Design and direct field current control scheme of a synchronous generator with PM exciter based on the reference frequency

This study presents the design and control scheme of a self-excited 10 kW-380 V synchronous generator using a permanent magnet (PM) exciter. The PM exciter generates field current according to the engine speed to maintain the output voltage of the proposed generator so that constant voltage can be produced regardless of the speed. For the direct control the field winding current, a current controller is designed and embedded on the shaft. In the proposed generator, the reference current is determined by an external voltage controller and it is transferred to the rotating embedded current controller using an infrared (IR) transmitter and receiver aligned to the shaft. In order to improve control performance, the reference field current is controlled by the actual frequency of the generator based on the reference frequency. Therefore, when the engine speed is fluctuating due to engine governor dynamics, the frequency-based field current can maintain the output voltage constant because of the compensation term for speed variations. In the compared experimental results between the conventional generator with winding type exciter and the proposed generator system, both dynamic performance and operating efficiency of the proposed system are improved.