Direct-Drive Wind Permanent Magnet Generators

Investigation shows increasing demand for wind generators with large output power used for hybrid generators in remote areas. There is a growing demand in remote areas for small to medium rating (till 20 kW) wind generators for the stand-alone generation-battery systems. The type of generator required for the purpose must be light and compact so that the generators can be coupled directly to wind turbines and be easily installed at the top of towers.

The rotor of a wind turbine rotates at speed of around 20-200 rpm. In conventional wind power plants a generator is coupled to a turbine with a gear so that it rotates at a speed of 1000 to 1500 rpm. Gears can be eliminated in a wind power plant by a low-speed generator with the rotor rotating at the same speed as the turbine rotor.

With the development of high-energy permanent magnet substances, it has become possible to make the permanent magnet variable speed generators more compact and reliable. The majority of the low speed wind turbine generators use permanent magnet generators. These offer advantages of high reliability and efficiency as conductor losses are removed from the rotor and there is no requirement of external excitation.

Direct-Coupled over Gearbox-Coupled Generator

In comparison to a traditional gearbox-coupled wind turbine generator, adirectly-coupled generator has several advantages such as:

– Reduced size of the system
– Lower maintenance and installation cost
– Flexible control method – Easy and fast response to load variations, wind fluctuation, etc.

A directly-coupled generator requires a very low-speed operation to match wind turbine speed and also to produce electricity with a normal frequency range (10-60 Hz).Permanent magnet generators offer a high efficiency in operation, and a simple, robust structure in construction as rotor winding and field current are not used.