Tadashi Sawata

Sensorless starting of a wound-field synchronous starter/generator for aerospace applications

The present paper describes an angle and speed estimation algorithm suitable for the control of a wound-field synchronous starter/generator (S/G) without position sensors for aircraft engine starting applications. The proposed control strategy is based on the injection of a high-frequency voltage signal and the subsequent demodulation of the resulting high-frequency stator current components. The coupling due to high-speed operation that degrades the estimation accuracy of similar algorithms based on signal injection is taken into account. Modeling of the machine response to a high-frequency voltage signal injected into the estimated d-axis is presented, also considering the influence of damping circuits both on the d- and q-axis. Local asymptotic stability of the proposed observer is also demonstrated. Through extensive experimental results, the proposed control technique is shown capable of guaranteeing full-torque sensorless operation at zero speed and sustained operation up to engine ignition speed.

A wide-speed-range hybrid variable-reluctance/permanent-magnet generator for future embedded aircraft generation systems

This paper presents recent research into the use of an embedded generation system as an alternative to the emergency ram air turbine on aircraft, the proposal being to utilize the windmill effect of the low-pressure turbine of the main aircraft engine for emergency power generation. A novel topology of a high specific output ac permanent-magnet generator is described that has been designed to be driven directly from the low-pressure turbine via an integral fixed-ratio gearbox, the requirement being to generate a regulated 270-V dc 0-20-kW emergency supply over a 12:1 3000-36000-r/min generator shaft speed range. The methodologies behind the machine design and operation are described together with test results taken from a prototype generator system.

Sensorless Operation of a Permanent-Magnet Generator for Aircraft

This paper considers the operation and control of a brushless AC prototype embedded aircraft generator that has been designed for use as an alternative to the emergency run air turbine. To meet the wide operating speed requirements, the generator utilizes a hybrid rotor construction comprising permanent magnet and variable reluctance sections. The constant current source characteristics of the design are exploited to derive the phase information required by the AC vector controller, thus avoiding the use of a shaft-mounted rotor position sensor. The methodology behind the controller operation is presented together with test results taken from a prototype generator system, and this is contrast with the results taken from the conventionally controlled machine with resolver position feedback.

A wide speed range permanent magnet generator for future embedded aircraft generation systems

The paper presents recent research into the use of an embedded generation system as an alternative to the emergency ram air turbine on aircraft. The proposal being to utilise the windmill effect of the low pressure turbine of the main aircraft engine for emergency power generation. A novel topology of a high specific output AC permanent magnet generator is described that has been designed to be driven directly from the low-pressure turbine via an integral fixed ratio gearbox. The requirement being to generate a regulated 270V DC, /spl theta/-20kW emergency supply over a 12:1, 3,000 to 36,000 rpm, generator shaft speed range. The methodologies behind the machine design and operation are described together with test results taken from a prototype generator system.

Thermal modeling of a short-duty motor

In some applications electric motors operate only for a very short period of time. Thermal designs of such motors are extremely important to optimize system weight and size. This paper discusses transient thermal performance of a short-duty rated motor. An analytical study shows that the quality of impregnation plays a significant role in transient performance. Thermal protection with temperature sensors will not be reliable due to delays in temperature measurement, and a predictive protection is essential. The analysis is confirmed by 2-dimentional finite element analysis and prototype motor testing.

Assessment of fluid drag loss in a flooded rotor electro-hydrostatic actuator motor

For a permanent magnet (PM) motor used in an electro-hydrostatic actuation system, fluid drag loss in the air gap can be as high as 60% of motor internal losses and affects the motor efficiency; especially at low temperatures where the viscosity of the hydraulic fluid increases significantly. A PM motor has been designed and built to assess electromagnetic, fluid drag loss and dynamic performance. The design process utilised a theoretical equation for the fluid drag loss estimation which assumes a laminar flow. Assumption of the laminar flow has been validated by computational fluid dynamic analysis. A dummy motor was built and the fluid drag losses were measured for various speeds and temperatures. The test results show reasonable agreement with the theoretical calculation although the self-heating effect of the fluid made measurements at constant temperatures difficult.

Design of brushless PM motor for high starting torque requirement for aircraft applications

This paper discusses the design of a brushless permanent magnet motor in which the performance requirement is dominated by breakout torque. It discusses the impact of a rotor position feedback error and how it affects the machine sizing in order to overcome breakout torque requirements. It is shown that the brushless AC drive is less sensitive to the position error compared with the brushless DC drive, and it could provide a 11% increase in breakout torque capablility for a given position error and RMS current. The effect of a conductive rotor sleeve on torque ripple is also analysed. Testing with a prototype system verifies the results.

Evaluation of winding stray capacitance in motors for aerospace applications

The use of inverter-driven motors in aircraft has been steadily increasing to replace hydraulic and pneumatic systems. Accurate knowledge of the motor parameters including the winding stray capacitance is required to construct a wider motor/drive systems model to investigate electromagnetic compatibility (EMC) issues and also to correctly size the common mode EMC filter components. In this paper, the capacitance effects are investigated using electrostatic 2D finite element models of the motor and verified with test hardware. Reliable evaluation of the stray capacitance requires very detailed knowledge of the conductor location in the slot, accurate material properties and the amount of impregnation present in the slots. Analysis shows that the reduced amount of impregnation lowers the stray capacitance but this may have an impact on thermal performance and mechanical integrity. Conductors located near the middle of the slot lead to lower capacitance compared to conductors located near the tooth edge.