Zhejiang. the University. Journal of Engineering (Engineering Edition) The influence of bookmark0 stator fasteners on the counter-rotating double-rotor permanent magnet motor Zhang Fengge, Chen Jinhua, Liu Guangwei, Li Jin (School of Electrical Engineering, Shenyang University of Technology, Shenyang 110870, Liaoning). The mechanical and electromagnetic effects of the two-rotor permanent magnet motor that caused the counter-rotation of the stator fastener were analyzed. Mechanical aspects: from the selection of the material of the stator fastener, the cooperation with the end cap and the force of the stator. Electromagnetic aspects: The distribution of the magnetic field of the stator core yoke is theoretically derived. The influence of stator fasteners on the air gap magnetic field and the magnetic field distribution of the core is analyzed by the finite element method. The results show that the size, number, shape, placement position and material of the stator fasteners have an important influence on the stator strength, concentricity and magnetic field distribution of the motor.
Fund Project: National Natural Science Foundation of China (50677040) Liaoning Provincial Higher Education Excellent Talent Support Program (2007R28).
Conventional motors mostly include a single-coupled field electromechanical energy conversion device with one electrical port and one mechanical port, while a rotor-winding induction motor controlled by slip energy and a brushless doubly-fed AC motor 111 appearing in recent years are used. It is an electromechanical energy conversion device with a dual electrical port and a single mechanical port. In fact, conceptually, the electromechanical energy conversion device can also be designed in the form of only one electrical port but with two mechanical ports, and both the electrical port and the mechanical port can be used as the input and output of the motor, so-called single electric port double Rotor motor. This kind of motor can have various structures and operating modes, and will lead to many "new members" of the motor family. Its application prospects and fields are also very wide, such as variable-controllable electromagnetic 'gearbox', hybrid electric 1M. Counter-rotating dual-rotor permanent magnet motor, such as automobile and multiple renewable energy combined power generation, has single-input electric port and 2 independent mechanical output ports, which is very suitable as propulsion motor for double-propeller underwater vehicle 141. Only a set of three-phase symmetrical AC power feeding can subtly realize the same speed and different direction rotation of the inner and outer double rotors, which not only greatly simplifies the structure of the mechanical propulsion system, reduces the system volume, reduces the system weight and cost, and has no brush slip. The ring is safer and more reliable. The two-mechanical output of the same speed is realized from the motor itself. However, due to the special structure of the motor, it is necessary to add one to fix the stator and ensure the inner rotor and stator. Fasteners with concentricity between the outer rotors.
This paper analyzes the influence of stator fasteners on the motor of this kind of structure from mechanical and electromagnetic aspects. It mainly analyzes the influence of the size, quantity, shape, material and placement position of the stator fastener on the mechanical and electromagnetic properties of the motor.
1 Mechanical impact analysis 1.1 Material selection The stator fastener not only serves as the axial fixing of the stator silicon steel sheet, but also plays the centering role of the inner and outer air gaps. Therefore, the material selection of the stator fastener is particularly important. Generally, carbon steel materials are commonly used for manufacturing fasteners. If the eddy current loss of the motor is reduced and the strength of the fastener is increased, the non-magnetic stainless steel 1Cr18Ni9Ti can be selected, but since the fastener may be part of the magnetic circuit, the reduction is reduced. Considering the degree of saturation of the core, steel No. 10 can be selected. There are two main functions for the bolt head in the fastener: one is the support or load bearing; the other is the wrenching action. The bolt head is made of a hexagon socket head that is suitable for high strength and can be tightened to a very large extent. However, the counter-rotating double-rotor permanent magnet motor has cogging inside and outside the stator, and cannot be positioned by the cleat or fastening rib on the inner side of the stator, and there is an air gap inside and outside the stator core, and the silicon steel sheet cannot be directly connected to the casing. The housing end cap cannot be used to position the inner and outer air gaps. Therefore, the motor selects the mechanical structure of the stator fasteners to be fastened and positioned from the front and rear sides of the stator core. In this paper, the 11kW 6-pole dual-rotor permanent magnet motor is studied. In order to save the space occupied by the winding end and the whole motor, the motor adopts a ring winding. In order to achieve the counter-rotation of the inner and outer rotors, the current phase sequence on the inner and outer sides of the stator must be reversed. As shown in the winding end connection, there are 6 windings without winding, theoretically just 6 stator fasteners can be placed.
In order to ensure the concentricity of the inner and outer rotors and the intermediate stator, in the mechanical design, the mechanical structure design of each part should consider this factor, especially the connection of the stator fasteners with the front and rear end caps of the stator is the weight of the motor concentricity. The weight of the middle. Initially, the end of the stator fastener is designed to be circular. When connected to the front and rear end caps of the stator, only the cylindrical sides of the six cylinders are matched with the groove faces of the front and rear end caps of the stator to ensure the coaxiality of the entire stator core. Degree, as shown in (a). This will be far more compatible with the seat end face of the common motor to ensure that the accuracy of the coaxiality of the stator core is much worse. Therefore, in order to improve the concentricity of the stator core in the mechanical process, the upper and lower surfaces of the end portions of the stator fastener are respectively convex and concave arc surfaces, as shown in (b). By the fact that the end structure is mated with the rear end surface, it becomes a face-to-face fit, so that the concentricity of the stator core is much higher than that of the line surface.
13 Stator force analysis The mechanical calculation of the strength and stiffness of the stator is an important part of the mechanical performance calculation of the double-rotor motor. It will determine the magnitude of the mechanical stator deformation and the magnitude of the single-sided magnetic pull force. It is the key to the stable operation of the motor. .
In material mechanics, the stator fasteners are beam structures. The overall stator calculation focuses on the strength and stiffness of the stator fasteners. In addition to the material's own influence, it can also reduce the stress on the stator fasteners in a reasonable mechanical structure design. Therefore, in order to reduce the stress on the material, when designing the stator fastener, the following structural improvements are required.
The circular structure: the end of the stator fastener and the stator fastener file adopt a circular structure, which is more effective than the rectangle to improve the bending moment resistance of the structural member.
The front and rear end caps of the stator are close to the stator: the end faces of the front and rear end caps of the stator are as close as possible to the stator without affecting the end of the stator, which can reduce the bending moment arm, thereby reducing the stator fasteners. The influence of the bending moment facilitates the improvement of the load distribution of the stator fasteners.
Variable cross-section structure: The shear stress is the largest at both ends of the stator fastener. In order to reduce the shear stress damage capacity, the diameter of the front and rear end cover of the stator is as thick as possible, but because the stator fastener needs to be placed on the stator core, Therefore, under the premise of not affecting the electromagnetic performance of the motor and covering the tooth gap, the wire diameter is appropriately increased to improve its mechanical strength.
In addition, as much as possible, the diameter of the stator fastener and the rear end of the stator is connected, which is also the maximum bending moment of the stator fastener, because it is also a cantilever beam, which is subjected to shear stress by the entire stator weight. Impact.
From the foregoing, it is found that the sectional view of the stator fastener is as shown in (a), and the physical diagram is as shown in (b).
The radial and tangential electromagnetic forces and torsion conditions experienced by the stator core of such a motor can be disregarded because the radial electromagnetic force can be regarded as the tensile force that the stator and the rotor attract each other in order to reduce the air gap. In the prototype design, the radial force on the stator is eliminated due to the symmetrical double rotor structure. Theoretically, the mechanical tension can be made zero, but the value is actually small. In addition, the electromagnetic torque acting on the stator in the inner and outer rotors is opposite in direction, which not only greatly reduces the tangential magnetic pulling force on the stator but also causes the stator to receive less combined torque, which is beneficial to the fastening of the stator and improves the mechanical stability. .
2 electromagnetic impact analysis 2. stator core magnetic field distribution 2.11 theoretical analysis In order to simplify the analysis, the following assumptions are made: the current in the winding changes sinusoidally with time (actually only considering the fundamental current) the current in the slot (conductor) is concentrated At the center of the groove; the core is not saturated, and the magnetic pressure drop in the core is proportional to the magnetic density.
Based on the above assumptions, the simplest pole pair number 1, the number of slots per phase per phase q = 1 is analyzed, because it is a counter-rotating double-rotation in a three-phase AC motor, the stator windings are symmetrically set, ie ABC The axes of the three-phase windings differ in space by 120° electrical angle, so the fundamental magnetomotive forces generated by the three-phase windings are 120° electrical angles in space. In symmetrical operation, the three-phase currents are also symmetrical, that is, the amplitudes are equal, and the electrical angles differ by 120° in time. Take the axis of the A-phase winding as the coordinate origin of the spatial electrical angle a, and take the positive phase sequence direction as the positive direction of x, and select the moment when the A-phase current reaches the maximum value as the starting point of time. Then, the currents flowing through the three-phase windings are respectively, then, the fundamental vibration of the phase vibration of the phase windings of A, B, C, Ai, Bi, and C is fya=FYicosacos. The synthetic magnetomotive force is a spatial position. The fixed, amplitude magnitude and positive and negative pulse vibrating potentials change with time. Therefore, the amplitude of the fundamental wave and all harmonic flux potentials oscillate in time with the frequency of the current change in the winding. Therefore, when the number of poles of the motor is 2p, when the spatial electrical angle a is 0, tc, 2t, the magnetomotive force is 0, that is, the magnetic density at this position is ideally 0, so when considering the armature magnetic field alone The position of the stator fasteners should be placed in this position.
212 finite element verification The analysis of Section 211 is based on a linear model of core unsaturation, while the permeability of the actual motor is variable. Therefore, in order to obtain the characteristics of the counter-rotating double-rotor motor more accurately, and verify the correctness of the theoretical analysis of section 2.1.1, the finite element method is used to simulate the nonlinear magnetic field of the motor. Modeling and analyzing a dual rotor permanent magnet motor using Ansoft software. The rated speed of the motor is 800r/min, that is, 25ms is an electrical cycle. As shown in the figure, the load magnetic field distribution diagram at a certain moment obtained by finite element analysis, wherein the 120° circular arc line at the center of the stator core yoke portion is a non-model line, just to extract the magnetic induction intensity. As shown, the magnetic induction intensity amplitude curve on the circular arc at 0ms, 5ms, 10ms, 15ms, 20ms, 25ms is obtained by finite element analysis. As can be seen from the figure, the yoke magnetic density curve is spatially fixed, amplitude magnitude and time-varying. In addition, the curve is no longer sinusoidal due to magnetic saturation and excitation potential.
2.2 Influence of stator fasteners on the magnetic field distribution of the motor 2.1 Influence on the air gap magnetic field The number and size of the stator fasteners not only affect the mechanical performance of the double rotor motor, but also affect the direction of the magnetic field lines, occupying a large amount of magnetic circuit space. Increased the saturation of some areas. Moreover, the position is different, and the influence on the magnetic field line is also different. If not designed properly, it will affect the motor magnetic field distribution, AC and DC reactance and the power factor of the motor. Considering that the stator fastener radius is chosen to be 7mm, it is obtained by finite element analysis: yes and no (as long as the properties of the stator fastener are the same as the silicon steel sheet in the analysis), the stator gap fastener, the air gap magnetic The density is basically certain. As shown, the average value of the internal and external air gap magnetic density B amplitude does not change with time, respectively. The effect of 2.22 on the core saturation is analyzed from the actual running state of the motor. The effect, as shown in the Ansoft analysis of the actual running magnetic field strength distribution of the counter-rotating dual-rotor permanent magnet synchronous motor (regardless of stator fasteners). The operating state is from (a) to (d), and the cycle is repeated. It can be seen from the figure that the high magnetic density of the double rotor permanent magnet motor appears in the fixed area, and there is no common part in the physical area where the stator fastener is located. . Conversely, the change in position of the stator fasteners will affect the saturation of the stator core to varying degrees. According to the above finite element magnetic field analysis, the number of stator fasteners is six, and the uniform distribution along the circumference is reasonable, and has little effect on the electromagnetic performance of the motor.
3 Conclusion The size, quantity, shape, placement position and material of the stator fastener have a very important influence on the mechanical properties and electromagnetic properties of the motor. It can be concluded that the stator fastener not only functions as a stator silicon steel sheet. It is axially fixed and serves as a centering action for the three components of the inner rotor-stator-outer rotor. The fastener is designed as a cylindrical variable cross-section structure, and the end of the rear end cover adopts a flat arc shape; (2) from a mechanical point of view, the material should be selected to have a relatively high strength, such as stainless steel, and without covering the teeth. Under the premise of the groove, the diameter of the stator fastener is maximized to increase its mechanical strength; when the stator winding is connected to the three-phase symmetrical current, the stator core is synthesized with a fixed spatial position and a magnitude of the pulse with time. Vibrating magnetic density; magnetic field strength distribution of the counter-rotating double-rotor permanent magnet motor The effect of the stator fastener on the air gap magnetic field is small and negligible, but the placement of the stator fasteners will cause the iron core to be saturated to different degrees; In order to reduce the local saturation of the magnetic tightness of the stator yoke of the motor, the position of the stator fasteners needs to be placed in a place where the magnetic density is small, and these positions are just six positions where the windings are not taken.
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