CN1247988A - Method for automatic measuring asynchronous machine rotor ohmic resistance - Google Patents

Abstract

Method of automated measurement of the ohmic rotor resistance (Rr) of an asynchronous machine controlled via an inverter while being acted upon by a non-rotating field, the method involving a. measuring the ohmic stator resistance (Rs), the leakage inductances (Lsigmas, Lsigmar) and the main inductance (Lm) of the asynchronous machine, b. leading a testing signal (Usa) being formed by a predetermined direct signal with a superimposed alternating signal corresponding approximately to the nominal slip frequency (fs) of the asynchronous machine, c. measuring the amplitude and the phase (phi) of the phase signal (Isa) resulting from the testing signal, and d. calculating the ohmic rotor resistance (Rr) from the measured values according to a) and c).

Description

The method for automatic measurement of asynchronous machine rotor ohmic resistance

The present invention relates to a kind of method for automatic measurement of asynchronous machine rotor ohmic resistance, this motor is to control by a transverter under non-rotating effect.

In the asynchronous motor that speed and moment are controlled, when adopting the control method relevant, need know all resistance (being Ohmage and induction reactance) especially with the field so that control accomplish accurate as far as possible.These resistance can and/or be measured by estimation to determine.

(braking) rotor that adopts rotatable non-loaded rotor during measurement or block.When the measuring current of measuring resistance flows through stator and rotor when non-loaded, most of electric current is received the principal reactance of flowing through electric main inductance (reciprocal inductance) decision, thereby can measure main inductance, but can not survey the Ohmage of rotor.Yet when the rotor of blocking when employing was measured, measuring current also flow through rotor, so its Ohmage also can be measured.But two kinds of methods all have its defective.Adopt the measuring method of rotatable non-loaded rotor impracticable often, for example be fixedly secured on the manufactured goods and it comes to this when being coupled with constant load when motor.On the other hand, block a motor, special when having added full moment, will strict requirement be proposed to mechanical brake device, therefore this method is more expensive in essence.Another difficulty that the rotor that employing is blocked is measured is that the current displacement that produces in the rotor bus-bar when high-frequency (30 to 60Hz scopes) will make the measured value of rotor ohmic resistance obviously bigger than normal.

In addition, when measuring Ohmage, usually do not consider that it is subjected to the influence of temperature change.According to the working temperature difference, it can increase or reduce 20% to 30%.This means that the asynchronous machine isoboles as Fundamentals of Measurement can not be used for normal duty.

U.S. Pat 5,689,169 have proposed a kind of method, can measure the leakage inductance of stator and rotor and the rotor ohmic resistance that remains static, and method therefor is that the q component of the control procedure of a kind of " relevant with the field " and d component are controlled.Thereby the frequency test signal that a phase winding of stator receives is approximately equal to frequency of operation, for example about 30Hz.Be set to zero for avoiding producing turning moment current component Iq, meanwhile measure virtual voltage Vq and the Vd that feeds back to control device.The stator Ohmage of knowing frequency test signal and originally measuring just can calculate the approximate value of rotor resistance.Why can do this approximate treatment, be because we move the frequency test signal choosing than higher, so can calculate with fairly simple numerical equation, needs the microprocessor in the control device to do what computing hardly., adopting the higher frequency test signal of ratio about 30Hz that a shortcoming is arranged, is exactly can produce current displacement in the rotor bus-bar, and this will make measured rotor ohmic resistance value too high.Measured value can exceed 100% to 150% under extreme case.Have only the converter of the transverter of current sensor to compare with band, this method also has a shortcoming, is exactly also must adopt voltage sensor.

The Danfoss Drives A/S of Denmark has described the similar approach described in a kind of and the foreword in one piece of article of the 3.370th to 3.374 page of EPE ' 97.This method need be carried out following measurements and calculations, at this moment will be with reference to the general isoboles of one phase of the asynchronous motor shown in attached Fig. 1 and 2, and wherein Fig. 1 is detailed static equivalent electrical circuit, on one side Fig. 2 is the simplification isoboles that stator is calculated by effective turn:

1. with test voltage U _SaBe added on the stator with predetermined DC voltage form, be added to more precisely on the phase winding of stator, and measure the stator current I of generation _SaBecause the leakage inductance L on stator limit _{σ s}And main inductance (reciprocal inductance) L _mInductive reactance (inductance) to be equivalent to direct current be short circuit, so can be from U _SaAnd I _SaValue calculate the Ohmage R of stator _s

2. calculate leakage inductance L according to Fig. 2 then to stator _{σ s}And L _{σ r}Summation, promptly " transient state " inductance is as follows: add a rectangular voltage short pulse of being made up of high fdrequency component on stator, its width is several milliseconds, and amplitude is U _Sa, according to Fig. 2, the inductance value of main inductance L ' m will be very big under these high-frequencies, so that flow through L ' _mElectric current can ignore.The electric current I that produces from this pulse then _SaThe rear side sampling of curve.According to sampling value accountable time constant L ' s/ (R _s+ R ' _r) and difference quotient dI _Sa/ dt.Thereby utilize equation U _Sa=R _sI _Sa+ L ' s (dI _Sa/ dt) can calculate L ' s.

Again after, it is low to making the electric current I that flows through rotor to add a frequency on stator _SyNegligible voltage, thereby stator current I _SaIn fact just equal to flow through the magnetization current I of main inductance _mKnown the Ohmage R of stator _sAnd electric current I _Sa, just can determine inductance L the s (=L of stator _m+ L _{σ s}).In addition, can determine dynamic main inductance L ' for the stator limit _Dm(also being the differential main inductance), and calculate its value L _DmWhen determining dynamic main inductance, a test voltage of being made up of alternating voltage of DC voltage superposition is added on the stator, and measures the alternating current (at place, working point) of generation by the DC current decision.This measurement is to carry out under different premagnetization DC current (working point).

4. therefore, in the isoboles of Fig. 1 and Fig. 2, all values except that rotor ohmic resistance all is known, so can calculate rotor ohmic resistance R in principle _rIf but this article and unspecified concrete way.

The present invention is as requested to determine quickly that than method up to now the task of rotor resistance proposes, and also will prevent simultaneously because the caused measuring error of current displacement.

The method of going to solve this task by the present invention is, the rotor ohmic resistance of the asynchronous machine controlled by a transverter under non-rotating field action is measured automatically, and this method comprises following step:

A. measure the Ohmage of asynchronous machine stator, leakage inductance and main inductance;

B. a test signal that is made of AC signal on the predetermined direct current signal superposition is added

To a phase winding of asynchronous machine, the frequency of this AC signal is approximately equal to asynchronous machine

Specified slip frequency;

C. measure the amplitude and the phase place of this phase signals that produces by test signal;

D. according to a) and c) measured value calculate rotor ohmic resistance.

Adopt this method, it is just enough only to need that the test signal and the mutual relationship of the phase signals that is produced are carried out one-shot measurement.Thereby can shorten time of measurement.Because the frequency ratio of AC signal is lower, be approximately equal to the very low specified slip frequency of asynchronous machine, be the frequency of operation of asynchronous machine, it can obtain according to the known rotation field frequency and the rated speed of asynchronous machine, so the measuring error that is caused by current displacement does not exist yet.

Preferably determine earlier rotor ohmic resistance to the stator limit, again according to a) and c) measured value calculate the true ohm resistance of rotor.

The frequency of AC signal is preferably in 1 to 8Hz scope.

An advantage of the invention is that direct current signal is a DC voltage, its value select make generation DC current also littler than half of the specified magnetization current of asynchronous machine.

The present invention also has an advantage to be, the amperage of DC current is selected to such an extent that make dynamic main inductance amount be approximately equal to the stator main inductance amount of asynchronous machine.

Test signal can be a phase voltage, and its reference value can be determined according to the relation property of phase current that is stored in the original mensuration in the storer and reference value.

To be that example is described the present invention and embodiment below with the accompanying drawing, in the accompanying drawing,

Fig. 1 is a common more detailed asynchronous machine isoboles;

Fig. 2 is the simplification isoboles of an asynchronous machine in stationary state, and wherein each amount is the value with respect to the stator limit;

The static main inductance L of Fig. 3 curve representation _mWith dynamic main inductance L _DmRelation with asynchronous machine magnetization DC current;

Fig. 4 is as the waveform of the phase voltage of test signal, is made up of triangle alternating voltage on the DC voltage superposition;

Fig. 5 is the block diagram of the converter of a control asynchronous machine, and the resistance of this motor is measured automatically by control device.

Fig. 6 is the detailed diagram of control device incident of the converter of Fig. 5.

Owing to will become stator limit parameter (scale with upper right left-falling stroke in Fig. 2 shows) and stator Ohmage R in the Parameters Transformation under the every phase effective turn in certain rotor limit _s, leakage inductance L _{σ s}And L _{σ r}And main inductance L _mDetermine, generally can be by the treatment step of originally describing 1), 2) and 3) carry out, below we describe asynchronous machine rotor ohmic resistance R in detail _rDefinite method.Except that above-mentioned three steps, for determining rotor ohmic resistance R _rAlso need one the 4th step.

Simplification isoboles with reference to Fig. 2, can write out following equation: $\left(1\right).......R_r^{\′}=\frac{\left|\stackrel{\‾}{U_m^{\′}}\right|}{\left|\stackrel{\‾}{I_{\mathrm{sy}}^{\′}}\right|}$ R in the formula _r' be the rotor ohmic resistance R ' that has converted the stator limit to _r, U ' _mBe by main inductance L ' _mThe voltage drop on main inductance of decision, I ' _SyIt is the electric current that flows through rotor.Horizontal line on each amount represents that this amount is a complex values.

In addition, from the rotor ohmic resistance that changes the stator limit into being write as in essence: $\left(2\right).......R_r^{\′}=\frac{L_m^2}{L_r^2}\·\frac{R_r}{s}$ L in the formula _rEqual L _m+ L _{σ r}, S represents the slip of asynchronous machine.Because the slip S of asynchronous machine quiescent period is 1, and measures and utilize dynamic main inductance to carry out, we can prove, $\left(3\right).......R_r=R_r^{\′}\·\frac{L_{\mathrm{Dm}}+L_{\mathrm{\σr}}}{L_{\mathrm{Dm}}^{\′}}$ Dynamic main inductance L _DmAnd L ' _DmCan know from original step 3) of describing.Unknown number is R ' _rSuppose L _{σ r}Be approximately equal to half of transient inductance L ' s.In the 4th treatment step, with one by phase voltage U that triangle alternating voltage (see figure 4) is formed on the DC voltage superposition _SaBe added on stator one phase winding as test signal, measure the stator current I that is produced _SaThe voltage drop U ' at main inductance two ends _mCan be write as: (4) U ' _m=U _Sa-R _sI _Sa-j ω L _s' I _SaRotor current I ' to the stator limit _SyBe (5) I _Sy'=I _Saθ is U ' in the cos θ formula _mAnd I _SaBetween phase shift.The arc tangent (Arctan) of the ratio of imaginary part and real part is U in the equation (4) _SaAnd U ' _mBetween phase shift α.Make U _SaAnd I _SaBetween phase shift be , θ=α+ then.Angle can determine by sad conversion in the discrete richness.For this reason, with the sampling value I of electric current _SaBe multiplied by a complex-exponential function, its index is an electric current I _SaFrequency, and vibration and test voltage homophase.Sampling value is carried out numerical integration can get a plural number, can draw the angle by the arc tangent of its real part and the ratio of imaginary part.

α and addition are just drawn θ, thus can by equation (5) obtain electric current I ' _SyFrom the simplification isoboles of Fig. 2 U ' as can be known _mAnd I ' _SyBe homophase, so R ' _rCan be by merchant U ' _m/ I ' _SyObtain.

For preventing to produce current displacement, we adopt low angular frequency.But, then can make electric current flow through main inductance, and not flow through rotor ohmic resistance if angular frequency is too low.The result proves, when this frequency can satisfy requirement aspect two in the scope (being generally 1 to 8Hz) of specified slip frequency fs.

In addition, because asynchronous machine impedance under static state is very little, the test signal voltage under this frequency must be very low.Yet, show the non-linear and idle time of transverter on-off element, its output current, thereby together with the stator current of asynchronous machine, be not proportional with the control voltage of transverter, and when control voltage be when controlling by the control device relevant with predefined reference value, not proportional with the reference voltage of control voltage yet.Therefore, not by the output voltage of an additional voltage sensor to transverter, and associated phase voltage U _SaMeasure, and at the same time to stator current, and associated phase current I _SaMeasure, just can not be only by measuring electric current I _SaDerive phase voltage U _SaSo before beginning to measure the Ohmage and inductance of asynchronous machine, will determine transverter output voltage or asynchronous machine input voltage and the relation property of controlling voltage reference value earlier, and will be with each stator current I _SaStore with the linear characteristic of representing ideal situation depart from (or error) down.This departs from the reference value that is used for to control voltage and carries out from normal moveout correction, to determine test signal.

By to dynamic main inductance L _DmWith magnetization current I _mRelation property and corresponding static main inductance L _mCharacteristic compares, and can derive by test signal U _SaThe stator current I that determines _SaIn the direct current amplitude.These characteristics are shown in Fig. 3, and wherein dot-and-dash line and solid line are represented dynamic main inductance L respectively _DmWith static main inductance L _mWith magnetization current I _mFuntcional relationship.Static inductance L _mBe defined as on the magnetization curve initial point to the gradient of working point line, i.e. ratio φ _m/ I _m, φ _m[Vs] is main flux.Dynamic inductance (also being the differential inductance) is equivalent to the gradient of a predetermined point on the magnetization curve.From being expressed as dynamic inductance in essence: $\left(6\right).......L_{\mathrm{Dm}}=\frac{{\mathrm{dL}}_m}{{\mathrm{dI}}_m}\·I_m+L_m$

The preceding measuring process of having narrated the 3rd) step, be to transient state dynamic inductance L ' _DmMeasure and calculate L with it _DmAccording to these values, other all value also must be represented with dynamic value.But, equation (3) is just had problem, because R ' _rMust be by U ' _m/ I ' _SyDetermine.Press equation (4), U ' _mAlso relevant with L ' s.Yet L ' s is a static inductance, and does not know that still how this static inductance is at leakage inductance L _{σ s}And L _{σ r}Between distribute, therefore, can't calculate transient state dynamic inductance L ' _DsBut to fully accurately calculate the Ohmage of rotor, should use transient state dynamic inductance L ' _DsReplace static inductance L ' s.Be head it off, measure, at this moment static main inductance L DC current _mEqual dynamic main inductance L _DmFrom in essence, static instantaneous inductor L ' s can be expressed as follows:

And dynamic instantaneous inductor L ' _DsCan be expressed as: $\left(8\right)........L_{\mathrm{Ds}}^{\′}=L_{\mathrm{Dm}}+L_{\mathrm{\σs}}-\frac{L_{\mathrm{Dm}}^2}{L_{\mathrm{Dm}}+L_{\mathrm{\σr}}}$ Work as L _DmWith L _mWhen equating, L ' s equals L ' _DsThis means, suitably select the magnetization current I of Fig. 3 _m, just can be the value of determined inductance L ' s as dynamic inductance L ' _DsValue.

When the rated power of asynchronous machine is output as 7.5KW, operating voltage is 380V, and when frequency of operation was 50Hz, dot-and-dash line and solid line were illustrated respectively in the dynamic main inductance L under the different DC current amplitudes among Fig. 3 _DmWith static main inductance L _mArticle two, curve is greatly about 40% specified magnetization current I _Mn, promptly the 14.64A place meets at a bit.Dynamic and static main inductance at this some place equates.This means when measuring rotor ohmic resistance DC current I _SaShould be set in about 40% specified magnetization current I _MnThe place.

Below we come referring to Fig. 5 and Fig. 6.The rotating speed of the threephase asynchronous machine 1 of converter control of Fig. 5.For realizing this purpose, converter comprises a bridge-type turbulator 3 and the direct-flow intermediate circuit 4 by three-phase supply 2 power supplies, and it is made up of a choking coil 5 and a filter capacitor 6.What be in parallel with filter capacitor is a resitstance voltage divider 7, take out a lower voltage is delivered to the three-phase transverter 8 of bridge architecture with measurement DC voltage from voltage divider, transverter has a lot of transistors, the diode that each connects with an inverse parallel, this lower voltage is delivered to the comparer of controller 11 by an analog to digital converter 9 and control module 10, element 9,10 and the 11 common control device that form transverter 8.What link to each other with asynchronous machine 1 every cable is a current sensor 12.The phase winding a that flows through asynchronous machine 1 that each current sensor 12 will record, the phase current Ia of b and c, Ib and Ic pass to analog to digital converter 9.Analog to digital converter 9 and control module 10 and current sensor 12 constitute current measuring device 13 (see figure 6)s together.In the asynchronous machine quiescent period, when measuring phase winding a, the Ohmage of b and c is during with the inductivity relevant with inductance, and phase current Ib is identical with Ia on phase place with Ic, but amplitude has only Ia half.According to these three phase current Ia, Ib and Ic, current measuring device 13 calculates stator current I _Sa, it and phase current Ia only differ from a relatively constant.Stator current I _SaBe sent in the function unit 14, by it according to stator current I _SaCalculate its amplitude, can also calculate with respect to the voltage U that is added in as test signal on the phase winding _SaPhase shift.For this reason will be to stator current I in function unit 14 _SaTake a sample.Sampling value be multiply by a complex-exponential function, and its index comprises electric current I _SaFrequencies omega=2 π f _s, its vibration and electric current I _SaU with this vibration of decision _RefHomophase, fs are the test or the slip frequencies of asynchronous machine 1.The sampling value numerical integration is obtained a plural number.The arctan function of this ratio when by real part and imaginary part can calculate phase shift .Therefore, according to stator current I _SaAmplitude, phase shift , fixed parameters R before the slip function f s _sAnd L ' s, just can in a function unit, calculate rotor ohmic resistance R _rIn order to determine desirable stator current I in advance _Sa(equaling Ia) is that (this voltage is again by a corresponding reference voltage U who gives controller 11 by the correct phase voltage that constitutes test signal _RefCome to determine) institute determine, and with idle time of transverter 8 and non-linear irrelevant, we will be determined by the I-E characteristic of transverter 8 departs from or the relation of corrected value and stator current is stored in the error correction function unit 16 in the mode of tabulating.Direct current signal and amount (being approximately 40% specified magnetization current) are according to specified magnetization current I _Mn, with the relation of original stator Ohmage of determining, be arranged in the function unit 71; Simultaneously in measuring signal generator 18, on the direct current signal superposition triangle alternating voltage (be shown in Figure 4), its frequency equals slip frequency f, then in error correction function unit 16 by and the stator current I of measurement _SaRelation proofread and correct, so the gained result is the correct reference value U of the control voltage of transverter 8 _Ref, just with stator current I _SaCorresponding phase voltage U _Sa

Determining correct reference value U _RefAnd phase voltage U _SaAfter, control module 10 or the function unit 15 that is included in wherein calculate voltage drop U ' according to equation (4) _m, after determining the θ angle, in function unit 15, press equation (5) and calculate rotor current I ' simultaneously according to the angle _Sy, and press equation (1) according to equation (4) and (5) and calculate rotor ohmic resistance R ' _r, the original inductance value of determining of last basis calculates rotor ohmic resistance R by equation (3) _r

Test signal U shown in Figure 4 _SaBe a triangular signal, but also can be a main pulse or a sine wave, and this signal be added to always the stator current that is produced is settled out till, that is to say, up to stator current I _SaPhase shift and till amplitude stabilization gets off.The time that test signal adds was approximately for 5 seconds, and is concrete how long relevant with the size of asynchronous machine.

By process of measurement of the present invention, to a 7.5kw, operating voltage 380v, the measurement that the asynchronous machine of frequency of operation 50Hz is done, the result who obtains in described in front three steps is as follows: R _s=0.65 Ω, L ' s=8.3mH, L ' _Dm=88.7mH.Can calculate dynamic inductance L in view of the above _DmBe 92.7mH.For determining through the rotor ohmic resistance after the conversion, test signal U _SaFrequency be at f _sSet under the specified slip frequency of=2Hz.Through the correction of error correction function unit 16, test signal U _SaAmount be 21V.The result of calculation of the of phase place is-0.226 radian, and the amplitude of stator current is I _Sa=20.4A.The R ' that obtains like this _rValue is 0.39 Ω, and can draw R by equation (3) _rValue be 0.44 Ω.Compare with correctness 0.45 Ω of rotor ohmic resistance, error is about 2.3%, and this is a typical value for this method, and at present, for a utilization and a transverter of relevant control, it is quite accurate to say so.

Equation (9) below utilizing can be in a certain temperature T ₁Definite down rotor ohmic resistance R _T1Convert at a different temperatures T ₂Under rotor ohmic resistance R _T2: $\left(9\right).......R_{T_2}=R_{{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A9911888600121.png"\; state="\{\{state\}\}">T</figure-callout>}}_1}\&CenterDot;\frac{T_2+{\mathrm{<figure-callout\; id="1"\; label="K\; T\; T"\; filenames="A9911888600121.png"\; state="\{\{state\}\}">K</figure-callout>}}_T}{T_{}}$ K in the formula _TBe that a material constant (for example, is worked as work temperature ₁And T ₂With ℃ when tolerance, the K of copper _T=235).

But, second temperature T of equation (9) supposition ₂Be known, and actual conditions such was the case with.But, utilize method of the present invention, can determine the Ohmage of rotor during static in that asynchronous machine is of short duration, and not need to know its temperature.Each physical quantity complete list U _SaTest signal, phase voltage, stator voltage I _SaPhase current, stator current, phase signals Ia, Ib, the phase current U in the Ic stator _mMain inductance both end voltage I _mMagnetization current I _MnSpecified magnetization current I _SyRotor current R _sStator Ohmage R _rRotor ohmic resistance U _RefReference voltage L _mStatic main inductance L _DmDynamic main inductance Ls stator inductance (L _m+ L _{σ s}) L _{σ s}Stator leakage inductance L _{σ r}Rotor leakage inductance L ' _mWith reference to main inductance L ' _DmWith reference to dynamic main inductance L ' _DsWith reference to dynamic instantaneous inductor L ' _sWith reference to instantaneous inductor (L _{σ r}+ L _{σ d}) U ' _mWith reference to the voltage drop I ' on the main inductance _mFlow through electric current I with reference to main inductance ' _SyReference rotor electric current R ' _rReference rotor resistance θ U ' _mAnd I _SaBetween phase shift α U _SaAnd U ' _mBetween phase shift U _SaAnd I _SaBetween phase shift ω angular frequency 2 π f _sf _sBe respectively test frequency or specified slip frequency s slip φ _mMain flux T ₁, T ₂The working temperature R of asynchronous machine _T1, R _T2Ohmage K under the different operating temperature _TThe material constant of rotor conductor material

Claims (6)

1. to the rotor ohmic resistance (R of the asynchronous machine (1) under non-rotating field action, controlled by a transverter (8) _r) method measured automatically, this method comprises:

A. measure the stator Ohmage (R of asynchronous machine _s), leakage inductance (L _{σ s}, L _{σ r}) and main

Sense (L _m);

B. with a test signal that constitutes by AC signal on the predetermined direct current signal superposition

(U _Sa) be added on one group of winding (a) of asynchronous machine, the frequency of this AC signal is near

Seemingly equal the specified slip frequency (f of asynchronous machine (1) _s);

C. measure the phase signals (I that produces by test signal _Sa) amplitude and phase place ();

D. according to a) and c) measured value calculate rotor ohmic resistance.

2. method according to claim 1, it is characterized in that at first be the rotor ohmic resistance of determining to be transformed to the stator limit (R ' _r), and press a) and c) measured value calculate actual rotor ohmic resistance (R _r).

3. according to the described method of claim 1 or 2, the frequency that it is characterized in that AC signal is in 1 to 8Hz scope.

4. according to arbitrary described method in the claim 1 to 3, it is characterized in that direct current signal is a DC voltage, its size should be selected to such an extent that make the specified magnetization current (I of the DC current of generation less than asynchronous machine (1) _Mn) half.

5. method according to claim 4 is characterized in that the DC current amperage should select to such an extent that make dynamic main inductance (L _Dm) be approximately equal to the static main inductance (L of asynchronous machine (1) _m).

6. according to arbitrary described method in the claim 1 to 5, it is characterized in that test signal is a phase voltage (U _Sa), its reference value (U _Ref) be according to be stored in the storer, phase current (I described _Sa) and reference value between characteristic that concern, that originally measured set.

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