Wind Industry Makes "The Switch" to Permanent Magnet Generators

One of the primary concerns for any wind turbine manufacturer is designing the highest-efficiency drivetrain possible.  Normal turbine drivetrain designs have the turbine driving a generator (which is virtually identical to a standard induction motor) via gearbox, which present several points of efficiency loss throughout the system: the gearbox, the generator, the bearings – all of these contribute to parasitic losses which drive down the amount of energy produced. Add in the inherent unpredictability of wind speeds within the planetary boundary layer, and it becomes easy to understand why turbines bring as many headaches as they do benefits.

Now a new company, called The Switch, has created an innovative drive arrangement called a permanent magnet generator (PMG), which is attached to a special converter when installed in a wind application. PMGs can be designed to operate at 98% efficiency, with the efficiency typically varying with speed – the higher the speed, the higher the efficiency. However, even in variable-load applications (i.e. low speed, direct drive), the lack of gearbox found in PMGs give them the advantage over traditional systems. This allows the efficiencies of PMGs to remain very high over a much wider range of wind speeds.

The key to the PMG’s efficiency lies in the use of permanent magnets in a synchronous generator. These magnets are either adhered onto the rotor (for low-speed applications), or embedded within the rotor (for high-speed applications). These permanent magnets, rather than an electric field, are what cause excitation within the PMG, eliminating the rotor losses found on a typical generator. Optimizing the power factor of the PMG also reduces stator losses; and because PMGs do not require a separate excitation system, they are significantly less expensive than traditional generators. Using permanent magnets also reduces maintenance costs, as no slip rings are needed.

PMGs can accommodate a wide range of speeds, enabling the turbine to operate at its optimal design point – without being limited by drivetrain concerns – at a variety of load conditions. This allows the turbine to adapt to site conditions, which is simply not possible with conventional systems. PMGs are available for turbines with a power output between 500kW to 5MW.


http://www.theswitch.com/