Showing papers by "Chris Gerada published in 2010"

Multiphase Power Converter Drive for Fault-Tolerant Machine Development in Aerospace Applications

Abstract: This paper describes an experimental tool to evaluate and support the development of fault-tolerant machines designed for aerospace motor drives. Aerospace applications involve essentially safety-critical systems which should be able to overcome hardware or software faults and therefore need to be fault tolerant. A way of achieving this is to introduce variable degrees of redundancy into the system by duplicating one or all of the operations within the system itself. Looking at motor drives, multiphase machines, such as multiphase brushless dc machines, are considered to be good candidates in the design of fault-tolerant aerospace motor drives. This paper introduces a multiphase two-level inverter using a flexible and reliable field-programmable gate-array/digital-signal-processor controller for data acquisition, motor control, and fault monitoring to study the fault tolerance of such systems.

Design of a high force density tubular permanent magnet motor

Abstract: This paper considers the design and analysis of a tubular linear permanent magnet machine for high force density applications, such as in the aerospace industry. Different machine topologies and slot-pole combinations are considered. Optimization with respect to machine geometry is addressed analytically and validated through finite element simulations. A technique to reduce heat build-up in the winding coils is introduced, allowing for higher current density and subsequently resulting in a higher output force for a given winding temperature rise.

Inductance characteristics of PMSMs and their impact on saliency-based sensorless control

Abstract: Advantages of operating a Permanent Magnet Synchronous Machine (PMSM) without a position sensor are many and are well known. This paper presents a study of the effects of space harmonics in the incremental inductances and their impact on the machine saliency. The effects of space harmonics exclusively due to the machine (i.e., the saturation saliency distribution) are given particular consideration. The results are illustrated through inductance analysis and measurement of inductance profiles of two similar PMSM machines. The space harmonics in the inductance profiles are correlated with the position estimate distortions through a Matlab/Simulink embedding finite element (FE) machine simulation. Significant differences in sensorless operation of the two machines are found which correlate to the inductance profiles. This illustrates that inductance profiling can inform upon machine design in order to improve sensorless capabilities.

A comparative study of permanent magnet - synchronous and permanent magnet - flux switching machines for fault tolerant drive systems

Abstract: Flux switching machines are quickly gaining popularity due their inherent advantages stemming from having both the current conductors and permanent magnets mounted on the stationary side of the electrical machine. Their power density has already been shown to be comparable to that of permanent magnet synchronous machines, however their fault tolerant capabilities are somewhat limited in their standard form. This paper looks at a novel design of a fault tolerant flux switching permanent magnet machine able to operate with both open circuit and short circuit winding faults and compares its healthy and faulty performance to a fault tolerant permanent magnet synchronous machine.

A Low-Intrusion Load and Efficiency Evaluation Method for In-Service Motors Using Vibration Tests With an Accelerometer

Abstract: This paper presents a novel low-intrusion load and efficiency evaluation method for in-service induction motors based on vibration measurements. This method enhances the traditional vibration analysis by providing motor load and efficiency information in addition to the mechanical health information. The application is in multimotor plants, where individual motor monitoring is too expensive to implement yet where motor operating conditions need to be known to work at improved plant efficiency. The vibration signature of the machine, measured by an accelerometer and processed by fast Fourier transform (FFT) is used to extract frequencies defining shaft speed and the supply frequency. This data, in conjunction with the basic motor performance data, enables the determination of the actual load and indirectly, the efficiency which the motor is operating at. For motors supplied form a variable-speed drive (VSD), the loss segregation method is used to yield the motor losses indirectly and thus, the efficiency.

A combined electromagnetic and thermal optimisation of an aerospace electric motor

Abstract: An innovative design strategy has been set up which is capable of optimising both the electromagnetic as well as the thermal design of permanent magnet synchronous machines (PMSM) for aerospace actuation systems. This has been achieved by linking up the electromagnetic design process and motor housing design process for an overall minimum mass. A validation process was initially performed on a PMSM to ensure the correct functionality of the thermal model. Tests were carried out to calibrate the model with experimental data. This paper further describes the adopted optimisation procedure of a 12.75Nm – 2000rpm, horizontally mounted, 12 slot 14 pole Aerospace Permanent Magnet Synchronous motor and highlights the significant weight and volume saving capabilities.

Fault tolerant winding technology comparison for Flux Switching Machine

Abstract: In safety critical aerospace applications, fault tolerant drives can help reach the necessary system reliability levels without replicating the entire drive system and thus minimizing the overall system weight. Machine selection and design for fault tolerance has to be considered at an early stage to ensure optimal performance at system level. Permanent magnet Flux Switching Machines have the distinct property of having a robust rotor construction with the permanent magnets embedded in the stator whilst having their operational characteristics similar to those of synchronous permanent magnet machines. Some slot-pole combinations with particular winding technologies possess natural fault tolerant capability. This paper analyses and compares the fault tolerant properties of permanent magnet flux switching machines of two recently proposed configurations fulfilling the key fault tolerant requirements. The configurations considered are 12 slot 14 pole Double Layer winding with ferromagnetic slot separator and 12 slot 13 pole Single Layer design.

Novel fault tolerant design of flux switching machines

Abstract: This paper looks at the fault tolerant properties of permanent magnet flux switching machines (PMFSM) and proposes a new configuration able to fulfil the fault tolerant requirements. PMFSM have the distinct property of having a robust rotor construction with the permanent magnets embedded in the stator whilst having their operational characteristics similar to those of synchronous permanent magnet machines. Whilst these machines have numerous inherent advantages for achieving high power density, in their basic form they are not tolerant to short circuit winding failures. This paper will look at a novel stator structure able to achieve 1pu winding inductance and will subsequently look at design iterations to maximise the torque density.

Fault ride through control for a delta connected induction motor with an open winding fault by controlling the zero sequence voltage

Abstract: This paper presents a modified fault ride through method for use when open circuit winding faults appear on an induction motor drive. The work includes a new feedforward compensation term introduced into the zero sequence component of the dq reference voltages which considerably reduces current and torque ripple in the faulted motor drive. A method for extending the operating range under fault conditions by employing intelligent field weakening control is presented. Experimental results are presented which demonstrate the effectiveness of the complete system and show that it can be incorporated onto existing commercial drives as a simple software addition.

Optimal split ratio for high speed induction machines

Abstract: The split ratio of several types of electrical machines has been identified as an important optimisation parameter. While the optimisation of split ratio in high-speed permanent magnet, switched reluctance and flux-switching machines has been researched, this parameter has often been neglected in the design of high-speed induction machines. In this paper, using a described multi-domain design environment which puts equal weight on the electromagnetic, mechanical and thermal aspects, the rotor split ratio together with the rotor slot shape and electric and magnetic loadings are identified as important and sensitive parameters in the design of high speed, high power density laminated-rotor induction machines. This is shown using a design case study which involves improving the power density of an existing 10kW, 75kpm laminated rotor induction machine.

Fault tolerant design of a high speed permanent magnet machine

Abstract: This paper details the design considerations of a permanent magnet (PM), three phase synchronous machine for fault tolerant operation. A multidisciplinary approach to the optimal design of the machine is adopted targeted at minimising the additional losses resulting from faulty operating conditions and accounting for the remedial control strategy implemented. The design of a closed slot, 6slots, 4pole machine is presented. (6 pages)

Design of a calorimeter for induction machine efficiency measurement by CFD modeling

Abstract: This paper introduces a novel design of an open air type calorimeter for testing induction machines rated up to 30kW. Developing a reliable design is much more difficult than it initially appears. This is one reason why calorimeters are not generally used for Standard tests. This paper demonstrates the degree of care required to define a precise calorimeter and attempts to construct a design for a general-purpose calorimeter. In this design, a novel Computational Fluid Dynamics (CFD) model of a calorimeter is proposed to investigate in detail the construction of this calorimeter and shows the improvements over the existing design at the University of Nottingham [1] based on simulations and tests.