Improved wind power conversion system using magnetic energy recovery switch (MERS)

This paper presents experimental results on an innovative power conversion technology using magnetic energy recovery switch (MERS) of a wind turbine system with a synchronous generator to improve the output power and the efficiency. An output voltage of the synchronous generator decreases with the increase of current because of synchronous reactance. The MERS, which consists of four MOSFET or IGBT elements and one small DC capacitor just like as a full bridge configuration, is inserted in series between the generator and ac-dc converter. The capacitor absorbs the magnetic energy stored in the synchronous inductance by forced LC resonance. Since MERS compensates the reactance voltage of the synchronous generator by the capacitor voltage, the output voltage of the generator increases and the excitation current of the generator can be extremely reduced. Also, the switching loss of converter in the MERS system is very small because the MERS is not required PWM control and the switching frequency is the same as the generator, and the downsizing of converter is realized. The effect of MERS is verified in a small scale experimental set-up of wind power generation with a permanent magnet type synchronous generator and a dc-excitation type synchronous generator. The data indicate a great potential of the new power conversion technology to make the actual wind turbine system compact and to improve the efficiency.