A new Permanent Magnet Doubly Fed Contra Rotor Induction Generator - Jun 29, 2023
A NEW PERMANENT MAGNET DOUBLY FED CONTRA ROTOR INDUCTION GENERATOR
KEYWORDS: Wind power, electrical generator, induction generator, permanent magnet generator, contra rotor generator
This generator, which is an permanent magnet induction generator is a type of electrical generator that operates on the principle of electromagnetic induction. Designed to be used in wind turbines, hydroelectric power plants and other renewable energy installations, it produces mechanical energy from electrical energy. This induction generator actually consists of a fixed stator of electrically insulated copper coils and a rotor. These coils are wound around the central axis of the generator in the form of a ring and create a magnetic field as shown in Fig.1. When alternating current is applied to the stator. In addition, the stator contains a rotor made of a soft iron structure and copper conductors connected in a short circuit. The relative movement of the rotor with respect to the rotating magnetic field created by the stator causes an electromagnetic induction. The changing magnetic field in the stator induces an electric voltage in the rotor conductors which generates electric current when the rotor is connected to an external load. It should be noted that the normal operation of convetional induction generators requires their synchronisation with the frequency and voltage of the existing electrical grid. This synchronisation involves the use of control and regulation devices, namely: synchronisation and frequency conversion systems. But in this design there is not need for voltage from grid because there are permanent magnets on the rotors, which will be described, create magnetic field and current. .
Fig. 1. The stator which has several windings coils on it creates a magnetics field.
There are two rotors in the generators. The first rotor which is a cage type rotor. The shaft is the central part that connects the first rotor to the generator and whose movement is driven by the rotor. In fact, it transmits this rotary motion to the generator to generate electricity. This rotor has a diameter smaller than the second rotor which will be described. In fact, this rotor is inside of the second rotor rotating in opposite direction of it..
Fig. 2. The first rotor is cage types rotor and the cage consisted for conductive bars fixed like a cage.
The second rotor is similar to the first rotor with this difference that not only has conductive bars but also magnet bars as indicated as red color in Fig.3. This cage shaped rotor has a larger diameter compared to the first rotor. It has own shaft which will be the second shaft of the electrical generator and will be second input of mechanical energy to the generator..
Fig. 2. The second rotor is caged shaped with conductive and also magentics bars and a shaft connected to it.
The first rotor rotates in side of the stator the simplified side view presentation of this rotor inside stator shown in Fig.4 .
Fig. 3. The second rotor inside stator rotating has a shaft .
The second rotor with larger diameter than first rotor inside the stator rotating. The side view presentation of the generator shown in Fig. 5. As seen the center of the first and the second rotors are center of the stator. Also, cross sectional of the magnetic bars shown in red circle. The cross sectional of the conductive bars shown in gray color. The two rotors has their own shaft each one is rotated using a separate wind turbines in opposite directions..
Fig. 4. The second and first rotors inside of the stator rotating in opposite directions.
As mentioned above, the stator is the fixed part of the induction generator and the rotor is the moving part. In fact, the stator consists of a coil wound around a core, usually made of laminated iron with windings supplied with alternating current at a fixed frequency. In addition, first squirrel cage rotor have a structure in the form of protruding magnetic poles, while the poles of wound rotors are equipped with windings. But the second rotor has perment magnet bars that create constant megntic field. It should be noted that the magnetic field also is created by the stator currents when the rotor is rotating inside the stator. It then induces an electric current in the rotor due to electromagnetic induction. In addition, the current induced in the first rotor cage and also in the second rotor (because it has also conductive bars) in turn produces a magnetic field opposite to the stator field which generates an electromagnetic torque that sets the rotor in rotation. When the rotor rotates, it generates an electrical voltage in the stator windings. .
Fig. 5. The simplified representation via of the generator with two rotors and turbines.
The envelope is the outer structure that houses the generator and protects it from the weather. It is usually made of steel or composite materials and protects it from the outside elements. The shafts are the central parts that connects the rotors to the generator and whose movement is driven by the rotors. In fact, they transmits the rotary motion to the generator to generate electricity. The electrical connections allow the generator to be connected to the electrical distribution system or to control devices to regulate the production of electricity. In addition, the cooling system dissipates excessive heat and keeps the generator at a safe operating temperature. As shown the electrical generator terminals connected to capacitors then connected to the electrical grid. This capacitors control the reactive power generated by the generator and keep the voltage of the generator in proper range. There is a control system shown in Fig.7 that controls the frequency of the electrical current of the generator..
Fig. 6. The hybird permanent magnetc induction contra rotor generator drived by two wind tubines connected to the grid .
The special feature of a this permanent magnet induction generator with two mechanical inputs is that it can be used in wind turbines to convert wind energy into electrical energy efficiently. This advanced generator consists of two rotor, one stator, two shafts, electrical connections and a cooling system. Two wind turbines which their blades angles are mirrored to rotate in different direction when wind blows to capture the kinetic energy of the wind and transfer it to the rotor via the two shafts, the rotors are connected to the shafts and rotates with the blades in the wind. As the fixed part of the generator, the stator consists of a laminated iron core and copper wire coils wound around it. In fact, the stator coils are placed in such a way as to favor the creation of a stationary magnetic field but magnets of the second rotor also amplify this magnetic field. When the rotors are in motion, its magnetic field of magnets on the second rotor interacts with that of the stator to generate an electric voltage. This generator is compact it means is has high energy to weight ratio. It generate electricity even in low wind speeds. More importantly, this generator does not need gear box to increase rotational speed of the rotors. Because it has two rotors rotating in opposite direction the relative speed between them at least doubled and eliminated the need to any gear box.
Due to problem of greenhouse effect of the fossil fuels, there is a focus on the wind energy generation technology to extract more energy efficiently. To extract wind energy efficiently a new hybrid permanent magnet induction contra rotor generator proposed. The generator has two rotors rotating in opposite directions in one stator. Each of the rotors has one shaft totally two shafts the generator has. One wind turbine connected to each shaft. The two wind turbines rotate in opposite direction of each others. The second rotor has magnetic elements that causes magnetic field even at low speed of rotation of rotor causes generation of electricity in stator winding while in conventional induction generators magnetic field is not created in low rotor speeds. Because the there are two rotor rotate in different directions their relative speeds is high and this generator does not need gear box which is heavy and costly reduces the total cost of the generator..
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