Modulation Index Limit Based Control Strategy for the More Electric Aircraft Generator System 2018-01-1937
Vector based control strategies have been extensively employed for drive systems, and in recent times to the More Electric Aircraft (MEA) generator based systems. The core functionalities of the control scheme are usually to sustain the bus voltage and field weakening to maintain drive system controllability throughout a wide speed range. Typically, the control schemes for high speed generator systems uses a dedicated controller for field weakening that ensures AC voltage regulation within the modulation index limit. A drawback to these types of control is that the modulation index limit can be exceeded due to change in operating conditions or disturbance factors. This may lead to generator system instability. In this paper, an alternative control strategy has been investigated to address this drawback. The control scheme includes a dynamic limit for the generator reference voltages such that the modulation index limit is adhered. Furthermore, a controller is introduced to address the lack of current limit of the proposed control scheme. The linear open loop plant is derived for the bus voltage and current limit controllers and verified against their equivalent non-linear counterparts. They are used to evaluate and design the controllers for stable operation. The performance of the proposed control scheme is then compared with a state of the art existing control method. Simulation results showed superior modulation index limit throughout and short duration stator current overshoots when operating at current limit. Overall, the proposed control strategy showed to be a suitable alternative control scheme for the MEA generator system.