A direct-drive permanent magnet flat-wire wind turbine generator and a low torque ripple design method

Abstract

The present invention discloses a direct-drive permanent magnet flat wire wind turbine suitable for wind power generation and a low-torque pulsation design method. The invention adopts a dual-rotor structure, and I-shaped winding frames are evenly arranged along the circumferential direction between the inner and outer stator shells. Two rectangular stator modulation blocks are fixedly embedded in each center column, and a three-phase centralized flat wire winding is wound around each center column. The generator has the design characteristics of a single stator fixed component and a single rotor moving component, as well as the design characteristics of an inner and outer double-layer air gap structure. A cosine shaping function is introduced into the originally straight shape of the outer surface of the permanent magnet steel in the inner and outer rotors close to the stator side so that the outer surface presents a partial curve of a smooth cosine function. The ratio coefficient of each harmonic introduced by the outer surface shaping function of the inner and outer rotor permanent magnet steel is adjusted to increase the fundamental wave content in the air gap magnetic density, and suppress the high-order odd harmonics in the inner and outer air gap magnetic density, thereby increasing the induced electromotive force and obtaining low torque pulsation.

Description

[0001] Technology Neighborhood

[0002] The present invention belongs to the technical field of generator design and manufacturing, and specifically is a permanent magnet direct-drive wind turbine suitable for wind power generation and other applications requiring high efficiency, high power density, low pulsation and light weight. Background Art

[0003] As a key clean energy generation project, wind power plays a vital role in promoting energy transition. Traditional wind turbines utilize a main shaft, gearbox, flexible coupling, and brake as their transmission mechanism. A speed-increasing gearbox increases the low rotor speed input to the generator's required speed to meet the generator's operating requirements. Permanent magnet generators, however, offer high torque at low speeds, making them ideally suited for low- and even ultra-low-speed wind power generation. Furthermore, their high power density, high efficiency, and robust fault tolerance offer significant competitive advantages in the wind power equipment sector. Direct-drive permanent magnet wind turbines further simplify the gearbox structure within wind turbines, reducing wind energy losses in the transmission system and further improving wind energy utilization and power generation efficiency. Furthermore, direct-drive generators are widely used due to their simplified transmission structure, improved generator reliability, reduced component count, and lowered operating and maintenance costs. However, the direct-drive permanent magnet generator has a low speed, so it has more poles, larger mass and volume, which will not only bring greater pressure on the transportation and lifting of the generator, but also cause greater mechanical wear on the bearings of the generator set. Therefore, the rotating mass in the unit is required to be as small as possible. In addition, when the wind is strong, the generator generates large power and the current on the winding is high, which will generate high heat on the winding. The traditional round wire generator has a serious skin effect under high working conditions, which will cause greater heat and reduced generator efficiency. Compared with traditional round wire generators, flat wire generators have a high slot fill rate, high power density, and good temperature performance. At the same current carrying capacity, the mass is lower than that of round wire generators. Therefore, flat wire generators are very suitable for use in situations where the current on the winding is unstable due to the strong and weak wind during actual operation of the wind turbine.

[0004] Current permanent magnet wind turbines focus on improving the reliability of the generator, and as a result, a number of direct-drive permanent magnet generator designs have emerged. The document with Chinese invention patent application number 202211729805.0 adopts an outer rotor topology design with a surface-mounted permanent magnet vernier, which has a higher torque density. In order to simplify the structure of the generator, the rotor permanent magnet steel is directly attached to the rotor casing. The rotor casing provides a magnetic path for the rotor flux, and the rotor casing also plays the role of supporting the generator structure. However, during the operation of the generator, eddy currents are induced in the rotor housing. Since the rotor housing is directly connected to the permanent magnets, more magnetic flux flows in the rotor housing, and the eddy currents induced are larger, resulting in greater eddy current losses. This will reduce the efficiency of the generator in actual applications. Since the permanent magnets are directly attached to the rotor, the difficulty of rotor processing is increased. In addition, when the wind is strong and the rotor rotates at a fast speed, the reliability of the rotor part is bound to be reduced. Moreover, the generator will also generate losses and heat in actual use, which will put greater pressure on the reliability of the rotor part. In actual use, the surface-mounted permanent magnets are more easily affected by the ambient temperature, which reduces the service life of the generator. This rotor structure design is not suitable for high-speed operation. When the wind is strong, the winding of the generator is seriously heated and cannot effectively dissipate heat when running at high speed. In addition, the magnetic lines of force of the rotor housing of the generator are easily saturated, which will reduce the utilization rate of the magnetic field. The document of Chinese invention patent 202223414484.3 adopts a permanent magnetic suspension design, which provides a dual-wind direction permanent magnet generator based on magnetic suspension. It adopts a bilaterally symmetrical "I"-shaped design, with two identical generators placed on the generator centerline as the symmetry axis. This design can utilize wind energy to a greater extent, solving the disadvantage that traditional wind turbines can only maximize the utilization of oncoming wind energy, and further improving the generator's power generation capacity. However, its process requirements are high. Not only does it require suspension magnetic rings, but it also requires extrusion magnetic rings and axial suspension magnetic rings to work together. In addition, anti-eccentric suspension magnetic rings are required to stabilize the generator's magnetic suspension structure. However, its relatively dispersed magnetic ring stacking design is difficult to maintain in actual use, and the types and requirements of parts are high, resulting in high maintenance costs. In addition, this generator only uses magnetic suspension to reduce the energy loss through the gearbox during wind energy transmission in traditional wind turbines. It still uses traditional synchronous generators, so there is no significant improvement in performance.The document of Chinese invention patent 202211627702.3 proposes a split-type orbital rotor permanent magnet direct-drive wind turbine. Its design structure is relatively novel. It is based on the background that the cost of the traditional permanent magnet direct-drive generator structure cannot be further compressed and the direct-drive generator manufacturers urgently need to transform their technology. However, the air inlet design of the generator greatly limits the overall size of the generator. Although the two-layer deflector design reduces the wear of sand and stones in the air on the main structure of the generator, it greatly reduces the wind force, which reduces the overall wind energy utilization rate of the generator. In addition, the overall unit design of the stator and rotor and then assembly reduces the overall reliability and safety of the generator, and subsequent maintenance is more frequent. Summary of the Invention

[0005] The purpose of the present invention is to solve the many problems currently existing in wind permanent magnet generators. In response to the problems of large power generation fluctuations and low power transmission efficiency caused by large bearing load burden in wind turbines and large generator torque pulsation, a direct-drive permanent magnet flat wire wind turbine based on the basic working principle of magnetic field modulation generator is proposed, which has high efficiency, high power density, light weight and low pulsation, double air gap magnetic field modulation, and a design method for its low torque pulsation, so as to meet the performance requirements of wind power generation and other occasions.

[0006] To achieve the above purpose, the present invention adopts a direct-drive permanent magnet flat wire wind turbine generator adopts the following technical solution: it includes an outer rotor, a stator, an inner rotor and a rotating shaft which are nested coaxially with a gap from the outside to the inside, and the inner rotor is uniformly fixed with N r The inner rotor has permanent magnets, and the outer rotor is evenly fixed with N r The inner and outer rotor permanent magnets are facing each other in the radial direction, and the magnetization directions of the adjacent inner and outer rotor permanent magnets are opposite in the radial direction. r is an even number; the outer surfaces of the inner and outer rotor permanent magnets on the side close to the stator are both curved, and a surface modification structure is adopted. The modification function of the inner rotor permanent magnet is h pm (x)=k1cos(px)+k2cos(3px)+k3cos(5px)+R pmi , the shape modification function of the outer rotor permanent magnet steel is h pm1 (x) = k 11 cos(px)+k 22 cos(3px)+k 33 cos(5px)+R pmo , k1>0, k2<0, k3<0, |k1|>|k2|>|k3|, k 11 <0,k 22 >0,k33 >0,|k 11 |>|k 22 |>|k 33 |, p = Nr / 2, R pmi R is the radius of the bottom of the inner rotor permanent magnet steel, pmi is the radius of the bottom of the outer rotor permanent magnet, and x is the absolute value of the tangential distance from each point on the modification function to the center line of the inner and outer rotor permanent magnets;

[0007] The stator includes a stator inner shell and a stator outer shell connected as a whole, and N is evenly arranged along the circumferential direction between the stator inner shell and the stator outer shell. s The winding frame is an I-shaped frame, with the top and bottom surfaces of the I-shape on the inner and outer sides respectively. The I-shaped center column is arranged radially. Two rectangular stator modulation blocks are fixedly embedded in each center column. The two stator modulation blocks are symmetrical along the center line of the center column. Three-phase centralized flat wire windings are wound on the center column of each winding frame.

[0008] The technical solution adopted by the low torque ripple design method of a direct-drive permanent magnet flat wire wind turbine described in the present invention includes the following steps:

[0009] Step (1): Perform Fourier decomposition on the radial and tangential air gap harmonics of the initial motor with both inner and outer rotor permanent magnets being rectangular and analyze their waveforms, calculate the contribution of each harmonic in the air gap harmonics to the torque and torque ripple, and select the first three harmonics that generate the main torque ripple, which are the fundamental, third and fifth harmonics;

[0010] Step (2): Inject harmonics on the surface of the rectangular inner rotor permanent magnet steel and change the inner rotor permanent magnet steel to the modification function h pm (x)=k1cos(px)+k2cos(3px)+k3cos(5px)+R pmi The curve represented is based on the amplitudes of the 1st, 3rd and 5th harmonics after Fourier decomposition of the initial air gap flux of the initial motor, and the weight of each of the three harmonics in the total amplitude of the three harmonics is calculated as the initial values ​​of k1, k2 and k3;

[0011] Step (3): Inject harmonics on the surface of the rectangular outer rotor permanent magnet steel and change the outer rotor permanent magnet steel to the modification function h pm1 (x) = k 11 cos(px)+k 22 cos(3px)+k 33 cos(5px)+R pmo The curve represented by the calculation of the weight of each of the three harmonics in the sum of the three harmonic amplitudes is k 11 , k 22 , k 33Initial values ​​of , to obtain the intermediate motor topology;

[0012] Step (4): Parameter screening is performed on the intermediate generator, and the objective function is defined as the function F[Max(H1th), Min(H3th), Min(H5th)] about the air gap harmonics. The constraints are the harmonic injection ratio in the modification function, the length and width of the inner and outer rotor permanent magnets, and the position of the permanent magnets. The sensitivity of the harmonic injection ratio and the position of the permanent magnets in the modification function to the function F is calculated. The sensitivity of each parameter to each harmonic is calculated and three sets are selected. The parameter set with high sensitivity to each harmonic is recorded as P H1 , the parameter set that is only highly sensitive to the harmonics that generate torque is recorded as P H2 , the parameter set that is only highly sensitive to the harmonics that generate torque ripple is recorded as P H3 ;

[0013] Step (5): Place two stator modulation blocks on the winding frame;

[0014] Step (6): Perform sensitivity analysis on the harmonic injection ratio and the length and width of the stator modulation block to the objective function F[Max(H1th), Min(H3th), Min(H5th)], calculate the sensitivity of each parameter to each harmonic and select three sets, among which the parameter set with high sensitivity to each harmonic is recorded as P H11 , the parameter set that is only highly sensitive to the generation of torque ripple harmonics is recorded as P H22 The parameter set with low sensitivity to the three harmonics is denoted as P H33 ;

[0015] Step (7): Select set P H1 and P H11 The parameter set in is named parameter set Q1, and the set P H2 and P H22 The parameter union in is named set Q2, and the set P H3 and P H33 The parameter union in is named set Q3, and the objective function of set Q1 is set to F[Max(T avg ), Min(T ripple )], set the objective function of set Q2 to F[Max(T avg )], set the objective function of set Q3 to F[Min(T ripple )], and the multi-objective genetic algorithm is solved simultaneously to determine the final variable parameters of the motor.

[0016] The present invention has the following beneficial effects after adopting the above solution:

[0017] 1. The permanent magnet flat wire wind turbine of the present invention adopts a dual-rotor structural design and a stator winding frame design that combines modules with the whole, so that the generator has the design characteristics of a single stator fixed component and a single rotor moving component, as well as the design characteristics of an inner and outer double-layer air gap structure. By using the iron rings of the inner and outer rotors, not only the leakage flux between the poles of the permanent magnet steel is cleverly utilized, but also support and convenience are provided for the parallel connection of the magnetic circuits between the magnets, so that the generator forms a distribution of the inner and outer rotor composite permanent magnet magnetic field in the radial space and has the distribution of the inter-pole and inter-phase parallel magnetic fields between the inner and outer rotors, thereby effectively improving and enhancing the permanent magnet utilization rate of the generator. Compared with the traditional single air gap magnetic field modulation permanent magnet generator, the dual rotor structure and the design of radial alternating magnetization of the permanent magnet steel not only increase the amplitude of the induced electromotive force, but also improve the torque output capacity of the generator. In addition, the stator winding slots are closed to protect the generator from unnecessary damage to the winding during operation and improve the reliability of the generator in severe weather.

[0018] 2. In the present invention, the outer surfaces of the permanent magnets in the inner and outer rotors close to the stator side are modified by a shaping technology. Specifically, the shaping technology introduces a cosine shaping function on the originally flat shape of the outer surface of the permanent magnet so that its outer surface presents a partial curve of the smooth cosine function. By adjusting the ratio coefficient of each harmonic introduced by the shaping function of the outer surface of the inner and outer rotor permanent magnets, the fundamental wave content in the air gap magnetic flux can be increased, and the high-order odd harmonics in the inner and outer air gap magnetic flux can be suppressed to a certain extent. On the one hand, the induced electromotive force is increased, and on the other hand, the torque pulsation is reduced, which has the advantage of obtaining low torque pulsation.

[0019] 3. In the stator of the present invention, two stator modulation blocks with a relatively close distance are placed in the middle column of each winding frame. The function of the two stator modulation blocks is to modulate the permanent magnetic potential generated by the inner and outer rotor permanent magnets accordingly, thereby improving the torque density and power density. The outer surface shaping functions of the inner and outer rotor permanent magnets adopt different shaping functions. The amplitudes of the main harmonics in the air gap magnetic flux are adjusted by adjusting the introduction ratios of the fundamental wave, the third harmonic and the fifth harmonic in the outer surface shaping function of the permanent magnet. At this time, the magnetic permeability of the stator modulation block modulates the harmonics of each order in the inner and outer air gap magnetic flux. By adjusting the offset angle and length and width of the stator modulation block, more harmonics can be modulated and the content of the harmonics that bring torque pulsation can be reduced to a certain extent. In addition, the stator modulation block provides more paths for the parallel connection between the inner and outer rotor permanent magnets, which increases the torque and suppresses the torque pulsation.

[0020] 4. The materials used for the stator and rotor of the generator are both steel and aluminum, which effectively reduces the overall mass of the generator. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1This is a radial topological structure diagram of a direct-drive permanent magnet flat wire wind turbine generator according to the present invention;

[0022] Figure 2 for Figure 1 Schematic diagram of the axial section;

[0023] Figure 3 for Figure 1 A magnified schematic diagram of the stator winding frame and stator modulation block structure in the middle part;

[0024] Figure 4 for Figure 1 An enlarged schematic diagram of the structure of the inner rotor permanent magnet 1.3.1;

[0025] Figure 5 for Figure 1 A magnified schematic diagram of the structure of the inner and outer rotor permanent magnets 3.2.1;

[0026] Figure 6 Schematic diagram of the topology of the initial generator M1, the intermediate generator M2 and the designed final generator M3;

[0027] Figure 7 Schematic diagram of the effect of the main air gap harmonics of the initial generator M1 on the torque and torque ripple;

[0028] Figure 8 for Figure 1 Schematic diagram of the permanent magnet potential of the inner rotor permanent magnet steel 1.3.1;

[0029] Figure 9 for Figure 1 Schematic diagram of the permanent magnet potential of the inner and outer rotor permanent magnets 3.2.1;

[0030] Figure 10 for Figure 1 Schematic diagram of the magnetic permeance of the stator modulation block 2.2.1 of the middle stator winding frame;

[0031] Figure 11 for Figure 6 Schematic diagram comparing the no-load induced electromotive force of the initial generator M1, the intermediate generator M2 and the final generator M3;

[0032] Figure 12 for Figure 6 Schematic diagram comparing the load torques of the initial generator M1, the intermediate generator M2 and the final generator M3;

[0033] Figure 13 for Figure 6 Schematic diagram of the comparison of air gap magnetic density harmonics before and after between the initial generator M1 and the final generator M3;

[0034] Figure 14 for Figure 6Schematic diagram of the comparison of the external air gap magnetic flux harmonics before and after between the initial generator M1 and the final generator M3;

[0035] Figure 15 for Figure 6 Schematic diagram of the comparison of the no-load induced electromotive force of the initial generator M1 and the final generator M3 before and after;

[0036] Figure 16 for Figure 6 Schematic diagram of the before and after comparison of the cogging torque of the initial generator M1 and the final generator M3;

[0037] Figure 17 for Figure 6 Schematic diagram of the before and after comparison of the load torque of the initial generator M1 and the final generator M3.

[0038] In the figure, 1. inner rotor; 2. stator; 3. outer rotor; 4. chassis; 5. rotating shaft; 1.1 inner rotor inner shell; 1.2 inner rotor iron ring; 1.3 inner rotor permanent magnet sleeve; 1.3.1 inner rotor permanent magnet; 1.4 inner rotor outer shell; 2.1 stator inner shell; 2.2 stator winding frame; 2.2.1 stator modulation block; 2.2.2 winding frame center column; 2.3 three-phase centralized flat wire armature winding; 2.4 stator outer shell; 3.1 outer rotor inner shell; 3.2 outer rotor permanent magnet sleeve; 3.2.1 outer rotor permanent magnet; 3.3 outer rotor iron ring; 3.4 outer rotor outer shell. DETAILED DESCRIPTION

[0039] See also Figure 1 and Figure 2 The present invention discloses a direct-drive permanent magnet flat-wire wind turbine generator, which is a permanent magnet wind turbine generator with high permanent magnet utilization, high efficiency, and low torque pulsation. It is essentially a dual-rotor permanent magnet generator, comprising an inner rotor 1, a stator 2, an outer rotor 3, a chassis 4, and a rotating shaft 5. The rotating shaft 5 is located in the center, and the inner rotor 1 is located near the rotating shaft 5. The outer rotor 3, stator 2, inner rotor 1, and rotating shaft 5 are coaxially nested with a gap from the outside to the inside. The stator 2 is located between the inner rotor 1 and the outer rotor 3, and the inner rotor 1 is coaxially nested inside the stator 2, sharing the same centerline. The inner rotor 1, outer rotor 3, and rotating shaft 5 are all mounted and fixed on the chassis 4 for coaxial rotation. The ends of the same rotor are fixed together by the bottom chassis 4, and the connection method is welding, so that the generator rotor forms a whole. The chassis 4 and the rotating shaft 5 are both made of steel. The stator 2 has a winding frame 2.2, on which a three-phase centralized flat wire winding 2.3 is wound.

[0040] The inner rotor 1 is composed of an inner rotor inner shell 1.1, an inner rotor iron ring 1.2, an inner rotor permanent magnet sleeve 1.3 and an inner rotor outer shell 1.4, which are tightly fitted in sequence from the inside to the outside. The inner rotor inner shell 1.1 is on the innermost side of the inner rotor 1 and is covered with the inner rotor iron ring 1.2. The inner wall of the inner rotor iron ring 1.2 is tightly connected to the outer wall of the inner rotor inner shell 1.1. The inner rotor permanent magnet sleeve 1.3 is tightly fitted outside the inner rotor iron ring 1.2. The inner rotor outer shell 1.4 is tightly fitted outside the inner rotor permanent magnet sleeve 1.3. N is evenly fixed and embedded in the inner rotor 1 along the circumferential direction. r The inner rotor permanent magnet steel 1.3.1 is fixed evenly along the circumferential direction on the inner rotor permanent magnet sleeve 1.3. r The inner rotor permanent magnet steel 1.3.1. The inner rotor permanent magnet sleeve 1.3 is first processed from aluminum into a solid ring structure, and then N is evenly cut along the circumference. r Each hole accommodates an inner rotor permanent magnet 1.3.1, and then the inner rotor permanent magnet 1.3.1 is inserted into the corresponding hole respectively; N r The inner rotor permanent magnet steel 1.3.1 is magnetized along the radial direction of the inner rotor 1, and the magnetization directions of two adjacent inner rotor permanent magnet steels 1.3.1 are opposite in radial direction. In order to avoid the influence of unilateral unbalanced magnetic pull on the generator performance, N r The inner rotor inner shell 1.1 and the inner rotor outer shell 1.4 are both made of steel.

[0041] The stator 2 is coaxially located between the inner rotor 1 and the outer rotor 3, and the central portion of the inner rotor 1 is used to place the shaft 5. Figure 3 As shown, the stator 2 includes a stator inner shell 2.1 and a stator outer shell 2.4 connected as a whole. The part closest to the inner rotor 1 is the stator inner shell 2.1. The stator inner shell 2.1 and the stator outer shell 2.4 are an integral structure. The stator inner shell 2.1 and the stator outer shell 2.3 are both made of steel. N is evenly opened along the circumferential direction between the stator inner shell 2.1 and the stator outer shell 2.3. s There are arc-shaped slots, and an I-shaped winding frame 2.2 is placed in each arc-shaped slot, so that N are evenly arranged along the circumferential direction between the stator inner shell 2.1 and the stator outer shell 2.3. sEach winding frame 2.2 is in the shape of an I, with its top and bottom surfaces on the inner and outer sides, respectively, and its center column 2.2.2 arranged radially. The winding frame 2.2 is made of aluminum, and two rectangular holes are opened in the center column 2.2.2 of each I-shaped winding frame 2.2. The two rectangular holes are symmetrical along the center line of the center column 2.2.2. A rectangular stator modulation block 2.2.1 is fixedly embedded in each rectangular hole. The length and width of the rectangular stator modulation block 2.2.1 are consistent with the length and width of the rectangular hole. The length direction of the rectangular stator modulation block 2.2.1 is consistent with the length direction of the center column 2.2.2, that is, the length is along the diameter direction. The rectangular stator modulation block 2.2.1 is made of iron. The stator modulation block 2.2.1 will form a modulation pole in the stator 2, which generates a stator modulation magnetic permeance. According to the modulation mechanism of the magnetic field modulation motor, the length and width of the stator modulation block 2.2.1 will respectively affect the peak height and waveform width of each order of magnetic permeance in the stator modulation magnetic permeance.

[0042] A three-phase centralized flat wire winding 2.3 is wound around the center column 2.2.2 of each winding frame 2.2. This three-phase armature winding utilizes a flat wire structure. Each coil of the centralized flat wire winding 2.3 is evenly spaced between two adjacent winding frames 2.2, with each winding span being 1. The stator inner shell 2.1 and stator outer shell 2.3 are sealed to secure the three-phase centralized flat wire winding 2.3 and prevent damage to the windings in harsh weather conditions during actual use.

[0043] See also Figure 1 The outer rotor 3 is composed of an outer rotor inner shell 3.1, an outer rotor permanent magnet sleeve 3.2, an outer rotor iron ring 3.3 and an outer rotor outer shell 3.4, which are tightly nested from the inside to the outside. N r The outer rotor permanent magnet steel 3.2.1 is similar to the inner rotor 1. The outer rotor permanent magnet sleeve 3.2 is also made of a solid ring structure made of aluminum. It is placed between the outer rotor inner shell 3.1 and the outer rotor outer shell 3.4. Then, a hole is opened in the circumferential direction at the corresponding position of the outer rotor permanent magnet sleeve 3.2 to accommodate N r The holes of the outer rotor permanent magnet steel 3.2.1 are opened, and then N r The outer rotor permanent magnets 3.2.1 are inserted in order, the outer rotor permanent magnets 3.2.1 are magnetized in the radial direction, and the magnetization directions of two adjacent permanent magnets 3.2.1 are opposite, wherein the outer rotor inner shell 3.1 and the outer rotor outer shell 3.4 are both made of steel.

[0044] The center lines of the inner rotor permanent magnet steel 1.3.1 and the outer rotor permanent magnet steel 3.2.1 coincide with each other and face each other in the radial direction. The arc occupied by the pole pitch of the two adjacent permanent magnet steels of the inner rotor permanent magnet steel 1.3.1 and the outer rotor permanent magnet steel 3.2.1 is θ pm ,θ pm =360° / N rThe inner rotor permanent magnet steel 1.3.1 and the outer rotor permanent magnet steel 3.2.1 both have curved outer surfaces on the side close to the stator 2, and adopt a surface modification structure.

[0045] The inner rotor permanent magnet 1.3.1 generates a periodic radial distribution of inner air gap flux in the inner air gap between the inner rotor 1 and the stator 2. At the same time, the outer air gap between the outer wall of the stator 2 and the inner wall of the outer rotor 3 also has a periodic radial outer air gap flux generated by the outer rotor permanent magnet 3.2.1. The thickness of the inner and outer air gaps is related to the power level of the generator, the selected permanent magnet material, and the processing technology of the inner and outer rotor inner shells and stator shells. In this generator, the thickness of the inner and outer air gaps is selected to be 1mm.

[0046] See also Figure 4 , N is evenly placed in the inner rotor permanent magnet sleeve 1.3 along the circumferential direction r The inner rotor permanent magnet steel 1.3.1 is magnetized alternately in the radial direction. The pole arc occupied by the pole pitch between two adjacent inner rotor permanent magnet steels 1.3.1 is β ri ,β ri =2π / N r The inner rotor permanent magnet 1.3.1 adopts a bread-shaped curve topology design, and the length along the tangential direction is l pm , the width of the edge of the modified arc in the inner and outer directions is h pm , cross-sectional area S = 35 mm 2 , the surface modification technology is used on the bread-shaped outer surface of the inner rotor permanent magnet steel 1.3.1 close to the stator 2 side. The modification function can be expressed as h pm (x)=k1cos(px)+k2cos(3px)+k3cos(5px)+R pmi In order to enhance the fundamental wave and weaken the harmonics, the weight coefficients k1>0, k2<0, and k3<0 are set. In addition, based on the amplitudes of the 1st, 3rd, and 5th harmonics after Fourier decomposition of the initial air gap magnetic flux of the initial generator M1, the weight of each harmonic in the total amplitude of the three harmonics is calculated to serve as the initial values ​​of k1, k2, and k3. Given that the fundamental wave has the highest amplitude and the third harmonic amplitude is higher than the fifth harmonic amplitude, |k1|>|k2|>|k3|, p=Nr / 2, and R pmi The radius of the bottom of the inner rotor permanent magnet 1.3.1 is 124mm <R pmi <126mm, x is the absolute value of the tangential distance from each point on the shaping function to the center line of the inner rotor permanent magnet steel 1.3.1.

[0047] See also Figure 5 , N is evenly placed in the outer rotor permanent magnet sleeve 3.2 along the circumferential direction rThe outer rotor permanent magnet steel 3.2.1 with radial alternating magnetization, the pole arc occupied by the pole pitch between two adjacent outer rotor permanent magnet steels 3.2.1 is β ro ,β ro =2π / N r The outer rotor permanent magnet 3.2.1 uses the same bread-like curve topology design as the inner rotor permanent magnet 1.3.1. The tangential length of the bread-like curve design of the outer rotor permanent magnet 3.2.1 is l pm1 , the inner and outer widths of the trimming arc edge are h pm1 , the cross-sectional area is also S = 35mm 2 The surface modification technology is used on the bread-shaped inner surface of the outer rotor permanent magnet 3.2.1 close to the stator 2, and the modification function is h pm1 (x), where h pm1 (x) = k 11 cos(px)+k 22 cos(3px)+k 33 cos(5px)+R pmo The injection ratio of the fundamental wave and harmonics of the outer rotor permanent magnet 3.2.1 modification function is reversed, so k 11 <0,k 22 >0,k 33 >0, at this time, the weight of each of the three harmonics in the sum of the three harmonic amplitudes is calculated as the weight coefficient k 11 , k 22 , k 33 Given that the fundamental wave has the highest amplitude and the third harmonic amplitude is higher than the fifth harmonic amplitude, |k 11 |>|k 22 |>|k 33 |, p = Nr / 2, R pmi The radius of the bottom of the outer rotor permanent magnet 3.2.1 is 146mm <R pmi <148mm, where x is the absolute value of the tangential distance from each point on the shaping function to the centerline of the outer rotor permanent magnet steel 3.2.1.

[0048] See also Figure 6 As shown, Figure 6 The generator M1 shown in (a) is used as the initial generator. The main topology of the generator is kept unchanged, including the inner and outer radii of the inner rotor 1, which are 117 mm and 130 mm respectively. The single inner and outer rotor permanent magnets of the initial generator M1 are both rectangular without any modification design. The cross-sectional area of ​​the permanent magnet is S = 35 mm. 2The inner and outer radii of the stator 2 are 131mm and 141mm respectively, and the inner and outer radii of the outer rotor 3 are 142mm and 154mm respectively. The topological shape of the permanent magnet, including the length and width of the permanent magnet steel and the length and width of the stator modulation block, need to be designed later. The radial and tangential air gap harmonics B of the initial generator M1 are simulated. r (θ,t) and B t (θ, t), and perform Fourier decomposition on it. Then, the contribution of each harmonic in the air gap harmonic to the torque and torque ripple is calculated according to the Maxwell stress tensor method, where each air gap harmonic order generates a torque T k (t) can be calculated by formula (1), and the torque pulsation T generated by each harmonic is kripple It can be calculated by (2). In addition, t is the generator operation time, which is between 0-T, T is the electrical cycle, T = 60 / np, n is the speed, p is the number of permanent magnet pole pairs, p = N r / 2.

[0049]

[0050] Where k is the air gap harmonic order, θ rk and θ tk are the radial and tangential phases of the kth air gap harmonic, R air is the radius of the generator air gap circle, La is the generator shaft length, μ0 is the vacuum permeability, Max represents the maximum value, Min represents the minimum value, Avg represents the average value, T kripple Represents the torque pulsation value generated by each order harmonic. The torque and torque pulsation generated by each main harmonic are calculated by formula (1) and (2), and the first three harmonics that generate the main torque pulsation are selected. Figure 7 As shown, the harmonics that generate the main torque pulsation in this generator are the fundamental wave, the third harmonic and the fifth harmonic, and the fundamental wave is also the main harmonic that generates torque.

[0051] like Figure 8 and 9 As shown, based on the initial generator M1 without permanent magnet steel modification design, after the inner and outer rotor permanent magnet steels adopt surface modification functions, the inner rotor permanent magnet magnetic potential can be expressed as the square magnetic potential F below pmi0 and the upper surface modification function F pmi1 The superposition of the cosine-shaped magnetic potential generated, where F pmi0 is the amplitude of the magnetic potential harmonics generated by the lower half of the square of the inner rotor permanent magnet 1.3.1, F pmi1 The magnetic potential harmonic amplitude generated by the outer surface modification of the upper part of the inner rotor permanent magnet 1.3.1 is the magnetic potential harmonic amplitude generated by the outer surface modification of the upper part of the inner rotor permanent magnet 1.3.1. pmi0 and the upper surface clipping function F pmi1The permanent magnet magnetic potential of the inner rotor obtained by Fourier decomposition can be expressed as formula (3), and the magnetic potential of each order generated by the harmonic injection of the permanent magnet steel can be expressed as formula (4).

[0052] The outer rotor permanent magnet 3.2.1 is designed with a modified function on its outer surface close to the stator 2, and the generated outer rotor permanent magnet magnetic potential is the upper square magnetic potential F pmo0 and the lower surface clipping function F pmo1 The superposition of the cosine-shaped magnetic potential, F pmo0 is the harmonic amplitude of the magnetic potential generated by the rectangular permanent magnet steel in the upper part of the outer rotor permanent magnet 3.2.1, F pmo1 The magnetic potential harmonic amplitude generated by the outer surface modification of the lower half of the outer rotor permanent magnet steel 3.2.1 is the magnetic potential harmonic amplitude generated by the outer surface modification of the upper square magnetic potential F pmo0 and the lower surface clipping function F pmo1 After Fourier decomposition, the permanent magnet magnetic potential of the outer rotor can be expressed as formula (5), and the magnetic potential of each order generated by the harmonic injection of the permanent magnet steel can be expressed as formula (6):

[0053]

[0054] Where i is a positive odd number, ω r is the mechanical speed of the inner rotor, θ is the air gap circumferential position angle, θ ri0 is the initial phase of the i-th harmonic of the permanent magnet potential of the inner rotor, θ rpm is the width of the inner rotor permanent magnet, θ rpm1 is the width of the outer rotor permanent magnet, B pm is the remanence of the permanent magnet, μ r is the relative magnetic permeability of the permanent magnet, θ ro0 is the initial phase of the i-th harmonic of the permanent magnet magnetic potential of the outer rotor, F pmi1i is the i-th harmonic amplitude of the magnetic potential generated by the outer surface modification of the upper half of the inner rotor permanent magnet steel, F pmo1i is the i-th harmonic amplitude of the magnetic potential generated by the outer surface modification of the lower half of the outer rotor permanent magnet steel.

[0055] From formulas (3), (4), (5) and (6), it can be seen that due to the modification design of the surface of the permanent magnet steel, the permanent magnet potential harmonics generated by the permanent magnet steel will also change accordingly, which will directly change the air gap harmonics. By specifically changing the injection ratio of the fundamental third and fifth harmonics in the modification functions of the inner and outer rotor permanent magnet steels 1.3.1 and 3.2.1, the purpose of reducing the torque pulsation harmonics and enhancing the torque harmonics can be achieved. After the inner and outer rotor permanent magnet steels 1.3.1 and 3.2.1 are both modified, the following is formed: Figure 6 The intermediate generator M2, such as Figure 6As shown in Figure (b), the change from the initial generator M1 to the intermediate generator M2 only changes the topology of the permanent magnet steel, while the other generator sizes remain unchanged.

[0056] Next, the parameters of the intermediate generator M2 are screened. Since the air gap harmonics of this generator will be affected not only by the topology of the permanent magnet steel, but also by the position of the permanent magnet steel, and one harmonic will also affect the performance of different generators, the objective function is then defined as the function F[Max(H1th), Min(H3th), Min(H5th)] about the air gap harmonics. The constraints are that the harmonic injection ratio in the shaping function, the length and width of the permanent magnet steel, and the position of the permanent magnet steel vary within their respective precise selection ranges. By calculating the sensitivity of the harmonic injection ratio and the position of the permanent magnet steel in the shaping functions of the inner and outer rotors to the function F, as shown in Table 1 below, the sensitivity of each parameter to each harmonic is calculated and three sets are screened out. The parameter set with high sensitivity to each harmonic is recorded as P H1 , the parameter set that is basically only sensitive to the harmonics that generate torque is recorded as P H2 , and the parameter set that is only sensitive to the harmonics that generate torque pulsation is recorded as P H3 .

[0057] Table 1

[0058]

[0059] See also Figure 3 and Figure 10 Based on the topological design of the permanent magnet of the intermediate generator M2, two iron stator modulation blocks 2.2.1 are placed in the winding frame 2.2 on the stator inner shell 2.1, which are symmetrical along the center line of the stator winding frame 2.2. This will form a modulation pole in the stator 2. The pole pitch between the two winding frames 2.2 occupies an arc of θ s , radians θ s The value of θ s =2π / N s The width of each winding frame 2.2 occupies an arc of θ rao ,θ rao Satisfy θ rao =k rao *θ s , k rao is the pole arc coefficient of the stator winding frame 2.2, of which 0.9 <k rao <0.95, where the arc occupied by the winding frame center column 2.2.2 is θ raoz ,θ raoz Satisfy θ raoz =k raoz *θ rao , k raozis the pole arc coefficient of the stator winding frame center column 2.2.2, where 0.5 <k raoz <0.6, two iron stator modulation blocks 2.2.1 are placed in the winding frame center column 2.2.2, each stator modulation block 2.2.1 is rectangular, and its length is l tie , width is h tie The distance between the stator modulation block 2.2.1 and the center line of the winding frame center column 2.2.2 occupies an arc of θ1, where 0.3deg<θ1<0.35deg, and the width of the modulation block 2.2.1 occupies an arc of θ tie , where θ tie =l tie / θ s , and θ2=θ1+θ tie The stator modulation permeance generated by the two symmetrically distributed stator modulation blocks 2.2.1 can be expressed as formula (7). According to the modulation mechanism of the magnetic field modulation generator, the length h of the iron modulation block 2.2.1 is tie and width tie It will affect the peak height and waveform width of each order of the modulated permeance, and the harmonics M of each order of the stator permeance stiem It can be expressed as formula (8):

[0060]

[0061] According to formulas (7) and (8), it can be found that the stator permeance is changed due to the introduction of stator modulation block 2.2.1. The change of stator permeance will change the modulation behavior of the permanent magnetic field and thus change the air gap harmonics, so that the harmonic changes can be achieved in a targeted manner. On this basis, the final generator M3 is formed, as shown in Figure 6 As shown in Figure (c), the final generator M3 and the intermediate generator M2 only change the structure inside the stator winding frame, that is, only the stator modulation block 2.2.1 is placed in the winding frame column 2.2.2, while the permanent magnet steel topology remains unchanged. In addition, the other topological structures are unchanged compared to the initial generator M1. The inner rotor permanent magnet flux density B generated by the inner air gap magnetic field of the final generator M3 pmi (θ ri ,t) is the permanent magnet potential F of the inner air gap magnetic field pmi (θ ri ,t) and stator permeability M stie (θ) is multiplied to obtain the permanent magnetic flux density B of the outer rotor generated by the external air gap magnetic field. pmo (θ ro ,t) is the permanent magnet potential F of the inner air gap magnetic field pmo (θ ro ,t) and stator permeability M stie (θ) and (θ) can be multiplied to obtain the two, which can be expressed as formulas (9) and (10) respectively:

[0062]

[0063] See also Figure 6 , Figure 11 and Figure 12 Finally, in the generator M3, due to the introduction of the stator modulation permeance, the harmonic order and amplitude in the air gap will be changed. Then, according to the modulation mechanism of the magnetic field modulation generator, the harmonic injected by the rotor permanent magnet will also be modulated to |iP r ±jN s Therefore, changing the injection ratio of each harmonic in the permanent magnet steel shaping function will change the air gap magnetic flux harmonics. Changing the length and width of the stator modulation block will also change the air gap magnetic flux harmonics. This is called multi-modulation design. The overall design process and performance comparison of generators M1, M2 and M3 are as follows. Figure 6 , as shown in Figures 11 and 12, after the two-step multi-modulation design, higher induced electromotive force and torque, as well as smaller torque ripple can be obtained.

[0064] Then, the parameters of the stator modulation block 2.2.1 are subjected to sensitivity analysis on the objective function F[Max(H1th), Min(H3th), Min(H5th)], as shown in Table 2 below. The sensitivity of each parameter to each harmonic is calculated and three sets are selected. The parameter set with high sensitivity to each harmonic is recorded as P H11 The parameter set that is basically only sensitive to the generation of torque pulsation harmonics is recorded as P H22 , and the parameter set with low sensitivity to the three harmonics is recorded as P H33 .

[0065] Table 2

[0066]

[0067]

[0068] Then, by selecting P H1 and P H11 The parameter set in is named parameter set Q1, and the set P H2 and P H22 The parameter union in is named set Q2, and the set P H3 and P H33 The parameter union in is named as set Q3. Since the interaction between air gap harmonics is the root cause of torque and torque ripple, the correlation degree of the main air gap harmonics is calculated and analyzed through the above parameters. The objective function of set Q1 is set as F[Max(T avg ), Min(T ripple )],Max(T avg ) is the average torque T avgThe maximum value Max, Min (T ripple ) is the torque ripple T ripple Minimum value Min, in addition, since the parameters in set Q2 are mainly harmonics associated with torque, the objective function of set Q2 is set to F[Max(T avg )], and the parameters in set Q3 are mainly parameters associated with torque pulsation harmonics, so the objective function of set Q3 is set to F[Min(T r ipple )], a multi-objective genetic algorithm is used to solve and determine the final variable parameters of the generator.

[0069] By designing and optimizing the harmonic injection ratios in the surface modification functions of the inner and outer rotor permanent magnets 1.3.1 and 3.2.1 and the parameters of the stator modulation block, the final generator with multi-modulation design was obtained. The performance of the initial design, the initial generator M1, was compared with the final generator. The outer surface modification function h of the inner rotor permanent magnet 1.3.1 of the final generator M3 is pm (x) can be determined as: h pm (x) = 4cos(18x) - 0.15cos(54x) - 0.04cos(90x) + 124.2, and finally the inner surface modification function h of the permanent magnet steel of the outer rotor of the generator M3 pm1 (x) can be determined as: h pm1 (x) = -5.3cos(18x) + 0.17cos(54x) + 0.03cos(90x) + 146.1, as shown in Table 3 below:

[0070] Table 3

[0071] Parameter name Parameter value Parameter name Parameter value Parameter name Parameter value <![CDATA[K1]]> 4 <![CDATA[K 11 ]]> -5.3 <![CDATA[h tie ]]> 0.7 <![CDATA[K2]]> -0.15 <![CDATA[K 22 ]]> 0.17 <![CDATA[l tie ]]> 7 <![CDATA[K3]]> -0.04 <![CDATA[K 33 ]]> 0.03 <![CDATA[θ tie ]]> 0.3 <![CDATA[R pmi ]]> 124.2 <![CDATA[R pmo ]]> 146.1 <![CDATA[R tie ]]> 132.5 <![CDATA[l pm ]]> 8.6 <![CDATA[l pm1 ]]> 8.8

[0072] like Figure 13 and Figure 14 As shown, before and after the generator design, the fundamental wave with 18 permanent magnet pole pairs still accounts for the highest proportion of the air gap magnetic flux in the generator air gap. However, due to the introduction of the stator modulation block 2.2.1, a harmonic component with 9 pole pairs as the fundamental wave of the armature winding pole pairs is generated in the generator. In addition, after the shaping of the rotor permanent magnet steel and the introduction and optimization design of the stator modulation block 2.2.1, the third and fifth harmonics that generate torque pulsation in the internal and external air gap magnetic flux are weakened to a certain extent, especially the amplitude of the fifth harmonic is greatly reduced. In addition, the increase in the fundamental wave brings about an increase in load torque, and since the modulation of the stator modulation block 2.2.1 participates in the asynchronous modulation of the permanent magnet magnetic field, a rich range of working harmonics are generated. Although some harmonics, such as the 63rd harmonic, will also generate torque pulsation, the positive impact they bring is greater than the negative impact.

[0073] like Figure 15The permanent magnet flat wire wind turbine has a high sinusoidal no-load induced electromotive force. The generator adopts a single stator single winding double rotor design structure. Therefore, the induced electromotive force on the stator winding is determined by the inner rotor air gap permanent magnet magnetic flux density B pmi (θ ri ,t) and the outer rotor air gap permanent magnet flux density B pmo (θ ro ,t) together, but due to the radial alternating magnetization adopted by the inner and outer rotors, there will be a magnetic potential offset in the radial permanent magnet magnetic potential. The no-load induced electromotive force on the stator winding is equivalent to the superposition of the two no-load induced electromotive forces generated by the inner and outer rotors respectively. The induced electromotive force can be expressed as the derivative of the magnetic flux on the winding with respect to time through Faraday's electromagnetic induction principle, and the magnetic flux can be obtained by integrating the magnetic density. Therefore, the no-load induced electromotive force is expressed as:

[0074]

[0075] Where k w is the winding factor, winding factor k w =k d *k p , distribution factor k d =1, Pitch factor N w is the number of turns per phase and per slot, R si is the inner diameter of the stator, R so is the stator outer diameter, L a is the generator shaft length, M s0 is the fundamental component of stator permeability, F pmi is the fundamental magnetic potential amplitude of the inner rotor permanent magnet, F pmo is the fundamental magnetic potential amplitude of the outer rotor permanent magnet, is the flat wire winding function. From the above formula, we can see that there will be a phase difference between the no-load induced electromotive force generated by the inner and outer rotors. The phase difference is only When the induced electromotive force generated by the inner and outer rotors is equal to the maximum value, the maximum induced electromotive force can be obtained on the stator winding.

[0076] like Figure 16 The cogging torque period of this low pulsation permanent magnet flat wire wind turbine is C cog =2π / LCM(N s , N r ), according to the “magnetic common energy difference method”, the cogging torque T cog The value of is the generator magnetic energy to the magnetic field rotation angle θ r The derivative of , in practical applications, can be taken as the equivalent formula:

[0077]

[0078] The above formula shows that the size of the cogging torque is proportional to the sum of the squares of the magnetic flux density amplitude. The magnetic flux harmonics in the air gap of this generator have good sinusoidal properties and low harmonic content. The fundamental wave is the main wave, followed by odd-order harmonics such as the third harmonic. As for the value of the sum of squares, the more harmonic content and the smaller the harmonic amplitude, the smaller the sum of squares and the smaller the cogging torque. Figure 13 and Figure 14 As shown, the generator's use of permanent magnet surface modification technology and stator permeability modulation produces more low-amplitude harmonics, reducing the amplitude of the original high-content third and fifth harmonics. The squared value of these reduced harmonics is even smaller, ultimately achieving a significant reduction in cogging torque. This also demonstrates, to a certain extent, the beneficial effect of this method on reducing load torque pulsation. The cogging torque can be reduced by weakening high-order odd harmonics. Since the stator modulation block 2.2.1 is placed in the middle column 2.2.2 of the stator winding frame, each pair of stator modulation blocks 2.2.1 will modulate the permanent magnet magnetic field of the inner rotor, thereby generating low-order harmonics in the air gap flux density of the inner rotor that are lower than the fundamental wave order, but their content is low. According to the formula of the cogging torque, it can be obtained that when the sum of the squares of the air gap flux density of each order harmonic is small, the cogging torque will also be reduced. Therefore, the cogging torque amplitude of the generator can be effectively reduced by the outer surface modification technology of the permanent magnet steel and the placement of the stator modulation block 2.2.1 in the middle column 2.2.2 of the stator winding frame.

[0079] The present invention utilizes a double-layer rotor design with inner and outer air gaps to improve the utilization rate of permanent magnets and increase the generator's torque. Furthermore, shaping technology is introduced on the inner and outer surfaces of the permanent magnets in the generator's inner and outer rotors, enabling harmonic injection design to reduce the generator's torque pulsation. Furthermore, the stator modulation block 2.2.1 is cleverly placed within the stator winding frame's center column 2.2.2 to increase the generator's induced electromotive force and output power. Furthermore, the stator modulation block 2.2.1 produces a beneficial asynchronous modulation phenomenon for the air gap flux density in the inner and outer air gaps, increasing the operating harmonics within the generator's air gap harmonics and further enhancing the generator's torque output capacity. Furthermore, by designing the generator winding as flat wire, losses generated during generator operation are reduced, improving the generator's efficiency and extending its service life. The overall generator housing is constructed of stainless steel, while internal materials, including the permanent magnet housing and winding frame, are constructed of lightweight, ductile aluminum. This significantly reduces the overall mass of the generator and increases its power density.

Claims

1. A direct-drive permanent magnet flat-wire wind turbine generator comprising an outer rotor, a stator, an inner rotor, and a rotating shaft, which are nested coaxially with a gap from the outside to the inside, and is characterized by: The inner rotor is evenly fixed with N r The inner rotor has permanent magnet steel (1.3.1), and the outer rotor is evenly fixed with N r The inner and outer rotor permanent magnets (1.3.1, 3.2.1) are radially opposite to each other, and the magnetization directions of the adjacent inner and outer rotor permanent magnets (1.3.1, 3.2.1) are radially opposite. r is an even number; The outer surfaces of the inner and outer rotor permanent magnets (1.3.1, 3.2.1) on the side close to the stator are both curved, and a surface modification structure is adopted. The modification function of the inner rotor permanent magnet (1.3.1) is h pm (x)=k1cos(px)+k2cos(3px)+k3cos(5px)+R pmi , the shape modification function of the outer rotor permanent magnet steel (3.2.1) is h pm1 (x)=k 11 cos(px)+k 22 cos(3px)+k 33 cos(5px)+R pmo , k1>0, k2<0, k3<0, |k1|>|k2|>|k3|, k 11 <0,k 22 >0,k 33 >0,|k 11 |>|k 22 |>|k 33 |, p = Nr / 2, R pmi R is the radius of the bottom of the inner rotor permanent magnet (1.3.1), pmi is the radius at the bottom of the outer rotor permanent magnet (3.2.1), and x is the absolute value of the tangential distance from each point on the shape modification function to the center line of the inner and outer rotor permanent magnets (1.3.1, 3.2.1); The stator comprises a stator inner shell (2.1) and a stator outer shell (2.4) connected as a whole, and N is evenly arranged along the circumferential direction between the stator inner shell (2.1) and the stator outer shell (2.4). s The winding frame (2.2) is in the shape of an I, and the top and bottom surfaces of the I are on the inner and outer sides respectively. The center column (2.2.2) of the I is arranged in the radial direction. Two rectangular stator modulation blocks (2.2.1) are fixedly embedded in each center column (2.2.2). The two stator modulation blocks (2.2.1) are symmetrical along the center line of the center column (2.2.2). A three-phase centralized flat wire winding (2.3) is wound on the center column (2.2.2) of each winding frame (2.2).

2. The direct-drive permanent magnet flat wire wind turbine according to claim 1, characterized in that: The inner rotor is composed of an inner rotor inner shell (1.1), an inner rotor iron ring (1.2), an inner rotor permanent magnet sleeve (1.3) and an inner rotor outer shell (1.4) which are tightly nested from the inside to the outside. N r The rotor permanent magnet steel block (1.3.1).

3. The direct-drive permanent magnet flat wire wind turbine according to claim 1, characterized in that: The inner rotor inner shell (1.1) and the inner rotor outer shell (1.4) are both made of steel, and the inner rotor permanent magnet sleeve (1.3) is made of aluminum.

4. The direct-drive permanent magnet flat wire wind turbine according to claim 1, characterized in that: The outer rotor is composed of an outer rotor inner shell (3.1), an outer rotor permanent magnet sleeve (3.2), an outer rotor iron ring (3.3) and an outer rotor outer shell (3.4) which are tightly nested from the inside to the outside. N r outer rotor permanent magnet steel (3.2.1).

5. The direct-drive permanent magnet flat wire wind turbine according to claim 4, characterized in that: The outer rotor inner shell (3.1) and the outer rotor outer shell (3.4) are both made of steel, and the material of the outer rotor permanent magnet sleeve (3.2) is aluminum.

6. The direct-drive permanent magnet flat wire wind turbine according to any one of claims 1 to 5, characterized in that: The material of the stator modulation block (2.2.1) is iron, the stator inner shell (2.1) and the stator outer shell (2.4) are both made of steel, the material of the winding frame (2.2) is aluminum, and the inner rotor, outer rotor and the same end of the shaft are all fixed on the chassis and rotate coaxially. The chassis and the shaft are both made of steel.

7. The direct-drive permanent magnet flat wire wind turbine according to any one of claims 1 to 5, characterized in that: Each coil of the centralized flat wire winding (2.3) is evenly placed in the space between two adjacent winding frames (2.2), and the span of each winding group is 1.

8. The direct-drive permanent magnet flat wire wind turbine according to any one of claims 1 to 5, characterized in that: The stator inner shell (2.1) and the stator outer shell (2.4) are sealed to fix the three-phase concentrated flat wire winding (2).

9. A low torque ripple design method for a direct-drive permanent magnet flat wire wind turbine according to claim 1, characterized in that The following steps are involved: Step (1): Perform Fourier decomposition on the radial and tangential air gap harmonics of the initial motor whose inner and outer rotor permanent magnets (1.3.1, 3.2.1) are both rectangular and analyze their waveforms, calculate the contribution of each harmonic in the air gap harmonics to the torque and torque ripple, and select the first three harmonics that produce the main torque ripple, which are the fundamental wave, the third harmonic and the fifth harmonic; Step (2): Inject harmonics on the surface of the rectangular inner rotor permanent magnet (1.3.1) and change the inner rotor permanent magnet (1.3.1) to the modification function h pm (x)=k1cos(px)+k2cos(3px)+k3cos(5px)+R pmi The curve represented is based on the amplitudes of the 1st, 3rd and 5th harmonics after Fourier decomposition of the initial air gap flux of the initial motor M1, and the weight of each of the three harmonics in the total amplitude of the three harmonics is calculated as the initial values ​​of k1, k2 and k3; Step (3): Inject harmonics on the surface of the rectangular outer rotor permanent magnet steel (3.2.1) and change the outer rotor permanent magnet steel 3.2.1 into a modification function h pm1 (x)=k 11 cos(px)+k 22 cos(3px)+k 33 cos(5px)+R pmo The curve represented by the calculation of the weight of each of the three harmonics in the sum of the three harmonic amplitudes is k 11 , k 22 , k 33 Initial values ​​of , to obtain the intermediate motor topology; Step (4): Parameter screening is performed on the intermediate generator, and the objective function is defined as the function F[Max(H1th), Min(H3th), Min(H5th)] about the air gap harmonics. The constraints are the harmonic injection ratio in the shaping function, the length and width of the inner and outer rotor permanent magnets, and the position of the permanent magnets. The sensitivity of the harmonic injection ratio and the position of the permanent magnets in the shaping function to the function F is calculated. The sensitivity of each parameter to each harmonic is calculated and three sets are screened. The parameter set with high sensitivity to each harmonic is recorded as P H1 , the parameter set that is only highly sensitive to the harmonics that generate torque is recorded as P H2 , the parameter set that is only highly sensitive to the harmonics that generate torque ripple is recorded as P H3 ; Step (5): Place two stator modulation blocks (2.2.1) in the winding frame (2.2); Step (6): Perform sensitivity analysis on the harmonic injection ratio and the length and width parameters of the stator modulation block (2.2.1) to the objective function F[Max(H1th), Min(H3th), Min(H5th)], calculate the sensitivity of each parameter to each harmonic and select three sets. The parameter set with high sensitivity to each harmonic is recorded as P H11 , the parameter set that is only highly sensitive to the generation of torque ripple harmonics is recorded as P H22 The parameter set with low sensitivity to the three harmonics is denoted as P H33 ; Step (7): Select the set P H1 and P H11 The parameter set in is named parameter set Q1, and the set P H2 and P H22 The parameter union in is named set Q2, and the set P H3 and P H33 The parameter union in is named set Q3, and the objective function of set Q1 is set to F[Max(T avg ), Min(T ripple )], set the objective function of set Q2 to F[Max(T avg )], set the objective function of set Q3 to F[Min(T ripple )], and the multi-objective genetic algorithm is solved simultaneously to determine the final variable parameters of the motor.

10. The low torque ripple design method according to claim 9, characterized in that: The outer rotor permanent magnet potential generated by the inner and outer rotor permanent magnets (1.3.1, 3.2.1) is the superposition of the upper square magnetic potential and the cosine magnetic potential generated by the lower surface clipping function. The upper square magnetic potential and the lower surface clipping function are Fourier decomposed respectively, and the base order in the shaping function of the inner and outer rotor permanent magnets (1.3.1, 3.2.1) is changed, and the third and fifth harmonic injection ratios are used to reduce the torque pulsation harmonics.

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