1. Types of Permanent Magnet Generator

1.1 Axial Permanent Magnet Generator

The axial permanent magnet generator is a generator with a high level of professional technology. It has a complex and compact structure inside and also has good power and efficiency. There are relatively many derivative models of this type of generator.

Usually, it is mainly divided by referring to the internal structure of the generator. It can be roughly divided into two types: slotless axial permanent magnet generators and slotted axial permanent magnet generators.

At present, this type of generator is commonly used in power generation enterprises. Because it is convenient to use and will not be greatly disturbed, it has been favored by a large number of enterprises. Among them, the use of slotless axial permanent magnet generators is more common.

However, the defects of this type of generator are also relatively obvious, and this type of generator does not have strong applicability in large-scale wind power generation systems.

1.2 Transverse Permanent Magnet Generator

Transverse permanent magnet generators operate somewhat differently than other types of generators in that the rotor is at a 90° angle to the direction of flux. Such a design method can further increase the space of the winding, and at the same time, it will not impose a large burden on the operation of the generator.

The internal structure of the transverse permanent magnet generator is divided into different forms, including claw pole type and single-side double type. However, this type of generator also has corresponding defects.

Due to its relatively complex internal structure, there is also the phenomenon of magnetic flux leakage, and the stability of its internal force density is slightly insufficient, and the actual applicability needs to be further improved.

1.3 Radial Permanent Magnet Generator

Compared with other types of generators, the radial permanent magnet generator has a big difference. The internal magnetic flux running line is a straight line.

At the same time, there are big differences between the inside and outside of the rotor. Because its structure is quite different from other permanent magnet generators, the management and control of its installation also need to be combined with a new process. For example, the installation of permanent magnets is mainly by embedding or surface-mounting.

Radial permanent magnet generators have the advantages of low cost and simple process structure. For most manufacturers, the use of such generators is relatively common, and radial permanent magnet generators have corresponding advantages in all aspects, such as It has good operational stability, and can meet the needs of various wind power generation systems. Therefore, the radial permanent magnet generator has strong competitiveness in the market.

2 Specific Applications of Permanent Magnet Generators

2.1 Reduce Pulsating Torque

In the process of supervising and controlling the running state of the generator, the enterprise usually takes the cogging torque and related data as the reference basis. The lower the relevant value is, the better the running state of the generator is. The torque value increases with the continuous operation of the generator.

Therefore, in order to ensure the good operating efficiency of the generator at all times, the torque value should be reduced by corresponding technical means.

Normally, the range of cogging ripple torque should be controlled within a reasonable range, which should be achieved by using the corresponding winding technology.

2.2 Anti-magnetic Protection Measures

The permanent magnet generator needs the corresponding magnetic force during operation. Generally, in the whole wind power generation system, the rotor generates the corresponding magnetic force through the movement of the permanent magnet core, so as to realize power generation.

In the process of wind power generation, if the permanent magnet generator is not effectively protected, it will easily lead to damage to the performance of the corresponding generator.

Therefore, in order to ensure that there will be no conflict between the wind power generation system and the permanent magnet generator, enterprises need to take necessary protective control measures to protect the generator system.

2.3 Low-speed Direct Drive Permanent Magnet Generator

The low-speed direct-drive permanent magnet generator has the characteristics of a flexible selection of poles, a large diameter, and low speed. Compared with the traditional high-speed permanent magnet generator, this type of generator uses more materials for production, and the cost of construction is relatively high.

In the management work of the current wind power generation system, the staff should consider reducing a series of costs in the process of power generation production through the reasonable combination of high-speed and low-speed direct-drive permanent magnet generators.

In the design process of low-speed direct-drive permanent magnet generators, designers need to consider the following aspects: first, designers need to select the generator structure scientifically and rationally, because the internal structures of permanent magnet generators are rich and diverse, such as Generally, there are transverse, radial, and axial.

Different structural types have a greater impact on the production cost of the generator and affect the operating power and performance of the generator. Secondly, the designer also needs to select the number of slots and poles scientifically and rationally.

Due to the large size of the low-speed direct-drive permanent magnet generator, there is no direct relationship between the generator speed and the output voltage. In the selection process of electromagnetic load, since the magnetic flux change of this type of generator is relatively small, but the number of stator windings is relatively large, the stator winding often has a large energy consumption, so the designer needs to adjust the stator winding reasonably. quantity.

In addition, the designer also needs to choose the cooling method scientifically and rationally. Since this type of generator generates a lot of heat, it needs to be combined with necessary air-cooling measures to ensure the normal and stable operation of the generator.

3 Development of Permanent Magnet Motor In Wind Power Generation Systems

3.1 Changes In The Motor Structure

Increasing the ventilation diameter of the motor can improve the cooling effect, and at the same time reduce the weight of the motor and reduce material consumption. Removing the iron core and stator is the main research direction of practitioners in recent years. In the total weight of the motor, the iron core and stator have a large proportion. Removing it can not only reduce the consumption and weight but also eliminate the vibration and noise generated during the operation of the motor.

In recent years, a winding structure using printed railway boards has been deeply studied at home and abroad. According to research calculations, an ordinary 2.5MW permanent magnet wind turbine (direct drive) can reduce weight by 40% to 50%. However, the research in this area has not achieved substantial results. After removing the iron core and stator, the permanent magnet material consumed by the motor manufacturing has increased by about 20%, and the manufacturing of the motor is also more complicated, and the manufacturing cost remains high.

3.2 Power Conversion Technology

Due to the high cost of converters, for permanent magnet motors below 3 MW, the rated voltage of the converter is generally 690 volts. Now that the power is increasing, if a converter with a lower voltage is used, the current flowing through the motor will be too large, and the motor windings will be too thick, which will cause great loss to the line, which is not conducive to the installation and maintenance of the unit.

For generators above 3 MW, the frequency converter voltage changes gradually, transitioning to the range of 3 kV to 6 kV. For permanent magnet generators, the converters used are low-voltage full-power types, and the topology used is a two-level form.

For medium-voltage converters, the topology structure is a multi-level form. For matrix As far as the converter is concerned, the use of a power conversion system can not only save the use of filter equipment, but also save the process of electrolytic capacitors, thereby reducing costs, increasing the active power of the converter, and gradually becoming one of the power conversion technological developments.

3.3 Motor Control Technology

For the permanent magnet motor control technology, more emphasis is placed on the research on the efficiency of the motor, and the practicability of the permanent magnet motor. Considering the motor control and its power control, a permanent magnet motor with multiple sets of surrounds and a single structure is used to provide sufficient power and improve the stability of the power generation system at the same time.
In recent years, more and more attention has been paid to the research of modular motors, mainly because the production process of this kind of motors is relatively simple, which is convenient for transportation and installation, and helpful for the development of later maintenance work.

3.4 Application and Development Of New Fields

In recent years, some subsystems in wind power generation equipment have gradually used permanent magnet motors, such as the cooling system motor mentioned above, and pitch motors. The use of permanent magnet motors for pitch motors has the characteristics of high energy efficiency and high control precision.

In addition, wind power generation has been extended from land and offshore land to offshore. As an offshore motor, new requirements have been put forward in terms of anti-corrosion and moisture-proof windings, and new requirements have been put forward for the corresponding process. At present, the research focuses on the materials and process ratio of the paint used in the motor.

Conclusion

Generally speaking, the use of permanent magnet generators in the current wind power generation system has great practical significance, and can further improve the power generation efficiency and the stability of wind power generation. Power companies need to increase technological innovation, refer to the operating environment of permanent magnet generators, and rationally set the internal structure of permanent magnet generators to ensure the continuous and stable operation of wind turbines.