Symmetrical Four-branch Connection Method for Fractional Slot Wave Winding

Abstract

The present invention discloses a symmetrical four-branch connection method for a fractional slot wave winding, comprising the following steps: dividing the Z slots of a motor into four phase-belt lines along an H pitch that is closest to the slot value of each pole, wherein every two phase-belt lines separated by 180 degrees are symmetrical in electrical angle; taking a group of 180-degree symmetrical phase-belt lines as basic phase-belt lines, and the remaining group as short-spacing phase-belt lines; dividing the slots on each phase-belt line into three equal parts to form phase belts of three phases A, B, and C, wherein each phase has two basic phase belts and two short-spacing phase belts, and the basic phase belt and the short-spacing phase belt of each phase are offset by s slots; taking a basic phase belt and a short-spacing phase belt, alternately using the upper conductors and the lower conductors of the basic phase belt and the short-spacing phase belt within the phase belt and connecting them in series at an H pitch, and connecting the phase belts with jumper wires according to polarity to form two loop branches; the front and rear structural pitches of the winding of the present invention are equal; the winding branches are composed of the basic phase belt and the short-spacing phase belt, which can weaken high-order harmonics.

Description

Technical Field

[0001] The present invention relates to the technical field of three-phase AC motor windings, and in particular to a symmetrical four-branch connection method for fractional slot wave windings. Background Art

[0002] The number of parallel branches a used in a three-phase motor's double-layer short-pitch wave winding is related to the number of pole pairs p corresponding to the motor's synchronous speed. Conventional motor theory posits that the number of branches a can only be a factor of 2p to achieve symmetrical winding branches. For a hydroelectric generator, at a 50Hz grid frequency, the pole pairs corresponding to speeds of 428.6, 272.7, 230.8, 176.5, and 157.9 rpm are odd numbers, p = 7, 11, 13, 17, and 19, respectively. Because 2p / 4 = p / 2 is not divisible, such a 2p pole number does not contain a factor of 4, and therefore, it is believed that symmetrical branches with a = 4 do not exist. On the other hand, for large-capacity, high-voltage hydroelectric generators with an odd p, limiting the number of branches to a = 1, 2, or p results in excessive or insufficient winding branch currents, limiting the motor's performance and economic indicators. Summary of the Invention

[0003] The present invention mainly solves the problem in the existing technology that the performance of the motor is limited by the number of branches; it provides a symmetrical four-branch connection method for fractional slot wave windings, which can still achieve the number of branches a=4 and symmetrical winding branches when the number of motor pole pairs p is an odd number. At the same time, the winding has a short-distance ratio to weaken high-order harmonics.

[0004] The above technical problems of the present invention are mainly solved by the following technical solutions: a symmetrical four-branch connection method for fractional slot wave windings, applied to a motor with an odd number of pole pairs and 4 symmetrical branches, the connection method includes the following steps: dividing the Z slots of the motor into 4 phase strips along the H pitch closest to the slot value of each pole, wherein each two phase strips are symmetrical at an electrical angle of 180°; taking a group of 180° symmetrical phase strips as the basic phase strips and the remaining group as the short-distance phase strips; dividing the slots on each phase strip into three equal parts to form A The phase belts of phases A, B, and C have two basic phase belts and two short-span phase belts for each phase, and the basic phase belts and short-span phase belts of each phase are offset by s slots; take one basic phase belt and one short-span phase belt, use the upper conductors and lower conductors of the basic phase belt and the short-span phase belt alternately in the phase belt and connect them in series with an H pitch, and use jumper wires between the phase belts according to polarity to form two loop branches; the remaining basic phase belts and short-span phase belts in the same phase form another two loop branches, forming four loop branches, and the four loop branches are opened at any connection point other than the outgoing line end to form four branches.

[0005] Preferably, the specific division method of the four phase belt lines is as follows: assuming the number of motor pole pairs is p, the number of motor slots is Z, the number of phases m=3, the number of pole pairs p is an odd number, and the number of slots per pole per phase q is expressed as q=Z / (2pm)=b+c / p, where b, c, and p are positive integers, and c / p is an irreducible proper fraction; define 3q=H±e / p, H is the positive integer closest to 3q, |e|=2, define the slot difference Δ=e / p, then the number of phase belt slots of each phase belt is N=q / Δ=(b+c / p) / (e / p)=(bp+c) / e; then the number of phase belt lines that can be constructed is n=(Z / m) / N=2pq / N=[2p(b+c / p)] / [(bp+c) / e]=2×|e|=4.

[0006] As a preferred method, the specific setting method of the two loop branches is: set a basic phase belt as Phase belt, a short-distance phase belt is phase belt; The upper conductor in the slot number to which the phase belt belongs is represented by The lower conductor is represented by The upper conductor in the slot number to which the phase belt belongs is represented by The lower conductor is represented by Phase belt The phase belts and the upper and lower conductors are used alternately within the phase belt and connected in series with an H pitch. Jumper wires are used between the phase belts according to polarity to form two loop branches.

[0007] Preferably, the upper conductor and the lower conductor corresponding to the jumper between the phase belts are determined by the odd or even number N of the phase belt slots.

[0008] Preferably, by reversely connecting the branches with potential phase differences of 180°, the four branches are connected in parallel to form a four-branch winding.

[0009] Preferably, the fundamental and harmonic waves of the electric potential and magnetic potential of the four-branch windings are the same, and there is no circulating current after being connected in parallel.

[0010] Preferably, the four parallel-connected windings have a short pitch ratio.

[0011] The beneficial effects of the present invention are as follows: through the winding branch connection method of the present invention, the effects of three-phase symmetry, the magnitude and phase of the electric potential and magnetic potential of the four branches in each phase are completely identical, and the parallel branches have no fundamental wave and harmonic circulating current. The front and rear structural pitches of the winding conductors are equal; the winding branches are composed of basic phase belts and short-distance phase belts, and the windings have a short pitch coefficient, which can weaken high-order harmonics. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a slot diagram and phase belt line distribution diagram of an embodiment of the present invention.

[0013] Figure 23. It is a diagram showing the division of three-phase phase bands and the structure of the A-phase loop branch according to an embodiment of the present invention.

[0014] Figure 3 Schematic diagram of the connection of the loop branch in an embodiment of the present invention.

[0015] Figure 4 It is a slot diagram and phase belt line distribution diagram combined with a specific application of an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the following embodiments and the accompanying drawings are used to further describe the technical solutions in the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] Example: A symmetrical four-branch connection method for fractional slot wave windings. The present invention assumes that the number of motor pole pairs is p, the number of motor slots is Z, the number of phases is m=3, the number of pole pairs p is an odd number, and the number of slots per pole per phase q is expressed as q=Z / (2pm)=b+c / p (where b, c, and p are positive integers, and c / p is an irreducible proper fraction). Under these conditions, 3q=3(b+c / p)=H+e / p is defined, where H is the integer closest to 3q, and e is the smallest (±) integer that makes H closest to 3q. Figure 1 The following is a schematic diagram of the slot positions when Z slots, q = b + c / p, and e = -2. H represents slots connected at intervals of H pitch, with a slot position difference of Δ = e / p. Therefore, within the q slot range, i.e., within a 60° phase band, the number of slots that can be connected according to the slot position difference of Δ is N = q / Δ = (b + c / p) / (e / p) = (bp + c) / e slots. These N slots are considered a phase band line for one phase. Since each phase has a total of Z / m slots, and each phase band has N slots, the number of phase bands that can be constructed per phase is n = (Z / m) / N = 2pq / N = [2p(b + c / p)] / [(bp + c) / e] = 2e. When e=±2 in the aforementioned 3q, then n=2×|e|=4, i.e., there are 4 phase strips. At the same time, when bp+c is an even number, N=(bp+c) / e=(bp+c) / 2=an integer, i.e., N slots connected at a pitch of H occupy exactly 60° electrical angle, denoted as Therefore, the number of slots per pole and phase q is expressed as q = b + c / p, and at the same time, 3q = H ± e / p, e = ± 2, bp + c is an even number, then in the slot diagram, the three phases A, B, and C can be divided into four phase belt lines along the H pitch, that is, Figure 1 The solid line, dashed line, double solid line, and double dashed line in the figure are shown in Figure 1. Among these four phase strip lines, every two phase strip lines are symmetrical at an electrical angle of 180 degrees.

[0019] The method of dividing phase zones in the present invention: Figure 1 In the middle, take a group of 180° symmetrical phase belt lines as the basic phase belt lines, and the remaining group as short-span phase belt lines. Divide the slots on each phase belt line into three equal parts to form phase belts of phases A, B, and C. The basic phase belt and short-span phase belt of each phase are offset by s slots, and we get Figure 2 Phase belt division is explained by taking phase A as an example. The two basic phase belts of phase A and the N slot numbers in the phase belt are recorded as and The two short-distance phase belts are recorded as and The relationship between the slot numbers in the phase belt: The slot numbers in the phase belt are The first slot number A0 can be any slot number, and the subsequent slot numbers differ by H, 2H, ... (N-1)H slots in sequence. The slot numbers of other phase belts also follow this rule. At the same time, the first slot number between phase belts satisfies A′0=A0+Z / 2, a0=A0±s, a′0=a0+Z / 2; when the calculated slot number value is greater than Z, the calculated value is subtracted from Z, and when the calculated value is less than or equal to 0, the calculated value is added to Z.

[0020] The specific method of forming four branches in the present invention is as follows: Figure 2 In the example of phase A, a basic phase belt and a short-distance phase belt are selected. Taking the phase belt as an example, The upper conductor in the slot number to which the phase belt belongs is represented by The lower conductor is represented by The slot numbers of the phase belts are also based on this rule. Indicates the upper and lower conductors. These upper and lower conductors are used alternately in the phase belt and connected in series with H pitch. Jumper wires are used between the phase belts according to polarity, forming the following two loop branches:

[0021] Article 1:

[0022] Article 2:

[0023] The wiring diagram of these two loop branches is shown in Figure 3 The upper and lower conductors corresponding to the crossover between phase belts are determined by the odd or even number of N. The phase belts follow the same pattern and method to form two additional loop branches, resulting in a total of four loop branches for phase A. Opening the four loop branches at any non-outgoing connection creates four branches. By reversing the connection of the branches with a 180° phase difference in potential, the four branches can be connected in parallel to form a four-branch winding. The fundamental and harmonic waves of the potential and magnetic potential of these four branches are identical, and there is no circulating current when connected in parallel. Furthermore, because the phase belts forming the windings have a short pitch s, the four-branch windings connected in parallel have a short pitch ratio β = s / 3q (when s < 3q) or β = 2-s / 3q (when 3q < s < 6q), making them electrically short-pitch windings that can attenuate higher harmonics.

[0024] If the symbols "A, a" used in the above-mentioned phase A are replaced with "B, b" and "C, c", then the above-mentioned description of the division of phase belts, the notation of phase belt slot numbers, and the four-branch winding structure are completely applicable to phases B and C. The phase belts of phases C and B are NH slots apart from the phase belt of phase A, that is, corresponding to the first slot number of phase A, the first slot numbers of phases C and B satisfy the relationship C0 = A0 + N × H, B0 = A0 + 2N × H. Therefore, the phase relationship of the fundamental wave of the three phases is: the phase difference between phase B and phase A is Electrical angle; Phase difference between phase C and phase A Electrical angle, so the phases of the three-phase windings A, B, and C are 120° electrical angle apart from each other and are completely symmetrical.

[0025] According to the technical theory and implementation route of the present invention, when p is an odd number, the number of poles 2p and the number of slots per pole per phase q that can achieve symmetrical four branches are listed in the following table, but the present invention is not limited to the listed number of poles and number of slots per pole per phase. As long as the combination of the number of poles and the number of slots per pole per phase meets the limitations of the claims and the method of the present invention, it is protected.

[0026] Table 1 Number of slots per pole and phase q listed

[0027]

[0028] Taking a generator motor with a capacity of 300MW, a voltage level of 15.75-18kV, and a speed of 428.6r / min in a 50Hz power grid, which is common in the pumped storage field, as an example, its number of poles 2p=14 (=1×2×7), the traditional view can only select the number of branches a=1, 2, 7, 14. Such a number of branches makes the slot current of the motor too large or too small. The present invention adopts the number of branches a=4, so that the various technical indicators and economic indicators of the motor can be easily achieved at a reasonable level.

[0029] Assume the motor has 3 phases, 2p = 14 poles, and p = 7 (an odd number). Select the number of slots, Z = 228. Then, the number of slots per pole per phase, q, is Z / (m × 2p) = 228 / (3 × 14) = 5.429 = 5 + 3 / 7 = b + c / p. Therefore, 3q = 15 + 9 / 7 = 16.286 = 16 + 2 / 7 = H + e / p, meaning H = 16 and e = 2. N = (bc + p) / e = (5 × 7 + 3) / 2 = 19. Each phase has a belt with 19 slots. If the short distance s is set to 13, the short distance ratio β is set to 3 / 3q = 13 / 16.286 = 0.80, and the 5th harmonic can be almost completely eliminated. If s is set to 19, the short distance ratio β is set to 2-3 / 3q = 2-19 / 16.286 = 0.83, and the 5th and 7th harmonics can be weakened at the same time. Figure 4 As shown, taking phase A as an example, the dotted line shows the basic phase belt and the solid line shows the short-distance phase belt.

[0030] like Figure 4 The first basic phase band of phase A The first slot number A0 is A0=11, then Right now

[0031] Another basic phase belt The first slot number A′0=A0+Z / 2=11+228 / 2=125, then

[0032] Short-range phase belt The first slot number a0=A0+s=11+13=24, then

[0033] 168,184,200,216,4,20,36,52,68,84); The first slot number a′0=a0+Z / 2=24+228 / 2=138, then

[0034] The method of forming the four loop branches of phase A is as follows:

[0035] ① Phase belt The two loop branches generated are:

[0036] Article 1 :

[0037]

[0038]

[0039] Article 2:

[0040]

[0041]

[0042] The slot numbers of the first and second bars are the same, only the upper and lower conductors are swapped. “→” indicates that the bars are directly connected through a pitch of H=16. Indicates jumper wire, the same below.

[0043] ② Phase belt Two more loop branches are generated:

[0044] Article 3 :

[0045] Article 4 :

[0046] The slot numbers of the 3rd and 4th branches are the same, only the upper and lower conductors are swapped; the direction of the arrow is opposite to that of the 1st and 2nd branches, which only indicates that the polarity is opposite.

[0047] After opening any connection at the non-outgoing end of the four loop branches of phase A above, the ends with the same polarity are connected in parallel to form a four-branch winding.

[0048] The winding branches formed by the wiring method of the present invention have the characteristics of three-phase symmetry, the magnitude and phase of the electric potential and magnetic potential of the four branches in each phase are completely the same, and the parallel branches have no fundamental wave and harmonic circulating current. The front and rear structural pitches of the winding conductors are equal, the winding branches are composed of basic phase belts and short-distance phase belts, and the windings have a short pitch coefficient, which can weaken high-order harmonics.

[0049] The embodiment described above is only a preferred solution of the present invention and does not limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solution described in the claims.

Claims

1. The symmetrical four-branch connection method of fractional slot wave winding is applied to motors with an odd number of pole pairs and 4 symmetrical branches. It is characterized by: The wiring method includes the following steps: Divide the motor's Z slots into four phase strip lines along the H pitch closest to the slot value of each pole. Among the four phase strip lines, every two phase strip lines are symmetrical at an electrical angle of 180 degrees. Take a group of 180° symmetrical phase belt lines as the basic phase belt lines, and the remaining group as the short-distance phase belt lines; Divide the slots on each phase belt line into three equal parts to form phase belts of phases A, B, and C. Each phase has two basic phase belts and two short-span phase belts. The basic phase belt and short-span phase belt of each phase are offset by s slots. Take a basic phase belt and a short-span phase belt, alternately use the upper and lower conductors of the basic phase belt and the short-span phase belt in the phase belt and connect them in series with an H pitch, and use jumper wires to connect the phase belts according to polarity to form two loop branches; The remaining basic phase belts and short-distance phase belts in the same phase are used to form two more loop branches, forming four loop branches. The four loop branches are opened at any connection point of the non-outgoing end to form four branches.

2. The symmetrical four-branch connection method of fractional slot wave winding according to claim 1 is characterized in that: The specific division method of the four phase belt lines is as follows: let the number of motor pole pairs be p, the number of motor slots be Z, the number of phases be m = 3, the number of pole pairs p is an odd number, and the number of slots per pole per phase q is expressed as q = Z / (2pm) = b+c / p, where b, c, and p are positive integers, and c / p is an irreducible proper fraction; Define 3q = H ± e / p, where H is the positive integer closest to 3q, |e| = 2, and define the slot difference Δ = e / p. Then the number of phase slots in each phase belt is N = q / Δ = (b + c / p) / (e / p) = (bp + c) / e. Then the number of phase lines that can be constructed is n = (Z / m) / N = 2pq / N = [2p(b+c / p)] / [(bp+c) / e] = 2×|e| = 4.

3. The symmetrical four-branch connection method of fractional slot wave winding according to claim 2, characterized in that: The specific setting method of the two loop branches is: set a basic phase belt as Phase belt, a short-distance phase belt is phase belt; The upper conductor in the slot number to which the phase belt belongs is represented by The lower conductor is represented by The upper conductor in the slot number to which the phase belt belongs is represented by The lower conductor is represented by Phase belt The phase belts and the upper and lower conductors are used alternately within the phase belt and connected in series with an H pitch. Jumper wires are used between the phase belts according to polarity to form two loop branches.

4. The symmetrical four-branch connection method of fractional slot wave winding according to claim 3 is characterized in that: The upper conductor and lower conductor corresponding to the jumper between phase belts are determined by the odd or even number N of the phase belt slots.

5. The symmetrical four-branch connection method for fractional slot wave winding according to claim 1 or 2, characterized in that: By reversing the connection of the branches with a potential phase difference of 180°, the four branches are connected in parallel to form a four-branch winding.

6. The symmetrical four-branch connection method for fractional slot wave winding according to claim 5, characterized in that: The fundamental and harmonic waves of the electric and magnetic potentials of the four-branch windings are the same, and there is no circulating current after being connected in parallel.

7. The symmetrical four-branch connection method for fractional slot wave winding according to claim 5, characterized in that: The four parallel windings have a short pitch ratio.

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