G. Fabri

High Reliability Permanent Magnet Brushless Motor Drive for Aircraft Application

Reliability is a fundamental requirement in aircraft safety-critical equipments. Its pursuing involves the adoption of protective design concepts such as fault-tolerant or redundant approaches, aiming to minimize mission failure probabilities. Multi-phase motor drives are gaining a growing interest to this extent, because they permit a boost in torque and power density, allowing the design of very compact high efficiency drives with intrinsic fault-tolerant capabilities. This paper presents a five-phase permanent magnet brushless motor drive developed for an aircraft flap actuator application. The motor is designed to satisfy the load specifications with one or two phases open or with a phase short circuited, while a failure in the rotor position sensors is remedied through a sensorless strategy. Design studies aiming to predict the faulty mode performance in case of different remedial strategies are presented. Experimental tests on the drive prototype are included, which confirm its capability to satisfy the planned degraded modes of operation.

Multi-phase permanent magnet motor drives for fault-tolerant applications

The recent markets crisis imposes the adoption of advanced technical solutions to match the requirements of energy efficiency, promoting a gradual transformation in the field of mechanical actuators for hazardous applications and moving the attention to more electric and efficient systems. Nevertheless the adoption of the electromechanical actuators are still limited in those fields that require a high degree of reliability, especially in the cases that involve huge hazard for peoples and environment or failures in systems characterized by heavy out-of-service or restarting costs. Multi-phase motor drives are gaining a growing interest because they permit a boost in torque and power density, allowing the design of very compact high efficiency drives with good improvement by the reliability point of view. The present paper recalls the basic concepts of multi-phase fault-tolerant design and illustrates their adoption in the development of two different systems for aircraft application such as a flap actuator and a cart lift system. Design details will be presented. Reports of analyses and tests carried out on the drives prototypes will be included to confirm the fault-tolerance capabilities with respect to the lack of one or two phases.

Multi-phase fault tolerant drives for aircraft applications

The demand for high reliability motor drives increases every day, especially in aircraft where traditional, nonelectric systems (hydraulic, pneumatic) are being replaced by electrical actuators following the More Electric Aircraft (MEA) trend. Electric drives for aerospace need a fault-tolerant design approach to achieve reliability objectives with optimized architectures reducing redundancies, over-sizing and costs. The presented work shows how fault tolerant design methodologies can be applied in two motors for typical aircraft application such as a Cart Lift System (CLS) and a Flap Actuator (FA). Analyses and tests are reported to demonstrate how the designed multi-phase motors are able to run at rated torque also with one or two phases faulted.

Electromechanical Actuator for Helicopter Rotor Damper Application

Development trends in aeronautics involve a better employment of electric motors also in safety critical hazardous applications until now covered by mechanical systems. The electromechanical actuators (EMAs) are gaining a growing interest owing to their force and power density capability and the high dynamical performance by electronic control. Hence, very compact and high-efficiency drives can be designed, with satisfactory characteristics from the reliability point of view. This paper refers to a rotor damper system for helicopter application, using specifically designed permanent-magnet motors as EMAs. Design criteria and details will be presented focused on the integration of the electrical machine inside such specific application. Reports of analyses and tests carried out on the motor prototypes are included to confirm the capabilities and the performances of the proposed solution.

Sensorless control of five-phase brushless DC motors

The present paper shows a rotor position estimation technique for a five-phase permanent magnet synchronous motor based on a back-EMF observer, focusing the attention on the design criteria that could be used to construct the sensorless strategy. Due to the polyphase structure of the machine this estimation method deals with a proper linear transformation which allows representing the five-phase motor through an equivalent two-phase model. After a short overview on the back-EMF model for the five-phase motor, the linear transformation and the observer-based estimation technique are presented. The analysis emphasizes on the choice of the observation dynamics through a proper design strategy of the related gain matrix and on some robustness criteria useful to enhance the sensorless strategy. Simulation and experimental results showing the response of the observer during transient and steady-state operation are presented.

Observer-based sensorless control of a five-phase brushless DC motor

This paper presents a rotor position estimation technique for a five-phase permanent magnet synchronous motor with independent phases, based on a back-EMF observer. The method involves the use of a proper linear transformation which allows representing the five-phase motor by an equivalent two-phase model. Due to its characteristics, the sensorless strategy can be used in multi-phase motors having non-sinusoidal back-EMF shape, such is the case of brushless DC motors used in fault-tolerant applications. After an overview of the back-EMF model for the five-phase motor, the linear transformation and the observer-based estimation technique are presented. Experimental results show the overall performance during transient and steady-state operation.

Fault-tolerant PM brushless DC drive for aerospace application

Reliability is a fundamental requirement in airborne equipments, it involves a particular approach of study on mission failure probabilities. Architectures robust to failure of single components like multi-phase fault-tolerant motors drives introduce in these systems an intrinsic improvement. By providing compensation for potential hardware failures, a fault-tolerant design approach may achieve reliability objectives without recourse to non-optimized redundancy or over-sizing. A fault-tolerant design approach differs from a pure design redundancy approach in that provisions are made for planned degraded modes of operation where acceptable. This study shows how a 5-phase motor is able to run at rated torque also with one or two phase open, by using suitable current commands defined as degraded modes. An experimental prototype has been arranged and tested.

A switched-reluctance motor for aerospace application

This paper presents a five-phase switched reluctance motor designed to satisfy the requirements of flap actuators in medium size aircrafts. In normal operation the machine operates with two-phases conducting simultaneously but it is designed to satisfy the load specifications also with one or two phases faulted. The finite-element studies aiming to predict the faulty mode performance are presented. Experimental tests on the motor prototype are included, which confirm its capability to satisfy the planned degraded modes of operation.

PM brushless motors comparison for a Fenestron®type helicopter tail rotor

This paper describes requirements and design principles of an electric motor for helicopter tail rotor application. The application demands high specific power and specific torque with little possibility to adopt a liquid cooling solution. The tail rotor shall also comply with severe safety requirements that directly affect the motor design. Volume and weight constraints make the design of the electrical machine challenging. Different solutions have been investigated to propose an effective alternative to the Fenestron® mechanical actuation system. In the paper two different permanent magnet motors with external rotor are illustrated and compared.

Parallel positioning of twin EMAs for Fault-Tolerant flap applications

This work describes the control technique of a Fault-Tolerant electromechanical system aimed to the actuation of the flap panels of the aircraft. The application provides the adoption of a couple of Fault-Tolerant permanent magnet synchronous motors designed to match minimum load requirements even in case of a fault in one or two phases. The consolidated mechanical synchronization of the mutual actuation is replaced by a fully electronic solution. The usual master-slave configuration of the two actuators with speed control and correction of the tracking error is replaced by the adoption of the parallel position control. This solution allows to avoid a complex management of the tracking error and applies to the couple of actuators the same Fault-Tolerant philosophy adopted inside for the single multiphase motor. The technique is developed and tested on a test-bed designed to emulate the real aerodynamic load condition. The achieved results show the effectiveness of the proposed solution.