Modulation Limit Based Control Strategy for 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 control schemes should maintain the bus voltage and adhere to the generator system voltage and current limits throughout a wide speed range. Typically, the current limit is prioritised first due to ease of implementation and simple control structure. As a result, the voltage limit can be exceeded due to change in operating conditions or disturbance factors. In flux weakening regions, this may affect the controllability of the power converter and lead to generator system instability. In this paper, an alternative control strategy has been investigated to address this drawback. The proposed control scheme refers to the modulation index limit which is the ratio between the power converter input and output voltages as the voltage limit. The control scheme uses 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.