Howard C Lovatt

A new and improved technique is presented for the measurement of iron loss in motor stators. The most accurate existing technique rotates dummy-test rotors, one for each field strength of interest, inside the stators to be tested and measures the reaction torque on the stators. The new technique uses a wound `rotor' component that does not rotate mechanically but does rotate electrically. Therefore, the speed and magnitude of the rotating flux can be controlled electrically without the inherent difficulties of rotating mechanically at high speed and without building different dummy-test rotors for each field strength test.

Sensorless and torque control of Switched Reluctance Motors (SRMs) is a well-researched field. Many techniques rely on the measurement of phase inductance and or flux-linkage which can be significantly affected by the mutual phase inductance. By measuring the mutual inductance over an electrical cycle or at particular locations, the accuracy of the sensorless and torque control techniques can be improved. This paper presents two novel techniques which profile the mutual inductance without an off-line calibration technique. Methods are discussed to increase the accuracy of the calculated phase inductance and flux-linkage integral using the mutual inductance information. The techniques are developed for three-phase SRMs. Test results of both techniques are investigated using a 1 kW three-phase SRM.

A linear actuator suitable for sun tracking applications, heliostats, was investigated. First, a benchmark actuator was modelled using Finite Element (FE) analysis and then a prototype was constructed. The electromagnetic force on the mover was simulated and was found to be in excellent agreement with experiment. Next; a three-phase, direct-drive, linear actuator was proposed, which has a step size of 1.81mm. Three different driving current waveforms: unipolar, bipolar, and sinusoidal were investigated using FE analysis. The analysis shows that the linear actuator is able to produce a force density of 850 N/m.

The switched reluctance motor (SRM) is a low cost motor option. However it has lower power factor than competing motors and this has led to the incorrect perception that the power electronics are expensive. This paper shows that using the inverse of power factor as a proxy for converter rating and hence cost is incorrect; in particular device utilization and device switching losses are just as relevant. When the complete picture is considered the ratings for the SRM are shown to be only 2/3rds that of the induction motor. Other authors have observed, but not explained, this reduced rating.

This paper proposes a technique to detect the rotor position in a Switched Reluctance Motor(SRM) which only requires knowledge of the phase resistance and the number of stator and rotor poles. Accuracy can be further improved if prior knowledge of the mutual phase inductance is known. The technique operates by sensing the minimum inductance location which allows positional information to be obtained. This is performed using a controlled low level sense current during the un-energised period. A Digital Phase Locked Loop is described to derive rotational positions between minimum inductance locations. Factors affecting the detection of the minimum inductance position are described and proposals to mitigate errors are discussed. The technique is implemented using a Field Programmable Gate Array(FPGA) with results showing good performance over a range of speeds and motor operating conditions.

Traditionally iron loss in motor stators is measured using loss separation, where overall loss is measured and then other losses like windage, bearings, copper, and rotor losses subtracted. This technique is unsatisfactory because the stator iron loss is typically smaller than the other losses subtracted and therefore a small error percentage wise in one of these other losses leads to a large error in the iron loss. A new technique is described that directly measures the stator iron loss and therefore offers much improved accuracy. This new technique is then applied to a series of known difficult measurements, like effect of temperature on iron loss, compression on iron loss, etc., to demonstrate its veracity and usefulness and to quantify these effects accurately for the first time.

An analytical modelling technique to calculate the generated magneto-motive force (MMF) and back-EMF of fractional slot concentrated wound (FSCW) permanent magnet synchronous machines (PMSMs) is reported. The generated MMF of a FSCW stator is analyzed and modelled using a Fourier series technique. General expressions of the harmonic winding factors for FCSW stators with different slot-pole combinations are then obtained. A general expression for the generated back-EMF of FSCW PMSMs is then derived. The obtained analytical results are validated through finite-element analysis (FEA) and experimental tests on a prototype FSCW PMSM. A comparison between the generated voltages of various FSCW stator topologies is also performed.

The switched reluctance motor (SRM) is a low cost motor option. However it has lower power factor than competing motors and this has led to the incorrect perception that the power electronics are expensive. This paper shows that comparing an inverter fed motor to an SRM requires consideration of more than just power factor. In particular device utilization and device switching losses are just as relevant. When the complete picture is considered the ratings for the SRM are shown to be only 2/3rds that of the induction motor. Other authors have observed, but not explained, this reduced rating.