WO2018103581A1

WO2018103581A1 - Method and system for estimating rotor resistance of induction motor

Info

Publication number: WO2018103581A1
Application number: PCT/CN2017/113807
Authority: WO
Inventors: 王凯
Original assignee: 蔚来汽车有限公司
Priority date: 2016-12-06
Filing date: 2017-11-30
Publication date: 2018-06-14
Also published as: CN106953569A; CN106953569B

Abstract

A method and system for estimating a rotor resistance of an induction motor. The method comprises: based on a model reference adaptive system, respectively establishing a magnetic flux current model and a magnetic flux voltage model for an induction motor (S10); respectively measuring stator temperatures at a plurality of different moments (S11); determining, on the basis of enabling a phase difference between outputs of the magnetic flux current model and the magnetic flux voltage model to be zero, estimated values of a rotor resistance corresponding to the plurality of different moments on a one-to-one basis (S12); calculating a temperature ratio of a rotor temperature to a stator temperature based on a correlation between the estimated values of the rotor resistance and the stator temperatures (S13); and calculating the rotor resistance online based on the temperature ratio, a current stator temperature, a stator reference temperature, a rotor reference resistance and a rotor material (S14). In the method, various main parameters for the operation of the motor are not only taken into consideration, but also the rotor resistance can be estimated at a low speed area of the motor, thus realizing more accurate estimation of the rotor resistance, and the present invention is widely applicable, is easy to implement, and has a high execution efficiency.

Description

Method and system for estimating rotor resistance of induction motor

Technical field

The present invention relates to the field of induction motor technology, and more particularly to an induction motor rotor resistance estimation technique.

Background technique

In the flux control of induction motors, the rotor resistance has a large influence on the final orientation angle. If the estimated flux angle is mismatched or significantly different from the actual value, the induction motor will not be able to produce the desired torque in torque control mode and will require higher currents when operating in speed control mode.

There are some rotor resistance determining or estimating methods in the prior art.

A more conventional method is to use a 50 Hz injection frequency to determine the rotor resistance in the case of locking the rotor. This is obviously inaccurate because of the skin effect, the rotor resistance will change at different injection frequencies; in practice, the operating frequency of the rotor copper strip is often less than the nominal sliding frequency, usually no more than 10 Hz. Even if the injection frequency is set to, for example, 5 Hz, it is not suitable because too low a frequency causes overheating to damage the motor. In addition, too low a frequency will also cause the stator main inductance to be ignored, thereby losing the meaning of locking the rotor identification parameter.

The more commonly used rotor resistance estimation method relies on the vector control system theory, which can estimate the rotor resistance relatively more accurately when the motor is operating in the high speed region. However, when operating in a low speed, high torque region, the rotor resistance cannot be accurately estimated.

Accordingly, those skilled in the art desire to obtain a method of estimating the rotor resistance of an induction motor that overcomes the above disadvantages.

Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple and reliable method for estimating rotor resistance of an induction motor, which is applicable to both a high speed zone and a low speed zone.

To achieve the above object, the present invention provides a technical solution as follows:

A method for estimating rotor resistance of an induction motor comprises the following steps: a) establishing a magnetic flux current model and a magnetic flux voltage model for the induction motor based on the model reference adaptive system; b) determining the stator temperature at a plurality of different times; c) And determining an estimated value of the rotor resistance corresponding to the plurality of different times based on a phase difference between the output of the magnetic flux current model and the magnetic flux voltage model; d), based on the estimated value of the rotor resistance and the stator temperature Correspondence, calculate the temperature ratio of the rotor temperature to the stator temperature; and e) calculate the rotor resistance online based on the temperature ratio, the current stator temperature, the stator reference temperature, the rotor reference resistance, and the material of the rotor.

Preferably, in step c), the phase difference between the magnetic flux current model and the output of the magnetic flux voltage model is adjusted using a PI controller such that the phase difference is zero to obtain an estimate of the rotor resistance.

Preferably, the step d) specifically comprises: plotting a relationship between the ratio of the rotor resistance to the rotor reference resistance and the stator temperature; performing a statistical operation on the slope; and determining the result of the statistical operation as the temperature ratio.

Preferably, steps a), b), c), and step d) are carried out in a laboratory environment.

The invention also provides an induction motor rotor resistance estimating system, comprising: a magnetic flux calculation model unit, which respectively establishes a magnetic flux current model and a magnetic flux voltage model for the induction motor based on the model reference adaptive system; the temperature measuring unit is at a plurality of different times Minute The stator temperature is not measured; and the central processing unit is coupled to the magnetic flux calculation model unit and the temperature measuring unit, respectively, and performs at least the following operations: based on making the phase difference between the output of the magnetic flux current model and the magnetic flux voltage model 0, Estimating the rotor resistance corresponding to a plurality of different times; calculating the temperature ratio of the rotor temperature to the stator temperature based on the correspondence between the estimated value of the rotor resistance and the stator temperature; and based on the temperature ratio, the current stator temperature, and the stator reference The rotor resistance is calculated online using the temperature, rotor reference resistance, and rotor material.

The rotor resistance estimating method and system provided by the embodiments of the present invention determine the rotor resistance in a laboratory environment by establishing a magnetic flux current model and a magnetic flux voltage model and based on the principle that the phase difference between the outputs of the two models is zero. The relationship between the estimated value and the stator temperature is used to calculate the temperature ratio of the rotor temperature to the stator temperature, and this temperature ratio is combined with other readily available parameters to estimate the value of the rotor resistance online. Compared with the prior art, the method and system not only take into account various main parameters of the motor operation, but also can estimate the rotor resistance in the low speed region of the motor, thereby achieving a more accurate estimation of the rotor resistance and a wide application range. Simple implementation and high execution efficiency.

DRAWINGS

Fig. 1 shows a rotor resistance estimating method provided by a first embodiment of the present invention.

2 illustrates a magnetic flux current model and a magnetic flux voltage model in accordance with an embodiment of the present invention.

3 is a graph showing the relationship between the ratio of rotor resistance to rotor reference resistance and stator temperature in accordance with an embodiment of the present invention.

detailed description

It should be noted that some conventional rotor resistance estimation schemes adopt a model reference adaptive system, which can relatively accurately identify the rotor resistance in the high speed region of the motor, but there is a large error in the low speed region. Therefore, the main contribution of the present invention is directed to It provides a rotor resistance estimation method suitable for both high speed and low speed areas.

The first embodiment of the present invention provides a rotor resistance estimating method which is applicable to both a high speed zone and a low speed zone. Specifically, it includes the following steps:

Step S10: The magnetic flux current model and the magnetic flux voltage model are respectively established for the induction motor based on the model reference adaptive system.

In step S11, the stator temperature is measured at a plurality of different times.

Step S12, based on the phase difference between the output of the magnetic flux current model and the magnetic flux voltage model being 0, the estimated value of the rotor resistance corresponding to the plurality of different times is determined.

Step S13: Calculate a temperature ratio of the rotor temperature to the stator temperature based on a correspondence between the estimated value of the rotor resistance and the stator temperature.

Step S14, calculating the rotor resistance online based on the temperature ratio, the current stator temperature, the stator reference temperature, the rotor reference resistance, and the material of the rotor.

It can be understood that it is possible to perform the above steps in a different order, for example, step S11 is performed first, and steps S10, S12, S13, and S14 are sequentially performed. It is possible to combine or split the above steps without affecting the technical effects of the present invention. Therefore, the simple deformation, combination or replacement of the steps in the embodiments of the present invention should fall within the protection scope of the present invention.

In order to better understand the above rotor resistance estimation method, the principle and operation idea of the present invention will be described below, and a detailed description of each step will be carried out.

In the following, the stator temperature is denoted as Temp _stator , which can be captured directly by the corresponding sensor; the rotor temperature is expressed as Temp _rotor , which cannot be directly measured. It is assumed that the stator temperature and the rotor temperature satisfy the following relationship:

Temp _rotor =η.Temp _stator (1)

Where η is defined as the temperature ratio of the rotor temperature to the stator temperature, which is the number to be determined.

On the other hand, assume that the rotor resistance at a certain temperature Temp _rotor satisfies the following formula:

R _r =[TempCof.(Temp _rotor _{-Temp rotor1} )+1].R _r1 (2)

Where TempCof represents the temperature coefficient, which is determined by the material of the rotor copper strip, which is a determinable value. Temp _rotor1 is the rotor reference temperature, and R _r1 is the resistance of the rotor under the rotor reference temperature Temp _rotor1 , defined as the rotor reference resistance.

Substituting formula (1) into formula (2) yields:

R _r =[TempCof.η.(Temp _stator _{-Temp stator1} )+1].R _r1 (3)

_Wherein, Temp stator represents a stator _temperature, Temp stator1 stator reference temperature.

It can be determined from the formula (3) that since the stator temperature Temp _stator is easy to measure, the temperature coefficient TempCof depends on the material of the rotor is almost constant, and the rotor reference temperature Temp _rotor1 and the corresponding rotor reference resistor R _r1 are also used as reference values. It is not difficult to determine, therefore, the accuracy of the estimated rotor resistance value is in fact more dependent on the accuracy of determining the value of the temperature ratio η.

It can also be understood from the above formula that if it is desired to determine the temperature ratio η between the rotor temperature and the stator temperature, it is necessary to first determine the rotor resistance values R _r1 , R _r2 when the stator is at the respective temperatures Temp _stator1 and Temp _stator2 .

According to an embodiment of the present invention, in order to determine the rotor resistance value, a Model Reference Adaptive System (MRAS) is introduced to establish a magnetic flux calculation model, which corresponds to step S10 in the first embodiment. The model specifically includes a magnetic flux current model (as an adaptive model) and a magnetic flux voltage model (as a reference model), as shown in FIG. The MRAS is established below based on data from a number of experiments conducted in a laboratory environment including at least rotor speed ω _r information, stator voltage u _s , stator current i _s , stator resistance R _{s ,} and stator magnetizing inductance L _m .

The magnetic flux voltage model can be expressed as follows:

The magnetic flux current model is expressed as follows:

Where α and β correspond to the direct and orthogonal axes of the stationary two-phase orthogonal coordinate system, where the components of the magnetic flux on the two coordinate axes are represented; p is a differential operator,

For laboratory estimates of rotor resistance, σL _s is the stator-side leakage inductance.

According to the magnetic flux voltage model in equation (4), the determined magnetic flux can be expressed as follows:

among them,

By two mutually orthogonal components

(corresponding to the direct axis and the intersecting axis of the stationary two-phase orthogonal coordinate system).

According to the magnetic flux current model in equation (5), the determined magnetic flux can be expressed as follows:

among them,

By two mutually orthogonal components

(corresponding to the straight axis of the stationary two-phase orthogonal coordinate system),

(corresponding to the intersection axis of the stationary two-phase orthogonal coordinate system).

The phase difference ε between the output of the magnetic flux current model and the magnetic flux voltage model can utilize the above two vectors

Vector product to calculate:

It can be understood that the above phase difference ε should be zero when the rotor resistance can be accurately determined. Here, for example, a conventional PI controller adjusts the above formula such that ε tends to zero to obtain rotor resistance.

The convergence value, that is, the laboratory estimate of the rotor resistance.

It can also be understood that the estimated value of the rotor resistance is determined according to the above formula (4) to formula (11).

It is suitable for use in a laboratory environment and requires the determination of multiple parameters, requires more complex calculations, and is therefore not suitable for direct (on-line) estimation of rotor resistance. The above formula (4) to formula (11) are used to determine the temperature ratio η between the rotor temperature and the stator temperature.

In the laboratory environment, the stator temperatures are determined to be Temp _stator1 , Temp _stator2 , Temp _stator3 , ... at a plurality of different times, and this process corresponds to step S11 in the first embodiment. Subsequently, according to the principle that the phase difference ε in the equation (7) is zero, the laboratory estimates R _r1 , R _r2 , R _r3 , ... of the corresponding rotor resistance are respectively determined, and they are directly regarded as the rotor resistance, which A process corresponds to step S12 in the first embodiment. Further, based on the results of a plurality of experiments, the relationship between the rotor resistance and the stator temperature (corresponding table) can be obtained. For the convenience of the following operations, a graph of the relationship between the rotor resistance to the rotor reference resistance and the stator temperature is plotted. It will be appreciated that other types of temperature-resistance fitting curves are equally applicable; in addition, the technical effects of the present invention can be achieved without drawing any curves, but only based on data calculations.

As described above, the rotor resistance estimation scheme of the prior art can accurately recognize the rotor resistance in the high speed region of the motor, but is not suitable for the low speed region. In this regard, the present invention avoids the drawbacks of the prior art by plotting a temperature-resistance fitting curve to provide a rotor resistance estimation method that can be applied to low speed regions.

Regarding the relationship between the ratio of the rotor resistance to the rotor reference resistance and the stator temperature, a possible relationship curve is shown in FIG. 3. For the sake of simplicity of explanation, only three different stator temperatures and one by one are shown in FIG. Corresponding rotor resistance. It will be appreciated that in order to obtain more accurate results, any number of such sets of data can be determined.

In Figure 3, the slope of the relationship between the ratio of the rotor resistance to the rotor reference resistance and the stator temperature is statistically calculated to fully determine the rotor temperature and the stator temperature closer to the actual situation based on multiple sets of experimental data. The temperature ratio η, this process corresponds to the step S13 in the above-described first embodiment.

As only one example, the slope of the first segment of the curve (corresponding to the change of the stator temperature from Temp _stator1 to Temp _stator2 ) is η ₁ , and the slope of the second segment of the curve (corresponding to the change of the stator temperature from Temp _stator1 to Temp _stator3 ) is η ₂ , considering that TempCof is a constant, η ₁ and η ₂ can be defined as follows:

According to various statistical algorithms, the slope of each segment of the curve can be statistically calculated, and the statistical operation result is used as an estimation of the temperature ratio η between the rotor temperature and the stator temperature. As a simple example, the average of η ₁ and η ₂ can be used as an estimate of the temperature ratio η

, as follows:

In determining the estimated value of the temperature ratio η

On the basis of this, we can correct the above formula (3) and get the following formula:

From the above equation (11) can be known, the rotor may be based on the resistance value of the temperature coefficient R _r TempCof, this stator temperature _Temp stator, the stator reference temperature _Temp stator1, the estimated value of the temperature ratio

And the rotor reference resistance R _r1 is determined or estimated online, this process corresponding to step S14 in the first embodiment described above. Where the temperature ratio is estimated

It is determined in the laboratory that the temperature coefficient TempCof is almost constant depending on the material of the copper strip, and the stator temperature Temp _stator is the current (on-line) measured stator temperature.

Further, the stator reference temperature Temp _stator1 and the rotor reference resistance R _{r1 are} used as reference values, which can be determined in advance in the laboratory, or the result of the previous estimation can be used as a reference value for the next estimation, which can produce more accurate The estimation results, therefore, can be taken as a preferred embodiment.

The induction motor rotor resistance estimating method according to the above embodiment can take into account various main parameters of the motor operation and is suitable for the low speed region of the motor, thereby achieving a more accurate estimation of the rotor resistance in the full speed range.

Further, the induction motor rotor resistance estimation method after collecting stator temperature _Temp stator, estimated according to a known temperature coefficient TempCof, a value proportional to the temperature

With the parameters, the value of the rotor resistance is calculated online, which is simple to implement and high in execution efficiency.

Another embodiment of the present invention provides an induction motor rotor resistance estimating system, comprising: a magnetic flux calculation model unit, a temperature measuring unit, and a central processing unit, wherein the central processing unit is coupled to the magnetic flux calculation model unit and the temperature measuring unit, respectively.

The magnetic flux calculation model unit separately establishes a magnetic flux current model and a magnetic flux voltage model for the induction motor based on the model reference adaptive system; the temperature measurement unit respectively determines the stator temperature at a plurality of different times; and the central processing unit performs at least the following operations: A. The phase difference between the output of the magnetic flux current model and the magnetic flux voltage model is set to 0, and the estimated value of the rotor resistance corresponding to a plurality of different times is determined; B. The correspondence between the estimated value of the rotor resistance and the stator temperature Calculate the temperature ratio of the rotor temperature to the stator temperature; and C. Calculate the rotor resistance online based on the temperature ratio, the current stator temperature, the stator reference temperature, the rotor reference resistance, and the material of the rotor.

The above description is only for the preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Various modifications may be made by those skilled in the art without departing from the spirit of the invention and the appended claims.

Claims

A method for estimating rotor resistance of an induction motor includes the following steps:

a) establishing a magnetic flux current model and a magnetic flux voltage model for the induction motor based on the model reference adaptive system;

b) measuring the stator temperature at a plurality of different times;

c) determining an estimated value of the rotor resistance corresponding to the plurality of different times based on a phase difference between the output of the magnetic flux current model and the magnetic flux voltage model;

d) calculating a temperature ratio of the rotor temperature to the stator temperature based on a correspondence between the estimated value of the rotor resistance and the stator temperature;

e) calculating the rotor resistance online based on the temperature ratio, the current stator temperature, the stator reference temperature, the rotor reference resistance, and the material of the rotor.
The method of claim 1 wherein in said step a) said magnetic flux current model is expressed as
The magnetic flux voltage model is expressed as
Where ω r is the rotor speed, u s is the stator voltage, i s is the stator current, R s is the stator resistance, L m is the magnetizing inductance of the stator, and α and β correspond to the direct axis of the stationary two-phase orthogonal coordinate system, respectively. And the intersection axis, p is the differential operator,
For the estimated value of the rotor resistance, σL s is the stator-side leakage inductance, and the magnetic flux determined by the magnetic flux voltage model is
The magnetic flux determined by the magnetic flux current model is
The method according to claim 1, wherein in said step c), said phase difference between said magnetic flux current model and an output of a magnetic flux voltage model is adjusted using a PI controller such that said The phase difference is zero to obtain an estimate of the rotor resistance.
The method according to claim 1, wherein the step d) specifically comprises:

Draw a relationship between the ratio of the rotor resistance to the rotor reference resistance and the stator temperature;

Performing a statistical operation on the slope;

The result of the statistical operation is determined as the temperature ratio.
The method of claim 1 wherein said rotor resistance is calculated as
Wherein, TempCof is a temperature coefficient depending on the material of the rotor, Temp stator is the current stator temperature, Temp stator 1 is the stator reference temperature, R r1 is the rotor reference resistance, and
Is the temperature ratio.
The method according to any one of claims 1 to 5, characterized in that said steps a), b), c), and step d) are carried out in a laboratory environment.
The method of claim 6 wherein said stator reference temperature is said current stator temperature measured when said method was previously performed, said rotor reference resistance being calculated when said method was previously executed The rotor resistance.
An induction motor rotor resistance estimation system includes:

a magnetic flux calculation model unit, which is respectively configured to establish a magnetic flux current model and a magnetic flux voltage model for the induction motor based on a model reference adaptive system;

a temperature measuring unit that measures stator temperature at a plurality of different times;

a central processing unit coupled to the magnetic flux calculation model unit and the temperature measurement unit, respectively, and performing at least the following operations:

Determining an estimated value of the rotor resistance in one-to-one correspondence with the plurality of different times based on a phase difference between the output of the magnetic flux current model and the magnetic flux voltage model being 0;

Calculating a temperature ratio of the rotor temperature to the stator temperature based on a correspondence between the estimated value of the rotor resistance and the stator temperature;

The rotor resistance is calculated online based on the temperature ratio, the current stator temperature, the stator reference temperature, the rotor reference resistance, and the material of the rotor.