Switched reluctance motor accurate modeling method based on small sample flux linkage characteristics
Technical Field
The invention relates to the technical field of switched reluctance motor flux linkage modeling, in particular to a switched reluctance motor accurate modeling method based on small sample flux linkage characteristics.
Background
At present, the switched reluctance motor has wide application prospect in the fields of oil field pumping units, wind power generation, electric vehicles and the like due to the advantages of simple structure, large starting torque, wide speed regulation range, high reliability and efficiency and the like. Establishing an accurate mathematical model is critical to SRM performance assessment and implementing advanced control strategies. However, the doubly salient structure and the magnetic saturation characteristics of the SRM itself make it difficult to derive an accurate nonlinear mathematical model thereof through conventional electromagnetic and physical property derivation. The current nonlinear modeling method of the switched reluctance motor mainly comprises the following steps: interpolation iteration method, equivalent magnetic circuit method, function fitting method and neural network approximation method. The equivalent magnetic circuit in the equivalent magnetic circuit method is difficult to divide, the accuracy of magnetic resistance calculation depends on assumption and estimation, and the universality is poor; the function fitting method adopts an analytic expression to carry out nonlinear fitting on the flux linkage characteristic, and the precision of the function fitting method excessively depends on the form of the function analytic expression and the fitting precision of the analytic expression coefficient; both the interpolation iteration method and the neural network approximation method need a large amount of flux linkage sample data, so that the application range is not large.
Disclosure of Invention
In order to solve the deficiencies in the above technical problems, the present invention aims to: the accurate modeling method of the switched reluctance motor based on the small sample flux linkage characteristics is provided, the characteristics of less flux linkage sample data, high accuracy and good rapidity can be realized, and support is provided for performance evaluation and advanced control strategy implementation of the switched reluctance motor.
The technical scheme adopted by the invention for solving the technical problem is as follows:
the accurate modeling method of the switched reluctance motor based on the small sample flux linkage characteristic comprises the following steps:
step 1), carrying out fuzzy space division on input and output variables of a flux linkage model according to the prior knowledge of a motor;
step 2), extracting fuzzy rules through a fuzzy logic system, and establishing a fuzzy rule base;
and 3) solving the flux linkage value under any current and position by solving the fuzzy problem through a gravity center method to complete flux linkage modeling.
Preferably, the following method is specifically adopted in the step 1):obtaining enough sample data of flux linkage changing along with current through experimental measurement, comprehensively considering model complexity and precision, and dividing phase current into 21 intervals by adopting a triangular membership function to perform fuzzy set division; specifically, the jth phase current fuzzy set AjThe membership function of (d) can be described as:
wherein i is a current value, j is a phase current, imaxAt maximum current, a ═ imaxAnd/20 is the step size of the current membership function.
Preferably, in the step 1), the prior knowledge of the SRM is introduced into the membership function selection and fuzzy set division of the rotor position for supplement, and a curve of flux linkage changing along with the rotor position can be divided into three regions, namely a region I [ theta ] (theta)u,θ1) Region II [ theta ]1,θhr) And region III [ theta ]hr,θa],θaThe complete alignment position of the salient poles of the stator and the rotor is as follows: calculating the alignment position theta of the leading edge of the rotor pole and the leading edge of the stator pole1And rotor pole centerline and stator pole leading edge alignment position θhrThe following formula is adopted:
in the formula, βsAnd βrThe pole arc widths of the stator and rotor, respectively, and satisfy the following relationship:
wherein, in the formula, m and NrRespectively representing the number of stator phases and the number of rotor poles of the motor, and m is 3, N is used for a three-phase 12/8-pole SRM modelrWhen formula (3) is substituted for formula (2), 8 can be obtained:
preferably, the change of the flux linkage along with the position of the rotor can be approximated to a linear relation in a region II, the change of the flux linkage along with the position of the rotor can be approximated to a cosine relation in regions I and III, the flux linkage-position characteristic is approximated to a linear relation in a position interval [7.5 degrees, 15 degrees ], and the linear membership function is adopted for division; the interval [0 degrees, 7.5 degrees ] and [15 degrees, 22.5 degrees ] are approximately cosine characteristics, and are divided by cosine membership functions.
Preferably, in step 1), in order to implement accurate solution of the flux linkage characteristics, a more refined fuzzy partition is adopted for fuzzy space partition of input and output variables of the flux linkage model, specifically as follows: dividing flux linkage into 201 regions by using a triangular membership function, wherein the ith flux linkage fuzzy set ClThe membership function of (d) can be described as:
in the formula, #maxIs the maximum value of flux linkage, c ═ ψmaxAnd 200 is the step size of the flux linkage membership function.
Preferably, the following method is specifically adopted in the step 2): a method for designing a fuzzy inference system based on input and output data of the system is adopted, and fuzzy rules are automatically extracted from sample data.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts a fuzzy logic system to solve the problem of accurate modeling when the flux linkage sample data of the switched reluctance motor is insufficient. Firstly, fuzzy space division is carried out according to motor priori knowledge; secondly, extracting fuzzy rules from small sample flux linkage data only containing a plurality of special positions through a fuzzy logic system, and forming a fuzzy rule base; and finally, solving the ambiguity by adopting a gravity center method, solving the flux linkage characteristic under any current and any rotor position, and completing the nonlinear accurate modeling of the flux linkage characteristic. Specifically, a fuzzy logic system accurate modeling method suitable for SRM small sample flux linkage characteristics is provided. The method can use the prior knowledge of the motor such as the change trend of the SRM pole logarithm and flux linkage along with the rotor position and the like for the selection of the fuzzy membership function and the division of the fuzzy set, and can automatically create a fuzzy rule base based on sample data, thereby realizing the accurate modeling under the SRM small sample flux linkage characteristic. The fuzzy modeling method not only makes full use of sample data, but also well combines inherent prior knowledge of the motor, greatly improves the modeling precision of the SRM flux linkage under the small sample data, and can provide powerful support for the analysis of the SRM operating characteristics and the verification of advanced algorithms.
Drawings
FIG. 1 is a block diagram of the present invention;
FIG. 2 is a schematic view of flux linkage characteristics at four particular positions of a rotor according to the present invention;
FIG. 3 is a schematic diagram of the input division (current) of the fuzzy logic system of the present invention;
FIG. 4 shows the flux linkage of the present invention as a function of rotor position;
FIG. 5 is a schematic diagram of the fuzzy logic system input partitioning (rotor position) of the present invention;
FIG. 6 is a schematic diagram of the input division (current) of the fuzzy logic system of the present invention;
FIG. 7 is a schematic diagram of the flux linkage modeling results of the present invention.
Detailed Description
Embodiments of the invention are further described below with reference to the accompanying drawings:
example 1
As shown in fig. 1 to 7, the method for accurately modeling a switched reluctance motor based on small sample flux linkage characteristics according to the present invention includes the following steps:
step 1), carrying out fuzzy space division on input and output variables of a flux linkage model according to the prior knowledge of a motor;
step 2), extracting fuzzy rules through a fuzzy logic system, and establishing a fuzzy rule base;
and 3) solving the flux linkage value under any current and position by solving the fuzzy problem through a gravity center method to complete flux linkage modeling.
In the specific method, a torque balance position measurement method is adopted to obtain small sample flux linkage data of four special positions of the three-phase switched reluctance motor, namely 0 degree, 7.5 degrees, 15 degrees and 22.5 degrees, as shown in fig. 2.
The following method is specifically adopted in the step 1): obtaining enough sample data of flux linkage changing along with current through experimental measurement, comprehensively considering model complexity and precision, and dividing phase current into 21 intervals by adopting a triangular membership function to perform fuzzy set division; specifically, the jth phase current fuzzy set AjThe membership function of (d) can be described as:
wherein i is a current value, j is a phase current, imaxAt maximum current, a ═ imaxAnd/20 is the step size of the current membership function.
For the rotor position in the step 1), flux linkage information of four special positions can be measured and obtained only based on a torque balance method. Flux linkage data of limited positions brings difficulty to membership function selection and fuzzy set division of rotor positions. Therefore, the prior knowledge of the SRM is introduced into the membership function selection and fuzzy set division of the rotor position for supplement, and the approximate change trend is very similar although the numerical values of the flux linkage-position (psi-theta) characteristics have differences for any given SRM prototype. Fig. 4 shows the flux linkage as a function of rotor position at a particular current. The curve of flux linkage changing with the position of rotor can be divided into three regions, I [ theta ] respectivelyu,θ1) Region II [ theta ]1,θhr) And region III [ theta ]hr,θa],θaThe complete alignment position of the salient poles of the stator and the rotor is as follows: calculating the alignment position theta of the leading edge of the rotor pole and the leading edge of the stator pole1And rotor pole centerline and stator pole leading edge alignment position θhrThe following formula is adopted:
in the formula, βsAnd βrThe pole arc widths of the stator and rotor, respectively, and satisfy the following relationship:
wherein, in the formula, m and NrRespectively representing the number of stator phases and the number of rotor poles of the motor, and m is 3, N is used for a three-phase 12/8-pole SRM modelrWhen formula (3) is substituted for formula (2), 8 can be obtained:
the change of the magnetic linkage along with the position of the rotor can be approximated to a linear relation in a region II and approximated to a cosine relation in regions I and III by combining experimental data, the magnetic linkage-position characteristic is approximated to a linear relation in a position interval [7.5 degrees, 15 degrees ], and a linear membership function is adopted for division; the interval [0 degrees, 7.5 degrees ] and [15 degrees, 22.5 degrees ] are approximately cosine characteristics, and are divided by cosine membership functions. The fuzzy set partitioning for rotor position is shown in fig. 5.
Rotor position ambiguity set B in FIG. 51And B2The membership functions of (a) can be described as:
fuzzy set B3And B4Are respectively connected with B2And B1Regarding the middle position symmetry, the principle of its membership functions is the same.
In step 1), in order to realize accurate solution of flux linkage characteristics, more precise fuzzy division is adopted for flux linkage model input and output variable fuzzy space division, and the method specifically comprises the following steps: dividing flux linkage into 201 regions by using a triangular membership function, wherein the ith flux linkage fuzzy set ClThe membership function of (d) can be described as:
in the formula, #maxIs the maximum value of flux linkage, c ═ ψmaxAnd 200 is the step size of the flux linkage membership function.
The following method is specifically adopted in the step 2): a method for designing a fuzzy inference system based on input and output data of the system is adopted, and fuzzy rules are automatically extracted from sample data.
The fuzzy rule is composed of a front piece and a back piece and can be expressed as follows: "If x
1is A
jand x
2is B
kthen y isC
l". For the SRM flux linkage fuzzy logic model, the fuzzy rule corresponding to each input/output data pair (i, theta; psi) can be described as "R
(s):If i
(s)is
andθ
(s)i s
thenψ
(s)is
". For each sample data, selecting the corresponding maximum membership function value, and calculating the corresponding fuzzy set as follows:
in the formula, q1,q2,q3The fuzzy set numbers of the front piece i, theta and the back piece psi, respectively. From the preceding fuzzy set partition, q1=4,q2=21,q3201. Extracted fuzzy rule R(s)Confidence of (D) (R)(s)) The following can be calculated:
it should be noted that some sample data have the same fuzzy front part, different fuzzy back parts will generate conflicting fuzzy rules, and the solution is to select the rule with the maximum confidence as the best fuzzy rule. Based on the measured special position flux linkage sample data, the fuzzy rule extraction is completed, as shown in table 1.
TABLE 1 fuzzy rule base extracted from experimental measurement data
Tab.1The final fuzzy rule base generated from the measured sampledata.
|
B1 |
B2 |
B3 |
B4 |
A1 |
C1 |
C1 |
C1 |
C1 |
A2 |
C3 |
C4 |
C8 |
C19 |
A3 |
C5 |
C8 |
C23 |
C37 |
A4 |
C8 |
C12 |
C35 |
C55 |
A5 |
C10 |
C15 |
C45 |
C71 |
A6 |
C12 |
C19 |
C61 |
C92 |
A7 |
C15 |
C23 |
C73 |
C109 |
A8 |
C17 |
C26 |
C80 |
C123 |
A9 |
C20 |
C30 |
C94 |
C137 |
A10 |
C22 |
C34 |
C105 |
C148 |
A11 |
C24 |
C38 |
C111 |
C157 |
A12 |
C27 |
C41 |
C120 |
C166 |
A13 |
C30 |
C45 |
C126 |
C172 |
A14 |
C32 |
C48 |
C132 |
C176 |
A15 |
C35 |
C52 |
C136 |
C181 |
A16 |
C37 |
C55 |
C141 |
C185 |
A17 |
C40 |
C58 |
C145 |
C188 |
A18 |
C43 |
C62 |
C149 |
C192 |
A19 |
C45 |
C65 |
C153 |
C195 |
A20 |
C48 |
C69 |
C157 |
C198 |
A21 |
C51 |
C72 |
C161 |
C200 |
Taking row 3, column 2 in table 1 as an example, the rules can be described as: "If phase current i is A3and rotor positionθis B2then flux-linkageψis C8”。
Solving the flux linkage value under any current and position by a gravity center method through ambiguity resolution to complete flux linkage modeling, which is concretely as follows:
flux linkage output of SRM under any current and position
The following can be calculated:
wherein
In the formula (I), the compound is shown in the specification,
representing fuzzy sets
The area of (a) is,
is that
The center of gravity of (a).
The SRM full period flux linkage values were calculated according to the proposed fuzzy logic system modeling method, as shown by the dotted line in fig. 7. In order to verify the modeling accuracy of the proposed method, the measured flux linkage value (shown as a solid line in fig. 7) is compared with the measured flux linkage value of the traditional rotor locking method, and the comparison result shows that the measured flux linkage value and the measured flux linkage value have better consistency.