Design method for low-harmonic winding of three-phase alternating-current motor

Abstract

The invention discloses a three-phase alternating-current motor low-harmonic winding design method, which comprises the following steps of: determining the equivalent slot number qe of each pole and each phase of a three-phase low-harmonic winding according to basic parameters of a motor, dividing an area in an iron core slot of the motor into an upper layer, a middle layer and a lower layer, placing a phase coil of the three-phase winding in a single layer, and determining a phase belt distribution table and a winding connection diagram of the winding; according to the principle that slot current is distributed along the surface of an iron core in a sine mode, the numerical relation of the number of turns of all coils in a phase belt is determined, the turn ratio of all the coils is n1: n2: n3... nqe, the symmetry axis of slot electromotive force in the phase belt is determined, the electrical angles of slot electromotive force phasors relative to the symmetry line are respectively alpha1, alpha2, alpha3... alphaqe, and the range of the number of effective series turns of each phase meeting the motor performance is determined; in consideration of the design principle of the minimum harmonic magnetic potential and the limited slot filling rate, the actual number of turns of the coil in the phase belt is N1, N2, N3... Nqe. According to the invention, the third harmonic electromotive force amplitude of each phase of the motor is reduced, and the motor efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of motor design, and in particular to a low harmonic winding design method for a three-phase AC motor. Background Art

[0002] Three-phase AC motors have the advantages of simple structure, stable operation, and high operating efficiency. They are widely used in modern industrial production, transportation, power systems and other fields. The three-phase winding is the main component of the three-phase AC motor. Although the three-phase windings have different forms, their construction principles are basically the same. These principles are: (1) The waveform of the synthetic magnetic motive force generated by the winding should be close to the sine shape and the amplitude should be large; (2) The magnetic motive force waveform of each phase of the three-phase winding should be symmetrical; (3) The copper loss of the winding should be small and the amount of copper should be saved. Since the surface of the motor core is slotted and each coil of the winding is embedded in the core slot, it is inevitable that there are harmonic components in the synthetic magnetic motive force of the winding. Harmonic magnetic potential components have many adverse effects on the performance of the motor, such as causing vibration noise, generating additional losses, increasing the temperature rise of the motor, and reducing efficiency.

[0003] In order to reduce the harmonic magnetic potential component of the winding, scientific and technological workers have proposed a variety of low-harmonic winding structures, such as star-delta sinusoidal winding, low-harmonic fractional slot winding, concentric unequal turn winding, etc. In a three-phase symmetrical winding, the coil design in any phase band is the same, where the phase band refers to the area occupied by each pole and each phase of the motor. Therefore, different types of low-harmonic winding designs are usually attributed to the coil parameter design within a phase band. For concentric unequal turn windings, its structural feature is that the winding is divided into two layers, upper and lower, which are respectively embedded in the motor slots. Its working principle is to adjust the number of turns of each coil in the phase band so that the slot current is distributed along the surface of the core according to the sinusoidal law to minimize the amplitude of the air gap harmonic magnetic potential. Obviously, the larger the number of adjustable coils, the higher the sinusoidality of the motor slot current waveform. The theoretical turn ratio of the unequal turn winding is a decimal. However, the number of turns of the coils in the actual winding is an integer, that is, the theoretically optimal effect of suppressing the harmonic magnetic potential cannot be achieved. At present, there are existing literatures that have studied this issue, such as the paper "Design and Application of New Single- and Double-layer Concentric Unequal Turn Windings", patent application number CN105958761 A "A Design and Calculation Method for Double-layer Concentric Unequal Turn Windings", and patent application number CN202311600862.3 "A Stator Structure, Design Method and Application of a Three-phase Motor with Unequal Turn Concentric Windings". However, most research results only consider weakening the phase-band harmonic components, while ignoring the third harmonic magnetic potential and the harmonic magnetic potential of multiples of 3 and their induced harmonic electromotive force. Considering the symmetrical connection of the three-phase windings, there is no third harmonic voltage at the winding line end, but a third harmonic circulating current will be generated in the triangle-connected motor, which will lead to increased stray losses and reduced efficiency. Therefore, the existing double-layer unequal turn windings mainly have the following two problems:

[0004] 1. When the number of slots per pole and per phase of the motor is small, the number of adjustable coils in the phase band is small, and the effect of the double-layer unequal turn winding in weakening the harmonic magnetic potential is poor;

[0005] Second, the double-layer unequal-turn winding has limited effect in weakening the third-order and multiple-of-3 harmonic magnetomotive force. Summary of the invention

[0006] In order to solve the technical problems existing in the background technology, the present invention proposes a low harmonic winding design method for a three-phase AC motor.

[0007] The present invention provides a method for designing a low harmonic winding of a three-phase AC motor, comprising the following steps:

[0008] S1. According to the basic parameters of the motor, determine the equivalent number of slots per pole and per phase of the three-phase low harmonic winding q e ,

[0009] S2. Divide the area inside the motor core slot into three layers: upper, middle and lower. Place one phase coil of the three-phase winding in a separate layer. Determine the phase band allocation table and winding connection diagram of the winding.

[0010] S3. According to the principle of sinusoidal distribution of slot current along the core surface, determine the numerical relationship of the number of turns of each coil in the phase belt, and the turn ratio of each coil: n1:n2:n3…n qe , determine the symmetry axis of the slot electromotive force in the phase belt, and the electrical angles of the slot electromotive force phasor relative to the symmetry line are: α1, α2, α3…α qe , calculate the effective series turns N of each phase of the winding k1 :

[0011]

[0012] Where: a is the parallel branch of the winding; α i is the electrical angle of the slot emf phasor relative to the symmetry line;

[0013] S4. Determine the range of effective series turns per phase that meets the motor performance. Considering the design principle of minimum harmonic magnetic potential and limited slot fill rate, the actual turns of the coils in the phase band are: N1, N2, N3...N qe .

[0014] Preferably, the number of slots of the motor in step S1 is Q, the number of poles is 2p, the parallel branch of the winding is a, the number of slots per pole per phase is q=Q / 6p, and the range of the equivalent number of slots per pole per phase is: 2q e ≤3q.

[0015] Preferably, in step S2, the coil of the A-phase winding is placed in the middle layer.

[0016] ​Preferably, in step S3, when q e =5, the symmetry axis of the slot electromotive force phase is on the third slot, so the electrical angles of the slot electromotive force relative to the symmetry line are: 60°, 30°, 0°, 30° and 60°; the effective value of the sinusoidal slot current is I m , the instantaneous current values ​​of phase A, phase B and phase C are i A 、i B and i C , the numerical relationship of the slot current in slots 1 to 5 of the winding is:

[0017] Phase A phase belt 1 slot 1 current value n1i A -n3i B +n5i C =I m cos60°

[0018] Phase A phase belt second slot 2 current value n2i A -n2i B =I m cos30°

[0019] Phase A phase belt 3 slot 3 current value n3i A -n1i B -n5i C =I m cos0°

[0020] Phase A phase belt 4 slot 4 current value n4i A -n4i C =I m cos30°

[0021] Phase A phase belt 5th slot 5 current value n5i A +n1i B -N3i C =I m cos60°.

[0022] Preferably, in step S3, when q e =6, the symmetry axis of the slot electromotive force phase is between the third slot and the fourth slot, so the electrical angles of the slot electromotive force relative to the symmetry line are: 75°, 45°, 15°, 15°, 45° and 75°, and the effective value of the sinusoidal distribution slot current is I m , the instantaneous current values ​​of phase A, phase B and phase C are i A 、i B and i C , the numerical relationship of the slot current in slots 1 to 6 of the winding is:

[0023] Phase A phase belt 1 slot 1 current value n1i A -n4i B +n5iC =I m cos75°

[0024] Phase A phase belt second slot 2 current value n2i A -n 3B i B +n6i C =I m cos45°

[0025] Phase A phase belt 3 slot 3 current value n3i A -n2i B -n6i C =I m cos15°

[0026] Phase A phase belt 4 slot 4 current value n4i A -n1i B -n5i C =I m cos15°

[0027] Phase A phase belt 5th slot 5 current value n5i A +n1i B -n4i C =I m cos45°

[0028] Phase A phase belt slot 6 current value n6i A +n2i B -N3i C =I m cos75°.

[0029] Preferably, in step S4, the effective series turns of the single-layer winding and the double-layer unequal-turn winding are calculated to be N respectively. k单 and N k双 , then the effective series turns range of the new winding is estimated to be N k1 =N k单 ~N k双 , select the effective series turns of the new winding as N k1 , according to N k1 Taking into account the minimum harmonic magnetic potential design, as well as the reduction of slot fill rate and winding copper usage, the actual number of turns of the three-layer unequal-turn winding is determined.

[0030] Preferably, the method further includes calculating three types of winding total harmonic distortion THD:

[0031]

[0032] Where: k dp1 is the fundamental wave winding factor; k dpνis the harmonic winding factor; ν is the order of the harmonic winding magnetic potential;

[0033] It should be noted that the three types of windings include the single-layer winding, double-layer winding and three-layer unequal-turn winding mentioned above.

[0034] Preferably, the parameter k determined in step S3 dp1 It can be expressed as:

[0035]

[0036] The order of the harmonic winding magnetic potential is ν = 3, 5, 7, 9, 11..., and the harmonic winding factor is k dpν It can be expressed as:

[0037]

[0038] In the present invention, the beneficial effects of the proposed three-phase AC motor low harmonic winding structure are:

[0039] 1. Compared with the double-layer unequal-turn winding, the low-harmonic winding in the present invention has more optimization variables, which helps to further weaken the harmonic magnetomotive force component, and the sinusoidality of the motor synthetic magnetomotive force waveform is better;

[0040] 2. Compared with the double-layer unequal-turn winding, the low-harmonic winding in the present invention helps to weaken the third and multiples of 3 harmonic magnetomotive force, reduce the amplitude of the third harmonic electromotive force of each phase of the motor, reduce the third harmonic circulating current and its stray loss in the triangle-connected motor, and improve the motor efficiency.

[0041] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic diagram of the low harmonic winding proposed by the present invention in any slot;

[0043] Figure 2 It is a phase band allocation table for a pair of poles of a 24-slot 4-pole motor in Example 1 of the present invention, wherein the equivalent number of slots per pole per phase of the new winding is 5;

[0044] Figure 3 It is a phase band allocation table for a pair of poles of a 24-slot 4-pole motor in Example 2 of the present invention, wherein the equivalent number of slots per pole per phase of the new winding is 6;

[0045] Figure 4 It is a winding connection diagram under a pair of poles of a new winding motor in Example 1 of the present invention;

[0046] Figure 5It is a winding connection diagram under a pair of poles of a new winding motor in Example 2 of the present invention;

[0047] Figure 6 Schematic diagram of the unequal-turn winding of phase A under a pair of poles of the motor model in Example 1 of the present invention, wherein half of the slots are double-layer windings and the other half of the slots are triple-layer windings;

[0048] Figure 7 It is a schematic diagram of the unequal turn winding of the A phase under a pair of poles of the motor model in the implementation example 2 of the present invention, and all the slots of the stator are three-layer windings;

[0049] Figure 8 is the harmonic winding factor of the control winding scheme and the new winding scheme in embodiments 1 and 2 of the present invention;

[0050] Fig. 9 is the finite element simulation result of the air gap harmonic flux density of the reference winding motor model and the new winding motor model in embodiments 1 and 2 of the present invention;

[0051] Fig.10 It is the finite element simulation result of the stator induced electromotive force of the control winding motor model and the new winding motor model in Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0052] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar symbols throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0053] Take a 1.5kW 4-pole three-phase asynchronous motor as an example. The number of stator slots of the motor is Q = 24, and the number of poles is 2p = 4. Then the number of slots per pole per phase is q = 2, and the equivalent range of slots per pole per phase is 4. e ≤6. To illustrate the advantages of the low harmonic winding of the present invention, two existing winding structures are used as control groups, one is a single-layer concentric winding with 68 turns, and the other is a double-layer full-span concentric winding with a turns ratio of 34:37. e =5 new winding design, implementation case 2 uses q e =6 new winding design.

[0054] Implementation case 1:

[0055] S1. According to the basic parameters of the motor, determine the equivalent number of slots per pole and per phase of the three-phase low harmonic winding q e ​, that is, the number of coils in the phase belt. The number of slots in the motor is Q, the number of poles is 2p, the parallel branch of the winding is a, the number of slots per pole per phase is q = Q / 6p, and the equivalent range of the number of slots per pole per phase is: 2q e ≤3q.

[0056] Here we determine the winding parameter q e =5.

[0057] S2. Divide the area inside the motor core slot into three layers: upper, middle and lower. Place any phase coil of the three-phase winding in a single layer. In particular, the coil of the A-phase winding is placed in the middle layer. Determine the phase band allocation table and winding connection diagram of the winding, which is specifically achieved by the method of "Design, Optimization, and Experimental Evaluation of Multilayer AC Winding for Induction Machine" disclosed in IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 55, NO. 4, July / August 2019.

[0058] According to the basic parameters of the motor winding, the phase belt allocation table of the new winding scheme can be determined as follows: Figure 2 As shown, the winding connection diagram of the new winding scheme is as follows Figure 4 shown.

[0059] S3. According to the principle of sinusoidal distribution of slot current along the core surface, determine the numerical relationship of the number of turns of each coil in the phase belt, and the turn ratio of each coil: n1:n2:n3…n qe Determine the symmetry axis of the slot electromotive force in the phase belt. The electrical angles of the slot electromotive force phasor relative to the symmetry line are: α1, α2, α3…α qe .

[0060] Taking the A phase positive phase belt as an example, the symmetry axis of the slot electromotive force phase is on the third slot, so the electrical angles of the slot electromotive force relative to the symmetry line are: 60°, 30°, 0°, 30° and 60°. If the effective value of the sinusoidal distribution slot current is I m , the instantaneous current values ​​of phase A, phase B and phase C are i A 、i B and i C The numerical relationship between the slot currents in slots 1 to 5 of the winding is:

[0061] Phase A phase belt 1 slot 1 current value n1i A -n3i B +n5i C =I m cos60°

[0062] ​Phase A phase belt second slot 2 current value n2i A -n2i B =I m cos30°

[0063] Phase A phase belt 3 slot 3 current value n3i A -n1i B -n5i C =I m cos0°

[0064] Phase A phase belt 4 slot 4 current value n4i A -n4i C =I m cos30°

[0065] Phase A phase belt 5th slot 5 current value n5i A +n1i B -N3i C =I m cos60°

[0066] Assuming that the current of phase A is at its maximum value, the current amplitude relationship i can be obtained: A =-2i B =-2i C =I m By simplification, we can know that the ideal turns ratio of each coil in a phase band is: n1+n3=1, n2=n4≈0.577, n1=n5.

[0067] S4. Determine the range of effective series turns per phase that meets the motor performance. Considering the design principle of minimum harmonic magnetic potential and other factors such as limited slot fill rate, compare and calculate and select the best turns design scheme. The actual turns of the coils in the phase band are: N1, N2, N3...N qe .

[0068] By calculating and comparing the winding schemes, the effective series turns of the single-layer winding and the double-layer unequal-turn winding are 262.8 and 264.2 respectively, so the effective series turns of the new winding are estimated to be Nk1=262~264. Taking into account the minimum harmonic magnetic potential design, as well as reducing the slot full rate and the amount of copper used in the winding, the actual turns of the three-layer unequal-turn winding are determined to be N1=N5=4, N2=N4=37, N3=64, and the effective series turns of the new winding is 264. The winding factors of the main harmonics of the three windings are as follows: Figure 8 As shown, the total harmonic content THD is calculated to be 0.291, 0.214 and 0.191 respectively.

[0069] Specifically, the total harmonic content THD of the three windings is calculated as follows:

[0070]

[0071] Where: k dp1 is the fundamental wave winding factor; k dpν is the harmonic winding factor; ν is the order of the harmonic winding magnetic potential; parameter k dp1 It can be expressed as:

[0072]

[0073] Among them, α i is the electrical angle of the slot emf phasor relative to the symmetry line, Ni is the actual number of turns of the coil in the phase band;

[0074] The order of the harmonic winding magnetic potential is ν = 3, 5, 7, 9, 11..., and the harmonic winding factor is k dpν It can be expressed as:

[0075]

[0076] Compared with the double-layer unequal turns winding, the three-layer unequal turns winding solution (q e =5) is reduced by about 11%.

[0077] In order to verify the beneficial effects of the present invention in the first implementation example, finite element models of three motors were established, and the stator winding structures were single-layer winding, double-layer unequal-turn winding and three-layer unequal-turn winding (q e =5), the motor model parameters are exactly the same except for the stator winding. The schematic diagram of the new winding motor model is as follows Figure 6 As shown in Figure 2. Through simulation calculation, the amplitudes of the air gap harmonic flux density of the three motors are as follows: Fig. 9 As shown, the induced phase electromotive force of the three motors is as follows Fig.10 As shown in the figure, compared with the double-layer unequal-turn winding scheme, the new winding scheme in this case has a better sinusoidal magnetic potential waveform, the total harmonic content of the air gap magnetic density is reduced from 0.041 to 0.039, and the third harmonic electromotive force is reduced from 8.1V to 7.3V, a reduction of about 10%.

[0078] Implementation case 2:

[0079] S1. According to the basic parameters of the motor, determine the equivalent number of slots per pole and per phase of the three-phase low harmonic winding q e , that is, the number of coils in the phase belt. The number of slots in the motor is Q, the number of poles is 2p, the parallel branch of the winding is a, the number of slots per pole per phase is q = Q / 6p, and the equivalent range of the number of slots per pole per phase is: 2q e ≤3q.

[0080] Here we determine the winding parameter q e =6.

[0081] ​S2. Divide the area inside the motor core slot into three layers: upper, middle and lower. Place any phase coil of the three-phase winding in a single layer. In particular, place the coil of the A-phase winding in the middle layer. Determine the phase band allocation table and winding connection diagram of the winding.

[0082] According to the basic parameters of the motor winding, the phase belt allocation table of the new winding scheme can be determined as follows: Figure 3 As shown, the winding connection diagram of the new winding scheme is as follows Figure 5 shown.

[0083] S3. According to the principle of sinusoidal distribution of slot current along the core surface, determine the numerical relationship of the number of turns of each coil in the phase belt, and the turn ratio of each coil: n1:n2:n3…n qe Determine the symmetry axis of the slot electromotive force in the phase belt. The electrical angles of the slot electromotive force phasor relative to the symmetry line are: α1, α2, α3…α qe .

[0084] Taking the A phase positive phase belt as an example, the symmetry axis of the slot electromotive force phasor is between the 3rd slot and the 4th slot, so the electrical angles of the slot electromotive force relative to the symmetry line are: 75°, 45°, 15°, 15°, 45° and 75°. If the effective value of the sinusoidal distribution slot current is I m , the instantaneous current values ​​of phase A, phase B and phase C are i A 、i B and i C The numerical relationship between the slot currents in slots 1 to 6 of the winding is:

[0085] Phase A phase belt 1 slot 1 current value n1i A -n4i B +n5i C =I m cos75°

[0086] Phase A phase belt second slot 2 current value n2i A -n3i B +n6i C =I m cos45°

[0087] Phase A phase belt 3 slot 3 current value n3i A -n2i B -n6i C =I m cos 15°

[0088] Phase A phase belt 4 slot 4 current value n4i A -n1i B -n5i C =I m cos15°

[0089] Phase A phase belt 5th slot 5 current value n5i A +n1i B -n4i C =I m cos45°

[0090] Phase A phase belt 6 slot 6 current value n6i A +n2i B -N3i C =I m cos75°

[0091] Assuming that the current of phase A is at its maximum value, the current amplitude relationship i can be obtained: A =-2i B =-2i C =I m By simplification, we can know that the ideal turns ratio of each coil in a phase band is: n1=n6, n2=n5≈n1+0.298, n3=n4≈0.817-n1.

[0092] S4. Determine the range of effective series turns per phase that meets the motor performance. Considering the design principle of minimum harmonic magnetic potential and other factors such as limited slot fill rate, compare and calculate and select the best turns design scheme. The actual turns of the coils in the phase band are: N1, N2, N3...N qe .

[0093] By calculating and comparing the winding schemes, the effective series turns of the single-layer winding and the double-layer unequal-turn winding are 262.8 and 264.2 respectively, so the effective series turns of the new winding are estimated to be Nk1=262~264. Taking into account the minimum harmonic magnetic potential design, as well as reducing the slot full rate and the amount of copper used in the winding, the actual turns of the three-layer unequal-turn winding are determined to be N1=N6=3, N2=N5=22, N3=N4=51, and the effective series turns of the new winding is 262. The winding factors of the main harmonics of the three windings are as follows: Figure 8 As shown in the figure, the total harmonic content THD is calculated to be 0.291, 0.214 and 0.155 respectively. Compared with the two-layer unequal turn winding, the three-layer unequal turn winding solution (q e =6) is reduced by about 28%.

[0094] In order to verify the beneficial effects of the present invention in the second implementation example, finite element models of three motors were established, and the stator winding structures were single-layer winding, double-layer unequal-turn winding and three-layer unequal-turn winding (q e =6), the motor model parameters are exactly the same except for the stator winding. The schematic diagram of the new winding motor model is as follows Figure 7 As shown in Figure 2. Through simulation calculation, the amplitudes of the air gap harmonic flux density of the three motors are as follows: Fig. 9 As shown, the induced phase electromotive force of the three motors is as follows Fig.10 As shown in the figure, compared with the double-layer unequal-turn winding scheme, the new winding scheme in this case has a better sinusoidal magnetic potential waveform, the total harmonic content of the air gap magnetic density is reduced from 0.041 to 0.035, and the third harmonic electromotive force is reduced from 8.1V to 4.8V, a reduction of about 41%.

[0095] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for designing low harmonic windings of a three-phase AC motor, characterized in that: The steps include: S1. According to the basic parameters of the motor, determine the equivalent number of slots per pole and per phase of the three-phase low harmonic winding q e , S2. Divide the area inside the motor core slot into three layers: upper, middle and lower. Place one phase coil of the three-phase winding in a separate layer. Determine the phase band allocation table and winding connection diagram of the winding. S3. According to the principle of sinusoidal distribution of slot current along the core surface, determine the numerical relationship of the number of turns of each coil in the phase belt, and the turn ratio of each coil: n1:n2:n3…n qe , determine the symmetry axis of the slot electromotive force in the phase belt, and the electrical angles of the slot electromotive force phasor relative to the symmetry line are: α1, α2, α3…α qe , calculate the effective series turns N of each phase of the winding k1 : Where: a is the parallel branch of the winding; α i is the electrical angle of the slot emf phasor relative to the symmetry line; S4. Determine the range of effective series turns per phase that meets the motor performance. Considering the design principle of minimum harmonic magnetic potential and limited slot fill rate, the actual turns of the coils in the phase band are: N1, N2, N3...N qe .

2. The method for designing low harmonic windings of a three-phase AC motor according to claim 1, characterized in that: The number of slots of the motor in step S1 is Q, the number of poles is 2p, the parallel branch of the winding is a, the number of slots per pole per phase is q=Q / 6p, and the range of the equivalent number of slots per pole per phase is: 2q e ≤3q.​ 3. The method for designing low harmonic windings of a three-phase AC motor according to claim 1, characterized in that: In step S2, the coil of the A-phase winding is placed in the middle layer.

4. The method for designing low harmonic windings of a three-phase AC motor according to claim 3, characterized in that: In step S3, when q e =5, the symmetry axis of the slot electromotive force phase is on the third slot, so the electrical angles of the slot electromotive force relative to the symmetry line are: 60°, 30°, 0°, 30° and 60°; the effective value of the sinusoidal slot current is I m , the instantaneous current values ​​of phase A, phase B and phase C are i A 、i B and i C , the numerical relationship of the slot current in slots 1 to 5 of the winding is: Phase A phase belt 1 slot 1 current value n1i A -n3i B +n5i c =I m cos60° Phase A phase belt second slot 2 current value n2i A -n2i B =I m cos 30° Phase A phase belt 3 slot 3 current value n3i A -n1i B -n5i C =I m cos 0° Phase A phase belt 4 slot 4 current value n4i A -n4i C =I m cos 30° Phase A phase belt 5th slot 5 current value n5i A +n1i B -N3i C =I m cos 60°.

5. The method for designing low harmonic windings of a three-phase AC motor according to claim 1, characterized in that: In step S3, when q e =6, the symmetry axis of the slot electromotive force phase is between the third slot and the fourth slot, so the electrical angles of the slot electromotive force relative to the symmetry line are: 75°, 45°, 15°, 15°, 45° and 75°, and the effective value of the sinusoidal distribution slot current is I m , the instantaneous current values ​​of phase A, phase B and phase C are i A 、i B and i C , the numerical relationship of the slot current in slots 1 to 6 of the winding is: Phase A phase belt 1 slot 1 current value n1i A -n4i B +n5i C =I m cos 75° Phase A phase belt second slot 2 current value n2i A -n3i B +n6i C =I m cos 45° Phase A phase belt 3 slot 3 current value n3i A -n2i B -n6i C =I m cos 15° Phase A phase belt 4 slot 4 current value n4i A -n1i B -n5i C =I m cos 15° Phase A phase belt 5th slot 5 current value n5i A +n1i B -n4i C =I m cos45° Phase A phase belt 6 slot 6 current value n6i A +n2i B -N3i C =I m cos 75°.

6. The method for designing low harmonic windings of a three-phase AC motor according to claim 1, characterized in that: Specifically, in step S4, the effective series turns of the single-layer winding and the double-layer unequal-turn winding are calculated as N and k单 and N k双 , then the effective series turns range of the new winding is estimated to be N k1 =N k单 ~N k双 , select the effective series turns of the new winding as N k1 , according to N k1 Taking into account the minimum harmonic magnetic potential design, as well as the reduction of slot fill rate and winding copper usage, the actual number of turns of the three-layer unequal-turn winding is determined.

7. The method for designing low harmonic windings of a three-phase AC motor according to claim 1, characterized in that: It also includes the calculation of three types of winding total harmonic distortion THD: Where: k dp1 is the fundamental wave winding factor; k dpν is the harmonic winding factor; ν is the order of the harmonic winding magnetic potential.

8. The method for designing low harmonic windings of a three-phase AC motor according to claim 7, characterized in that: According to the parameter k determined in step S3 dp1 It can be expressed as: The order of the harmonic winding magnetic potential is ν = 3, 5, 7, 9, 11..., and the harmonic winding factor is k dpν It can be expressed as: Where: α i is the electrical angle of the slot electromotive force phasor relative to the symmetry line, and Ni is the actual number of turns of the coil in the phase band.

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