Model predictive control of six-phase variable frequency electrically excited starter generator for more electric aircraft

This paper proposes a predictive control strategy for the voltage stability of a six-phase electrically excited starter generator for the aircraft DC power system. The starter generator is a synchronous machine coupled to the aircraft engine, and it is connected to 270V DC bus via a dual three-phase voltage source inverter that utilizes the DC output power. In the generation mode, the external 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 synchronous machine at different load conditions and at different rotor speeds using Model Predictive Control. In the Model Predictive Control, the voltage vector to be applied to the machine is determined based on the minimization of the cost function. The control unit takes into consideration the variations of the system parameters to achieve an improved performance during the transients so that the DC voltage is kept within the boundaries defined by the aircraft standards. The harmonic content of the generator current is analyzed for different electrical frequencies.