CN102651627A - Magnetic field reconstruction method for eliminating torque pulsation of doubly-fed induction motor - Google Patents

Abstract

The invention relates to a magnetic field reconstruction method for eliminating torque pulsation of a doubly-fed induction motor. In order to eliminate the torque pulsation problem of the doubly-fed asynchronous induction motor caused by electric network voltage unbalance and electric network voltage harmonic waves to the greatest degree, the invention provides the motor magnetic field reconstruction method. On the basis of the structure, the dimension, the materials, the electric parameters and the like of the actual motor, Infolytica Magnet electromagnetic field simulation software is adopted for studying the torque generation from the motor magnetic field angle, and in addition, the unexpected torque pulsation is eliminated through the optimization on the rotor current. As an alternative excitation scheme, the method avoids the control precision problem caused by motor equivalent model inaccuracy. The magnetic field reconstruction method has the characteristics that the calculation speed is high, the torque pulsation elimination effect of the doubly-fed induction motor is obvious, and the like. The magnetic field reconstruction method can be used for solving the vibration problem of the doubly-fed induction motor for wind power generation caused by electric network voltage unbalance or electric network voltage harmonic waves.

Description

Eliminate the magnetic field reconstructing method of doubly fed induction generator torque pulsation

Technical field

The present invention relates to a kind of magnetic field reconstructing method of eliminating the doubly fed induction generator torque pulsation; (Field Reconstruction Method FRM) solves the used for wind power generation doubly fed induction generator because the method for the vibration problem that unbalanced source voltage or Voltage Harmonic cause to be specifically related to a kind of use magnetic field reconstructing method.

Background technology

Doubly fed induction generator (Doubly Fed Induction Generator; DFIG) has meritorious, reactive power independent regulation ability; Can realize the variable speed constant frequency operation that maximal wind-energy is followed the trail of; And since its excitation with the current transformer capacity less than wind-powered electricity generation unit rated capacity, reduced cost, become the main flow generator type in the utilization of current wind energy development.But, produce undesirable torque pulsation because the system that electrical network causes is uneven and system harmonics can worsen motor properties.The situation of concussion appears in the power that these torque pulsations will make generator transfer to electrical network, also makes the Mechanical Reliability of tower tube suffer to worsen potentially, reduces being attached to the life-span of the moving component on the alternator shaft, and can produce bigger noise.Along with the lifting of wind turbine generator power grade, sizes of wind turbines is in continuous increase, and the natural frequency of mechanical resonance also reduces thereupon, therefore receives the influence of the mechanical resonance that is caused by system problem more easily.System's this phenomenon uneven and that system harmonics causes has more and more caused people's attention.

As a rule, the method that reduces torque pulsation mainly contains two kinds:

1, machine design method is optimized design to electric machine structure in the Machine Design in early stage, comprises inclined rotor or stator slot, fractional-slot apart from winding etc., thereby reaches the purpose of restriction or compensation.Although this is one of effective method that reduces at present torque pulsation, it is in some application scenarios and inappropriate.Particularly, inclination and fractional slot winding will cause the minimizing of average torque.In addition, also have some methods for designing then to need high-precision manufacturing industry, cost significantly increases.

2, motor control method

Reaching the purpose that reduces torque pulsation through the optimal control to motor is a kind of reasonable method, and traditional Control of Induction Motors method (for example field orientation vector, Direct Torque, every ampere of breakdown torque, V/F etc.) is mostly based on the lumped parameter model of motor.

The field orientation vector control method is adopted in the research that has; Second harmonic generation properties according to torque pulsation; D axle rotor voltage and q axle rotor voltage compensate component have been increased respectively in d axle in the classical control algolithm of rotor-side converter and the q shaft current ring; This method is similar to has increased a control ring that in rotor circuit, injects the negative phase-sequence amount, compensates the negative sequence component in the stator circuit in this way, thus the pulsation of compensation torque and reactive power under the unbalanced electric grid voltage.

The research that has for further improving torque responsing speed and reducing torque pulsation, has been introduced fuzzy logic thought in full speed degree flux observation Mathematical Modeling on the basis of traditional direct torque control, proposed full speed degree fuzzy model direct torque control.This model as fuzzy variable, and carries out the selection that rational fuzzy classification is optimized space vector of voltage to magnetic linkage phase angle, magnetic linkage sum of errors torque error to it, has solved the torque pulsation problem effectively.

In addition; The document that has has proposed dual feedback asynchronous wind power generator rotor side inverter or the grid side rectifier control method optimized; Through changing traditional P I adjuster into the PIR adjuster; And the setpoint frequency in the PIR adjuster is set at two times of synchronous angular velocity of rotations, the negative sequence component of two frequencys multiplication in the disturbance quantity is carried out complete inhibition, thereby avoid the pulsation situation of the generator electromagnetic torque that unbalanced electric grid voltage causes.

Although above-mentioned method based on lumped parameter model proves effective in practice; But they are assumed to be prerequisite with some; Comprise stator and rotor three phase windings symmetry fully; The every phase air-gap mmf of rotor is Sine distribution in the space, ignores harmonic wave factor (slot effect) that stator slot and rotor cause etc.In fact, motor windings (especially rotor winding) seldom is symmetrical fully, and air-gap mmf possibly not be sinusoidal in spatial distributions, and the teeth groove harmonic wave also is an exist actually.In addition, the precision of Electric Machine Control is influenced greatly by the motor model parameters precision, and feasible control to motor is overly dependent upon the accurate understanding to the motor equivalent electric circuit.

Summary of the invention

In order to address the above problem, the present invention proposes a kind of magnetic field reconstructing method of eliminating the doubly fed induction generator torque pulsation, eliminates these undesirable vibrations through the careful selection to rotor current.

In order to eliminate the torque pulsation problem of the double-fed asynchronous induction generator that causes by unbalanced source voltage and Voltage Harmonic to greatest extent; And reduce owing to of the influence of motor model parameters precision to Electric Machine Control; The present invention proposes a kind of motor-field reconstructing method; Based on structure, size, material and the electric parameter etc. of real electrical machinery, from the generation of magnetic field angle research moment, and through the optimization of rotor current being gone to eliminate these undesirable torque pulsations; As a kind of alternative excitation scheme, this method has avoided because the control precision problem that the inaccuracy of motor equivalent model is brought.

Through calculating optimum rotor current, the torque oscillation phenomenon introduced of attenuation systems effectively, thus reduce the uneven and system harmonics of system to greatest extent to used for wind power generation doubly fed induction generator Effect on Performance.

Description of drawings

Fig. 1 is a magnetic field reconstructing method sketch map;

Fig. 2 is the doubly fed induction generator circuit diagram;

Fig. 3 is the application of doubly fed induction generator in wind power generation;

Three phase network voltage waveform when Fig. 4 is A phase electric network electric voltage drop 20%;

The torque pulsation oscillogram of Fig. 5 for causing by 20% unbalanced source voltage situation;

Fig. 6 is DFIG model and coordinate system sketch map thereof;

Fig. 7 is magnetic flux density and electromagnetic force normal direction and the tangential component in the air gap;

Fig. 8 distributes for the uniconductor surrounding magnetic field through the 1A electric current;

Fig. 9 is the simple computation-tangential basic function that is applied to the basic function among the FRM;

Figure 10 is the simple computation-normal direction basic function that is applied to the basic function among the FRM;

The distribution of magnetic flux density among DFIG when Figure 11 leads to the three phase sine alternating current for stator winding;

Figure 12 optimizes flow chart for rotor current;

Figure 13 is a magnetic field reconfiguration system experiment porch;

Figure 14 is the torque waveform after under unbalanced electric grid voltage, optimizing;

Figure 15 is the schematic flow diagram of method of the present invention.

Embodiment

Present invention is described with reference to the accompanying drawings.

In order to obtain the distribution of magnetic flux density, motor at first uses finite element to resolve device to carry out modeling, the present invention's utilization be business software Infolytica Magnet.This thought shows in Fig. 1, is input as stator three-phase current and rotor-position, is output as magnetic density normal direction and tangential part.At any rotor-position, the synthetic method of air gap flux density is to trying to achieve through finite element method with the tangential part, and corresponding force density f uses electromagnetic stress tensor (MaxwellStress Tensor) method to calculate.

Because the unbalanced influence of system, magnetomotive force will produce the part of not expecting in doubly fed induction generator (the doubly fed induction generator circuit diagram is as shown in Figure 2) air gap.Especially, the unbalanced existence of stator three-phase current amplitude can produce a clockwise direction rotation and a magnetic field part that counterclockwise rotates in the doubly fed induction generator air gap.Suppose that stator winding is a Sine distribution, the magnetomotive force that in face of uneven stator current, produces can provide with following formula:

${\mathrm{MMF}}_s=\frac{{\mathrm{<figure-callout\; id="2"\; label="N\; s"\; filenames="HSA00000440974100021.png,HSA00000440974100061.png"\; state="\{\{state\}\}">N</figure-callout>}}_s}{2}\sqrt{2}[\left(\frac{I_A+I_B+I_C}{2}\right)\mathrm{Cos}({\mathrm{\&omega;}}_{e}t-{\mathrm{\&phi;}}_s)+\left(\frac{{2I}_A-I_B-I_C}{4}\right)\mathrm{Cos}({\mathrm{\&omega;}}_{e}t+{\mathrm{\&phi;}}_s)+\frac{\sqrt{3}}{4}(I_B-I_C)\mathrm{Sin}({\mathrm{\&omega;}}_{e}t+{\mathrm{\&phi;}}_s)]......\left(1\right)$

Wherein, ω _eRepresent stator electric angle frequency, I _A, I _B, I _CRepresent the amplitude of A, B, C phase current respectively, φ _sRepresent the stator displacement factor, N _sRepresent every phase lower conductor number.Similarly, because the existence of current harmonics, the magnetomotive force that stator winding produces is explained as follows:

${\mathrm{MMF}}_s=\frac{{3\mathrm{<figure-callout\; id="4"\; label="N\; s"\; filenames="HSA00000440974100061.png"\; state="\{\{state\}\}">N</figure-callout>}}_s}{4}\sqrt{2}{I}_A\mathrm{Cos}(k{\mathrm{\&omega;}}_{e}t-{\mathrm{\&phi;}}_s)......\left(2\right)$

Suppose that DFIG will be connected on the infinitely great electrical network, as shown in Figure 3, electrical network will determine the amplitude of phase voltage.If there is unbalanced situation (phase place or amplitude) in line voltage, these unbalanced situation will be imposed to above the stator winding of DFIG.In this case, even the motor side connection is the balance resistive load, a series of unsymmetrical currents still will produce, and will cause the appearance of negative phase-sequence in the motor gas-gap, positive sequence and zero sequence magnetic-field component.

Under this uneven situation, phenomenon that torque pulsation increases will appear that average torque reduces and in the torque response of motor.The increase of torque pulsation will aggravate the unbalanced degree in magnetic field that caused by stator current again.In a single day this uneven magnetic field be broken down into symmetrical component, just can cause the magnetic field of a positive sequence and a negative phase-sequence rotation.Positive sequence magnetic field will make motor produce with poised state under similar characteristic, negative phase-sequence magnetic field will make motor produce electronic trend, thereby makes torque pulsation increase and average torque minimizing.

Because the negative sequence component of stator field is consistent with the negative sequence component direction of rotation of rotor field, synthetic field frequency will be the twice of stator field frequency, and this also is double feedback electric engine common phenomena when under non-equilibrium state, moving.

Shown in Figure 4 is the unbalanced source voltage situation, as shown in the figure, occurs 20% range of decrease mutually at 0.05s moment line voltage A; Fig. 5 has provided the electromagnetic torque waveform of DFIG under line voltage situation shown in Figure 4; Can find out that the electromagnetic torque waveform is comparatively level and smooth before 0.05s, bigger pulsation situation appears in the torque waveform when the Voltage unbalance situation appears in 0.05s constantly; Through calculating, its ripple frequency is the twice (120Hz) of system frequency.

In order to eliminate the torque pulsation problem of the double-fed asynchronous induction generator that causes by unbalanced source voltage and Voltage Harmonic to greatest extent; The present invention proposes a kind of motor-field reconstructing method; Structure, size, material and electric parameter etc. based on real electrical machinery; Generation from magnetic field angle research moment; And through the optimization of rotor current being gone to eliminate these undesirable torque pulsations, as a kind of alternative excitation scheme, this method has avoided because the control precision problem that the inaccuracy of motor equivalent model is brought.

Figure 15 is the schematic flow diagram of method of the present invention.At first use Infolytica Magnet electromagnetic field simulation software to draw out the DFIG model, define its coordinate system; Under the situation of unicoil excitation, the finite element equality of setting up negligible amounts according to electromagnetic nature confirm magnetic flux density in the air gap radially and tangential component; Utilize these results to set up the set of base functions of magnetic flux density then, be used for predicting acting on the magnetic field of motor internal under rotor-exciting and the rotor speed arbitrarily, and calculate electromagnetic force radially reach tangential component; Obtain the torque equality from magnetic field angle, thereby through optimizing torque pulsation and the deviation that rotor current reduces motor.

The present invention is an example with a three-phase four-stage motor, 72 grooves of stator, and 54 grooves of rotor, the winding mode is double-deck lap winding.As shown in Figure 6, φ _SmBe defined as the angle position of stator, φ along circumference _RmBe defined as the angle position of rotor along circumference, the rotor mechanical position is by θ _RmExpression, the mechanical angle speed of rotor is ω _RmStator mechanical location, rotor mechanical position and rotor mechanical angle have following relation:

φ _sm＝φ _rm+θ _rm

The used model of the present invention is the dual-feed asynchronous wind power generator of a 45kW, and stator and rotor groove shape and size etc. are all carried out emulation according to the real electrical machinery parameter.

Calculating for electromagnetic force; Many digitizing solutions and formula are arranged; All based on the approximate evaluation that the electromagnetic field of motor perhaps is stored in electromagnetic energy wherein, method mainly comprises: [10] such as limited element analysis technique, finite difference calculus, magnetic equivalent electric circuit, Fourier series methods for they.In these analytical methods and since limited element analysis technique have modeling simple, applied widely, advantage such as can process later on, it also becomes a most popular technology.

Spatial distribution through analyzing the motor magnetic force component can provide very valuable information for the optimal design and the control of motor.The present invention adopts the electromagnetic stress tensor method, and (MaxwellStress Tensor method, MST), utilization Infolytica Magnet software is through obtaining the distribution of its electromagnetic force to the emulation of DFIG model.

In the electromagnetic stress tensor method, the normal direction of electromagnetic force density and tangential component can be expressed by following formula in the motor gas-gap:

$f_n=\frac{1}{2{\mathrm{\&mu;}}_0}({B_n}^2-{B_t}^2)---\left(1\right)$

$f_t=\frac{1}{\mathrm{\&mu;}0}{B}_n{B}_t---\left(2\right)$

Wherein, f _n, f _tRepresent the normal component and the tangential component of electromagnetic force density in the air gap respectively, B _n, B _tRepresent the normal component and the tangential component of magnetic flux density respectively, μ ₀Be absolute permeability.

Above-mentioned two functions that drawn by the electromagnetic stress tensor method are bases of analyzing electromagnetic force in the motor, and use formula (1) and formula (2) and magnetic density (magnetic flux on the unit are) just can calculate and act on each surperficial tangential, air gap middle and normal direction electromagnetic force density.

In motor, most power conversion occurs in the very little air gap of thickness.Fig. 7 has provided the method direction of the electromagnetic force in the middle of the double feedback electric engine air gap; (

) and tangent direction; (

) unit vector.Use cylindrical coordinate system that electromagnetic force density is carried out integration, just can obtain acting on the normal direction and the tangential component of each lip-deep actual electrical magnetic force, shown in (3) and formula (4).

$F_n=l\underset{0}{\overset{2\mathrm{\&pi;}}{\&Integral;}}r{f}_n\&CenterDot;d{\mathrm{\&phi;}}_s=\frac{1}{2{\mathrm{\&mu;}}_0}\underset{0}{\overset{2\mathrm{\&pi;}}{\&Integral;}}(B_n^2-B_t^2)d{\mathrm{\&phi;}}_s---\left(3\right)$

Wherein, S is the surface (being the periphery of cylindrical coordinate system) in the limit of integration, and l is the stator stack thickness that extends along the z axle, and r is a rotor radius, φ _sBe stator angle (being the angle part of cylindrical coordinate system), and have P is a motor progression.

In reality, B _nBe greater than B _t, so F _nBe forever on the occasion of, this explanation normal direction electromagnetic force component points to stator by rotor in the air gap profile.

In double feedback electric engine, each root conductor all affects the distribution of magnetic flux density normal direction and tangential component in the air gap in stator and the rotor.The FRM model based formula of describing an AC Windings can use truncated fourier series to represent.The FRM formula of the multi phase stator winding that for example, is made up of N circle coil is as follows:

$B_{\mathrm{ts}}\left({\mathrm{\&phi;}}_s\right)=\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{i}_{\mathrm{sk}}\&CenterDot;h_{\mathrm{ts}}({\mathrm{\&phi;}}_s-{\mathrm{\&phi;}}_{\mathrm{sk}})---\left(5\right)$

$B_{\mathrm{ns}}\left({\mathrm{\&phi;}}_s\right)=\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{i}_{\mathrm{sk}}\&CenterDot;h_{\mathrm{ns}}({\mathrm{\&phi;}}_s-{\mathrm{\&phi;}}_{\mathrm{sk}})---\left(6\right)$

Wherein, φ _SkBe stator winding N circle coil position, i _SkBe the electric current of flowing through on the stator winding N circle coil, k=1 ..., N.h _Ts(φ _s) and h _Ns(φ _s) represent the tangential component of magnetic flux density in the air gap and the basic function of normal component respectively.

Through to being arranged in reference frame φ _sThe conductor dbus of position is the electric current (as shown in Figure 8) of 1A with the size, basic function h _Ts(φ _s) and h _Ns(φ _s) just can use the steady magnetic field method to calculate.From the MagNet simulation waveform, can see; The basic function of tangent and normal direction has represented the attribute of even number and odd number analytical function respectively (like Fig. 9 and shown in Figure 10; Transverse axis is the mechanical angle of air gap among the figure, and the longitudinal axis is respectively tangential magnetic flux density and the normal direction magnetic flux density in the air gap).

In routine processes, these basic functions can use their trigonometric fourier series expansion or adopt the mode of simply tabling look-up by storage easily.So, the magnetic flux density of stator winding phase current generation just can use sum of products to calculate.Certainly, do not comprise electromagnetism non-linear factor (like magnetic saturation etc.) in our derivation.

The quadrature of basic function equally also can be calculated, and can be used for simplifying computing formula.

$\underset{0}{\overset{2\mathrm{\&pi;}}{\&Integral;}}{h}_{\mathrm{ts}}\left({\mathrm{\&phi;}}_s\right)\&CenterDot;h_{\mathrm{ns}}\left({\mathrm{\&phi;}}_s\right)d{\mathrm{\&phi;}}_s=0---\left(7\right)$

Make to use the same method, can calculate the magnetic flux density that electric current produces in the DFIG three-phase rotor winding, shown in (8) and (9).

$B_{\mathrm{tr}}\left({\mathrm{\&phi;}}_r\right)=\underset{j=1}{\overset{M}{\mathrm{\&Sigma;}}}{i}_{\mathrm{rj}}\&CenterDot;h_{\mathrm{tr}}({\mathrm{\&phi;}}_r-{\mathrm{\&phi;}}_{\mathrm{rj}})---\left(8\right)$

$B_{\mathrm{nr}}\left({\mathrm{\&phi;}}_r\right)=\underset{j=1}{\overset{M}{\mathrm{\&Sigma;}}}{i}_{\mathrm{rj}}\&CenterDot;h_{\mathrm{nr}}({\mathrm{\&phi;}}_r-{\mathrm{\&phi;}}_{\mathrm{rj}})---\left(9\right)$

In the double feedback electric engine actual application, rotor and stator current are measurable in fact.Therefore, the real-time monitoring through rotor and stator current we can the magnetic flux density of stator winding and rotor winding be combined and obtain magnetic flux density total in air gap:

$B_t\left({\mathrm{\&phi;}}_g\right)=\underset{j=1}{\overset{M}{\mathrm{\&Sigma;}}}{i}_{\mathrm{rj}}\&CenterDot;h_{\mathrm{tr}}({\mathrm{\&phi;}}_r-{\mathrm{\&phi;}}_{\mathrm{rj}})+\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{i}_{\mathrm{sk}}\&CenterDot;h_{\mathrm{ts}}({\mathrm{\&phi;}}_s-{\mathrm{\&phi;}}_{\mathrm{sk}})---\left(10\right)$

$B_n\left({\mathrm{\&phi;}}_g\right)=\underset{j=1}{\overset{M}{\mathrm{\&Sigma;}}}{i}_{\mathrm{rj}}\&CenterDot;h_{\mathrm{nr}}({\mathrm{\&phi;}}_r-{\mathrm{\&phi;}}_{\mathrm{rj}})+\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{i}_{\mathrm{sk}}\&CenterDot;h_{\mathrm{ns}}({\mathrm{\&phi;}}_s-{\mathrm{\&phi;}}_{\mathrm{sk}})---\left(11\right)$

N wherein, M, φ _g, φ _s, φ _r, φ _Sk, φ _Rj, h _Ts, h _Tr, h _Ns, h _Nr, i _Sk, i _RjRepresent the stator conductors number respectively, rotor conductor number, air gap displacement factor, stator displacement factor; The rotor displacement factor, the position of k conductor in the stator, the position of j conductor in the rotor; Stator tangential basic function, rotor tangential basic function, stator normal direction basic function; Rotor normal direction basic function, the amplitude through electric current in k conductor of stator, amplitude through electric current in k conductor of rotor.Figure 11 has provided when stator winding passes to the three phase sine alternating current distribution situation of magnetic flux density among the DFIG.

In case the tangent of magnetic flux density and normal direction part is calculated in the DFIG air gap; Use Maxell electromagnetic field strain method; We can calculating air-gap in the density of the positive tangential component of electromagnetic force; Just the torque of double feedback electric engine is analyzed above, drawn the relation between electromagnetic torque and the magnetomotive force density from magnetic field angle.Therefore electromagnetic torque can be used following expression:

$f_t\left({\mathrm{\&phi;}}_g\right)=\frac{1}{{\mathrm{\&mu;}}_0}{B}_n\left({\mathrm{\&phi;}}_g\right)B_t\left({\mathrm{\&phi;}}_g\right)---\left(12\right)$

$T=\mathrm{LR}\underset{0}{\overset{2\mathrm{\&pi;}}{\&Integral;}}{f}_t\left({\mathrm{\&phi;}}_g\right)d{\mathrm{\&phi;}}_g---\left(13\right)$

With the discrete n of being of the profile of an air gap part that equates, can estimate (with corresponding rotor-position) whole torque in given instantaneous time:

$T\left({\mathrm{\&theta;}}_r\right)\&ap;\frac{2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="LR"\; filenames="HSA00000440974100021.png,HSA00000440974100061.png"\; state="\{\{state\}\}">LR</figure-callout>}}^2}{{\mathrm{\&mu;}}_{0}n}\underset{m=1}{\overset{n}{\mathrm{\&Sigma;}}}{B}_n\left({\mathrm{\&phi;}}_g\right)B_t\left({\mathrm{\&phi;}}_g\right)---\left(14\right)$

Wherein, θ _rThe expression rotor-position, relevant (θ with the displacement factor of stator and rotor _r=φ _s-φ _r).

By on can know, through the continuous calculating of electromagnetic torque in power frequency period, can estimate the average torque of double feedback electric engine and the size of torque pulsation.

FRM is a kind of analytical method that Distribution of Magnetic Field is estimated of in the middle of unsaturated double feedback electric engine air gap, carrying out.The position of rotor connection, the number of turn, winding confirmed and the situation that in whole process, can not change under, the basic function of each phase just can be calculated soon.In case the FRM formula is set up, just can predict the tangential and the normal direction part of electromagnetic force.In this piece article, FRM is used to calculate the rotor phase current, thereby makes the magnetic field as result of calculation can produce level and smooth torque.

Figure 12 has explained the optimization method that the present invention mentions with the mode of flow chart.In optimizer, the desired value of average tangential force is transfused to as a constraints, and the thermal limit of rotor current is as another one constraints.Suppose that the real-time numerical value of stator current can be measured come out and is correct, stator winding is that the contribution of air-gap field is just calculated with the form of field so.Known the rotor basic function, will make us calculate rotor current,, can make synthetic electromagnetic torque pulsation in one-period, be in minimum level through this rotor current is constantly detected and revises.In addition, according to actual conditions, it should be noted that and under DFIG is in power generation mode, to alleviate torque pulsation, and make it have gratifying average torque.

Magnetic field reconfiguration system experiment porch is shown in figure 13, and doubly fed induction generator has been installed an accelerometer, can monitor stator radially, tangential and axial vibration.Bandwidth is that the torque meter of 500Hz is used for monitoring mean value and the pulsation situation that acts on epitrochanterian direct tangential force.Motor shown in Figure 13 drags doubly fed induction generator and carries out work, and the rotating speed requirement of motor can be provided by frequency converter.The double-fed type current transformer can provide the field power supply of changeable frequency for doubly fed induction generator, adopts the closed-loop vector control method, and controller is TMS320F2407.

Be the checking result who under the unbalanced source voltage situation, adopts the FRM method below, the software platform of use is professional electromagnetic field simulation software Infolytica MagNet 6.22 and MATLAB2009b.The unbalanced influence of system can use A phase current magnitude landing 20% to be example, and as shown in Figure 4, the torque pulsation oscillogram that causes is as shown in Figure 5.Visible from figure, it is the pulsation of system frequency 2 times (120Hz) that frequency has appearred in electromagnetic torque, and pulsation source is the clockwise direction component of stator field.Through using the above-mentioned optimization step of mentioning, optimum rotor current can calculate.The purpose of this optimization is to alleviate torque pulsation greatly as far as possible under the heat limit prerequisite of rotor current being no more than.Figure 14 is the torque waveform after optimizing.Can see that torque pulse is by obvious elimination, and still keep average torque.

System's imbalance will exert an influence to the doubly fed induction generator performance, mainly be the low frequency component of the torque pulsation that undesirable component causes in the magnetomotive force.Use magnetic field reconstructing method FRM, set up the optimization rotor current of eliminating torque pulsation, the vibration that the result of study display system is introduced is alleviated effectively.

Claims (7)

1. a magnetic field reconstructing method of eliminating the doubly fed induction generator torque pulsation is characterized in that, comprising:

1) according to structure, size, material and the electric parameter of doubly fed induction generator, sets up doubly fed induction generator DFIG model, define its coordinate system through Finite Element Method;

2) under the situation of unicoil excitation,, set up normal direction and tangential component that the finite element equality is confirmed each surperficial magnetic flux density that air gap is middle according to electromagnetic nature;

3) utilize said normal direction and tangential component to set up the set of base functions of magnetic flux density, predict arbitrarily acting on the magnetic field of motor internal under rotor-exciting and the rotor speed, and calculate electromagnetic force radially reach tangential component; And

4) obtain the torque equality from magnetic field angle, optimize the torque pulsation that rotor current reduces motor.

2. the magnetic field reconstructing method of elimination doubly fed induction generator according to claim 1 torque pulsation is characterized in that, said step 2) also comprise:

Normal direction and tangential component through electromagnetic force density in the electromagnetic stress tensor method calculating air-gap.

3. the magnetic field reconstructing method of elimination doubly fed induction generator according to claim 1 torque pulsation is characterized in that, said step 3) also comprises:

Utilize the steady magnetic field method to calculate said set of base functions.

4. the magnetic field reconstructing method of elimination doubly fed induction generator according to claim 3 torque pulsation is characterized in that, said step 3) also comprises:

Through rotor and stator current the magnetic flux density of stator winding and rotor winding is combined and to obtain magnetic flux density total in air gap.

5. the magnetic field reconstructing method of elimination doubly fed induction generator according to claim 4 torque pulsation is characterized in that, said step 3) also comprises:

Use the said tangential component that radially reaches of electromagnetic force in the electromagnetic field strain method calculating air-gap of Maxell.

6. the magnetic field reconstructing method of elimination doubly fed induction generator according to claim 1 torque pulsation is characterized in that, said step 4) also comprises:

Be n part that equates with the profile of air gap is discrete, estimate in given instantaneous time whole torques with corresponding rotor-position; And

Through in power frequency period, calculating electromagnetic torque continuously, estimate the average torque of doubly fed induction generator and the size of torque pulsation.

7. the magnetic field reconstructing method of elimination doubly fed induction generator according to claim 6 torque pulsation is characterized in that, said step 4) also comprises:

Measure the real-time numerical value of stator current, calculate rotor current,, export current stator current value when average tangential force meets average tangential force threshold value and the rotor current that calculates when satisfying predefined thermal limit through the rotor basic function.

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