Overview of Electric Motor Technologies Used for More Electric Aircraft (MEA)

This paper presents an overview of motor drive technologies used for safety-critical aerospace applications, with a particular focus placed on the choice of candidate machines and their drive topologies. Aircraft applications demand high reliability, high availability, and high power density while aiming to reduce weight, complexity, fuel consumption, operational costs, and environmental impact. New electric driven systems can meet these requirements and also provide significant technical and economic improvements over conventional mechanical, hydraulic, or pneumatic systems. Fault-tolerant motor drives can be achieved by partitioning and redundancy through the use of multichannel three-phase systems or multiple single-phase modules. Analytical methods are adopted to compare caged induction, reluctance, and PM motor technologies and their relative merits. The analysis suggests that the dual (or triple) three-phase PMAC motor drive may be a favored choice for general aerospace applications, striking a balance between necessary redundancy and undue complexity, while maintaining a balanced operation following a failure. The modular single-phase approach offers a good compromise between size and complexity but suffers from high total harmonic distortion of the supply and high torque ripple when faulted. For each specific aircraft application, a parametrical optimization of the suitable motor configuration is needed through a coupled electromagnetic and thermal analysis, and should be verified by finite-element analysis.

I. Introduction

Air Passenger traffic has increased at an annual rate of 9% since the 1960s [1] and has brought the world closer to a global village. However, today's civil air transport remains costly and accounts for 2% of the man-made emissions [1]. As a result, both the aircraft operators and the aerospace industry are expected to offer continuous improvements in safety, capability, and availability while reducing costs, noise, and emissions. To meet these expectations, aerospace systems are undergoing a long-term transition from using mechanical, hydraulic, and pneumatic power systems toward globally optimized electrical systems. Electric motor drives are capable of converting electrical power to drive actuators, pumps, compressors, and other subsystems at variable speeds. Used in conjunction with advanced power electronics and control strategies [2], electric drives can offer gains in overall efficiency, weight saving, and cost effectiveness, while meeting reliability requirements. On this basis, the ultimate goal for the aircraft industry is to achieve the “all electric aircraft” (AEA), migrating all power systems to electrical power. It is estimated that an AEA can reduce aircraft weight by 10% and fuel consumption by 9% [3]. Therefore, the Airbus A380 and next-generation Boeing 787 airplanes feature electrically powered actuators [4]: the Airbus A380 has new variable frequency 115 V alternating current (ac) power supplies, whereas the Boeing 787 has ±270 V direct current (dc) power distribution buses.