Induction methods used in low temperature physics

A study has been made of induction bridges used in low temperature physics.\ud \ud In Part 1 the design of a mutual inductance bridge of the Hartshorn type is discussed. This design is based on a critical analysis of impurity effects of the different parts of the Hartshorn bridge. With this equipment frequencies up to 0.5 MHz can be used. Two methods have been developed to examine the secondary signal. In one of these use has been made of AD conversion techniques. In the other one, the secondary signal, produced by a superconducting sample, which is generally distorted, is analysed by using a Fourier expansion.\ud \ud In Part 2 equipment is described which enables us to measure the phase and amplitude of the harmonics of the output signal of the bridge. For synchronous detection a reference signal of the same frequency of the harmonic of interest is required. This reference signal is generated from the input signal of the bridge by means of a digital frequency multiplier with programmable multiplication factor N.\ud \ud In Part 3 some experimental results, showing the possibilities of the equipment, on some superconductors are presented

Measurement of permeability for ferrous metallic plates using a novel lift-off compensation technique on phase signature

Lift-off of sensor affects the prediction of electromagnetic properties for both ferrous and non-ferrous steel plates. In this paper, we developed a strategy to address this issue for ferrous plates. With increased lift-off, the phase of the measured impedance for steel plates reduces. Meanwhile, the magnitude of the impedance signal decreases. Based on these facts, a phase compensation algorithm is developed which corrects the phase change due to lift-off considering the magnitude of the impedance signal. Further, a new magnetic permeability prediction technique is presented, which has been validated by analytical and measured results. With this new technique, the error in permeability prediction is less than 2% within the range of lift-offs tested

Evaluation of Flexible Rogowski Coil Performances In Power Frequency Applications

This paper investigates the effects of some influence quantities on the measurement of power frequency sinusoidal currents by means of flexible Rogowski coil sensors. The analysis is carried out through a numerical model, which is specifically developed and allows both the prediction of the circuital and coil parameter effects and the improvement of the coil design. The estimate of the measurement uncertainty associated with the on-site use of a flexible and openable Rogowski coil is finally given by assuming relatively controlled operating conditions

Numerická analýza a simulace Rogowského cívky

This work illustrates an analysis of Rogowski coils for power applications, when operating under non ideal measurement conditions. The developed numerical model, validated by comparison with other methods and experiments, enables to investigate the effects of the geometrical and constructive parameters on the measurement behavior of the coil and we also study the behavior of Rogowski coils coupled with bar conductors under quasi-static conditions. Through a finite element (FEM) analysis, we estimate the current distribution across the bar and the flux linked by the transducer for various positions of the primary conductor and for various operating frequencies. Simulation and experimental results are reported in the text.Tato práce ilustruje analýzu rogowských cívek pro energetické aplikace při provozu v podmínkách bez ideálního měření. Vyvinutý numerický model, ověřený porovnáním s jinými metodami a experimenty, umožňuje zkoumat vliv geometrických a konstrukčních parametrů na chování měření cívky a také studujeme chování rogowských cívek spojených s tyčovými vodiči za kvazi-statických podmínek . Pomocí analýzy konečných prvků (FEM) odhadujeme rozložení proudu přes tyč a tok spojený snímačem pro různé polohy primárního vodiče a pro různé provozní frekvence. Simulační a experimentální výsledky jsou uvedeny v textu.410 - Katedra elektroenergetikydobř

Data-driven online temperature compensation for robust field-oriented torque-controlled induction machines

Squirrel-cage induction machines (IMs) with indirect field-oriented control are widely used in industry and are frequently chosen for their accurate and dynamic torque control. During operation, however, temperature rises leading to changes in machine parameters. The rotor resistance, in particular, alters, affecting the accuracy of the torque control. The authors investigated the effect of a rotor resistance parameter mismatch in the control algorithm on the angular rotor flux misalignment and the subsequent deviation of stator currents and motor torque from their setpoints. Hence, an online, data-driven torque compensation to eliminate the temperature effect is proposed to enable robust torque-controlled IMs. A model-based analysis and experimental mapping of the temperature effect on motor torque is presented. A temperature-torque lookup-table is subsequently implemented within the control algorithm demonstrating the ability to reduce the detrimental effect of temperature on torque control. Experimental results on a 5.5 kW squirrel-cage induction motor show that the proposed data-driven online temperature compensation method is able to reduce torque mismatch when compared to having no temperature compensation. Up to 17% torque mismatch is reduced at nominal torque and even up to 23% at torque setpoints that are lower than 20% of the nominal torque. A limited torque error of <1% remains in a broad operating range

Improved rotor-position estimation by signal injection in brushless AC motors, accounting for cross-coupling magnetic saturation

This paper presents an improved signal-injection- based sensorless-control method for permanent-magnet brushless ac (BLAC) motors, accounting for the influence of cross-coupling magnetic saturation between the d- and q-axes. The d- and q-axis incremental self-inductances, the incremental mutual inductance between the d-axis and q-axis, and the cross-coupling factor are determined by finite-element analysis. An experimental method is proposed for measuring the cross-coupling factor which can be used directly in the sensorless-control scheme. Both measurements and predictions show that a significant improvement in the accu- racy of the rotor-position estimation can be achieved under both dynamic and steady-state operation compared with that which is obtained with the conventional signal-injection method

Improved rotor position estimation by signal injection in brushless AC motors, accounting for cross-coupling magnetic saturation

The paper presents an improved signal injection- based sensorless control method for permanent magnet brushless AC (BLAC) motors, accounting for the influence of cross-coupling magnetic saturation between the d- and q-axes. The d- and q-axis incremental self-inductances, the incremental mutual-inductance between the (d-axis and q-axis, and the cross-coupling factor are determined by finite element analysis. A method is also proposed for measuring the cross-coupling factor which can be used directly in the sensorless control scheme. Both measurements and predictions show that a significant improvement in the accuracy of the rotor position estimation can be achieved under both dynamic and steady-state operation, compared with that which is obtained with the conventional signal injection method