A high power density permanent magnet assisted synchronous reluctance machine and a design method thereof

Abstract

The application relates to a high-power-density permanent-magnet-assisted synchronous reluctance motor, which comprises a rotor and magnetic poles, each of which comprises an outermost magnetic barrier and a corresponding permanent magnet, a U-shaped middle magnetic barrier and a corresponding permanent magnet, and a U-shaped innermost magnetic barrier and a corresponding permanent magnet. The outermost magnetic barrier is an embedded arc shape embedded on the surface of the rotor; the permanent magnets of each layer are asymmetrically arranged, and the permanent magnets have two arrangement forms. The first form is that for all the magnetic poles, the permanent magnets of the outermost magnetic barriers are arc-shaped and located on the left side, and the lengths of the permanent magnets located on the left side of the U-shaped outermost magnetic barriers and the U-shaped innermost magnetic barriers are greater than those located on the right side; the second form is that for all the magnetic poles, the permanent magnets of the outermost magnetic barriers are arc-shaped and located on the right side, and the lengths of the permanent magnets located on the right side of the U-shaped outermost magnetic barriers and the U-shaped innermost magnetic barriers are greater than those located on the left side. The application also provides a design method.

Description

Technical Field

[0001] This invention belongs to the field of motor optimization design, specifically relating to a rotor structure optimization design method for a high power density permanent magnet assisted synchronous reluctance motor (PMSRM). Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) are widely used in electric vehicles, aerospace, and industrial production due to their significant advantages such as small size, low loss, and high efficiency. However, PMSMs require a large amount of rare-earth permanent magnet materials, resulting in high cost and unstable supply. To address these issues, PMSMs with lower permanent magnet content have attracted widespread attention. The electromagnetic torque of a PMSM consists of two parts: the permanent magnet torque generated by the permanent magnets and the reluctance torque generated by the difference in inductance between the direct and quadrature axes. Because the permanent magnet torque of a PMSM is relatively low, and the utilization rate of both permanent magnet torque and reluctance torque in traditional rotor structures is low, the power density of traditional PMSMs is low.

[0003] To increase the power density of the PMSRM, it can be achieved by increasing the maximum value of the permanent magnet torque, or by increasing the utilization rate of the total torque to each torque component.

[0004] When optimizing the design of various parameters of a motor, it is necessary to consider not only the mutual influence between multiple optimization variables but also the different performance characteristics of the motor. Therefore, multi-objective optimization design methods are generally adopted. Currently, commonly used multi-objective optimization design methods mainly include genetic algorithms, differential evolution algorithms, and particle swarm optimization algorithms. However, these intelligent optimization algorithms suffer from problems such as complex solution processes and excessively long solution times. In contrast, the Taguchi method, developed by Dr. Genichi Taguchi of Japan, is a low-cost and high-efficiency multi-objective optimization design method. This method can significantly reduce the number of experiments, lower experimental costs, and improve design efficiency, and is currently widely used in the field of motor design. Summary of the Invention

[0005] This invention provides an improved rotor structure for high power density PMSRMs, and its design method is given. On the one hand, by changing the outermost straight magnetic barrier and the built-in straight permanent magnet of each magnetic pole to an embedded arc shape, the maximum value of the permanent magnet torque is improved. On the other hand, by asymmetrically placing the embedded permanent magnet under the same magnetic pole on one side of the arc-shaped magnetic barrier, and asymmetrically placing the straight permanent magnet in the middle of the U-shaped magnetic barrier on both sides of the U-shaped magnetic barrier, the permanent magnet torque is shifted, improving the utilization rate of the total torque for permanent magnet torque and reluctance torque. This structure increases the output torque without increasing the amount of permanent magnets used. Furthermore, to achieve optimal matching of key parameters in the improved structure, the Taguchi method is used to optimize the key parameters of the proposed rotor structure to further increase the output torque and reduce torque fluctuation. The technical solution is as follows:

[0006] A high-power-density permanent magnet assisted synchronous reluctance motor includes a rotor and magnetic poles. Each magnetic pole includes an outermost magnetic barrier and a corresponding permanent magnet, a U-shaped middle magnetic barrier and a corresponding permanent magnet, and a U-shaped innermost magnetic barrier and a corresponding permanent magnet. The outermost magnetic barrier is an embedded arc shape, embedded in the rotor surface. The permanent magnets in each layer are asymmetrically placed, with two placement configurations: First, for all magnetic poles, the permanent magnets of the outermost magnetic barrier are arc-shaped and located on the left side, and the lengths of the permanent magnets on the left side of both the U-shaped outer and inner magnetic barriers are greater than the lengths of the permanent magnets on the right side; Second, for all magnetic poles, the permanent magnets of the outermost magnetic barrier are arc-shaped and located on the right side, and the lengths of the permanent magnets on the right side of both the U-shaped outer and inner magnetic barriers are greater than the lengths of the permanent magnets on the left side.

[0007] This invention also provides a design method for the high power density permanent magnet assisted synchronous reluctance motor, which utilizes the Taguchi method to optimize the key parameters in the improved structure to achieve the best matching of the key parameters. The steps are as follows:

[0008] 1) Determine the optimization variables of the Taguchi method based on the proposed improved structure. The optimization objectives are to maximize the electromagnetic torque and minimize the torque fluctuation. The constraint is that the amount of permanent magnets used should not be greater than the amount of permanent magnets used in the motor before the improvement.

[0009] 2) The influence of each optimization variable on electromagnetic torque and torque fluctuation and the relative importance of the influence are obtained by means of mean value analysis and variance analysis, so as to realize the matching design of key structural parameters in the improved structure.

[0010] 3. The design method of the high power density permanent magnet assisted synchronous reluctance motor according to claim 2, for the first permanent magnet placement form of the three-layer magnetic barrier, is characterized in that the permanent magnets under the same magnetic pole are named as 1 to 5 respectively, the arc-shaped permanent magnet in the outermost magnetic barrier is permanent magnet 1; the right permanent magnet in the middle magnetic barrier is permanent magnet 2, and the left permanent magnet is permanent magnet 3; the right permanent magnet in the innermost magnetic barrier is permanent magnet 4, and the left permanent magnet is permanent magnet 5; the lengths of permanent magnets 2 to 5 are l2 to l5 respectively, and the selection of optimization variables is as follows: variable A is the angle between the inner side of permanent magnet 1 and the positive X-axis direction, variable B is the angle between the outer side of permanent magnet 1 and the positive X-axis direction, variable C is the length l2 of permanent magnet 2, and variables D and E are respectively:

[0011] D = l3 - l2

[0012] E = l4 - l2 = l5 - l3.

[0013] This invention improves the rotor structure of the PMSRM and optimizes the key parameters of the proposed rotor structure using the Taguchi method, resulting in the following advantages:

[0014] 1. This invention improves the rotor structure of the PMSRM, proposing an improved structure that can increase power density. On one hand, by changing the outermost straight magnetic barrier and the built-in straight permanent magnet of each magnetic pole to an embedded arc shape, the maximum value of the permanent magnet torque is increased. On the other hand, by asymmetrically placing the embedded permanent magnet under the same magnetic pole on one side of the arc-shaped magnetic barrier, and asymmetrically placing the straight permanent magnet in the middle of the U-shaped magnetic barrier on both sides of the U-shaped magnetic barrier, the permanent magnet torque is offset, improving the utilization rate of the total torque to the permanent magnet torque and reluctance torque. Therefore, this structure can improve the torque density of the motor from two aspects: increasing the maximum value of the permanent magnet torque and improving the utilization rate of the total torque to the permanent magnet torque and reluctance torque, thereby increasing the power density of the motor.

[0015] 2. The Taguchi method was used to optimize the key parameters in the improved structure. By analyzing the influence of each optimization variable on torque and torque ripple and the relative importance of the influence, a high power density PMSRM rotor structure with low torque ripple was obtained. Compared with the original structure, the optimized structure increased the total torque by 18% and reduced the torque ripple by 41.45%. Attached Figure Description

[0016] Figure 1 This is the original structure diagram of PMSRM;

[0017] Figure 2 This is a diagram of the improved structure of PMSRM;

[0018] Figure 3A schematic diagram of the optimization variables for improving the structure;

[0019] Figure 4 This is an optimized structure diagram of PMSRM. Detailed Implementation

[0020] This invention provides a rotor structure for high power density PMSRMs. On one hand, by changing the outermost linear magnetic barrier and the built-in linear permanent magnet of each magnetic pole to an embedded arc shape, the maximum value of the permanent magnet torque is increased. On the other hand, by asymmetrically placing the embedded permanent magnets under the same magnetic pole on one side of the arc-shaped magnetic barrier, and asymmetrically placing the linear permanent magnets in the middle of the U-shaped magnetic barrier on both sides of the U-shaped magnetic barrier, the permanent magnet torque is shifted, improving the utilization rate of the total torque for both permanent magnet torque and reluctance torque. This structure increases the output torque without increasing the amount of permanent magnets used. Furthermore, to achieve optimal matching of key parameters in the improved structure, the Taguchi method is used to optimize the key parameters of the proposed rotor structure to further increase the output torque and reduce torque ripple.

[0021] The rotor structure optimization design for high power density PMSRM includes:

[0022] (1) Determine how to improve the torque density of the motor from two aspects: increasing the maximum value of the permanent magnet torque and the utilization rate of the total torque to each torque component, thereby improving the power density of the motor.

[0023] (2) An improved rotor and magnetic pole structure for the motor is proposed to increase the maximum value of the permanent magnet torque and the utilization rate of the total torque to each torque component; the specific improved structure is as follows:

[0024] 1) By changing the outermost linear magnetic barrier of each magnetic pole and the built-in linear permanent magnet to an embedded arc shape, magnetic leakage was reduced, which increased the maximum value of permanent magnet torque by 25.1%.

[0025] 2) By asymmetrically placing the embedded permanent magnets under each magnetic pole on the left side of the arc-shaped magnetic barrier, and asymmetrically placing the straight permanent magnets in the middle of the U-shaped magnetic barrier on both sides of the U-shaped magnetic barrier, where the length of the permanent magnet on the left side of the U-shaped magnetic barrier is greater than the length of the permanent magnet on the right side, the permanent magnet torque is shifted, reducing the current angle difference between the maximum value of the permanent magnet torque and the maximum value of the reluctance torque, thus increasing the utilization rate of the total torque to the permanent magnet torque by 17.5% and the utilization rate of the total torque to the reluctance torque by 3%.

[0026] In summary, the improved structure increased the total electromagnetic torque by 10.3% by improving both the maximum value of the permanent magnet torque and the utilization rate of each torque component. However, the torque fluctuation increased from 15.2% to 20.4%, mainly because the key parameters in the improved structure did not achieve optimal matching. Therefore, further optimization design of the improved structure is still needed.

[0027] (3) The Taguchi method is used to optimize the key parameters in the improved structure to achieve the best match among them. The specific steps for optimization are as follows:

[0028] 1) Determine the optimization variables of the Taguchi method based on the proposed improved structure. The optimization objectives are to maximize the electromagnetic torque and minimize the torque fluctuation. The constraint is that the amount of permanent magnets used should not exceed the amount of permanent magnets used in the original motor.

[0029] 2) The influence of each optimization variable on electromagnetic torque and torque fluctuation and the relative importance of the influence are obtained by means of mean value analysis and variance analysis, so as to realize the matching design of key structural parameters in the improved structure. Compared with the original structure, the total torque of the optimized structure is increased by 18%, and the torque fluctuation is reduced by 41.45%.

[0030] The following describes the implementation of the present invention in detail using a 4-pole 36-slot PMSRM as an example. The parameters of the motor are shown in Table 1.

[0031] Table 1. Specific parameters of PMSRM

[0032] parameter symbol numerical values unit Rated speed <![CDATA[n N ]]> 3000 r / min Rated current <![CDATA[I N ]]> 42 A Extreme logarithm p 2 - Number of stator slots Q 36 - Rotor air gap radius <![CDATA[R r ]]> 89.6 mm Air gap length δ 0.5 mm radius at stator yoke <![CDATA[R s ]]> 132.6 mm motor axial length l 155 mm Remanence of permanent magnets <![CDATA[B r ]]> 1.12 T

[0033] (1) The original structure of PMSRM is as follows Figure 1 As shown, each magnetic pole has three layers of magnetic barriers and three layers of permanent magnets. The outermost magnetic barrier is in the shape of a straight line, and the permanent magnet is located in the middle of the straight line magnetic barrier. The middle and innermost magnetic barriers are U-shaped, and the permanent magnet is located in the straight line position in the middle of the U-shaped barrier.

[0034] (2) Propose such Figure 2 The improved PMSRM structure shown still consists of three magnetic barriers and three permanent magnets per pole. However, the outermost linear magnetic barrier has been replaced with an embedded arc-shaped magnetic barrier, and the linear permanent magnets have been replaced with arc-shaped permanent magnets located on the left side of the embedded arc-shaped magnetic barrier. The middle and innermost magnetic barriers remain U-shaped, but the permanent magnets are asymmetrically placed on both sides of the U-shaped magnetic barrier, with the length of the permanent magnet on the left side of the U-shaped magnetic barrier being greater than the length of the permanent magnet on the right side. The specific steps are as follows:

[0035] 1) By changing the outermost built-in straight permanent magnet of each magnetic pole to an embedded arc-shaped permanent magnet, leakage flux is reduced and the maximum value of permanent magnet torque is increased.

[0036] 2) By placing the embedded permanent magnets under the same magnetic pole asymmetrically on one side of the arc-shaped magnetic barrier, and placing the straight permanent magnets in the middle of the U-shaped magnetic barrier asymmetrically on both sides of the U-shaped magnetic barrier, the permanent magnet torque is shifted, the current angle difference corresponding to the maximum value of the permanent magnet torque and the maximum value of the reluctance torque is reduced, and the utilization rate of the total torque for the permanent magnet torque and the reluctance torque is improved.

[0037] 3) For ease of expression, the permanent magnet (resistance) torque utilization rate is defined as the ratio of the permanent magnet (resistance) torque to the maximum value of the permanent magnet (resistance) torque in the total electromagnetic torque. By decomposing the total electromagnetic torque corresponding to the original and improved structures of the motor, the maximum value and utilization rate of each torque component can be obtained, as shown in Table 2.

[0038] Table 2 Comparison of Torque Results

[0039]

[0040] As shown in Table 2, after adopting the improved structure, the maximum value of the permanent magnet torque increased by 25.1% due to the conversion of the outermost built-in linear permanent magnet to an embedded permanent magnet. The asymmetrical placement of the permanent magnets under the same magnetic pole caused a shift in the permanent magnet torque, resulting in a 17.5% increase in permanent magnet torque utilization and a 3% increase in reluctance torque utilization. The increase in the maximum value of the permanent magnet torque and the shift in the permanent magnet torque axis led to a 10.3% increase in the total electromagnetic torque. However, the torque fluctuation increased from 15.2% to 20.4%, mainly because the key parameters in the improved structure did not achieve optimal matching. Therefore, further optimization of the improved structure is needed to achieve a larger average torque and smaller torque fluctuation.

[0041] (3) The key parameters in the improved structure are optimized using the Taguchi method. The specific steps are as follows:

[0042] 1) To facilitate the description of the optimization variables, permanent magnets under the same magnetic pole are named 1 to 5, such as... Figure 3 As shown, the arc-shaped permanent magnet in the outermost magnetic barrier is permanent magnet 1; the right permanent magnet in the middle magnetic barrier is permanent magnet 2, and the left permanent magnet is permanent magnet 3; the right permanent magnet in the innermost magnetic barrier is permanent magnet 4, and the left permanent magnet is permanent magnet 5; the lengths of permanent magnets 2 to 5 are l2 to l5, respectively. The optimization variables are selected as follows: variable A is the angle between the inner side of permanent magnet 1 and the positive X-axis direction, variable B is the angle between the outer side of permanent magnet 1 and the positive X-axis direction, variable C is the length l2 of permanent magnet 2, the relationship between variable D and the lengths of permanent magnets 2 and 3 is shown in Equation 1, and the relationship between variable E and the lengths of permanent magnets 2 to 5 is shown in Equation 2. The optimization objective is to maximize the average electromagnetic torque and minimize torque fluctuation, and the constraint is that the amount of permanent magnets used is not greater than the amount of permanent magnets used in traditional motors.

[0043] D = l3 - l2(1)

[0044] E = l4 - l2 = l5 - l3(2)

[0045] 2) Based on the structural parameters of the motor, determine the value range of the above five optimization variables. To ensure the asymmetrical placement of the embedded permanent magnets, the minimum value of variable A is 45°. To ensure that the outermost magnetic barrier does not cross the second magnetic barrier, the maximum value of variable B is 69°. In addition, to ensure that permanent magnet 1 provides a path for the flow of magnetic lines of force to permanent magnets 2 and 4 and that the value of A does not exceed the value of B, the maximum value of variable A is 57° and the minimum value of variable B is 57°. That is, the value range of variable A is 45°~57° and the value range of variable B is 57°~69°. To ensure that permanent magnet 2 can provide sufficient permanent magnet torque and does not cross the magnetic barrier, the value range of variable C is 5mm~17mm. To ensure the asymmetrical placement of permanent magnets 2 and 3 and that permanent magnet 3 does not cross the magnetic barrier, the value range of variable D is 0mm~6mm. To ensure that permanent magnets 4 and 5 do not cross the magnetic barrier, the value range of variable E is 4mm~10mm.

[0046] 3) Select four level values ​​evenly according to the value range of each optimization variable, and establish a factor level table, as shown in Table 3.

[0047] Table 3 Factor Level Table

[0048]

[0049] 4) Construct the corresponding orthogonal array L based on the factor level table. 16 (4 5 As shown in Table 4.

[0050] Table 4L 16 (4 5 Orthogonal array

[0051] Number of trials A B C D E 1 1 1 1 1 1 2 1 2 2 2 2 3 1 3 3 3 3 4 1 4 4 4 4 5 2 1 2 3 4 6 2 2 1 4 3 7 2 3 4 1 2 8 2 4 3 2 1 9 3 1 3 4 2 10 3 2 4 3 1 11 3 3 1 2 4 12 3 4 2 1 3 13 4 1 4 2 3 14 4 2 3 1 4 15 4 3 2 4 1 16 4 4 1 3 2

[0052] 5) Calculate the electromagnetic torque T and torque fluctuation T corresponding to the 16 sets of orthogonal tests using finite element software. r The specific calculation results are shown in Table 5.

[0053] Table 5. Test Results

[0054]

[0055]

[0056] 6) The average values ​​of the test results of each group were analyzed. The average values ​​of electromagnetic torque and torque fluctuation at each level of each factor are shown in Table 6.

[0057] Table 6. Average values ​​of each factor at each level

[0058]

[0059] Table 6 shows that the combination of level values ​​for the factors that maximize electromagnetic torque is A(1)B(4)C(4)D(3)E(3), and the combination of level values ​​for the factors that minimize torque fluctuation is A(3)B(4)C(3)D(4)E(1). However, the level values ​​for the factors that maximize electromagnetic torque and minimize torque fluctuation are different. Therefore, in order to comprehensively consider the relative importance of each optimization variable to electromagnetic torque and torque fluctuation, it is necessary to conduct variance analysis on the orthogonal experimental results to obtain the optimal combination of each level of each factor that takes into account both electromagnetic torque and torque fluctuation.

[0060] 7) A variance analysis was performed on the test results of each group. The variances of electromagnetic torque and torque fluctuation under each factor are shown in Table 7.

[0061] Table 7 Variance under each factor

[0062] factor <![CDATA[S T ]]> <![CDATA[S Tr ]]> A 1.78 13.36 B 2.05 10.99 C 8.76 3.25 D 1.36 0.65 E 0.59 0.64

[0063] By comparing the proportion of variance for each factor, we can more intuitively determine the relative importance of each optimization variable to electromagnetic torque and torque fluctuation. The formula for calculating the proportion of electromagnetic torque to the variance for each factor is as follows:

[0064]

[0065] In the formula, K STx Let the variance S Tx The proportion of total variance.

[0066] Similarly, the formula for calculating the percentage of torque ripple in each factor's variance is as follows:

[0067]

[0068] In the formula, K STrx Let the variance S Trx The proportion of total variance.

[0069] The specific results of the variance proportions of electromagnetic torque and torque fluctuation under various factors are shown in Table 8.

[0070] Table 8. Percentage of Differentials

[0071] factor <![CDATA[K STx (%)]]> <![CDATA[K STrx (%)]]> A 12.25 46.27 B 14.1 38.05 C 60.26 11.24 D 9.334 2.24 E 4.06 2.21

[0072] As shown in Table 8, factor C has the greatest impact on electromagnetic torque. Therefore, factor C is selected to maximize electromagnetic torque, i.e., C(4). Factors A and B have the greatest impact on torque fluctuation. Therefore, factor A is selected to minimize torque fluctuation. Since the torque fluctuations of A(1) and A(3) are both small, A(1) or A(3) is selected. Factor B is selected to minimize torque fluctuation, i.e., B(4). Factors D and E have a greater impact on electromagnetic torque than on torque fluctuation. Therefore, factors D and E are selected to maximize electromagnetic torque, i.e., D(3) and E(3). Finally, two combinations of the level values ​​of each optimization variable are determined, namely combination one: A(1)B(4)C(4)D(3)E(3) and combination two: A(3)B(4)C(4)D(3)E(3). Finite element simulation of the two combinations shows that the electromagnetic torque and torque fluctuation of combination one are better than combination two. Therefore, combination one is selected as the final optimized structure. The corresponding motor structure is as follows. Figure 4 As shown.

[0073] 8) By decomposing the total electromagnetic torque of the optimized motor structure, the maximum value and utilization rate of each torque component can be obtained. The specific results corresponding to the original structure and the improved structure are shown in Table 9.

[0074] Table 9: Comparison of Specific Data

[0075]

[0076] As shown in Table 9, although the permanent magnet torque utilization rate of the optimized structure is slightly lower than that of the improved structure, the maximum value of the permanent magnet torque is increased by 33%. Although the maximum value of the reluctance torque of the optimized structure is 11.6% lower than that of the improved structure, the utilization rate of the reluctance torque is further improved, and the total torque is increased by 6.9%. In addition, compared with the original structure, the total torque of the optimized structure is increased by 18%, and the torque fluctuation is reduced by 41.45%, which demonstrates the effectiveness of the optimized structure.

Claims

1. A high power density permanent magnet assisted synchronous reluctance motor, comprising a rotor and magnetic poles, each magnetic pole comprising an outermost magnetic barrier and a corresponding permanent magnet, a U-shaped intermediate magnetic barrier and a corresponding permanent magnet, and a U-shaped innermost magnetic barrier and a corresponding permanent magnet, characterized in that, The outermost magnetic barrier is an embedded arc shape, embedded in the rotor surface. The permanent magnets in each layer are asymmetrically placed, with two placement configurations: First, for all magnetic poles, the permanent magnets in the outermost magnetic barrier are arc-shaped and located on the left side, with the length of the permanent magnets on the left side of both the U-shaped outer and inner magnetic barriers being greater than the length of those on the right side; Second, for all magnetic poles, the permanent magnets in the outermost magnetic barrier are arc-shaped and located on the right side, with the length of the permanent magnets on the right side of both the U-shaped outer and inner magnetic barriers being greater than the length of those on the left side. The Taguchi method is used to optimize the key parameters in the improved structure to achieve the best match. The steps are as follows: 1) Determine the optimization variables of the Taguchi method based on the proposed improved structure. The optimization objectives are to maximize the electromagnetic torque and minimize the torque fluctuation. The constraint is that the amount of permanent magnets used should not be greater than the amount of permanent magnets used in the motor before the improvement. 2) The influence of each optimization variable on electromagnetic torque and torque fluctuation and the relative importance of the influence are obtained by means of mean value analysis and variance analysis, so as to realize the matching design of key structural parameters in the improved structure; For the first type of permanent magnet placement, the permanent magnets under the same magnetic pole are named 1 through 5. The arc-shaped permanent magnet in the outermost magnetic barrier is permanent magnet 1; the right permanent magnet in the middle magnetic barrier is permanent magnet 2, and the left permanent magnet is permanent magnet 3; the right permanent magnet in the innermost magnetic barrier is permanent magnet 4, and the left permanent magnet is permanent magnet 5. The lengths of permanent magnets 2 through 5 are respectively... l 2~ l 5. The selection of optimization variables is as follows: Variables A The angle between the inner side of permanent magnet 1 and the positive X-axis is a variable. B The angle between the outer side of permanent magnet 1 and the positive X-axis direction is a variable. C The length of permanent magnet 2 l 2. Variables D and variables E They are respectively: .

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