CN103986261A - A Method of Improving the Air Gap Flux Density Waveform of Permanent Magnet Synchronous Motor - Google Patents

Abstract

The invention relates to a method for improving the air-gap magnetic density waveform of a permanent magnet synchronous motor. The thickness of any point on the magnetization direction of the magnetic steel is from the maximum value of the center thickness to the minimum value H _min of the thickness of both sides, and the linear transition or step Shape transition; determine the width of the magnetic isolation air gap at both ends of the magnetic steel to be 1 to 1.5 times the minimum thickness of the magnetic steel, and the length of the magnetic isolation air gap ensures the thickness requirements of the magnetic isolation bridge designed for the motor. The invention designs the shape of the magnetic steel and the magnetic isolation air gap so that the waveform of the magnetic density in the air gap is sinusoidal. Reduce the harmonic content in the back electromotive force of the motor, reduce the eddy current loss of the motor, reduce the temperature rise, improve the efficiency and improve the performance of the motor.

Description

A Method of Improving the Air Gap Flux Density Waveform of Permanent Magnet Synchronous Motor

technical field

The invention belongs to the technical field of motors, in particular to a method for improving the air-gap flux density waveform of a permanent magnet synchronous motor

Background technique

With the gradual maturity and completeness of the design, development and control technology of permanent magnet synchronous motors, as well as the continuous development of permanent magnets in terms of performance and industrialization, permanent magnet synchronous motors have both good speed regulation characteristics of DC motors and AC motors. Due to the advantages of simple structure, convenient maintenance, stable operation and reliable performance, the demand in various fields is increasing, and the development prospect is getting better and better. At present, permanent magnet synchronous motors are widely used in various servo motors, wind power generation fields, electric vehicle drive fields, and CNC machine tool electric spindle motors. the

However, the harmonic content of the AC winding back electromotive force of the current permanent magnet synchronous motor is relatively large, especially for the fractional slot permanent magnet synchronous motor with embedded concentrated windings, the large back electromotive force harmonic content will increase the eddy current loss of the motor and increase the temperature rise , the efficiency of the motor decreases, which has a serious impact on the performance of the motor. The main reason for the high harmonic content of the back electromotive force in the permanent magnet synchronous motor winding is that the waveform of the air-gap flux density of the motor is poor in sinusoidality, and more even-order harmonics are mixed in, so that the air-gap flux density of the motor presents a trapezoidal wave, so the winding The harmonic content of the back EMF will be relatively large. In the design of salient pole induction motors, designers often use the method of non-uniform air gap to obtain the sinusoidal air gap flux density waveform. However, this method is not suitable for permanent magnet synchronous motors, so it is necessary to find a suitable The method of improving the air-gap flux density waveform of permanent magnet synchronous motor is particularly important. the

Therefore, how to improve the waveform of the air-gap magnetic field and the waveform of the back electromotive force is a technical problem to be solved by those skilled in the art. the

Contents of the invention

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a method for improving the waveform of the air-gap flux density of a permanent magnet synchronous motor, by designing a special-shaped magnetic steel to improve the waveform of the air-gap flux density. the

Technical solutions

A method for improving the air-gap magnetic density waveform of a permanent magnet synchronous motor, characterized in that: the shape of the magnetic steel and the magnetic isolation air gap are designed so that the air-gap magnetic density waveform is sinusoidal, and the design steps are as follows:

Step 1. Determine the minimum value H _min of the thickness of the magnetic steel in the direction of magnetization to be 1-3mm, and the pole arc coefficient α _p to be 0.6-0.95;

Step 2: Determine the maximum value H _max > H _min of the thickness of the magnetic steel in the direction of magnetization;

Step 3: The thickness of any point in the magnetization direction of the magnetic steel is from the maximum value of the center thickness to the minimum value H _min of the thickness of both sides, in a linear transition or a stepped transition;

Step 4: Determine the width of the magnetic isolation air gap at both ends of the magnetic steel to be 1 to 1.5 times the minimum thickness of the magnetic steel, and the length of the magnetic isolation air gap ensures the thickness requirements of the magnetic isolation bridge designed for the motor. the

The maximum value of the thickness of the magnetic steel in the step 2 magnetization direction

The thickness of any point on the magnetic steel magnetization direction of the step 3 Among them: S is the distance from any point in the magnetic steel to the maximum value of the thickness of the magnetic steel in the direction of magnetization of the magnetic steel centerline, and L is the length of the magnetic pole.

The thickness of the magnetic isolation bridge is 1-2mm. the

Beneficial effect

A method for improving the air-gap magnetic density waveform of a permanent magnet synchronous motor proposed by the present invention, the thickness of any point on the magnetization direction of the magnetic steel is from the maximum value of the center thickness to the minimum value H _min of the thickness of both sides, with a linear transition or Step-shaped transition; determine the width of the magnetic isolation air gap at both ends of the magnetic steel to be 1 to 1.5 times the minimum thickness of the magnetic steel, and the length of the magnetic isolation air gap ensures the thickness requirements of the magnetic isolation bridge designed for the motor. The invention designs the shape of the magnetic steel and the magnetic isolation air gap so that the waveform of the magnetic density in the air gap is sinusoidal. Reduce the harmonic content in the back electromotive force of the motor, reduce the eddy current loss of the motor, reduce the temperature rise, improve the efficiency and improve the performance of the motor.

Description of drawings

Figure 1: Schematic diagram of the scheme structure of the sinusoidal change in the thickness of the magnetization direction in Embodiment 1;

Figure 2: Schematic diagram of the structure of the linear variation scheme of thickness in the magnetization direction in Example 2;

Figure 3: Schematic diagram of the structure of the linear variation scheme of thickness in the magnetization direction in Example 3;

In the figure, 1 is the rotor core, 2 is the permanent magnet, 3 is the magnetic air gap, 4 is the axis between poles, and 5 is the axis of magnetic poles. the

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

According to the magnetic circuit Ohm's law, the magnetic flux Φ is equal to the magnetic potential F divided by the magnetic resistance R _m . Under the same magnetic pole of the motor, the magnetic circuit is basically the same, and the magnetic resistance is also basically the same, so the place where the magnetic potential is large will produce larger The magnetic flux will also generate a larger magnetic density in the air gap. According to this principle, as long as the waveform of the magnetic potential generated by the permanent magnet is reasonably controlled, the waveform of the no-load air gap flux density can be controlled. The magnetic potential of the permanent magnet is proportional to the length of the permanent magnet in the direction of magnetization, so the reasonable design of the length of the permanent magnet in the direction of magnetization can control the waveform of the air-gap flux density and achieve the purpose of improving the waveform of the air-gap flux density.

In order to obtain a sinusoidal air-gap flux density waveform, it is necessary to design the magnetic steel so that the thickness in the direction of magnetization changes sinusoidally. The design process is as follows. the

Step 1: Determine the minimum value H _min of the thickness of the magnetic steel in the direction of magnetization and the pole arc coefficient α _p

The minimum value of the thickness of the magnetic steel is mainly limited by the mechanical strength of the magnetic steel and the required magnetic field strength. The thicker the magnetic steel, the stronger the mechanical strength and the greater the magnetic field strength. However, if H _min is too large, it will As a result, the maximum value H _max of the thickness of the magnetic steel in the direction of magnetization will be larger, which will increase the amount of permanent magnet materials, which will not only increase unnecessary costs but also increase the volume of the motor. Therefore, the selection of H _min should comprehensively consider the above factors, and the selection range is more suitable between 1-3mm. The polar arc coefficient α _p has a significant impact on the performance of the motor, so α _p can be selected appropriately according to the design requirements. In the design of the motor, the selection of the polar arc coefficient is generally based on empirical values, and its range is generally 0.6 to 0.95.

Step 2: Determine the maximum value H _max of the thickness of the magnetic steel in the direction of magnetization

In order to obtain a sinusoidal air gap magnetic density, H _max , H _min and α _p need to satisfy the sinusoidal relationship, so H _max can be calculated according to the following formula.

The third step: determine the thickness transition process

The thickness of the permanent magnet will transition from the place where the middle thickness is H _max to the place where the thickness is the thinnest on both sides according to a certain law, and in order to obtain the magnetic potential waveform closest to the sinusoidal waveform, this method adopts the sinusoidal law transition. Suppose the distance between any point in the magnetic steel and the center line of the magnetic steel is S, the thickness of the magnetic steel at this point in the direction of magnetization is H (H _min < H < H _m ) _a , and the length of the magnetic pole is L, then change to a permanent magnet for magnetization The thickness H in the direction can be obtained by the following formula.

Step 4: Design the Magnetic Isolation Air Gap

Since the permanent magnet of the rotor with this structure is thick in the middle and thin on both sides, the magnetic flux leakage between two adjacent magnetic poles is relatively large, so it is very necessary to design a magnetic isolation air gap to reduce the magnetic flux leakage between adjacent magnetic poles. The magnetic isolation air gap is on both sides of the magnetic pole, next to the permanent magnet. The magnetic isolation air gap is rectangular, and its thickness is 1-3mm. It can be adjusted according to the size of the motor. The length is from the bottom of the permanent magnet to the rotor close to the air gap of the motor. There is a magnetic isolation bridge between the magnetic isolation air gap and the edge of the rotor. Due to the limitation of the mechanical strength of the rotor, the mechanical strength of the rotor will deteriorate if the magnetic isolation bridge is too thin, and the magnetic isolation effect is not good if it is too thick. The thickness of the magnetic bridge is more suitable to be 1-2 mm. the

The rotor structure designed according to the above method can optimize the motor air gap flux density waveform to the greatest extent, thereby reducing the harmonic content of the back electromotive force, improving the waveform of the back electromotive force, reducing eddy current loss, reducing the temperature rise of the motor, improving the efficiency of the motor, and improving motor performance. the

However, in the application of general occasions, due to the requirements of the rotor magnetic pole shape on the processing technology, the processing technology requirements in the rotor punching process, and the limitations of various factors such as processing accuracy, it may be difficult to implement according to the above method, so We provide a second method that is relatively easy to implement, which is actually a compromise. the

By observing the air-gap flux density waveform produced by traditional magnets, we found that the top of the air-gap flux density waveform is relatively flat, and the even-order harmonic content is relatively large. This is because the magnetic potential generated by the uniform thickness of the magnet in the direction of magnetization is also uniform. Therefore, as long as the odd harmonics in the permanent magnet magnetic potential waveform are appropriately increased, the air gap flux density waveform can be improved. This is the design idea of the second method, and its difference from the first method is mainly reflected in the second and third steps. In the second step above, it is no longer required that H _max , H _min and α _p must strictly satisfy the formula It is only necessary to ensure that H _max >H _min , and at the same time, the maximum value of the thickness appears in the middle of the magnetic pole, and the minimum value appears on both sides of the magnetic pole. In the third step, it is no longer required that the transition process must transition according to the sinusoidal law, as long as the thickness of the permanent magnet magnetization direction is monotonously transitioned from the thickest part in the middle magnetization direction to the thinnest part in the magnetization direction on both sides, The transition process is not necessarily continuous, it can be a linear transition or a stepped transition.

Specific examples are as follows:

Embodiment 1: The first step is to select the appropriate polar arc coefficient as α _p and the minimum value H _min of the upward thickness of the magnetic steel magnetization side (this example is radial magnetization), where α _p = 0.85, H _min = 2 mm. The second step is based on the formula Calculate the maximum value H _max of the thickness of the magnetic steel in the direction of magnetization to be 8.267mm. The third part transitions from the center line of the magnetic steel thickness H _max to the two sides of the magnetic pole according to the sinusoidal law. The fourth step is to design the magnetic isolation air gap. In this example, the thickness of the magnetic isolation air gap is 2mm, and a 1mm magnetic isolation bridge is left between the magnetic isolation air gap and the edge of the rotor. This solution can optimize the air gap flux density waveform, reduce eddy current loss, and improve motor efficiency. According to this scheme, the structure diagram obtained is shown in Figure 1.

Embodiment 2 and Embodiment 3: Due to the limitations of cost, material strength, manufacturability and other factors in actual design, Embodiment 1 is relatively difficult to realize, so in order to meet the constraints of various factors and achieve the optimal gas The purpose of the gap flux density waveform is now designed in the second method, and this implementation is actually a compromise of scheme 1. The difference from Scheme 1 is that in the second step, H _max is directly selected as 7mm, so that the diameter of the rotor can be reduced. At the same time, the transition is no longer performed according to the sine law, but the transition is directly performed by a linear transition or a stepped transition. This scheme is simple in design, easy to realize, good in manufacturability, and relatively low in production cost. The design result of the linear transition mode is shown in Figure 2, and the design result of the stepped transition mode is shown in Figure 3.

The above design schemes can optimize the air-gap magnetic density waveform to a certain extent, improve the back electromotive force waveform, reduce the temperature rise of the motor, reduce the eddy current loss, and improve the efficiency of the motor. Among them, the implementation scheme 1 has the best effect, but the implementation scheme 2 has the best effect on the processing technology. The requirements are lower, and it is easier to implement, so the first and second options have their own advantages, and the selection depends on the application. the

Claims (4)

1. a method of improving PMSM Air Gap Flux waveform, is characterized in that: design magnet steel shape and every magnetic air gap so that air gap flux density waveform is sinusoid, design procedure is as follows:

Step 1, determine the minimum value H of thickness on magnet steel magnetizing direction _minbe 1～3mm, pole embrace α _pbe 0.6～0.95;

Step 2: the maximum H that determines thickness on magnet steel magnetizing direction _max> H _min;

Step 3: on magnet steel magnetizing direction the thickness of any point by the maximum of center thickness the minimum value H to the thickness on both sides _min, with linear transitions or stairstepping transition;

Step 4: the width every magnetic air gap of determining magnet steel two ends is 1～1.5 times of magnet steel minimum thickness, every the length of magnetic air gap guarantee design of electrical motor every magnetic bridge thickness requirement.

2. improve according to claim 1 the method for PMSM Air Gap Flux waveform, it is characterized in that: the maximum of thickness on the magnet steel magnetizing direction of described step 2

3. improve according to claim 1 the method for PMSM Air Gap Flux waveform, it is characterized in that: the thickness of any point on the magnet steel magnetizing direction of described step 3 wherein: S is that in magnet steel, any point is apart from the peaked distance of thickness on the magnet steel magnetizing direction of magnet steel center line, and L is magnetic pole length.

4. improve according to claim 1 the method for PMSM Air Gap Flux waveform, it is characterized in that: the described thickness every magnetic bridge is 1～2mm.