Wind turbine is a key device to realize the utilization of wind energy, and it has been highly valued by all countries. But the mechanical gear transmission of the existing wind power device has the disadvantages of high vibration and noise, high failure rate, and short service time. Magnetic field modulation electromagnetic gear transmission is a new non-contact transmission method. However, the conventional modulation magnetic gear has low torque density and torque defects with large fluctuations. In order to overcome the gear transmission problems of the existing semi-direct drive wind power generation machinery and improve the electromagnetic performance of the traditional magnetic gear transmission, this paper proposes a new transmission scheme of a non-contact semi-direct drive wind generator with a surface mount Halbach array modulated magnetic gear method, and considers the electromagnetic properties of the semi-direct drive modulation magnetic gear of the wind turbine. The finite element software is used to construct the model of the surface-mounted Halbach array magnetic gear and the conventional gear, analyzed the distribution of magnetic field lines of the two magnetic gears, calculated the air gap magnetic flux density of the inner and outer air gap, and obtained the main harmonics of the inner and outer air gap magnetic density; calculated the static torque and steady-state operating torque of the inner and outer rotors in the model, compared the air gap flux density, harmonics and torque of the magnetic gears. The simulation results show that the magnetic field modulation type magnetic gear of the surface mount Halbach array magnetic gear method improves the magnetic induction waveform of the inner and outer air gap, reduces the pulse torque fluctuation, and has a 60% higher static torque. Applying it to semi-direct drive wind power generation equipment not only overcomes the shortcomings of mechanical gears, but also has higher electromagnetic performance. Therefore, the surface-mounted Halbach array modulated magnetic gear can be used to replace the mechanical gearbox in the semi-direct drive wind power generation equipment.

With the increasing demand for energy in human society, wind energy has received attention as a pollution-free and renewable new energy [

In recent years, the concept of magnetic gears has received extensive attention from scholars. Because of the theory of magnetic field modulation proposed by Atallah et al. [

In order to improve the torque density and electromagnetic performance of the magnetic gear. Some scholars have proposed for magnetic gear permanent magnet material type, magnetic gear structure, permanent magnet installation method, magnetic modulator ring profile and other aspects of the improvement. For example, Chen et al. [

To compensate for the shortcomings of mechanical gearing and to improve the electromagnetic properties of magnetic gears, in this paper, magnetic gears using a Halbach array of permanent magnet mountings are proposed to be placed between the impeller and generator of a wind turbine, as shown in

The magnetic gears proposed in this paper are constructed with Halbach arrays on both the inner and outer rotors. First, modeling and analysis of the structure and the distribution of magnetic susceptibility lines by means of finite element software. Then make simulation analysis of gears in static and steady-state operation. According to the comparison with conventional magnetic gears in terms of air gap magnetic field distribution and harmonic content, it is found that the Halbach array magnetic gear has higher torque density, smaller pulse torque fluctuation, higher output speed and more stable output, and is more suitable to replace the mechanical gearbox of semi-direct drive wind turbines.

In this paper, Ansoft software is used to model and analyze the magnetic gears. As shown in

Parameter | Value |
---|---|

Axial length (mm) | 50 |

Pole pairs of the inner rotor | 4 |

Pole pairs of the outer rotor | 23 |

Pole pieces of flux modulators | 27 |

The outer radius of the outer rotor yoke/mm | 100 |

The inner radius of the outer rotor yoke/mm | 85 |

The thickness of the stationary ring/mm | 10 |

The outer radius of the inner rotor yoke/mm | 71 |

The thickness of permanent magnets on the inner rotor/mm | 10 |

The thickness of the air gap/mm | 2 |

In magnetic gears, the relationship between the number of adjusting magnets and the number of pole pairs of permanent magnets is as follows:

_{in} and _{out} were the pairs of permanent magnet poles assembled on the inner and outer rotors respectively; N_{S} was the number of magnetizing blocks. When the model is running, the magnetic control rings remain stationary and the inner and outer rotors rotate in opposite directions. Because the inner and outer rotor iron yokes and the magnetic pole pieces are insulated and coated with silicon steel sheets axially laminated, it prevents the occurrence of eddy currents greatly.

The magnetic inductance intensity in the air gap, without considering the action of the magnetic modulation ring, can be expressed as

In the equation: _{m} and _{m} were the Fourier coefficients and they were only related to the polar moment _{r} was the magnetic pole angular velocity, and _{0} was the initial rotor angle.

After the introduction of the demagnetizing ring and after the magnetic field modulation effect, the magnetic induction strength produced by the rotor permanent magnet field is

The magnetic field modulation ring primarily affects the internal and external air-gap magnetic fields so that the magnetic fields excited by the internal and external permanent magnets can be effectively coupled for torque transfer.

The magnetic field modulation ring primarily affects the magnetic field harmonics generated by the internal and external rotors. These same-pole synchronous harmonic pairs can be effectively coupled to generate stable magnetic torque to achieve torque transmission.

The magnetic field contains a large number of harmonic components, and their spatial pole pairs can be represented as

In the air gap, there is a specific number of rotational speed and spatial pole pairs for the harmonic component. The rotational speed corresponding to the harmonic component of the magnetic field can be expressed as

That _{m,k} was the spatial harmonic component angular velocity, _{r} was the magnetic gear rotor rotation speed and _{s} was the magnetic modulation ring rotation speed.

While

In fact, due to the limitation of the strength and rigidity of the magnetic gear, the modulation ring is usually fixed. Therefore, the gear ratio (

It is calculated that the transmission ratio of the two magnetic gears mentioned in this paper is 5.75.

The software analysis of the two magnetic gear models can be used to obtain the distribution of magnetic inductance lines shown in

The spatial harmonic spectrum of the air-gap magnetic susceptibility intensity is obtained by Fourier transform of the breath magnetic susceptibility data by mathematical calculation software in

Static torque is a measure of the magnetic gears by setting one rotor to stand still and not rotate and the other rotor to rotate in a fixed direction. From the Maxwell tensor method, the magnetic torque produced by this field coupling can be expressed as

Among them, _{ef} represented the axial length of the magnetic gear, _{0} was the vacuum permeability, _{R} and _{T} were the radial and tangential magnetic flux densities, respectively.

The static torque diagram of

Conventional magnetic gear | Halbach array magnetic gear | Increase rate | |
---|---|---|---|

Inner rotor | 21.4 N·m | 34.3 N·m | 60.3% |

Outer rotor | 123.1 N·m | 197.4 N·m | 60.3% |

Set the inner rotor of both magnetic gears in the simulation software at 40 r/min, doing clockwise rotation. The outer rotor rotates counterclockwise at 230 r/min. Obtaining the _{ripple} can be calculated as:

In formula _{max} and _{min} were the maximum and minimum values of dynamic torque, and _{avg} was the average value of dynamic torque. By calculating the data obtained in

Conventional magnetic gear | Halbach array magnetic gear | |
---|---|---|

_{min} of inner rotor (N·m) |
21. 4680 | 24. 5215 |

_{max} of inner rotor (N·m) |
21. 3741 | 24. 4940 |

_{avg} of inner rotor (N·m) |
21.4210 | 24.5077 |

_{max} of outer rotor (N·m) |
123.2321 | 140.9667 |

_{min} of outer rotor (N·m) |
122.9947 | 140.9405 |

_{avg} of outer rotor (N·m) |
123.1134 | 140.9536 |

_{ripple} of inner rotor |
0.43% | 0.11% |

_{ripple} of outer rotor |
0.19% | 0.02% |

In this paper, a scheme for replacing mechanical gearboxes with magnetic gears is proposed for the transmission system of Semi-Direct Drive Wind Turbines, and structural analysis and finite element performance analysis of this Halbach coaxial magnetic gear is performed. In terms of mechanical construction, magnetic gears offer the advantages of no contact, low noise, no frictional vibration, no lubrication and no overload protection. These properties can overcome the structural shortcomings of mechanical gearboxes. The permanent magnet mounting structure of the Halbach array magnetization method has greatly improved the torque performance of this coaxial magnetic gear. The self-shielded nature of the Halbach arrays allows for a unilateral increase in magnetic induction strength, which reduces the amount of inner and outer rotor yokes and the size of the wind power turbine. In addition, the Halbach array magnetization method generates more harmonics useful for torque and suppresses interference harmonics. Performance analysis showed that the static torque of Halbach magnetic gears was increased by 60%, with less torque fluctuations. Halbach array magnetic gears can transmit more torque, improve the magnetic induction strength waveform of the inner and outer layers, greatly reduce the torque fluctuation, and improve the transmission stability of magnetic gears. Therefore, this Halbach magnetic gear overcomes the disadvantages of mechanical gears and improves electromagnetic performance. It can better replace the mechanical gearbox in the semi-direct-drive wind turbine.