Field weakening control of PM generator used for small wind turbine aplication

Small wind turbines (in the range 2-50kW) harvest wind energy to provide carbon free energy for residential and small commercial applications and remote or developing economies. Current state-of-the art technologies generally utilize simple diode bridge rectification of the output from brushless permanent magnet (PM) generators and grid connection via DC-DC converters and voltage source inverters. Such simplified systems do not utilize the full capacity of the generator, power conversion electronics and therefore the turbine due, in part, to inappropriate or simplified control but also generator over-design for protection/safety reasons. This paper presents a different approach to the design procedure for a wind turbine generator drive system that actively controls the generator upto and above the system base speed imposed by the (electrical) supply voltage constraint. The paper demonstrates the impact of wind generator power characteristics over the annual energy production. In addition, it shows the reasons for field weakening control of a PM generator, that is verified experimentally using a market available system.