Fractional slot concentrated winding induction motor

Abstract

The invention discloses a fractional slot concentrated winding induction motor, and belongs to the technical field of electromechanical equipment. The fractional-slot concentrated winding induction motor comprises a casing, a rotating shaft, a stator core and a fractional-slot concentrated winding, and further comprises a rotor core arranged on the rotating shaft, the rotor core is located in the stator core and the fractional-slot concentrated winding, the side wall of the rotor core is provided with a plurality of first grooves, and the plurality of first grooves are arranged in parallel; the double-squirrel-cage rotor structure comprises two squirrel-cage rings and a plurality of rotor conducting bars, the two squirrel-cage rings are arranged at the two ends of the rotor core respectively, each rotor conducting bar is arranged in one first groove, the plurality of rotor conducting bars are divided into two groups, the two groups of rotor conducting bars are arranged at intervals, one group of rotor conducting bars is electrically connected with one squirrel-cage ring, and the other group of rotor conducting bars is electrically connected with the other squirrel-cage ring. And the other group of rotor conducting bars is electrically connected with the other squirrel cage ring. According to the double-squirrel-cage fractional-slot concentrated winding induction motor, the output performance of the motor can be effectively improved, and low-cost application of the fractional-slot concentrated winding on the squirrel-cage induction motor is realized.

Description

Technical Field

[0001] The invention relates to the technical field of electromechanical equipment, and in particular to a fractional-slot concentrated winding induction motor. Background Art

[0002] Fractional slot concentrated winding technology has been maturely applied in the field of permanent magnet motors due to its advantages such as high slot fill rate and low end copper loss, but its promotion in induction motors has long been constrained by electromagnetic compatibility problems. Traditional design theory is based on the assumption of an ideal sinusoidal magnetic field, which has failed under asymmetric harmonic excitation conditions. Although existing harmonic suppression technologies such as multi-phase phase-shifting windings and star-delta hybrid connection can partially improve the magnetic field quality, they generally have some difficult-to-solve technical problems.

[0003] The technical bottleneck of the above-mentioned fractional-slot concentrated winding induction motor is due to the deep contradiction between the winding characteristics and the energy conversion mechanism of the induction motor: on the one hand, the inherent low-order spatial harmonics of the winding are coupled with the magnetic field of the rotor bars of the squirrel cage rotor, which will significantly affect the coupling of the asynchronous operation mechanism of the motor rotor cage and induce multiple asynchronous torques, including torque characteristic distortion caused by the reverse rotating magnetic field, parasitic oscillation and high-frequency pulsation in the starting stage, resulting in degradation of dynamic performance; on the other hand, the non-uniform distribution of the air gap magnetic field aggravates the local magnetic saturation of the core, induces electromotive force and current on the rotor bars, triggers lateral circulation of the rotor bars and high-frequency additional losses, resulting in significant efficiency attenuation, thereby affecting the electromagnetic torque and starting performance of the induction motor, resulting in unstable electromagnetic torque output of the motor, large torque pulsation, poor starting performance, and poor speed stability during the starting process. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems in the prior art and provide a fractional-slot concentrated winding induction motor, which can improve the problems of unstable electromagnetic torque output and poor starting performance of the induction motor caused by uneven air gap magnetic field, thereby improving the output performance of the motor.

[0005] The present invention provides a fractional slot concentrated winding induction motor, comprising a housing, a rotating shaft, a stator core and a fractional slot concentrated winding, wherein the rotating shaft is rotatably connected to the housing, the fractional slot concentrated winding is arranged on the stator core, and further comprising: A rotor core is arranged on the rotating shaft, the rotor core is located in the stator core and the fractional slot concentrated winding, a side wall of the rotor core is provided with a plurality of first grooves, the plurality of first grooves are arranged in parallel, and a length direction of each first groove is parallel to an axial direction of the rotating shaft; The double-cage rotor structure includes two cage rings and a plurality of rotor bars. The two cage rings are respectively arranged at the two ends of the rotor core. Each rotor bar is arranged in a first groove. The plurality of rotor bars are divided into two groups. The two groups of rotor bars are arranged at intervals. One group of rotor bars is electrically connected to one cage ring, and the other group of rotor bars is electrically connected to the other cage ring.

[0006] Preferably, a plurality of second grooves are evenly distributed on the inner wall of the stator core, the fractional-slot concentrated winding is composed of a plurality of coils, the plurality of coils are divided into three groups, the three groups of coils correspond to a three-phase power supply, each group of coils is electrically connected to its corresponding phase power supply, the three groups of coils are arranged in a manner that the number of slots per pole per phase is 1 / 2, each coil is arranged in two adjacent second grooves on the stator core, and the ends of the coils of each group are electrically connected to each other.

[0007] Preferably, the plurality of coils are arranged in a connection manner of 12 slots and 8 poles.

[0008] Preferably, the plurality of second grooves on the stator core are all skew groove structures.

[0009] Preferably, the rotor core and the stator core are separated by an insulating material layer.

[0010] Preferably, the rotor core and the stator core are both formed by laminating silicon steel sheets.

[0011] Preferably, the ends of each set of coils are connected to each other by welding to form a complete circuit.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: a fractional slot concentrated winding induction motor of the present invention adopts a staggered double cage rotor structure, so that the tooth harmonic order increases, and the higher the tooth harmonic order, the lower the amplitude of the tooth harmonic. The staggered structure reduces the sudden change of air gap permeance by dispersing the position of the rotor bars, making the magnetic field distribution closer to a sine shape. The layout of the staggered cage changes the rotor harmonic order to avoid overlap with the stator harmonic order, thereby reducing the synchronous additional torque of the induction motor. The staggered double squirrel cage rotor structure will significantly affect the stator air gap magnetic field harmonics, effectively weaken the tooth harmonics and higher harmonics in the stator air gap magnetomotive force harmonics, and weaken the influence of magnetomotive force harmonics, thereby improving the uneven air gap magnetic field of the motor caused by the rich magnetomotive force harmonic content of the fractional slot concentrated winding, thereby affecting the electromagnetic torque and starting performance of the induction motor, causing the motor electromagnetic torque output to be unstable, the torque pulsation to be large, the starting performance to be poor, and the speed stability to be poor during the starting process, thereby effectively improving the output performance of the motor and realizing the low-cost application of fractional slot concentrated windings in squirrel cage induction motors.

[0013] The three groups of coils of the fractional slot concentrated winding correspond to the three-phase power supply, and each group of coils is electrically connected to the corresponding phase power supply. The multiple coils are arranged in a way that the number of slots per pole per phase is 1 / 2, so as to achieve the controllability of the harmonic weakening of the magnetomotive force of the fractional slot concentrated winding of the induction motor. The 12-slot 8-pole fractional slot concentrated winding two-rotor squirrel cage induction motor shows unique advantages in structure and performance. Its two rotor squirrel cage structure effectively improves the speed stability of the motor and reduces torque pulsation and various losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of a two-dimensional model of a fractional slot concentrated winding induction motor of the present invention; Figure 2 A three-dimensional schematic diagram of a squirrel cage rotor of a fractional slot concentrated winding induction motor of the present invention; Figure 3 A three-dimensional schematic diagram of a rotor cage of a fractional-slot concentrated winding induction motor according to the present invention; Figure 4 It is a schematic diagram of the connection of the armature winding of the fractional slot concentrated winding induction motor of the present invention; Figure 5 It is a three-dimensional schematic diagram of the armature winding of the fractional slot concentrated winding induction motor of the present invention; Figure 6 A three-dimensional schematic diagram of a double-squirrel cage induction motor with fractional slot concentrated windings according to the present invention; Figure 7 The spatial distribution of magnetomotive force of the armature winding of the present invention; Figure 8 This is a spectrum analysis diagram of the armature winding of the present invention; Fig. 9 This is a simulation comparison flow chart of the startup process of the present invention; Fig.10 A comparison diagram of the starting speeds of the single-cage rotor structure and the double-cage rotor structure of the present invention; Fig.11 A comparison diagram of starting torques between a single-cage rotor structure and a double-cage rotor structure of the present invention; Fig.12 A comparison diagram of the core loss during the rated speed rotation of the single-cage rotor structure and the double-cage rotor structure of the present invention; Fig.13 This is a comparison diagram of eddy current losses during the rated speed rotation of the single-cage rotor structure and the double-cage rotor structure of the present invention.

[0015] Description of reference numerals: 101. stator core, 102. fractional-slot concentrated winding, 103. coil, 104. second groove, 105. rotor core, 106. first groove, 107. rotor bars, 108. rotating shaft, 109. squirrel cage ring. DETAILED DESCRIPTION

[0016] The following is combined with Figure 1-Figure 13 , the specific implementation of the present invention is described in detail, but it should be understood that the protection scope of the present invention is not limited by the specific implementation. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] After in-depth research, it is found that the electromagnetic characteristics of a single squirrel cage rotor are difficult to adapt to the multi-band harmonic excitation of the fractional slot concentrated winding 102. In view of this, the present invention proposes to suppress the air gap magnetomotive force harmonics as much as possible by designing a double squirrel cage rotor structure and configuring a rotor cage with an appropriate number of rotor bars 107, thereby achieving the suppression of the harmonic magnetic field.

[0018] like Figure 1-Figure 13 As shown, the fractional slot concentrated winding induction motor provided by the present invention comprises a housing, a rotating shaft 108, a stator core 101 and a fractional slot concentrated winding 102, wherein the rotating shaft 108 is rotatably connected to the housing, and the fractional slot concentrated winding 102 is arranged on the stator core 101. The motor further comprises: a rotor core 105 and a double squirrel cage rotor structure, wherein the rotor core 105 is arranged on the rotating shaft 108, and the rotor core 105 is located inside the stator core 101 and the fractional slot concentrated winding 102, and a plurality of first grooves 106 are arranged on the side wall of the rotor core 105, and a plurality of first grooves 106 are arranged on the side wall of the rotor core 105. The first grooves 106 are arranged in parallel, and the length direction of each first groove 106 is parallel to the axial direction of the rotating shaft 108; the double-cage rotor structure includes two cage rings 109 and a plurality of rotor bars 107, the two cage rings 109 are arranged at both ends of the rotor core 105, each rotor bar 107 is arranged in a first groove 106, and the plurality of rotor bars 107 are divided into two groups, and the two groups of rotor bars 107 are arranged at intervals, one group of rotor bars 107 is electrically connected to one cage ring 109, and the other group of rotor bars 107 is electrically connected to the other cage ring 109.

[0019] The working principle of the above embodiment is briefly described: When three-phase AC is applied to the fractional slot concentrated winding 102, a rotating magnetic field is immediately generated in the stator core 101. The speed of the rotating magnetic field (synchronous speed) is With power frequency and the number of poles of the motor is closely related, and the calculation formula is The rotor bars 107 are in the stator rotating magnetic field. According to the law of electromagnetic induction, the rotor bars 107 will cut the magnetic lines of force, thereby generating induced electromotive force and induced current in the rotor bars 107. The rotor bars 107 carrying the induced current are acted upon by electromagnetic force in the stator magnetic field. This electromagnetic force forms an electromagnetic torque on the rotating shaft 108, driving the rotor to rotate in the direction of the stator rotating magnetic field.

[0020] The staggered double squirrel cage rotor structure changes the distribution of the first grooves 106 and increases the number of equivalent first grooves 106 (from the number of first grooves 106 of a single squirrel cage to the number of first grooves 106 of a single squirrel cage). Z total = Z 2. Increase the number of first grooves 106 to two cages Z total =2 Z 2) Increase the harmonic order of the first groove 106 teeth (from a single squirrel cage tooth harmonic, i.e. γ = Z 2 / p ±1 order harmonics become two squirrel cage tooth harmonics, that is γ =2 Z 2 / p ±1st harmonic, where k is a positive integer), the higher the tooth harmonic order, the lower the amplitude of the tooth harmonic. The staggered structure reduces the sudden change of the air gap magnetic permeability by dispersing the position of the rotor bars 107, making the magnetic field distribution closer to a sinusoidal shape. The layout of the staggered cages changes the order of the rotor harmonics to avoid overlap with the stator harmonics, thereby reducing the synchronous additional torque of the induction motor. The staggered double-cage rotor structure will significantly affect the stator air gap magnetic field harmonics and effectively weaken the tooth harmonics and higher harmonics in the stator air gap magnetomotive force harmonics. Therefore, the double-cage rotor structure adopted in the present invention can weaken the influence of magnetomotive force harmonics.

[0021] Then, the number of rotor bars 107 and the number of first grooves 106 for placing the rotor bars 107 in each cage of the double-cage rotor structure are analyzed. , which can be expressed as: ; In the formula, is the number of rotor bars 107 of a single squirrel cage, which may also be referred to as the number of first grooves 106; I is the effective value of the current of a specific order in the double squirrel cage rotor structure; is the magnetomotive force or the spatial harmonic order of the magnetic field; p is the number of motor pole pairs, where p is the magnetomotive force or the spatial harmonic order of the magnetic field; is the current frequency induced in the rotor bars 107 of the double-cage rotor structure, α The electrical angle spacing between the rotor bars 107 of the double-cage rotor structure, α= Based on this analysis, when the number of rotor bars 107 of a single rotor cage is is the maximum non-working space harmonic order value, that is =8, The harmonic of the magnetic field intensity of this order is 0, which means that the harmonic influence of the 8th order non-working harmonic order magnetomotive force in the motor air gap can be minimized.

[0022] According to this analysis, when the number of rotor bars 107 of a single rotor cage is the maximum non-working spatial harmonic order value, i.e., 8, the magnetic field intensity harmonic of this order is 0, which means that the influence of the 8th order non-working harmonic order magnetomotive force harmonic in the motor air gap can be minimized, and the influence of the 8th order non-working harmonic order magnetomotive force harmonic can be effectively weakened. At this time, the number of rotor bars 107 of each cage of the motor is 8, and a double-cage rotor structure is staggered, and the total number of first grooves 106 for placing rotor bars 107 in the motor is 16.

[0023] The fractional-slot concentrated winding induction motor of the present invention can improve the uneven air gap magnetic field of the motor caused by the rich harmonic content of the fractional-slot concentrated winding magnetomotive force, thereby affecting the electromagnetic torque and starting performance of the induction motor, causing the problems of unstable electromagnetic torque output of the motor, large torque pulsation, poor starting performance, and poor speed stability during the starting process. Therefore, the output performance of the motor can be effectively improved, and the low-cost application of the fractional-slot concentrated winding on the squirrel-cage induction motor can be realized.

[0024] As a preferred solution, Figure 1 and Figure 5 As shown, a plurality of second grooves 104 are evenly distributed on the inner wall of the stator core 101, the fractional slot concentrated winding 102 is composed of a plurality of coils 103, the plurality of coils 103 are divided into three groups, the three groups of coils 103 correspond to a three-phase power supply, each group of coils 103 is electrically connected to its corresponding phase power supply, the three groups of coils 103 are arranged in a manner that the number of slots per pole per phase is 1 / 2, each coil 103 is arranged in two adjacent second grooves 104 on the stator core 101, and the ends of each group of coils 103 are electrically connected to each other.

[0025] As a preferred solution, Figure 1 , Figure 4 and Figure 1-Figure 13 As shown, the multiple coils 103 are arranged in a connection manner of 12 slots and 8 poles.

[0026] The three groups of coils 103 of the fractional slot concentrated winding 102 correspond to the three-phase power supply, each group of coils 103 is electrically connected to its corresponding phase power supply, and the multiple coils 103 are arranged in a manner that the number of slots per pole per phase is 1 / 2, so as to achieve the controllability of the harmonic weakening of the magnetomotive force of the fractional slot concentrated winding of the induction motor. Figure 4 1-12 represent the serial numbers of the plurality of second grooves 104 .

[0027] The plurality of coils 103 are connected in order according to the connection mode of the 12-slot 8-pole fractional slot concentrated winding 102, and the ends of the coils 103 are connected to each other by welding or the like to form a complete circuit; The calculation formula for the number of slots per pole per phase q of a 12-slot 8-pole motor is: ; in: Z=12 (total number of slots); 2p=8 (number of magnetic poles), so p=4; m is the number of phases; Three-phase motor (m = 3): ; Then the number of slots per pole per phase is 0.5, which belongs to fractional slot winding.

[0028] First, since the fractional slot concentrated winding 102 has rich magnetomotive force harmonic content, in order to reduce the influence of magnetomotive force harmonic content on the induction motor, the winding connection method with fewer slots and fewer poles is selected as much as possible. The induction motor with 12 stator slots has a larger tooth width, a more compact structure, and a larger starting torque. When the number of slots per pole per phase is 0.5, the number of motor slots and poles is 12 slots and 8 poles, the working magnetomotive force harmonic is 4 times, and the non-working magnetomotive force harmonic order is k times the working harmonic order. Except for the magnetomotive force working harmonic, the maximum non-working order magnetomotive force harmonic is the 8th spatial harmonic. There is no low-order harmonic lower than the 4th magnetomotive force working harmonic. It is only necessary to weaken the influence of the 8th spatial harmonic. Therefore, the magnetomotive force harmonic order under this number of slots and poles is adjustable.

[0029] Electromagnetic torque pulsation comparison: Fig.11 As shown, during the motor starting process, the electromagnetic torque pulsation of the two rotor cage structures of the 12-slot 8-pole fractional-slot concentrated winding 102 is smaller than the electromagnetic torque pulsation of the 12-slot 8-pole single rotor cage structure, which reduces the torque pulsation caused by the use of the fractional-slot concentrated winding 102 to a certain extent.

[0030] Loss comparison: When the motor rotates at rated speed, Fig.12 As shown, the core loss of the double-cage rotor structure with 12 slots and 8 poles and fractional-slot concentrated winding 102 is smaller than the core loss of the single-cage rotor structure with 12 slots and 8 poles; Fig.13 As shown, the eddy current loss of the two rotor cages of the 12-slot 8-pole fractional-slot concentrated winding 102 is smaller than the eddy current loss of the single rotor cage of the 12-slot 8-pole.

[0031] Magnetomotive force analysis: Fig. 9As shown, the spatial distribution of the magnetomotive force of the 12-slot 8-pole armature winding and its spectrum analysis diagram show that the working magnetomotive force harmonic with a spatial order of 4 is about 0.4135 ampere-turns, and the non-working magnetomotive force harmonic with a spatial order of 8 is about 0.2067 ampere-turns.

[0032] Simulation experiment: Preparation Figure 1 The simulation model of the two-dimensional 12-slot 8-pole fractional-slot concentrated winding induction motor shown in Fig. 9 ), set the three-phase power excitation, set the load torque of the induction motor according to the design target, set the motor starting speed to 0rpm, set the simulation time and step size, and start the starting process simulation.

[0033] Speed ​​comparison: from Fig.10 It can be seen that the rated speed of the single rotor cage motor with 12 slots and 8 poles and fractional slot concentrated winding 102 is about 644 rpm, and the speed fluctuation value is about 118 rpm; the rated speed of the motor with 12 slots and 8 poles and double cage rotor is about 700 rpm, and the speed fluctuation value is about 40 rpm. Compared with the single rotor cage structure, the double cage rotor structure has a higher rated speed, a smaller speed fluctuation value, and a higher speed stability.

[0034] In summary, the 12-slot 8-pole fractional-slot concentrated winding 102 double rotor squirrel cage induction motor shows unique advantages in structure and performance. Its double squirrel cage rotor structure effectively improves the speed stability of the motor and reduces torque pulsation and various losses.

[0035] As a preferred solution, Figure 5 As shown, the multiple second grooves 104 on the stator core 101 are all skewed slot structures. The use of a double squirrel cage rotor structure for the slot-pole induction motor and setting the multiple second grooves 104 on the stator core 101 as skewed slot structures can weaken the influence of non-working order magnetomotive force harmonics in the air gap, thereby improving the problem of unstable electromagnetic torque output and poor starting performance of the induction motor caused by unevenness, thereby ensuring good output performance of the motor. Through this technical means, the purpose of improving the air gap magnetic field is achieved, and the influence of magnetomotive force harmonics rich in magnetomotive force of fractional slot concentrated winding on the induction motor is reduced.

[0036] As a preferred solution, Figure 6 As shown, the rotor core 105 is separated from the stator core 101 by an insulating material layer. The rotor core 105 is separated from the stator core 101 by the insulating material layer, thereby ensuring the electrical properties of the entire motor, thereby ensuring the performance of the entire motor.

[0037] As a preferred solution, Figure 2As shown, the rotor core 105 and the stator core 101 are both made of laminated silicon steel sheets. The silicon steel sheets themselves have a certain resistivity. Compared with ordinary steel, the use of silicon steel sheets as the rotor core 105 and the stator core 101 can effectively hinder the flow of eddy currents. At the same time, the silicon steel sheets are laminated and the sheets are insulated from each other, which further cuts off the path of the eddy current, so that the eddy current can only flow in each silicon steel sheet, greatly reducing the flow area of ​​the eddy current, thereby significantly reducing the eddy current loss.

[0038] As a preferred solution, Figure 5 and Figure 6 As shown, the ends of each group of coils 103 are connected to each other by welding or the like to form a complete circuit.

[0039] The fractional-slot concentrated winding induction motor of the present invention can improve the problems of unstable electromagnetic torque output and poor starting performance of the induction motor caused by uneven air gap magnetic field, thereby improving the output performance of the motor.

[0040] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. A fractional slot concentrated winding induction motor, comprising a housing, a rotating shaft (108), a stator core (101) and a fractional slot concentrated winding (102), wherein the rotating shaft (108) is rotatably connected to the housing, and the fractional slot concentrated winding (102) is arranged on the stator core (101), characterized in that: Also includes: A rotor core (105) is disposed on the rotating shaft (108); the rotor core (105) is located inside the stator core (101) and the fractional slot concentrated winding (102); a side wall of the rotor core (105) is provided with a plurality of first grooves (106); the plurality of first grooves (106) are arranged in parallel, and the length direction of each first groove (106) is parallel to the axial direction of the rotating shaft (108); A double-cage rotor structure comprises two cage rings (109) and a plurality of rotor bars (107), wherein the two cage rings (109) are disposed at two ends of a rotor core (105), each rotor bar (107) is disposed in a first groove (106), the plurality of rotor bars (107) are divided into two groups, the two groups of rotor bars (107) are disposed at intervals, one group of rotor bars (107) is electrically connected to one cage ring (109), and the other group of rotor bars (107) is electrically connected to the other cage ring (109).

2. The fractional-slot concentrated winding induction motor according to claim 1, characterized in that: A plurality of second grooves (104) are evenly distributed on the inner wall of the stator core (101); the fractional-slot concentrated winding (102) is composed of a plurality of coils (103); the plurality of coils (103) are divided into three groups; the three groups of coils (103) correspond to a three-phase power supply; each group of coils (103) is electrically connected to its corresponding phase power supply; the three groups of coils (103) are arranged in a manner such that the number of slots per pole per phase is 1 / 2; each coil (103) is arranged in two adjacent second grooves (104) on the stator core (101); and ends of each group of coils (103) are electrically connected to each other.

3. The fractional-slot concentrated winding induction motor according to claim 2, characterized in that: The multiple coils (103) are arranged in a 12-slot 8-pole connection manner.

4. The fractional-slot concentrated winding induction motor according to claim 2, characterized in that: The plurality of second grooves (104) on the stator core (101) are all inclined groove structures.

5. The fractional-slot concentrated winding induction motor according to claim 2, characterized in that: The rotor iron core (105) and the stator iron core (101) are separated by an insulating material layer.

6. The fractional-slot concentrated winding induction motor according to claim 1, characterized in that: The rotor iron core (105) and the stator iron core (101) are both formed by laminating silicon steel sheets.

7. The fractional-slot concentrated winding induction motor according to claim 1, characterized in that: The ends of each set of coils (103) are connected to each other by welding to form a complete circuit.

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