Predictive Control of Variable Frequency Brushless Excited Synchronous Generator for More Electric Aircraft Power System

This paper proposes a predictive control strategy for the voltage stability of brushless excited synchronous generator for the aircraft power system using dead-beat control. The synchronous generator is coupled to the aircraft engine and it delivers the power to 270VDC bus via a 12-pulse diode bridge rectifier. Due to the speed variations of the aircraft engine, the brushless excitation is used so that the output voltage can be kept at the set point by adjusting the excitation current. The control system is designed based on an analytical model of the generator with the bridge rectifier at different load conditions and at different rotor speeds. This analytical model represents the dynamic behavior of the average value of the output DC voltage. This model is utilized to design the control unit of the generator in order to stabilize the output DC voltage of the aircraft power grid under load and speed variations. The control unit takes into consideration the variations of the system parameters in order to have an improved performance during the transients so that the DC voltage is kept within the standard boundaries. The harmonics content of the generator current is analyzed for different frequencies.