阅读说明：本技术 一种无轴承磁通切换电机的电磁场性能获取方法 (Method for acquiring electromagnetic field performance of bearingless flux switching motor ) 是由 周扬忠 吴鑫 陈垚 陈艳慧 屈艾文 钟天云 于 2019-09-29 设计创作，主要内容包括：本发明涉及一种无轴承磁通切换电机的电磁场性能获取方法,将整个电机划分成6个子域,包括转子槽子域、内部气隙子域、定子槽子域、永磁体槽气隙子域、永磁体子域和外部气隙子域；根据子域与铁芯间的边界条件以及相邻子域交界面上的连续条件,确定各个子域的磁场分布；通过各个子域的磁场分布计算出相应定、转子铁芯的磁压降,再根据实际铁芯的B-H特性曲线完成对定、转子铁芯磁饱和的计算,从而得到饱和情况下电机的电磁性能。本发明能够解决无轴承磁通切换电机电磁性能的快速、精确计算和分析的需要。(The invention relates to a method for acquiring the electromagnetic field performance of a bearingless flux switching motor, which divides the whole motor into 6 sub-domains, including a rotor slot sub-domain, an internal air gap sub-domain, a stator slot sub-domain, a permanent magnet slot air gap sub-domain, a permanent magnet sub-domain and an external air gap sub-domain; determining the magnetic field distribution of each sub-domain according to the boundary condition between the sub-domains and the iron core and the continuous condition on the interface of the adjacent sub-domains; and calculating the magnetic voltage drop of the corresponding stator and rotor iron cores according to the magnetic field distribution of each sub-domain, and then completing the calculation of the magnetic saturation of the stator and rotor iron cores according to the B-H characteristic curve of the actual iron core, thereby obtaining the electromagnetic performance of the motor under the saturation condition. The invention can solve the requirement of quick and accurate calculation and analysis of the electromagnetic performance of the bearingless flux switching motor.)

1. A method for obtaining the electromagnetic field performance of a bearingless flux switching motor is characterized in that,

dividing the whole motor into 6 subdomains, including a rotor slot subdomain, an internal air gap subdomain, a stator slot subdomain, a permanent magnet slot air gap subdomain, a permanent magnet subdomain and an external air gap subdomain; determining the magnetic field distribution of each sub-domain according to the boundary condition between the sub-domains and the iron core and the continuous condition on the interface of the adjacent sub-domains; and calculating the magnetic voltage drop of the corresponding stator and rotor iron cores according to the magnetic field distribution of each sub-domain, and then completing the calculation of the magnetic saturation of the stator and rotor iron cores according to the B-H characteristic curve of the actual iron core, thereby obtaining the electromagnetic performance of the motor under the saturation condition.

2. The method for acquiring the electromagnetic field data of the bearingless flux switching motor according to claim 1, comprising the following steps:

step S1: dividing a motor into subdomains to obtain a rotor slot subdomain, an internal air gap subdomain, a stator slot subdomain, a permanent magnet slot air gap subdomain, a permanent magnet subdomain and an external air gap subdomain; and (3) establishing a Maxwell equation of the motor by taking the vector magnetic potential A as a solving variable:

in the formula, mu₀Is a vacuum magnetic conductivity; mu.s_rIs relative magnetic permeability; j is the current density; m is the remanent magnetization vector;

step S2: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the rotor slot sub-domain by adopting a separation variable method according to the Neniemann boundary condition between the sub-domain and the iron core_1iGeneral solution expression of (1):

in the formula, A_imAnd A_i0The undetermined coefficient of the rotor slot subdomain is obtained; m is the harmonic frequency of the magnetic field of the rotor slot domain; r₁Is the rotor slot inner diameter; r₂Is the rotor slot outer diameter; beta is a_rIs the rotor slot opening width; theta_iIs the centerline position of the ith rotor slot;

step S3: in a two-dimensional polar coordinate system (r, theta), calculating vector magnetic potential A of an inner air gap sub-domain by adopting a separation variable method according to a neyman boundary condition between the sub-domain and an iron core₂General solution expression of (1):

in the formula, B_1n、B_2n、B_3nAnd B_4nIs the undetermined coefficient of the inner air gap subdomain; n is the harmonic order of the magnetic field of the inner air gap sub-region; r₃Is the stator slot inner diameter;

step S4: in a two-dimensional polar coordinate system (r, theta), according to the Neezeman boundary condition between a sub-domain and an iron core, a vector magnetic potential A of a stator slot sub-domain is calculated by adopting a separation variable method_3jGeneral solution expression of (1):

in the formula, C_jpAnd C_j0Is the undetermined coefficient of the stator slot subdomain; p is a radicalHarmonic order of the sub-slot sub-region magnetic field; j. the design is a square_j0And J_jpCoefficients of a Fourier series expansion of the current density of the jth stator slot; r₄Is the stator slot outer diameter; beta is a_sIs the stator slot opening width; theta_jIs the position of the center line of the jth stator slot;

step S5: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the air gap sub-field of the permanent magnet slot by adopting a separation variable method according to the Neniemann boundary condition between the sub-field and the iron core_4kGeneral solution expression of (1):

in the formula, D_k1q、D_k2q、D_k20And D_k10The undetermined coefficient of the air gap subdomain of the permanent magnet slot; q is the harmonic frequency of the air gap subdomain magnetic field between the stator cores; r₅Is the permanent magnet slot inner diameter; beta is a_fIs the permanent magnet slot opening width; theta_kIs the centerline position of the kth permanent magnet slot;

step S6: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the permanent magnet sub-field by adopting a separation variable method according to the Neniemann boundary condition between the sub-field and the iron core_5kGeneral solution expression of (1):

in the formula, E_k1s、E_k2s、E_k20And E_k10Is the undetermined coefficient of the permanent magnet subdomain; s is the harmonic frequency of the magnetic field of the subdomain of the permanent magnet; b is_remIs the remanence of the permanent magnet; r₆Is the permanent magnet slot outer diameter;

step S7: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the external air gap sub-domain by adopting a separation variable method according to the Neniemann boundary condition between the sub-domain and the iron core₆General solution expression of (1):

in the formula, F_1tAnd F_2tIs the undetermined coefficient of the outer air gap subdomain; t is the harmonic order of the magnetic field of the outer air gap sub-region; r₇Is the radius of the outer air gap;

step S8: establishing the relation between the screwdriver domains according to the continuous conditions met by the adjacent sub domains, and specifically adopting the following formulas:

step S9: and calculating undetermined coefficients in each general solution expression by adopting numerical analysis software according to the formula of the step S8, and calculating corresponding flux density distribution according to each subdomain vector magnetic potential:

in the formula, B_rRepresents the radial component of flux density; b is_θRepresents the tangential component of flux density;

step S10: calculating saturation coefficients of all parts of the stator core and the rotor core:

in the formula, V_stlxAnd V_stuxRespectively representing the magnetic voltage drop of the lower half part and the upper half part of the x-th stator tooth; h_gsxRepresenting the magnetic field strength before the x-th stator tooth; v_rtzRepresents the magnetic pressure drop of the z-th rotor tooth; h_grzRepresenting the magnetic field strength before the z-th rotor tooth;

step S11: the calculation takes into account the radial component of the air gap flux density in the saturation case:

in the formula, B_2rRepresents the radial component of the air gap flux without taking into account saturation; k_satsAnd K_satrRespectively representing the saturation coefficient distribution of the stator core and the rotor core;

step S12: electromagnetic torque T under saturation condition is calculated by adopting Maxwell stress-strain method_eAnd levitation forces F in the x and y directions_xAnd F_y：

Wherein L represents a bearing length of the motor; r_gA radius representing a motor air gap center circumference; b is_{2θ_sat}Representing the tangential component of the air gap flux density.

3. The method of claim 2, wherein in step S1, after the sub-field division of the motor, the positions of all slots in the two-dimensional polar coordinate system are calculated as follows:

in the formula, N_rtThe number of rotor teeth; n is a radical of_stThe number of stator teeth.

4. The method as claimed in claim 2, wherein the step S4 of calculating the coefficients of the fourier series expansion of the current density of the stator slots comprises the steps of:

step S41: obtaining the current density in the jth stator slot according to the structure of the stator winding:

in the formula, J_j1The current density of the first coil side of the jth stator slot is shown; j. the design is a square_j2The current density of the second coil side of the jth stator slot is shown;

step S42: obtaining a mirror image waveform of the current density of the jth slot according to the distribution of the current density, and performing Fourier series expansion on the mirror image waveform to obtain:

wherein the content of the first and second substances,

5. the method of claim 2, wherein the step S8, the continuity condition satisfied between adjacent sub-fields includes:

the rotor slot sub-region and the inner air gap sub-region satisfy:

the inner air gap sub-region, the stator slot sub-region and the permanent magnet slot air gap sub-region satisfy:

the space between the permanent magnet slot air gap subdomain and the permanent magnet subdomain satisfies:

the permanent magnet sub-region and the outer air gap sub-region satisfy:

6. the method for acquiring electromagnetic field data of a bearingless flux switching motor according to claim 2, wherein in step S10, the magnetic voltage drop is acquired by:

step S101: when the magnetic saturation coefficient of the stator is calculated, the slotting effect of a rotor core is ignored, and the rotor is assumed to be a linear core; when the magnetic saturation coefficient of the rotor is calculated, the slotting effect of the stator core is ignored, and the stator is assumed to be a linear core;

step S102: calculating the radial component of the inner air gap flux density and the tangential component of the permanent magnet slot air gap subdomain flux density according to the flux density distribution expression of step S9:

in the formula, B_2rA radial component of magnetic density for the inner air gap subdomain; b is_4kθIs the tangential component of the magnetic flux density of the k-th permanent magnet slot air gap subdomain;

step S103: calculating the magnetic flux flowing through the xth stator tooth, the yth permanent magnet slot and the z-th rotor tooth:

in the formula phi_stlxRepresents the magnetic flux of the lower part of the x-th stator tooth; phi_pmsyRepresents the flux of the y-th permanent magnet slot; phi_ryzRepresents the flux of the z-th rotor yoke;

step S104: calculating the magnetic flux of the upper half of the x-th stator tooth:

in the formula phi_stuxRepresenting the magnetic flux at the upper part of the x-th stator tooth;

step S105: and calculating the magnetic densities of the lower half part and the upper half part of the x-th stator tooth and the magnetic density of the z-th rotor tooth:

in the formula, B_stlxRepresenting the magnetic density of the lower part of the x-th stator tooth; b is_stuxRepresenting the magnetic density of the upper part of the x-th stator tooth; phi_ryzRepresents the flux density of the z-th rotor yoke;

step S106: and calculating the magnetic pressure drop of the lower half part and the upper half part of the x-th stator tooth and the magnetic pressure drop of the z-th rotor tooth according to the B-H characteristic curve of the stator core:

V_rtz＝H_rtzl_rt；(58)

in the formula I_stIs the radial length of the stator teeth; l_rtIs the rotor tooth radial length; h_stlxAnd H_stuxRespectively representing the magnetic field intensity of the lower half part and the upper half part of the x-th stator tooth; h_rtzRepresenting the magnetic field strength of the z-th rotor tooth.

Technical Field

The invention relates to the field of design of electromagnetic field performance of a motor, in particular to an electromagnetic field performance acquisition method of a bearingless flux switching motor.

Background

The permanent magnet of the bearingless flux switching motor (BFSPMM) is embedded into the stator core, and the rotor is of a winding-free iron core structure, so that the demagnetization risk of the permanent magnet caused by temperature rise can be effectively avoided, and the bearingless flux switching motor has the advantages of high working efficiency, stable rotor operation, suitability for high-speed operation and the like. Because the bearingless flux switching motor adopts a rotor tooth and slot structure to modulate an air gap magnetic field, a stator iron core is not integral, the nonlinearity of the motor is very serious, and no good modeling analysis method exists at present.

The finite element method has high precision, but needs a large amount of operations such as excitation, boundary and the like for drawing and setting a model topological graph, the early-stage work is complicated and the consumed time is long, the later-stage finite element solution needs a large amount of computing power and needs a large amount of time cost, and the finite element method cannot clearly show the relation between the electromagnetic performance and the size of the motor, so that the finite element method has great limitation in the initial design and performance optimization links of the motor needing a large amount of repeated design.

The equivalent magnetic circuit network method is to use the flux tube to carry out equivalence on each part of the motor, so that the whole motor model is converted into a magnetic circuit form to be solved, and the magnetic field distribution of the motor can be obtained in an iterative calculation mode. Although the saturation effect of the iron core is considered in the process of establishing the model, the magnetic circuit network method has the problems of complex modeling process, long iterative computation time and the like.

The sub-domain model method is to divide the motor into a plurality of sub-domains, establish Laplace's equation or Poisson's equation in each sub-domain, solve the equation according to the boundary condition between the sub-domain and the iron core and the continuous condition between adjacent sub-domains, thereby carrying out analytic calculation on each electromagnetic performance of the motor. The sub-domain model method takes into account the interaction between the cells and has a higher computational accuracy than other analytical methods. However, the sub-domain model method does not consider the saturation effect and does not accord with the magnetic circuit characteristics of the actual motor.

Disclosure of Invention

In view of the above, the present invention provides a method for obtaining electromagnetic field performance of a bearingless flux switching motor, so as to solve the need of fast and accurate calculation and analysis of electromagnetic performance of the bearingless flux switching motor.

The invention is realized by adopting the following scheme: a method for acquiring electromagnetic field performance of a bearingless flux switching motor comprises the following steps:

dividing the whole motor into 6 subdomains, including a rotor slot subdomain, an internal air gap subdomain, a stator slot subdomain, a permanent magnet slot air gap subdomain, a permanent magnet subdomain and an external air gap subdomain; determining the magnetic field distribution of each sub-domain according to the boundary condition between the sub-domains and the iron core and the continuous condition on the interface of the adjacent sub-domains; and calculating the magnetic voltage drop of the corresponding stator and rotor iron cores according to the magnetic field distribution of each sub-domain, and then completing the calculation of the magnetic saturation of the stator and rotor iron cores according to the B-H characteristic curve of the actual iron core, thereby obtaining the electromagnetic performance of the motor under the saturation condition.

Firstly, constructing a sub-domain model of electromagnetic field calculation of a bearingless flux switching motor under a linear magnetic circuit; then, in order to consider the saturation effect of the motor core, a magnetic saturation coefficient model of the motor is further constructed based on the sub-domain model; and finally, correcting the electromagnetic field calculated by the sub-field model under the linear magnetic circuit by using the magnetic saturation coefficient to obtain accurate electromagnetic field data. And based on accurate electromagnetic field calculation, performance parameters such as electromagnetic torque, levitation force and the like of the motor are quickly calculated. The method specifically comprises the following steps:

step S1: dividing a motor into subdomains to obtain a rotor slot subdomain, an internal air gap subdomain, a stator slot subdomain, a permanent magnet slot air gap subdomain, a permanent magnet subdomain and an external air gap subdomain; and (3) establishing a Maxwell equation of the motor by taking the vector magnetic potential A as a solving variable:

in the formula, mu₀Is a vacuum magnetic conductivity; mu.s_rIs relative magnetic permeability; j is the current density; m is the remanent magnetization vector;

step S2: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the rotor slot sub-domain by adopting a separation variable method according to the Neniemann boundary condition between the sub-domain and the iron core_1iGeneral solution expression of (1):

in the formula, A_imAnd A_i0The undetermined coefficient of the rotor slot subdomain is obtained; m is the harmonic frequency of the magnetic field of the rotor slot domain; r₁Is the rotor slot inner diameter; r₂Is the rotor slot outer diameter; beta is a_rIs the rotor slot opening width; theta_iIs the centerline position of the ith rotor slot;

step S3: in a two-dimensional polar coordinate system (r, theta), calculating vector magnetic potential A of an inner air gap sub-domain by adopting a separation variable method according to a neyman boundary condition between the sub-domain and an iron core₂General solution expression of (1):

in the formula, B_1n、B_2n、B_3nAnd B_4nIs the undetermined coefficient of the inner air gap subdomain; n is the harmonic order of the magnetic field of the inner air gap sub-region; r₃Is the stator slot inner diameter;

step S4: in a two-dimensional polar coordinate system (r, theta), according to the Neezeman boundary condition between a sub-domain and an iron core, a vector magnetic potential A of a stator slot sub-domain is calculated by adopting a separation variable method_3jGeneral solution expression of (1):

in the formula, C_jpAnd C_j0Is the undetermined coefficient of the stator slot subdomain; p is the stator slot domain fieldThe harmonic order of (d); j. the design is a square_j0And J_jpCoefficients of a Fourier series expansion of the current density of the jth stator slot; r₄Is the stator slot outer diameter; beta is a_sIs the stator slot opening width; theta_jIs the position of the center line of the jth stator slot;

step S5: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the air gap sub-field of the permanent magnet slot by adopting a separation variable method according to the Neniemann boundary condition between the sub-field and the iron core_4kGeneral solution expression of (1):

in the formula, D_k1q、D_k2q、D_k20And D_k10The undetermined coefficient of the air gap subdomain of the permanent magnet slot; q is the harmonic frequency of the air gap subdomain magnetic field between the stator cores; r₅Is the permanent magnet slot inner diameter; beta is a_fIs the permanent magnet slot opening width; theta_kIs the centerline position of the kth permanent magnet slot;

step S6: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the permanent magnet sub-field by adopting a separation variable method according to the Neniemann boundary condition between the sub-field and the iron core_5kGeneral solution expression of (1):

in the formula, E_k1s、E_k2s、E_k20And E_k10Is the undetermined coefficient of the permanent magnet subdomain; s is the harmonic frequency of the magnetic field of the subdomain of the permanent magnet; b is_remIs the remanence of the permanent magnet; r₆Is the permanent magnet slot outer diameter;

step S7: in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the external air gap sub-domain by adopting a separation variable method according to the Neniemann boundary condition between the sub-domain and the iron core₆General solution expression of (1):

in the formula, F_1tAnd F_2tIs the undetermined coefficient of the outer air gap subdomain; t is the harmonic order of the magnetic field of the outer air gap sub-region; r₇Is the radius of the outer air gap;

step S8: establishing the relation between the screwdriver domains according to the continuous conditions met by the adjacent sub domains, and specifically adopting the following formulas:

step S9: and calculating undetermined coefficients in each general solution expression by adopting numerical analysis software according to the formula of the step S8, and calculating corresponding flux density distribution according to each subdomain vector magnetic potential:

in the formula, B_rRepresents the radial component of flux density; b is_θRepresents the tangential component of flux density;

step S10: calculating saturation coefficients of all parts of the stator core and the rotor core:

in the formula, V_stlxAnd V_stuxRespectively representing the magnetic voltage drop of the lower half part and the upper half part of the x-th stator tooth; h_gsxRepresenting the magnetic field strength before the x-th stator tooth; v_rtzRepresents the magnetic pressure drop of the z-th rotor tooth; h_grzRepresenting the magnetic field strength before the z-th rotor tooth;

step S11: the calculation takes into account the radial component of the air gap flux density in the saturation case:

in the formula, B_2rRepresents the radial component of the air gap flux without taking into account saturation; k_satsAnd K_satrRespectively representing the saturation coefficient distribution of the stator core and the rotor core;

step S12: electromagnetic torque T under saturation condition is calculated by adopting Maxwell stress-strain method_eAnd levitation forces F in the x and y directions_xAnd F_y：

Wherein L represents a bearing length of the motor; r_gA radius representing a motor air gap center circumference; b is_{2θ_sat}Typical qiThe tangential component of the flux density of the gap.

Further, in step S1, after the sub-field division is performed on the motor, the positions of all slots in the two-dimensional polar coordinate system are calculated as follows:

in the formula, N_rtThe number of rotor teeth; n is a radical of_stThe number of stator teeth.

Further, in step S4, the calculating the coefficients of the fourier series expansion of the stator slot current density includes the following steps:

step S41: obtaining the current density in the jth stator slot according to the structure of the stator winding:

in the formula, J_j1The current density of the first coil side of the jth stator slot is shown; j. the design is a square_j2The current density of the second coil side of the jth stator slot is shown;

step S42: obtaining a mirror image waveform of the current density of the jth slot according to the distribution of the current density, and performing Fourier series expansion on the mirror image waveform to obtain:

wherein the content of the first and second substances,

further, in step S8, the continuous condition satisfied between the adjacent subfields includes:

the rotor slot sub-region and the inner air gap sub-region satisfy:

the inner air gap sub-region, the stator slot sub-region and the permanent magnet slot air gap sub-region satisfy:

the space between the permanent magnet slot air gap subdomain and the permanent magnet subdomain satisfies:

the permanent magnet sub-region and the outer air gap sub-region satisfy:

further, in step S10, the obtaining of the magnetic voltage drop specifically includes:

step S101: when the magnetic saturation coefficient of the stator is calculated, the slotting effect of a rotor core is ignored, and the rotor is assumed to be a linear core; when the magnetic saturation coefficient of the rotor is calculated, the slotting effect of the stator core is ignored, and the stator is assumed to be a linear core;

step S102: calculating the radial component of the inner air gap flux density and the tangential component of the permanent magnet slot air gap subdomain flux density according to the flux density distribution expression of step S9:

in the formula, B_2rA radial component of magnetic density for the inner air gap subdomain; b is_4kθIs the tangential component of the magnetic flux density of the k-th permanent magnet slot air gap subdomain;

step S103: calculating the magnetic flux flowing through the xth stator tooth, the yth permanent magnet slot and the z-th rotor tooth:

in the formula phi_stlxRepresents the magnetic flux of the lower part of the x-th stator tooth; phi_pmsyRepresents the flux of the y-th permanent magnet slot; phi_ryzRepresents the flux of the z-th rotor yoke;

step S104: calculating the magnetic flux of the upper half of the x-th stator tooth:

in the formula phi_stuxRepresenting the magnetic flux at the upper part of the x-th stator tooth;

step S105: and calculating the magnetic densities of the lower half part and the upper half part of the x-th stator tooth and the magnetic density of the z-th rotor tooth:

in the formula, B_stlxRepresenting the magnetic density of the lower part of the x-th stator tooth; b is_stuxRepresenting the magnetic density of the upper part of the x-th stator tooth; phi_ryzRepresents the flux density of the z-th rotor yoke;

step S106: and calculating the magnetic pressure drop of the lower half part and the upper half part of the x-th stator tooth and the magnetic pressure drop of the z-th rotor tooth according to the B-H characteristic curve of the stator core:

V_rtz＝H_rtzl_rt； (58)

in the formula I_stIs the radial length of the stator teeth; l_rtIs the rotor tooth radial length; h_stlxAnd H_stuxRespectively representing the magnetic field intensity of the lower half part and the upper half part of the x-th stator tooth; h_rtzRepresenting the magnetic field strength of the z-th rotor tooth.

Compared with the prior art, the invention has the following beneficial effects:

1. compared with the traditional finite element analysis method, the method has high calculation speed, greatly reduces the calculation time, and does not need to pay high authorization cost required by commercial finite element analysis software authorization;

2. compared with an equivalent magnetic network method, the method disclosed by the invention does not need complex and complicated model construction and reconstruction work sensitive to structural parameters of the motor, does not need multiple iterations, and greatly shortens the calculation time;

3. by the magnetic saturation compensation method in the method, the problem of local magnetic saturation of the iron core under the condition of large current of the bearingless flux switching motor is solved, and the calculation precision of the electromagnetic field after the local magnetic saturation of the motor is improved.

Drawings

Figure 1 is a cross-sectional view of a BFSPMM of an embodiment of the present invention.

Fig. 2 illustrates the sub-domain partitioning and slot location definition of the BFSPMM according to an embodiment of the present invention.

Fig. 3 is a jth stator slot current density distribution of a BFSPMM of an embodiment of the present invention.

Fig. 4 is a magnetic flux distribution for calculating a saturation coefficient of a stator according to an embodiment of the present invention.

Fig. 5 is a magnetic flux distribution for calculating a saturation coefficient of a rotor according to an embodiment of the present invention.

FIG. 6 is a flowchart illustrating a method according to an embodiment of the present invention.

FIG. 7 is a radial component of the flux density of the air gap at saturation for an embodiment of the present invention. Wherein (a) is theta₀In the case of 9 °, (b) is θ₀18 deg. is the case.

FIG. 8 is a radial component of load gap flux density at saturation for an embodiment of the present invention. Wherein (a) is theta₀In the case of 9 °, (b) is θ₀18 deg. is the case.

FIG. 9 is a graph comparing electromagnetic torque at saturation for an embodiment of the present invention.

FIG. 10 is a graph comparing the levitation forces at saturation for embodiments of the present invention. Wherein (a) is F_xAnd (b) is F_y。

Detailed Description

The invention is further explained below with reference to the drawings and the embodiments.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As shown in fig. 1, the BFSPMM studied in this example is an 12/10-pole structure, and its topology is shown in fig. 1. The stator part consists of 12U-shaped iron cores, and a permanent magnet alternately magnetized along the tangential direction is clamped between two adjacent U-shaped iron cores; the rotor portion is formed by stacking silicon steel sheets, and has 10 teeth in total. The motor has six-phase windings, each phase winding is formed by connecting two coil groups in series, for example, the A-phase winding is formed by A1 and A2 coils. The motor is in a single-winding structure, so that a torque current component i for controlling the tangential rotation of the rotor is simultaneously introduced into the six-phase winding_AT～i_FTAnd controlling the levitation current component i of the radial levitation of the rotor_AS～i_FS。

This embodiment defines an x-y rectangular spatial coordinate system, with x being the horizontal axis and coinciding with the stator a1 coil axis and y being the vertical axis and coinciding with the a2 coil axis. Defining θ in FIG. 1₀Is the position angle of the rotor; beta is a_rIs the rotor slot opening width; beta is a_sIs the stator slot opening width; beta is a_fThe width of an opening between two adjacent U-shaped iron cores (permanent magnet slots); r₁Is the rotor slot inner diameter; r₂The rotor slot outside diameter; r₃Is the inner diameter of the stator slot; r₄The outer diameter of the stator slot; r₅Is the permanent magnet slot inner diameter; r₆Is the outer diameter of the permanent magnet slot. The proposed subdomain model analysis method is calculated in a two-dimensional polar coordinate system (r, θ), where the r-axis coincides with the x-axis.

Among the various analytical methods, the sub-domain model method has higher accuracy. Therefore, the present embodiment proposes a saturation effect compensation method based on a sub-domain model method, which considers the magnetic saturation of the stator and rotor cores according to the B-H characteristics of the actual cores.

The embodiment provides a method for acquiring electromagnetic field performance of a bearingless flux switching motor, which specifically comprises the following steps:

dividing the whole motor into 6 subdomains, including a rotor slot subdomain, an internal air gap subdomain, a stator slot subdomain, a permanent magnet slot air gap subdomain, a permanent magnet subdomain and an external air gap subdomain; determining the magnetic field distribution of each sub-domain according to the boundary condition between the sub-domains and the iron core and the continuous condition on the interface of the adjacent sub-domains; and calculating the magnetic voltage drop of the corresponding stator and rotor iron cores according to the magnetic field distribution of each sub-domain, and then completing the calculation of the magnetic saturation of the stator and rotor iron cores according to the B-H characteristic curve of the actual iron core, thereby obtaining the electromagnetic performance of the motor under the saturation condition.

The method comprises the steps of firstly, constructing a sub-domain model of electromagnetic field calculation of the bearingless flux switching motor under a linear magnetic circuit; then, in order to consider the saturation effect of the motor core, a magnetic saturation coefficient model of the motor is further constructed based on the sub-domain model; and finally, correcting the electromagnetic field calculated by the sub-field model under the linear magnetic circuit by using the magnetic saturation coefficient to obtain accurate electromagnetic field data. And based on accurate electromagnetic field calculation, performance parameters such as electromagnetic torque, levitation force and the like of the motor are quickly calculated. The method specifically comprises the following steps:

step S1: dividing the BFSPMM into 6 subdomains, as shown in FIG. 2, sequentially comprising a rotor slot subdomain, an internal air gap subdomain, a stator slot subdomain, a permanent magnet slot air gap subdomain, a permanent magnet subdomain and an external air gap subdomain; in addition, in the process of analysis calculation, the spatial position of each groove needs to be determined, so the positions of all the grooves are defined in a two-dimensional polar coordinate system:

in the formula, theta_iIs the centerline position of the ith rotor slot.

According to the electromagnetic field theory, the magnetic field of the motor can be expressed by quantity magnetic potential, vector magnetic potential A is used as a solving variable, and Maxwell equation of the motor is established:

in the formula, mu₀Is a vacuum magnetic conductivity; mu.s_rIs relative magnetic permeability; j is the current density; m is the remanent magnetization vector;

step S2: the rotor slot sub-region satisfies the laplace equation:

in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the rotor slot subfield by adopting a separation variable method according to the Neniemann boundary condition between the subfield and the iron core (according to the Neniemann boundary condition between the rotor slot and the rotor iron core, namely the tangential component of the magnetic field intensity along the bottom and the side of the rotor slot is equal to 0)_1iGeneral solution expression of (1):

in the formula, A_imAnd A_i0The undetermined coefficient of the rotor slot subdomain is obtained; m is the harmonic frequency of the magnetic field of the rotor slot domain; r₁Is the rotor slot inner diameter; r₂Is the rotor slot outer diameter; beta is a_rIs the rotor slot opening width; theta_iIs the centerline position of the ith rotor slot;

step S3: the Laplace equation satisfied by the inner air gap sub-region is:

in a two-dimensional polar coordinate system (r, theta), calculating vector magnetic potential A of an inner air gap sub-domain by adopting a separation variable method according to a neyman boundary condition between the sub-domain and an iron core₂General solution expression of (1):

in the formula, B_1n、B_2n、B_3nAnd B_4nIs the undetermined coefficient of the inner air gap subdomain; n is the harmonic order of the magnetic field of the inner air gap sub-region; r₃Is the stator slot inner diameter;

step S4: the 12/10 pole BFSPMM employs concentrated windings with two coil sides per stator slot. Each coil is attributed to a different winding, so the current density in the jth stator slot can be expressed as:

in order to reduce the computational complexity, the current density is subjected to Fourier series expansion by adopting a mirror image method. A mirror image waveform of the current density of the jth slot can be obtained according to the distribution of the current density, as shown in fig. 3;

the current density waveform is subjected to Fourier series expansion to obtain:

wherein the content of the first and second substances,

the stator slot subfield satisfies the poisson equation:

in a two-dimensional polar coordinate system (r, theta), according to the Neezeman boundary condition between a sub-domain and an iron core, a vector magnetic potential A of a stator slot sub-domain is calculated by adopting a separation variable method_3jGeneral solution expression of (1):

in the formula, C_jpAnd C_j0For stator slot regionsThe undetermined coefficient of (2); p is the harmonic number of the magnetic field of the stator slot sub-region; j. the design is a square_j0And J_jpCoefficients of a Fourier series expansion of the current density of the jth stator slot; r₄Is the stator slot outer diameter; beta is a_sIs the stator slot opening width; theta_jIs the position of the center line of the jth stator slot;

step S5: the magnet slot air gap sub-region satisfies the laplace equation:

in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the air gap sub-field of the permanent magnet slot by adopting a separation variable method according to the Neniemann boundary condition between the sub-field and the iron core_4kGeneral solution expression of (1):

in the formula, D_k1q、D_k2q、D_k20And D_k10The undetermined coefficient of the air gap subdomain of the permanent magnet slot; q is the harmonic frequency of the air gap subdomain magnetic field between the stator cores; r₅Is the permanent magnet slot inner diameter; beta is a_fIs the permanent magnet slot opening width; theta_kIs the centerline position of the kth permanent magnet slot;

step S6: in a two-dimensional polar coordinate system, the remanent magnetization vector can be expressed as:

M＝M_re_r+M_θe_θ；

in the formula, e_rIs the radial component of the unit vector; e.g. of the type_θIs the tangential component of the unit vector;

in the motor topology used, the permanent magnets are alternately magnetized in the tangential direction, so the tangential and radial components of the remanent magnetization vector of each permanent magnet can be expressed as:

the poisson equation satisfied by the permanent magnet subdomains is:

in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the permanent magnet sub-field by adopting a separation variable method according to the Neniemann boundary condition between the sub-field and the iron core_5kGeneral solution expression of (1):

in the formula, E_k1s、E_k2s、E_k20And E_k10Is the undetermined coefficient of the permanent magnet subdomain; s is the harmonic frequency of the magnetic field of the subdomain of the permanent magnet; b is_remIs the remanence of the permanent magnet; r₆Is the permanent magnet slot outer diameter;

step S7: for a flux switching motor, because a permanent magnet is in contact with an external air gap, a part of flux linkage generated by the permanent magnet or an armature reaction is interlinked with the external air gap to form an external leakage flux linkage, so that an external air gap sub-domain is required to be included when sub-domain model calculation is carried out;

the outer air gap sub-domain satisfies the laplace equation:

since the flux linkage is always closed and therefore cannot extend to infinity, the available dirichlet boundary conditions are:

in a two-dimensional polar coordinate system (r, theta), calculating the vector magnetic potential A of the external air gap sub-domain by adopting a separation variable method according to the Neniemann boundary condition between the sub-domain and the iron core₆General solution expression of (1):

in the formula, F_1tAnd F_2tIs the undetermined coefficient of the outer air gap subdomain; t is the harmonic order of the magnetic field of the outer air gap sub-region; r₇Is the radius of the outer air gap;

step S8: establishing the relation between the screwdriver domains according to the continuous conditions met by the adjacent sub domains, and specifically adopting the following formulas:

the four formulas are obtained by the interface constraint of a rotor slot subdomain and an internal air gap subdomain;

the six formulas are obtained by the interface conditions of an internal air gap subdomain, a stator slot subdomain and a permanent magnet slot air gap subdomain;

the above four formulas are obtained by the boundary condition of the interface of the permanent magnet slot air gap subdomain and the permanent magnet subdomain;

the above four formulas are obtained by the boundary condition of the interface of the permanent magnet subdomain and the external air gap subdomain;

step S9: and calculating undetermined coefficients in each general solution expression by adopting numerical analysis software according to the formula of the step S8, and calculating corresponding flux density distribution according to each subdomain vector magnetic potential:

in the formula, B_rRepresents the radial component of flux density; b is_θRepresents the tangential component of flux density;

that is, the 18 relational expressions obtained above are converted into a matrix form, and through simultaneous 18 matrix equations and taking the limited number of the harmonic times of each sub-domain, the undetermined coefficients of each sub-domain can be calculated by using numerical analysis software, and the magnetic field distribution of all the sub-domains can be obtained;

step S10: calculating saturation coefficients of all parts of the stator core and the rotor core:

in the formula, V_stlxAnd V_stuxRespectively representing the magnetic voltage drop of the lower half part and the upper half part of the x-th stator tooth; h_gsxRepresenting the magnetic field strength before the x-th stator tooth; v_rtzRepresents the magnetic pressure drop of the z-th rotor tooth; h_grzRepresenting the magnetic field strength before the z-th rotor tooth;

step S11: the calculation takes into account the radial component of the air gap flux density in the saturation case:

in the formula, B_2rRepresents the radial component of the air gap flux without taking into account saturation; k_satsAnd K_satrRespectively representing stator core and rotorThe saturation factor distribution of the iron core;

step S12: electromagnetic torque T under saturation condition is calculated by adopting Maxwell stress-strain method_eAnd levitation forces F in the x and y directions_xAnd F_y：

Wherein L represents a bearing length of the motor; r_gA radius representing a motor air gap center circumference; b is_{2θ_sat}Representing the tangential component of the air gap flux density.

In this embodiment, in step S8, the continuous condition satisfied between the adjacent subfields includes:

between the rotor slot sub-region and the inner air gap sub-region, it is satisfied that the vector magnetic potential at the interface of each rotor slot and the inner air gap is continuous and the tangential components of the magnetic field strength are equal, from which it follows:

the boundary conditions of the interfaces of the inner air-gap subdomains, the stator slot subdomains and the permanent magnet slot air-gap subdomains are as follows:

the boundary conditions of the interface of the permanent magnet slot air gap subdomain and the permanent magnet subdomain are as follows:

the boundary conditions of the interface of the permanent magnet subdomain and the external air gap subdomain are as follows:

in this embodiment, when a large load is applied or a large levitation current is required, the BFSPMM stator core and the rotor core may enter a saturation state, but the rotor is not fixed, and therefore it is difficult to uniformly consider the saturation effects of the stator and rotor cores by using one saturation factor. Therefore, in this embodiment, an 12/10-pole BFSPMM is taken as an example, and a saturation effect compensation method is proposed, in which the saturation coefficients of the stator core and the rotor core are calculated.

When the saturation factor of the stator core is calculated, the slotting effect of the rotor core is ignored, and assuming that the rotor is a linear core, the magnetic flux distribution for calculating the saturation factor of the stator as shown in fig. 4 can be obtained.

Wherein phi_stl1-Φ_stl24Respectively representing the magnetic flux of the lower parts of the 24 stator teeth; phi_stu1-Φ_stu24Respectively representing the magnetic flux of the upper parts of the 24 stator teeth; phi_sy1-Φ_sy12Respectively represent the magnetic fluxes of the 12 stator yokes; phi_pm1-Φ_pm12Respectively representing the sum of the magnetic flux flowing through the 12 permanent magnets and the leakage magnetic flux outside the permanent magnets; phi_pms1-Φ_pms12Representing the flux of 12 permanent magnet slots respectively.

In order to quantitatively calculate the magnetic flux distribution of the BFSPMM, the relationship between the magnetic field distribution of each sub-domain and the vector magnetic potential can be expressed by means of the sub-domain model proposed above:

for the magnetic flux in the lower part of the stator teeth, it is necessary to obtain a radial flux density distribution in the air gap sub-region, considering that the magnetic flux is mainly in the radial direction. The analytical expression of the radial magnetic density of the air gap subdomain obtained by the formula is as follows:

based on the magnetic field distribution of the air gap sub-regions, the magnetic flux flowing through each stator tooth can be found to be:

then the magnetic density of the lower portion of the stator teeth can be calculated by:

according to the B-H characteristic curve of the stator core, the magnetic field intensity H of the corresponding stator tooth lower part can be obtained_stlxTherefore, the magnetic pressure drop of the lower part of the stator tooth can be calculated:

also for the magnetic flux flowing through the permanent magnet slots, which is mainly in the tangential direction, a tangential flux density distribution of the permanent magnet slot sub-areas needs to be obtained. Then the analytic expression of the tangential flux density of the permanent magnet slot domain is as follows:

based on the magnetic field distribution of the permanent magnet slot sub-regions, the magnetic flux flowing through each permanent magnet slot can be found as:

the flux of the remaining part can be calculated from the flux of the lower part of the stator tooth and the flux of the permanent magnet slot.

Calculating the magnetic flux of the upper part of the stator teeth to obtain:

then the magnetic density of the upper portion of the stator teeth can be calculated by:

according to the B-H characteristic curve of the stator core, the magnetic field intensity H of the upper part of the corresponding stator tooth can be obtained_stuyTherefore, the magnetic pressure drop of the lower part of the stator tooth can be calculated:

for BFSPMM, the stator tooth portion is prone to saturation, while the stator yoke typically operates in a linear regime, so for ease of calculation the magnetic pressure drop of the stator yoke is ignored. And it can be found that when the iron core is not in a saturated state, the magnetic conductivity of the iron core is very large, so that the magnetic voltage drop of the iron core is close to 0; when the iron core enters a saturated state, the magnetic conductivity of the iron core is sharply reduced, and the magnetic voltage drop of the iron core is increased. It follows that the magnitude of the core magnetic voltage drop reflects the degree of saturation of the core. Therefore, the saturation factor of each stator tooth can be defined as:

the stator saturation factor distribution K can be obtained_satsWhich reflects the effect of the saturation effect of the stator core on the air gap field.

When the saturation factor of the rotor core is calculated, the slotting effect of the stator core is ignored, and assuming that the stator is a linear core, the magnetic flux distribution for calculating the saturation factor of the rotor as shown in fig. 5 can be obtained. Wherein phi_rt1-Φ_rt10Respectively representing the magnetic flux of 10 rotor teeth; phi_ry1-Φ_ry10Representing the magnetic flux of 10 rotor yokes, respectively.

Also, the magnetic flux flowing through each rotor tooth can be found as:

then, the magnetic density of the rotor teeth can be calculated by:

according to the B-H characteristic curve of the rotor core, the magnetic field intensity H of the corresponding rotor tooth can be obtained_rtzSo that the magnetic pressure drop of the rotor teeth can be calculated:

V_rtz＝H_rtzl_rt；

similarly, the rotor yoke core is generally in a linear state, and the magnetic pressure drop of the rotor yoke is ignored for the convenience of calculation. Therefore, the saturation factor of each rotor tooth can be defined as:

according to the above formula, the rotor saturation coefficient distribution K can be obtained_satrWhich reflects the effect of the saturation effect of the rotor core on the air gap field.

By combining the saturation coefficients of the stator and the rotor, the nonlinear air gap flux density of the motor can be predicted, and an expression of the radial component of the air gap flux density compensated by the saturation coefficients can be obtained; since the value of the tangential component of the air gap flux density is small, the tangential component of the air gap flux density in the saturated case is substantially consistent with the expression for the tangential component in the saturated case:

B_{2θ_sat}＝B_2θ。

in summary, the program flow chart of the embodiment is shown in fig. 6.

In particular, the present embodiment performs the following validity verification on the above technical solution.

1. And verifying the magnetic density distribution of the saturated air gap. Fig. 7 and 8 are comparisons of air gap flux density radial components at saturation, no load and load, respectively. The remanence of the permanent magnet is expanded to be twice of the original remanence under the no-load condition, the remanence of the permanent magnet is not changed under the load condition, and the amplitude value i of the input current_mLoad current of 30A. From the figure, it can be found that the magnetic flux density radial component calculated by the BFSPMM subdomain modeling method considering magnetic saturation proposed in the present embodiment is close to the simulation result of finite elements. Therefore, the correctness of the BFSPMM subdomain model establishing method considering the magnetic saturation provided by the invention is verified by the comparison result.

2. And verifying the electromagnetic torque and the suspension force. FIG. 9 shows the motor energizing i during one electrical cycle_mThe waveform of the electromagnetic torque at the current of 30A is compared with the waveform of the electromagnetic torque. Fig. 9 shows that the error between the theoretical calculation result and the finite element simulation result is small, which further proves the correctness of the method provided by the embodiment. FIG. 10 shows levitation forces in the x and y directions resulting from the application of a 30A levitation current component to the A-phase windingAnd (4) waveform. The comparison result shows that the analytic calculation result obtained by the method provided by the embodiment is more fit with the finite element simulation, so that the method can be used for the analytic calculation of the suspension force under the saturation condition.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.