Showing papers by "Chris Gerada published in 2008"

Integrated PM Machine Design for an Aircraft EMA

Abstract: This paper looks at the requirements and challenges of designing a permanent-magnet (PM) motor for a directly driven electromechanical actuator for aerospace applications. Having a directly driven system, the intermediate gearbox is eliminated, bringing advantages in terms of lower component count and reduced jamming probability. The design of a low-speed high pole number PM motor will be investigated as a potential solution. The main goals of the design are a high level of actuator integration in order to minimize weight and volume, fault tolerance, and high reliability. The design will be tailored to the requirements of a typical midspoiler actuation system for a large civil aircraft.

Identification of Induction Machine Electrical Parameters Using Genetic Algorithms Optimization

Abstract: This paper introduces a new heuristic approach for identifying induction motor equivalent circuit parameters based on experimental transient measurements from a vector controlled induction motor (I.M.) drive and using an off line genetic algorithm (GA) routine with a linear machine model. The evaluation of the electrical motor parameters is achieved by minimizing the error between experimental responses (speed or current) measured on a motor drive and the respective ones obtained by a simulation model based on the same control structure as the experimental rig, but with varying electrical parameters. An accurate and fast estimation of the electrical motor parameters is so achieved. Results are verified through a comparison of speed, torque and line current responses between the experimental IM drive and a Matlab-Simulink model.

Investigation of induction machine phase open circuit faults using a simplified equivalent circuit model

Abstract: An induction motor model based on the per-phase equivalent circuit is used to simulate operation with an open circuit fault. The model considers both spatial field harmonics as well as saturation effects to correctly model the motor's behaviour under faulty conditions, where the non-linearities may produce problematic torque pulsations due to the unbalanced nature of the winding distribution. A model is presented which takes into account the most prominent nonlinearities, however keeping simulation times low in order to enable the development of fault tolerant control strategies. In addition, this paper presents a study of the behaviour of an induction motor drive with a phase open circuit fault. A new fault remedial control strategy for this type of fault will also be described. Experimental tests on an instrumented vector controlled rig have been used to verify simulation results.

On-line detection of stator winding short-circuit faults in a PM machine using HF signal injection

Abstract: This paper presents a high frequency (HF) injection scheme to detect short-circuits faults in the stator winding of a VSI-fed permanent magnet (PM) machine. The proposed approach is derived from sensorless control schemes based on HF voltage signal injection for tracking position in a surface-mount PM machine. In this paper the method of space-modulation profiling (SMP) is used to obtain a magnetic signature of the machine operating under healthy conditions. This signature can then be compared with the on-line measured saliency profile during normal operation to detect any abnormality in the drive's performance. The main application of the presented scheme is for the detection of windings problems such as insulation breakdowns and short circuits. Experimental results are shown for the case of a PM servo drive where incipient and full short-circuit faults have been emulated and successfully detected. Due to its relatively simple implementation and since no additional transducers are required, this approach presents an interesting alternative for condition monitoring.

Induction Motor parameters identification using Genetic Algorithms for varying flux levels

Abstract: This paper describes a novel approach for identifying induction motor electrical parameters in function of flux levels based on experimental transient measurements from a vector controlled induction motor (I.M.) drive and using an off line genetic algorithm (GA) routine with a linear machine model. The evaluation of the electrical motor parameters is achieved by minimizing the error between experimental and simulation model responses. An accurate and fast estimation of the electrical motor parameters is performed by running a number of optimizations using experimental tests taken under different operating conditions (flux level). Results are verified through a comparison of speed, torque and line current responses between the experimental IM drive and a Matlab - Simulink model.

A power converter 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. The paper introduces a multi-phase two level inverter using a flexible and reliable FPGA/DSP controller for data acquisition, motor control and fault monitoring to study the fault tolerance of such systems.

A simplified model for induction machines with faults to aid the development of fault tolerant drives

Abstract: A new mathematical model of a three-phase induction machine, suitable for the simulation of machine behaviour under fault conditions is presented. The model employs a simple state space equivalent circuit based model of the induction machine, which is enhanced to include space harmonics and main flux saturation effects. The model has been improved by including a variation of machine inductances with rotor and flux position, and creates a simulation with reasonable accuracy and fast computation time. For healthy and fault conditions, comparisons show that the simulated saturation and space harmonic frequencies and magnitudes match those obtained from experiment. This model can be used to develop and optimise control strategies for fault ride through.

Condition monitoring for mechanical faults in fully integrated servo drive systems

Abstract: A modified motor current signature analysis (MCSA) approach to monitor the performance of a servo drive system using only one set of current transducers at the input side of the rectifier is proposed. The paper introduces a mathematical analysis to determine how the harmonic frequencies related to a fault propagate from the motor to the input inverter, and includes the effect of the DC link components. Experimental results are presented for a permanent magnet servo drive system with faulty bearings to validate the proposed scheme.

Modelling and simulation of a signal injection self-sensored drive

Abstract: This paper presents a new induction motor model specifically developed for simulating self-sensored variable speed drives which employ signal injection based sensorless control techniques. The model is to be used to investigate improved filtering algorithms and closed loop speed controllers. The model employs a simple state space equivalent circuit based model of the induction machine, which is enhanced to include rotor slotting and main flux saturation effects. The improvement is obtained by including a variation of machine inductances variation with the rotor position and the flux position. The new model is verified against experimental results.