzed, but only the condition that the power grid voltage disappears or decreases for a short time is considered in the text.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for establishing an energy efficiency evaluation model of an asynchronous motor under voltage fluctuation and flicker.
In order to solve the technical problems, the invention adopts the technical scheme that: a method for establishing an energy efficiency evaluation model of an asynchronous motor under voltage fluctuation and flicker comprises the following steps:
s1: setting disturbance sources of simulated voltage fluctuation and flicker;
s2: establishing an equivalent circuit of the asynchronous motor;
s3: determining the inter-harmonic current fundamental magnetomotive force steering;
s4: calculating the energy efficiency of the asynchronous motor;
s5: determining the model parameters of the simulated motor, and the value ranges of the fluctuation frequency and the amplitude;
s6: compiling simulation codes of the MATLAB file according to the simulation flow and running;
s7: and according to the simulation data, obtaining an energy efficiency evaluation formula of the three-phase asynchronous motor along with the voltage fluctuation amplitude and frequency change by utilizing a curve fitting toolbox of MATLAB.
Further, in step S1, the disturbance source is:
u(t)＝A(1+mcosΩt)sinωt (2)
wherein m is the amplitude of the voltage fluctuation;
Ω -angular frequency of voltage fluctuation, rad/s.
Further, in step S2, equation (5) is obtained by integrating and differentially solving equation (2), and a T-shaped equivalent circuit of the fundamental wave and each inter-harmonic is established:
Figure GDA0002165420710000021
further, in step S3, the inter-harmonic current fundamental magnetomotive force steering in the range of 15Hz to 85Hz is determined by vector calculation, and the slip of each sub-harmonic is converted:
Figure GDA0002165420710000022
in the formula, the positive rotation magnetic potential takes the formula I, and the reverse rotation magnetic potential takes the formula II.
Further, in step S4, the copper loss, iron loss, stray loss, mechanical loss, and input power of the stator and rotor of the fundamental wave and each inter-harmonic circuit are calculated respectively according to the equivalent circuit, and are superimposed to obtain an energy efficiency calculation formula of the asynchronous motor:
Figure GDA0002165420710000031
compared with the prior art, the invention has the beneficial effects that:
MATLAB simulation software is utilized, a T-shaped equivalent circuit of the asynchronous motor is combined, the energy efficiency influence of the power quality problem of voltage fluctuation and flicker on the asynchronous motor is analyzed qualitatively and quantitatively for the first time, an energy efficiency evaluation model of the three-phase asynchronous motor changing along with fluctuation frequency and amplitude is fitted through simulation data, and the relation between the motor energy efficiency and voltage fluctuation flicker is expressed more visually through a mathematical expression.
Drawings
FIG. 1 is a schematic diagram of an inter-harmonic equivalent circuit of the present invention;
FIG. 2 is a simulation flow diagram of the present invention;
FIG. 3 shows the energy efficiency indexes of phase A when the amplitude modulation frequency of the present invention is 8.8 Hz;
fig. 4 shows each energy efficiency index of the a phase when amplitude m of amplitude modulated wave is 0.1;
FIG. 5 is a three-dimensional graph of the A-phase stator copper loss of the present invention;
FIG. 6 is a three-dimensional diagram of the A-phase rotor copper loss of the present invention;
FIG. 7 is a three-dimensional diagram of phase A iron loss of the present invention;
FIG. 8 is a three-dimensional diagram of the phase A performance of the present invention.
Detailed Description
The present invention will be further described with reference to the following embodiments. Wherein the showings are for the purpose of illustration only and are shown by way of illustration only and not in actual form, and are not to be construed as limiting the present patent; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. based on the orientation or positional relationship shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but it is not intended to indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and are not to be construed as limiting the present patent, and the specific meaning of the terms may be understood by those skilled in the art according to specific circumstances.
Example (b):
as shown in fig. 1 to 8, a method for establishing an energy efficiency evaluation model of an asynchronous motor under voltage fluctuation and flicker includes the following steps:
s1: setting disturbance sources of simulated voltage fluctuation and flicker;
s2: establishing an equivalent circuit of the asynchronous motor;
s3: determining the inter-harmonic current fundamental magnetomotive force steering;
s4: calculating the energy efficiency of the asynchronous motor;
s5: determining the model parameters of the simulated motor, and the value ranges of the fluctuation frequency and the amplitude;
s6: compiling simulation codes of the MATLAB file according to the simulation flow and running;
s7: and according to the simulation data, obtaining an energy efficiency evaluation formula of the three-phase asynchronous motor along with the voltage fluctuation amplitude and frequency change by utilizing a curve fitting toolbox of MATLAB.
Specifically, step S1: the method comprises the following steps of setting disturbance sources of simulated voltage fluctuation and flicker:
s1.1. Voltage fluctuation is rapid voltage variation obviously deviating from a rated value and is usually described by relative voltage variation d%, namely two adjacent extreme values U in a series of voltage root mean square value variationsmaxAnd UminDifference DeltaU and rated voltage UNRelative percentage of (A):
Figure GDA0002165420710000041
s1.2, flicker is visual reaction of human eyes caused by unstable lamplight illumination (lamplight flicker) due to voltage fluctuation, and is a voltage fluctuation phenomenon when the voltage fluctuation frequency is 0.05Hz-35 Hz. Therefore, voltage fluctuation and flicker are essentially the same voltage quality problem, and the modeling method is the same.
S1.3, voltage fluctuation is generally regarded as modulation of a voltage fluctuation component (amplitude modulation wave) on a power frequency rated voltage (carrier) root mean square value. Amplitude modulated waves of any periodic waveform can be decomposed into sinusoidal components of various frequencies by fourier transform. For simplifying the model and being convenient for analysis without losing generality, the voltage fluctuation source can be set as the modulation of the sinusoidal amplitude modulation wave with single frequency to the power frequency carrier wave:
u(t)＝A(1+mcosΩt)sinωt (2)
in the formula, A is the power frequency carrier voltage amplitude, V;
omega-power frequency carrier voltage angular frequency, rad/s;
m is amplitude modulation wave modulation coefficient;
omega-amplitude modulated wave voltage angular frequency, rad/s.
The relation between the modulation coefficient of amplitude modulation wave and the relative voltage variation is as follows:
Figure GDA0002165420710000051
in the formula, Vm-amplitude modulated wave voltage amplitude, V;
Umthe carrier voltage amplitude, V.
The voltage fluctuation frequency can be expressed as:
Figure GDA0002165420710000052
as can be seen from equation (2), when voltage fluctuation and flicker occur, the energy efficiency change of the asynchronous motor and the frequency and amplitude of the voltage fluctuation are closely related.
S2, establishing an equivalent circuit of the asynchronous motor
S2.1, the formula (2) can be decomposed into the following components by the sum-difference formula:
Figure GDA0002165420710000053
in the latter two terms of equation (5), the angular frequency ω ± Ω is generally not an integer multiple of the fundamental frequency ω but a fractional multiple, i.e., an inter-harmonic.
S2.2, when the asynchronous motor contains inter-harmonic components, an effective method is also provided for analyzing inter-harmonic loss by adopting an equivalent circuit. The inter-harmonic equivalent circuit is substantially the same as the fundamental wave, as shown in fig. 1.
In the figure, v is the number of inter-harmonics, r1v、x1vResistance and reactance on the stator side, respectively, in units: omega; r ismv、xmvRespectively, excitation resistance and reactance, unit: omega; r is2v′/sv、x2v' rotor resistance and reactance after frequency reduction, respectively, unit: omega; u shape1vIs the input voltage effective value, unit: v; i is1v、I2v、ImvEffective values of stator current, rotor current and exciting current respectively, unit: a; svIs the slip.
S2.3, the circuit parameter relation of the inter-harmonic waves and the fundamental waves is as follows:
Figure GDA0002165420710000054
Figure GDA0002165420710000055
f2v＝sv·f1v
where h is rotor conductor height, m;
μ -permeability, H/m;
rho-material conductivity, Ω · m;
f1ν-stator ν subharmonic current frequency, Hz;
f2ν-rotor ν th inter-harmonic current frequency, Hz;
sv-slip.
S2.4, when the rotating speed of the motor is n, the slip ratio S of the v-th order inter-harmonic current fundamental wave magnetic potentialvComprises the following steps:
Figure GDA0002165420710000061
in the formula, n1Fundamental synchronous speed, unit: r/min; s1Is the fundamental slip. The positive rotation magnetic potential is expressed by formula I, and the reverse rotation magnetic potential is expressed by formula II.
It can be easily found by combining fig. 1 and formula (5) that the frequency and amplitude of the voltage fluctuation directly affect the impedance and input voltage of the inter-harmonic equivalent circuit, respectively, and further affect the calculation of loss and energy efficiency.
S3, determining the inter-harmonic current fundamental wave magnetomotive force steering
When the voltage fluctuates and flickers, non-integral harmonics, i.e. inter-harmonics, are generated. Under the premise that flicker is perceivable by people, the inter-harmonic frequency range is 15-85 Hz.
The direction of the whole harmonic magnetic field has been determined. The key point is to determine the rotating direction of the fundamental wave magnetomotive force of the inter-harmonic current flowing through the three-phase winding in the frequency range and convert the slip ratio of the T-shaped equivalent circuit is to compare the amplitude values of the fundamental wave positive and negative sequence magnetomotive force. When the positive sequence magnetomotive force amplitude is larger than the negative sequence magnetomotive force amplitude, the rotating magnetic field rotates in the positive direction (the rated rotating speed direction), otherwise, the rotating magnetic field rotates in the reverse direction:
Figure GDA0002165420710000062
in the formula, ω1-angular velocity of rotation, rad/s, of the resulting magnetomotive force;
f-amplitude of the resulting magnetomotive force, A;
F+、F--positive and negative sequence magnetomotive force amplitude, a.
S3.1, when the inter-harmonic frequency fv(unit: Hz) in the [15, 50) range, the stator three-phase current is expressed as:
Figure GDA0002165420710000063
in the formula, omega is the rated angular frequency, rad/s;
s3.1.2, each phase winding pulsated magnetomotive force expression is
Figure GDA0002165420710000071
In the formula, Fm1Is single-phase fundamental wave magnetomotive force amplitude.
S3.1.3, each phase of pulsating magnetomotive force is decomposed into two rotating magnetomotive forces with equal magnitude and opposite directions, i.e. the rotating magnetomotive forces
Figure GDA0002165420710000072
And because of
Figure GDA0002165420710000073
Figure GDA0002165420710000074
Figure GDA0002165420710000075
Thus, for equation (11), the three-phase forward rotating magnetic fields add, with amplitude f+Is provided with
Figure GDA0002165420710000076
Three-phase counter-rotating field addition of amplitude f-having
Figure GDA0002165420710000077
Is obvious f+>f-Since this is always true, the fundamental wave magnetomotive force is positively rotated in the present inter-harmonic frequency range.
S3.2 when the inter-harmonic frequency fv(unit: Hz) at (50, 85)]Within the range, the same reasoning can be derived:
Figure GDA0002165420710000081
and is also provided with
Figure GDA0002165420710000082
S3.2.1 the inter-harmonic frequency being 75Hz, i.e. fvWhen/50 is 1.5:
Figure GDA0002165420710000083
Figure GDA0002165420710000084
it is easy to find that f+＝f-Three-phase synthetic pulsating magnetic potential with the rotating speed of 0, an equivalent circuit with an open circuit at the rotor side and zero output power;
s3.2.2, when the inter-harmonic frequency (unit: Hz) satisfies 50<fv<At 75:
Figure GDA0002165420710000085
Figure GDA0002165420710000086
Figure GDA0002165420710000087
for equation (14), the three-phase forward and reverse rotating magnetic fields are added, with the amplitude f+、f-Is provided with
Figure GDA0002165420710000088
Is obvious f+>f-Since this is always true, the fundamental wave magnetomotive force is positively rotated in the present inter-harmonic frequency range.
S3.3, when the inter-harmonic frequency (unit: Hz) satisfies 75<fvWhen the temperature is less than or equal to 85 percent: the method comprises the following steps:
Figure GDA0002165420710000089
Figure GDA00021654207100000810
Figure GDA00021654207100000811
amplitude f according to equation (14)+、f-Comprises the following steps:
Figure GDA0002165420710000091
is obvious f+<f-It is always true that the fundamental wave magnetomotive force is inverted in this inter-harmonic frequency range.
In summary, the fundamental magnetic potential rotation directions at different inter-harmonic frequencies are shown in table 1:
TABLE 1 fundamental wave magnetomotive force rotation direction at different frequencies
Tab.1 Rotational direction of fundamental magnetic potential at different frequencies
Figure GDA0002165420710000092
S4, calculating the energy efficiency of the asynchronous motor
The losses of asynchronous motor can be divided into 5 categories, which are stator copper loss, rotor copper loss and iron loss respectivelyStray losses and frictional losses. Wherein the friction loss PmecThe total loss is extremely small, about 1% -2%, and the rotor can be approximately regarded as unchanged on the premise that the rotating speed of the rotor does not change greatly. The equivalent circuit calculation method of other losses of the motor when the harmonic factors are considered is as follows:
s4.1, stator copper loss
The skin effect of the motor stator winding under the harmonic magnetic field is not obvious:
Figure GDA0002165420710000093
s4.2, rotor copper loss
Influenced by the higher harmonic magnetic field, the skin effect of the rotor conducting bar is obvious, and the rotor resistance is obviously increased, so that the larger harmonic copper loss is caused:
Figure GDA0002165420710000094
s4.3, iron loss
S4.3.1, the harmonic magnetic field causes additional iron loss. For a stator core, the total iron loss can be calculated by:
Figure GDA0002165420710000095
s4.3.2 harmonic flux alternation frequency (2-s) f in rotor when power supply contains harmonic component, especially harmonic magnetic field, and rotates reversely1vAnd the iron loss of the harmonic rotor is high and cannot be ignored. Due to the complex magnetic field distribution, the harmonic rotor iron loss is usually calculated by an empirical formula:
Figure GDA0002165420710000101
in the formula, PFe1-fundamental stator iron loss, W;
B1、Bvfundamental waveV-order inter-harmonic flux density amplitude, T. When non-linear factors such as iron core saturation are not considered, BvAnd B1The ratio of (A) can be the ratio of the excitation branch current of the fundamental wave and the v-th order inter-harmonic equivalent circuit (I)mv/Im) And (4) replacing.
Gs、GrThe weight of the stator and rotor iron cores is kg.
S4.4, stray losses
The stray loss is closely related to the structure and the process of the motor. In nominal operation, 0.5% -2% of the input active power is usually taken as the stray loss.
The harmonic stray loss generated by the harmonic current and the harmonic magnetic action can be estimated by adopting the following formula:
Figure GDA0002165420710000102
in the formula I1-fundamental stator current effective value, a;
Iv-the effective value of the v subharmonic stator current, a;
Ps1the fundamental stray loss, W.
To sum up, the total stray loss is
Figure GDA0002165420710000103
S4.5, Motor energy efficiency
The input active power of the motor is equal to the sum of the active power of the fundamental wave and each harmonic:
Figure GDA0002165420710000104
in the formula, θ is a phase difference between a voltage and a current.
The energy efficiency expression of the motor is as follows:
Figure GDA0002165420710000105
in the formula, Δ P is a total motor loss:
ΔP＝PCu1+PCu2+PFe+Ps+Pmec (25)
s5, setting simulation parameters
S5.1, the specific parameters of the asynchronous motor are as follows: rated power Pn11kW, rated voltage V1n380V, rated frequency fnThe mechanical loss reference value under rated operation is 161.76W, the conducting bar resistivity is 0.2 x 10-7 omega.m, the magnetic conductivity is 0.4 pi.10-6H/m, the rotor conducting bar height is 0.0265m, and the weight of the stator iron core and the rotor iron core is 27.69kg and 18.61kg respectively. The fundamental equivalent circuit parameters are as follows: r is1＝0.98Ω，r2′＝0.82Ω，rm＝3.83Ω，x1＝2.52Ω，x2′＝4.58Ω，xm77.31 Ω. According to the estimation method given by the IEEE112 standard, the fundamental spurious loss takes 1.8% of the fundamental input power.
S5.2, counting that the maximum frequency range of human perception to flicker does not exceed 0.05-35Hz, so that the frequency of amplitude modulation waves in the simulation is controlled within 0-35Hz, and the step length is 0.1 Hz; the maximum relative voltage variation d% of the low-voltage distribution network cannot exceed 4% (national standard), but in order to discuss the influence rule of voltage fluctuation on the energy efficiency of the motor, the simulated relative voltage variation is controlled to be 0-40%, namely the modulation wave m is 0-0.2, and the step length is 0.001. The carrier source is a power frequency sinusoidal voltage source with an effective value of 220V.
S6, writing simulation codes
The energy efficiency model was built from the m-file of MATLAB r2016 a. In the whole simulation process, the load driven by the motor is regulated to keep the rotating speed close to the rated value. The simulation flow is shown in fig. 2.
S7, fitting of formula
S7.1, influence of fluctuation amplitude on motor energy efficiency
The maximum visual sensitivity frequency of human to flicker is about 8.8Hz, and the variation trend of the copper consumption, iron consumption and energy efficiency of the stator and the rotor of the motor along with the amplitude of the amplitude modulation wave at the flicker frequency is shown in figure 3.
Through curve fitting of MATLAB software, when the fluctuation frequency is 8.8Hz, the influence of the voltage fluctuation amplitude on the motor energy efficiency can be represented by the following formula:
η＝-0.6175·m2+88.66％ (26)
in the formula, m is amplitude of amplitude modulated wave.
It can be seen that, with a constant fluctuation frequency, the energy efficiency of an asynchronous motor decays in the form of a quadratic function as the fluctuation amplitude increases.
S7.2, influence of fluctuation frequency on motor energy efficiency
On the other hand, under the condition that the amplitude of the amplitude modulation wave is 0.1 (the relative voltage variation is 20%), the variation trends of the copper loss, the iron loss and the energy efficiency of the stator and the rotor of the motor along with the frequency of the amplitude modulation wave are shown in fig. 4.
When the amplitude of the amplitude modulation wave is 0.1, the influence of the voltage fluctuation frequency on the energy efficiency of the motor can be represented by the following three sections through data fitting of MATLAB:
Figure GDA0002165420710000121
wherein f is amplitude modulation wave frequency, Hz.
It can be seen that, for an asynchronous motor, the energy efficiency is attenuated in the form of a linear function along with the increment of the fluctuation frequency when the fluctuation amplitude is unchanged, and 25Hz is a sudden change point of the energy efficiency.
S7.3, influence of fluctuation amplitude and frequency on motor energy efficiency
Three-dimensional graphs of the variation trend of the stator and rotor copper loss, the iron loss and the working efficiency of the asynchronous motor along with the voltage fluctuation parameters are shown in figures 5-8, and partial data of the energy efficiency are shown in table 2.
TABLE 2 variation tendency of motor energy efficiency with voltage fluctuation
Tab.2 Trend of motor’s efficiency with voltage fluctuation
Figure GDA0002165420710000122
The two factors of the fluctuation frequency and the amplitude are comprehensively considered, and through the surface fitting of simulation data, the energy efficiency evaluation expression of the motor is as follows:
Figure GDA0002165420710000131
it can be seen that under the action of dual factors of the fluctuation amplitude and the frequency, the energy efficiency change of the motor is not only the superposition of the two factors which are affected independently, but also affected by the interactivity of the two factors:
η∝-mf (29)
namely, under the influence of dual factors of fluctuation amplitude and frequency, the reduction of the operation energy efficiency of the motor is aggravated by the increase of any parameter.
According to the scheme, MATLAB simulation software is utilized, a T-shaped equivalent circuit of the asynchronous motor is combined, the energy efficiency influence of the power quality problem of voltage fluctuation and flicker on the asynchronous motor is analyzed qualitatively and quantitatively for the first time, an energy efficiency evaluation model of the three-phase asynchronous motor changing along with fluctuation frequency and amplitude is fitted through simulation data, and the relation between the motor energy efficiency and voltage fluctuation flicker is expressed more visually through a mathematical expression. The specific conclusions are as follows:
(1) when the fluctuation frequency is constant, along with the rising of the fluctuation amplitude, the copper consumption of the motor is obviously increased, the iron consumption is slightly increased, and the energy efficiency is attenuated along with the quadratic power of the fluctuation amplitude;
(2) when the fluctuation amplitude is fixed, the additional loss caused by voltage fluctuation is continuously increased along with the rising of the fluctuation frequency, and the energy efficiency is attenuated along with the first power of the fluctuation frequency. And when the amplitude modulation wave frequency is equal to 25Hz, the additional loss is subjected to a sudden change point due to 1.5 times of pulse magnetic potential decomposed in the air gap:
(a) when the amplitude modulation wave frequency is less than 25Hz, the copper loss of the motor is obviously increased along with the increase of the fluctuation frequency, and the iron loss is not obviously increased;
(b) when the amplitude modulation wave frequency is greater than 25Hz, the resolved fractional reversal of the air-gap field causes greater energy loss to the motor than the forward magnetic potential. The iron loss is not changed greatly all the time;
(3) the energy efficiency of an asynchronous motor is also influenced by the interactivity of fluctuation amplitude and frequency, and the higher the fluctuation amplitude or frequency is, the faster the energy efficiency is reduced.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims (5)

1. A method for establishing an energy efficiency evaluation model of an asynchronous motor under voltage fluctuation and flicker is characterized by comprising the following steps:
s1: setting disturbance sources of simulated voltage fluctuation and flicker;
s2: establishing an equivalent circuit of the asynchronous motor;
s3: determining the inter-harmonic current fundamental magnetomotive force steering;
s4: calculating the energy efficiency of the asynchronous motor;
s5: determining the model parameters of the simulated motor, and the value ranges of the fluctuation frequency and the amplitude;
s6: compiling simulation codes of the MATLAB file according to the simulation flow and running;
s7: and according to the simulation data, obtaining an energy efficiency evaluation formula of the three-phase asynchronous motor along with the voltage fluctuation amplitude and frequency change by utilizing a curve fitting toolbox of MATLAB.
2. The method for modeling the energy efficiency of an asynchronous motor under voltage fluctuation and flicker according to claim 1, wherein in step S1, the disturbance sources are:
u(t)＝A(1+mcosΩt)sinωt (2)
wherein m represents the amplitude of the voltage fluctuation;
Ω represents the angular frequency of voltage fluctuation, rad/s;
a represents the power frequency carrier voltage amplitude, V;
and omega represents the angular frequency of the power frequency carrier voltage, rad/s.
3. The method for establishing the energy efficiency evaluation model of the asynchronous motor under the voltage fluctuation and flicker according to claim 2, wherein in step S2, the formula (5) is obtained by integrating and differentiating the formula (2), and a T-shaped equivalent circuit of the fundamental wave and each order inter-harmonic is established:
Figure FDA0003197309940000011
in the formula (I), the compound is shown in the specification,
Ω represents the angular frequency of voltage fluctuation, rad/s;
a represents the power frequency carrier voltage amplitude, V;
and omega represents the angular frequency of the power frequency carrier voltage, rad/s.
4. The method for establishing the energy efficiency evaluation model of the asynchronous motor under the voltage fluctuation and flicker according to the claim 1, wherein in the step S3, the inter-harmonic current fundamental wave magnetomotive force steering in the range of 15Hz to 85Hz is determined through vector calculation, and then the slip ratio of each sub-harmonic is converted:
Figure FDA0003197309940000021
in the formula, the positive rotation magnetic potential is taken as the first formula, and the reverse rotation magnetic potential is taken as the second formula;
n1the fundamental wave synchronous rotating speed; s1Is the fundamental wave slip, v is the inter-harmonic frequency, and n is the motor rotor speed.
5. The method for establishing the energy efficiency evaluation model of the asynchronous motor under the voltage fluctuation and flicker according to claim 1, wherein in step S4, the copper loss, the iron loss, the stray loss, the mechanical loss and the input power of the stator and the rotor of the fundamental wave and each subharmonic circuit are respectively calculated according to the equivalent circuit and are mutually overlapped to obtain the energy efficiency calculation formula of the asynchronous motor:
Figure FDA0003197309940000022
in the formula, P1 represents the input power, and Δ P represents the total motor loss.
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