A rotor with low electromagnetic torque pulsation and low noise and its parameterized modeling method

Abstract

The present invention discloses a rotor with low electromagnetic torque pulsation and low noise and a parametric modeling method thereof, and relates to the field of motor technology, wherein the rotor structure comprises a rotor core, a plurality of magnetic poles are evenly arranged along the circumference of the rotor core, each of the magnetic poles is formed by two magnetic steels, a magnetic isolation bridge is arranged between two adjacent magnetic poles in the rotor core, and the outer contour of the rotor core is cut into a piecewise inverse cosine function curve. This rotor structure can effectively reduce electromagnetic torque pulsation. In addition, due to the sinusoidalization of the air gap magnetic density, the harmonic amplitude of the air gap magnetic density is reduced, so that the electromagnetic radial force is reduced, thereby achieving vibration reduction and noise reduction of the motor.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and in particular to a rotor with low electromagnetic torque pulsation and low noise and a parameterized modeling method thereof. Background Art

[0002] In recent years, with the rapid development of electric vehicles, people's requirements for driving comfort have become higher and higher. Noise, vibration and harshness are one of the most important performance indicators of automobiles. As one of the key components of electric vehicles, the performance of the drive motor determines the main performance of electric vehicles.

[0003] Permanent magnet synchronous motors have the advantages of simple structure, reliable operation, low loss, high efficiency, and flexible size, and are widely used in the drive of electric vehicles. The vibration and noise of the motor is one of the problems that need to be solved urgently. The sources of motor noise can be roughly divided into three categories: aerodynamic noise, mechanical noise, and electromagnetic noise. For permanent magnet synchronous motors, electromagnetic noise is the main motor noise.

[0004] The electromagnetic noise of permanent magnet synchronous motors is mainly caused by the radial force applied to the stator teeth. Since the radial electromagnetic force depends on the air gap flux density, many scholars have reduced the electromagnetic noise by reducing the harmonics of the air gap flux density, but no one has proposed a corresponding rotor structure to solve the electromagnetic noise problem of permanent magnet synchronous motors. Summary of the invention

[0005] In order to solve the above problems, the present invention discloses a rotor which can effectively reduce electromagnetic torque pulsation and noise at the same time.

[0006] In order to achieve the above purpose, the present invention provides the following technical solution: a rotor with low electromagnetic torque pulsation and low noise, comprising a rotor core, wherein a plurality of magnetic poles are evenly arranged along the circumference of the rotor core, each of the magnetic poles is formed by two magnetic steels, and a magnetic isolation bridge is arranged between two adjacent magnetic poles in the rotor core, and the outer contour of the rotor core is cut into a piecewise arccosine function curve, and the piecewise arccosine function curve of the outer contour of the rotor core is determined by the following formula:

[0007]

[0008] In the formula, l g (θ) is the air gap length, B m is the air gap flux density generated by the magnetic steel when the rotor is not changed, l g is the initial length of the air gap, and k is the amplitude of the air gap flux density after the rotor shape is changed.

[0009] In the above scheme: the multiple magnetic poles in the rotor core are arranged alternately as N poles and S poles.

[0010] In the above scheme: the rotor core is formed by stacking nonlinear silicon steel sheets, and magnetic steel slots for accommodating magnetic steel are opened in the rotor core.

[0011] In the above solution: the magnetic isolation bridge is arranged at the connection between the magnetic steel and the edge of the rotor core.

[0012] The parametric modeling method of a rotor with low electromagnetic torque pulsation and low noise comprises the following steps:

[0013] S1: Parameter acquisition:

[0014] 1). Calculate the air gap magnetomotive force generated by the rotor magnets when no load

[0015]

[0016] In the formula, F m is the magnetic potential generated by the magnetic steel in the air gap, B r is the remanent magnetic density; A m is the cross-sectional area of ​​the magnetic steel; l m is the thickness of the magnetic steel; μ rec A is the recovery permeability of the magnetic steel; g is the cross-sectional area of ​​the air gap, μ0 is the vacuum permeability, l g is the initial length of the air gap;

[0017] 2). Calculate the air gap length function l based on the conventional arccosine function g (θ):

[0018]

[0019]

[0020] In the formula, B m is the air gap flux density generated by the magnetic steel when the rotor is not changed, and k is the amplitude of the air gap flux density after the rotor shape is changed;

[0021] S2: Start ANASYS Electronics Desktop software;

[0022] S3: Draw a motor model, which includes a stator, a rotor, a winding and a magnetic steel;

[0023] S4: Enable the Equation Based Curve function module of ANASYS Electronics Desktop software, input the parameters of step S1 above and plot lg(θ);

[0024] S5: Generate the rotor outer contour curve through Boolean operation.

[0025] Compared with the prior art, the present invention has the following advantages: the outer contour of the rotor core of the present invention is cut into a piecewise arccosine function curve, and the rotor structure can effectively reduce the electromagnetic torque pulsation (in the embodiment, the rotor structure calculated by the piecewise arccosine function can reduce the electromagnetic torque pulsation by 54.16%, from ±2.4Nm to ±1.1Nm);

[0026] In addition, due to the sinusoidalization of the air gap magnetic flux, the harmonic amplitude of the air gap magnetic flux is reduced, so the electromagnetic radial force is reduced, achieving vibration reduction and noise reduction of the motor (the sound pressure level of the electromagnetic noise is reduced by approximately 5 decibels in the embodiment). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the local composition of the rotor;

[0028] Figure 2 Flowchart for parametric modeling;

[0029] Figure 3 It is a schematic diagram of the local components of the motor;

[0030] Figure 4 This is the motor torque simulation diagram;

[0031] Figure 5 This is the motor noise simulation result diagram;

[0032] Figure 6 This is a schematic diagram of the overall structure of the rotor. DETAILED DESCRIPTION

[0033] The present invention will be further explained below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the accompanying drawings, and the words "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0034] Example: See Figure 1-6 , a rotor with low electromagnetic torque pulsation and low noise, comprising a rotor core 3, wherein a plurality of magnetic poles are evenly arranged along the circumference of the rotor core 3, each magnetic pole is formed by two magnetic steels 2, a magnetic isolation bridge 4 is arranged between two adjacent magnetic poles in the rotor core 3, an air slot 5 is arranged between adjacent magnetic isolation bridges 4, and the outer contour of the rotor core 3 is cut into a segmented arccosine function curve, the specific shape of which is shown in FIG. Figure 1 , 3 , 6, the rotor core edge 1, the piecewise arccosine function curve of the outer contour of the rotor core 3 is determined by the following formula:

[0035]

[0036] In the formula, l g (θ) is the air gap length, B m is the air gap flux density generated by the magnet 2 when the rotor is not changed, l g is the initial length of the air gap, k is the amplitude of the air gap flux density after changing the rotor shape;

[0037] The plurality of magnetic poles in the rotor core 3 are alternately arranged as N poles and S poles, and the same pole is in the same column, so as to achieve the effect of magnetic concentration.

[0038] The rotor core 3 is formed by stacking nonlinear silicon steel sheets, and a magnetic steel slot for accommodating the magnetic steel 2 is provided in the rotor core 3 .

[0039] The magnetic isolation bridge 4 is arranged at the connection between the magnetic steel 2 and the edge of the core 3. Since the rotor core 3 is a nonlinear material, the magnetic isolation bridge 4 is often partially saturated to achieve the purpose of reducing magnetic leakage.

[0040] The parametric modeling method of a rotor with low electromagnetic torque pulsation and low noise comprises the following steps:

[0041] S1: Parameter acquisition:

[0042] 1). Calculate the air gap magnetomotive force generated by the rotor magnet 2 when no load

[0043]

[0044] In the formula, F m is the magnetic potential generated by magnet 2 in the air gap, B r is the remanent magnetic density; A m is the cross-sectional area of ​​the magnetic steel 2; l m is the thickness of magnetic steel 2; μ rec A is the recovery permeability of magnetic steel 2; g is the cross-sectional area of ​​the air gap, μ0 is the vacuum permeability, l g is the initial length of the air gap;

[0045] 2). Calculate the air gap length function l based on the conventional arccosine function g (θ):

[0046]

[0047]

[0048] In the formula, B m is the air gap flux density generated by the magnet 2 when the rotor is not changed, and k is the amplitude of the air gap flux density after the rotor shape is changed;

[0049] When calculating directly according to this formula, it is important to note that: (1) The air gap length on both sides of the magnetic steel is infinite in theory, but in practice it needs to be approximated locally. (2) The air gap length in some areas may be less than the minimum air gap length, in which case it is necessary to manually adjust the value of the calculated air gap magnetomotive force;

[0050] S2: Start ANASYS Electronics Desktop software;

[0051] S3: drawing a motor model, which includes a stator, a rotor, a winding and a magnetic steel 2;

[0052] S4: Enable the Equation Based Curve function module of ANASYS Electronics Desktop software, input the parameters of step S1 above and plot lg(θ);

[0053] S5: Generate the rotor outer contour curve through Boolean operation.

[0054] Calculation example:

[0055]

[0056] Then when θ is equal to 0.5π, B m is 0.58T, at which point lg(θ) reaches its minimum value of 0.8mm, so k is equal to 0.58. This gives:

[0057]

[0058] When θ is equal to 0.192π, B m is 0.175T, then lg(θ) is equal to 0.426mm, which is lower than the minimum air gap length. m Adjusted from 0.175T to 0.329T. After adjustment and simplification, B m for:

[0059]

[0060] So

[0061]

[0062] According to the obtained l g (θ), the edge of the rotor core 3 is drawn using the parametric modeling function of the finite element software. The specific process is as follows Figure 2 shown.

[0063] Figure 6 Schematic diagram of the entire motor, which includes a stator core 6 and an armature winding 7 in addition to the rotor core 3 .

[0064] like Figure 4 The figure shows the torque simulation diagram of the rotor of the present invention and the conventional round edge rotor. The finite element simulation software used is ANASYS Electronics Desktop, and the mesh of the rotor surface is encrypted to obtain more accurate results. Under the excitation of the same armature current, the electromagnetic torque of the rotor structure of the present invention is reduced by 1Nm, but the electromagnetic torque pulsation can be reduced by 54.16%. It is reduced from ±2.4Nm to ±1.1Nm, and the attenuation effect is obvious.

[0065] like Figure 5 The figure shows the noise sound pressure levels of the rotor of the present invention and a conventional circular rotor motor. It can be seen that the rotor of the present invention can attenuate noises of most frequencies, and the maximum noise is attenuated by about 5 decibels.

[0066] The present invention modifies the rotor edge shape by means of a segmented arccosine function, so that the air gap magnetic flux density of the motor is closer to a sine when unloaded, and the amplitude of each harmonic of the magnetic flux density is reduced. In the present invention, the rotor magnet is a double-layer type. Compared with a single-layer type, i.e., a "one" or "V" shaped structure, the magnetic potential of the rotor is more complex, so it is necessary to perform segmented processing based on the traditional arccosine function. Ultimately, the goal of reducing electromagnetic torque pulsation and noise is achieved.

[0067] There are many advantages to the sinusoidal distribution of the air gap flux density of the permanent magnet synchronous motor when it is unloaded. When a sinusoidal phase current is used, the phase electromotive force will be more sinusoidal, which will reduce the electromagnetic torque pulsation generated by the motor; secondly, the cogging torque will also be reduced. Since the magnitude of the air gap radial force is proportional to the square of the radial component of the air gap flux density, the spatial distribution of the radial force in the air gap will contain a large number of spatial harmonics, which will also weaken the vibration noise of the motor.

[0068] ANASYS Electronics Desktop is a large-scale general-purpose finite element analysis (FEA) software developed by ANSYS, an American company. It is the fastest growing computer-aided engineering (CAE) software in the world. It can interface with most computer-aided design (CAD) software to achieve data sharing and exchange, such as Creo, NASTRAN, Algor, I-DEAS, AutoCAD, etc.

[0069] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above-mentioned technical features. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims

1. A rotor with low electromagnetic torque pulsation and low noise, characterized in that: The invention comprises a rotor core, wherein a plurality of magnetic poles are evenly arranged along the circumference of the rotor core, each of the magnetic poles is formed by two magnetic steels, a magnetic isolation bridge is arranged between two adjacent magnetic poles in the rotor core, and the outer contour of the rotor core is cut into a segmented arccosine function curve, so that the air gap magnetic flux density of the motor is closer to sine when it is unloaded. The parametric modeling method of a rotor with low electromagnetic torque pulsation and low noise comprises the following steps: S1: Parameter acquisition: 1). Calculate the air gap magnetomotive force generated by the rotor magnet when no-load: In the formula, F m is the magnetic potential generated by the magnetic steel in the air gap, B r is the residual magnetic density; A m is the cross-sectional area of ​​the magnetic steel; l m is the thickness of the magnetic steel; μ rec A is the recovery permeability of the magnetic steel; g is the cross-sectional area of ​​the air gap, μ0 is the vacuum permeability, l g is the initial length of the air gap; 2). Calculate the air gap length function l based on the conventional arccosine function g (θ): In the formula, l g (θ) is the air gap length, B m is the air gap flux density generated by the magnetic steel when the rotor is not changed, l g is the initial length of the air gap, k is the amplitude of the air gap flux density after changing the rotor shape; The piecewise arccosine function curve of the outer contour of the rotor core is determined by formula (3); S2: Start ANASYS Electronics Desktop software; S3: Draw a motor model, which includes a stator, a rotor, a winding and a magnetic steel; S4: Enable the Equation Based Curve function module of ANASYS Electronics Desktop software and input the parameters of step S1 above. g (θ) draw; S5: Generate the rotor outer contour curve through Boolean operation.

2. A rotor with low electromagnetic torque pulsation and low noise according to claim 1, characterized in that: The plurality of magnetic poles in the rotor core are arranged alternately as N poles and S poles.

3. A rotor with low electromagnetic torque pulsation and low noise according to claim 1, characterized in that: The rotor core is formed by stacking nonlinear silicon steel sheets, and a magnetic steel slot for accommodating magnetic steel is provided in the rotor core.

4. A rotor with low electromagnetic torque pulsation and low noise according to claim 1, characterized in that: The magnetic isolation bridge is arranged at the connection between the magnetic steel and the edge of the rotor core.

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