Low Speed Direct Drive Permanent Magnet Alternator For Wind Turbine

Low-Speed Direct-Drive PMG Permanent Magnet AC Alternator For Wind Turbine
 

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What is the permanent magnet generator?

The permanent magnet generator is a device that converts mechanical energy to electrical energy. In this device, the rotor windings have been replaced with permanent magnets. Permanent magnet generators are used mostly in industrial applications like turbines and engines to produce commercial electrical energy, the permanent magnet alternator is an alternate source of energy and has multiple benefits which make it a great device for a variety of residential, commercial, and industrial applications.
 
The structure
 
The permanent magnet generator is mainly composed of a rotor, end cover, and stator. The structure of the stator is very similar to that of an ordinary alternator. The biggest difference between the structure of the rotor and the alternator is that there are high-quality According to the position of the permanent magnet on the rotor, the permanent magnet generator is usually divided into a surface rotor structure and a built-in rotor structure.

Working Principle
The main components of permanent magnet generators are stators and rotors.
The rotor is made from permanent magnets, and it could generate magnetic fields. Magnetic parts are set around the stators as well, so fluxes could compass them.
The stator is composed of rotating coils. Once receiving the magnetic power, the stator generates electricity consequently.
In this way, the movement of the rotors is transformed into electric energy. The more stator coils we have, the more electric currents we get.
 

 

The permanent magnet alternator’s rotor is directly equipped with a wind turbine so that it can generate fixed electrical power. The efficiency of permanent magnet synchronous alternators is way higher than that of asynchronous generators. It offers a variety of merits over asynchronous generators and they are as follows:
 
 
· Direct drive (No speed multiplier, no gearbox needed)
 

· Virtually no maintenance
 

· Highest power-to-weight ratio in direct drive
 

· High efficiency
 

· Simplification of mechanical design

· Easy mechanical interface
 

· Cost optimization
 

· They are environmentally friendly and do not rely on the external weather to produce electricity
 

· They are smaller in size and hence require very less space compared to other types of generators.
 

· These permanent magnet generators run for years and beyond without any wear and tear. Additionally, they are soundless and noise-free thus making zero sound pollution.

Permanent magnet generators are widely adopted by the wind power industry. Because there are no wearing parts, PMGs ensure low failure rates and require less maintenance. The use of permanent magnets requires no external power source to initiate a magnetic field. This reduces costs, simplifies the structure, and improves system efficiency.

How do permanent magnets work in wind turbines?

The operation of wind turbine generators is based on electromagnetic principles, usually following the first electromagnetic principle devised by Michael Faraday in 1831. When an electrical conductor rotates in a magnetic field, it generates electricity. When the blades of the turbine rotate in the direction of the wind, electromagnetic induction occurs within the magnetic field of the permanent magnets in the turbine to generate electricity. An electric generator connected to the shaft of the wind turbine converts the movement of the blades converted into electrical energy. However, instead of the slip rings used in electromagnets, the permanent magnets in wind turbines use the magnetic fields of strong rare-earth magnets.

 
The classification of permanent magnet generator:
 
Permanent magnet generators (PMGs) can be classified based on various factors, such as the type of magnet, the application, the number of phases, and the power rating. Here are some common classifications of permanent magnet generators:
 
Based on magnet type: a. Ferrite Magnet PMG: These generators use ferrite magnets, which are less expensive and have lower magnetic strength than rare-earth magnets. b. Rare-Earth Magnet PMG: These generators use neodymium or samarium-cobalt magnets, which are more expensive but have a higher magnetic strength than ferrite magnets.
 
Based on application: a. Wind Turbine PMG: These generators are designed for use in wind turbines and are typically used in small-scale or off-grid applications. b. Hydroelectric PMG: These generators are designed for use in hydroelectric power plants and are typically used in large-scale applications.
 
Based on the number of phases: a. Single-phase PMG: These generators have a single output phase and are used in low-power applications. b. Three-phase PMG: These generators have three output phases and are used in high-power applications.
 
Based on power rating: a. Low-power PMG: These generators have a power rating of up to a few kilowatts and are used in small-scale applications. b. High-power PMG: These generators have a power rating of several megawatts and are used in large-scale applications, such as wind turbines and hydroelectric power plants.
 
These are some common classifications of permanent magnet generators, but there may be other ways to classify them based on specific parameters.

Applications of permanent magnet generators:

· Low-speed, direct-drive PMGs operate without any gearbox and fast-rotating parts, resulting in increased reliability and superior drive train efficiency.
 

· Generator can be designed with a segmented stator construction. This provides redundancy and makes it possible to repair the generator in the nacelle without full disassembly. Optionally, our generator design can use the generator bearing as a turbine main bearing to integrate the turbine brake system into the generator construction. Benefits are simplicity, fewer components, and therefore, higher reliability.
 

· With the rising cost of electricity, an increasing number of populations are looking for an alternate source of energy and permanent magnet generators fit this gap perfectly. These generators can also reduce the strain on the environment as they do not use any non-renewable sources of energy for producing electricity.
 

The following points should be paid attention to when designing wind turbines:

(1) The operating environment of the generator is harsh, and the generator is required to have high safety and reliability and be able to prevent rain, snow, and dust.

(2) When the generator is directly driven by the wind wheel (the commonly used speed-increasing gearbox is omitted), the rated speed of the generator is required to be low.

(3) The generator's initial pressure build speed is required to be low to maximize the utilization factor of wind energy.

(4) The starting resistance torque of the generator is as small as possible, so that the generator can start well at a lower wind speed, and the utilization of wind energy is also improved.

Benefits of Permanent Magnet Generators Over Induction Generators:

1. Free Energy Source
Permanent magnet generators produce electricity using their own magnetism. So, you do not need to pay high electric bills, and a large budget is saved. Besides, these devices do not need any other resources, which are quite environmentally friendly.
 
2. Reliable Power Output
Permanent magnet generators do not need any special operating environments. Hence, they can offer reliable performance compared with wind turbine motors. Additionally, permanent magnet generators do not suffer from energy loss, while induction generators typically lose 20-30% of energy. Additionally, there are no temperature rises in the magnetic machines, so the life of the bearings can be prolonged.
 
3. Low Maintenance Fee
Due to the features mentioned above, you do not need to spend lots of money and time on the maintenance of permanent magnet generators. And they do not have slip rings and brushes, which are supposed to be checked at regular intervals.
 
4. Compatibility
Permanent magnet generators can be employed with turbines and diesel generators.
 
5. Extremely high availability due to simple and robust design
 
6. Superior efficiency over the entire wind speed range, even at partial loads, resulting in higher efficiency and increased AEP rates.
 
7. Optimized and tailored to each wind turbine and the environment in which it will operate.
 
8. Highly serviceable design speeds up maintenance routines. PMG technology eliminates wearing parts, ensuring fewer failures and significantly reducing the need for maintenance.
 
9. The PMG coupled with a full-power converter provides future-proof grid code compliance, including fault ride-through and 100% reactive power compensation capability.

Qingdao ENNENG Motor Co., Ltd is a global supplier which focuses on permanent magnet generators and energy-saving solutions. We provide customized 5KW to 2MW Permanent Magnet Generators suitable for Wind turbines, Hydro turbines, and other renewable energy systems. With strong flexibility and competitive capabilities, we can help clients to customize the overall new energy system solution. ENNENG team has delivered many generators to the industry in Europe, America, Africa, and other countries and is working on many different projects, at all speeds (from standard speed to direct drive). We’re living our promise to the planet by offering only products with environmental benefits and operating with a zero-carbon footprint.