Key advantages of permanent magnet generators:
– Higher efficiency – Permanent magnet generators tend to be more efficient than wound rotor generators since they don’t waste energy energizing electromagnets on the rotor. This means they can convert a higher percentage of mechanical power into electrical power.
– Compact size – Permanent magnets allow the generator to produce a strong magnetic field without heavy electromagnets. This allows for a more compact design compared to wound rotor generators.
– Simple design – With no electro-magnets to energize, the design of a permanent magnet generator is simpler than a wound rotor generator. They have fewer moving parts.
– Higher power density – The strong magnetic field lets permanent magnet generators produce more power from a smaller package size compared to wound rotor designs.
– Lower maintenance – Since they don’t rely on slip rings and brushes to energize the rotor, permanent magnet generators have no commutator or brush gear requiring periodic maintenance.
– Smooth output – The consistent magnetic field results in a smoother, lower ripple electrical output compared to variable field wound rotor designs.
– Used in renewable energy – Permanent magnet generators are commonly used in wind turbines and hydroelectric plants due to their high efficiency, low maintenance needs, and suitability for remote operation.
– Robust design – Lack of brushes and commutators make permanent magnet generators more resilient to environmental factors like dirt, dust, or vibrations.
– Materials – Rare earth magnets like neodymium iron boron are commonly used due to their very strong magnetic properties. Samarium cobalt is another option.
– Excitation – Unlike wound field generators, PMGs require no external power source to energize the rotor coils. The magnetic field is fixed by the permanent magnets.
– Construction – Magnets may be embedded in slots inside the rotor or attached to its surface. The stator contains windings that produce a voltage as they cut the magnetic flux lines.
– Speed ranges – Most effective at medium to high speeds depending on pole count. Can also be designed for lower rpm using more poles/magnets.
– Load regulation – Output varies slightly with load as field strength is constant. Voltage regulation may require an external controller.
– Sizing – Power output depends on magnet volume, airgap size, rotor/stator diameters, and pole count/shape design.
– Cost – Rare earth magnets increase materials cost but PMG packages can be 30-50% cheaper than equivalent wound rotor units due to simplicity.
Some key renewable energy applications where permanent magnet generators are widely employed:
– Wind turbines – A very popular choice for both horizontal and vertical axis wind turbines due to their high power density, efficiency, and ability to generate electricity at varying wind speeds.
– Hydropower – Used in micro-hydropower schemes and tidal power installations to convert the kinetic energy of running water into electricity. Their robust underwater design makes them suitable.
– Wave power – Permanent magnet generators are integrated into wave energy converters to generate power from ocean wave motion without added complexity.
– Solar photovoltaic systems – Used in off-grid and battery-based solar setups to charge batteries from excess solar panel power during daylight hours.
– Hybrid diesel-solar/wind systems – Provide generator backups and allow integrating renewables into existing diesel grids more easily.
– Rural electrification projects – Their simple, reliable design has made PMGs popular for powering remote villages, telecom towers, and irrigation pumps.
– Electric vehicles – Power motors in electric cars, trucks, buses, boats, and other transport powered by electric drivetrains.
– Uninterruptible power supplies – Provide battery backup power to critical loads using renewable sources like fuel cells or micro-hydro.
– Distributed/decentralized generation – Ideal for modular power stations located near the point of consumption.
