Incremental Inductance Research Articles

Winding condition monitoring scheme for a permanent magnet machine using high-frequency injection

This study presents a new technique for condition monitoring of motor windings in variable speed drive systems. The technique employs high-frequency injection to monitor the machine's incremental inductances. These inductances can provide an indication of changes in the magnetic signature owing to the presence of electrical faults. The Space modulation profiling (SMP) technique is used to create a look-up table that defines the healthy incremental inductance signature of the drive as a function of load and rotor position. A similar signature is obtained online; this is compared with the SMP look-up table to derive an error signal which can be used to trigger warnings or alarms as faults develop. In this study, the emphasis is on the detection of stator winding faults in a permanent magnet AC machine, including incipient and short-circuit faults. The result is a monitoring scheme with improved sensitivity with respect to monitoring schemes based on the passive measurement of terminal quantities. Experimental results show that the monitoring scheme has a fast response and high sensitivity which make it suitable for predicting faults at an early stage of development, before they degenerate into a serious fault which requires drive shutdown.

High-performance current control for switched reluctance motors based on on-line estimated parameters

To reduce torque ripple in a switched reluctance motor (SRM) by current profiling, a high-performance current controller is necessary. This study presents a high-performance current controller for SRM drives. A B-spline neural network is used to model the non-linearity of the SRM and estimate back electromotive force (EMF) and incremental inductance on-line in real time. The on-line modelling scheme does not require a priori knowledge of the machine's electromagnetic characteristics. Based on the on-line estimated parameters, a current controller with adjustable PI gains and back-EMF decoupling is implemented. The performance of the current controller has been demonstrated in simulation and experimentally using a four-phase 8/6 550'W SRM drive system.

Effect of rotor eccentricity on electric parameters in a PM brushless motor with parallel winding connections

In this paper, the parallel winding of a 20-pole, 18-slot permanent magnet (PM) brushless motor with common and uncommon neutral points is used to investigate static rotor eccentricity effects. Static rotor eccentricity will cause an imbalance of the back-EMF in each parallel winding and may result in high torque ripple. However, as the common neutral point is applied, it can be observed that the back-EMF becomes balanced and may reduce torque ripple. Moreover, the winding current and inductance in the eccentric motor with a common neutral point are also discussed. This paper provides motor designers with analyses of the relationship between static rotor eccentricity and electric motor parameters, such as back-EMF, winding current, and incremental inductances.

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 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.

A Simple and Accurate Analysis of Conductivity Loss in Millimeter-Wave Helical Slow-Wave Structures

Electromagnetic field analysis of a helix slow-wave structure was carried out and a closed form expression was derived for the inductance per unit length of the transmission-line equivalent circuit of the structure, taking into account the actual helix tape dimensions and surface current on the helix over the actual metallic area of the tape. The expression of the inductance per unit length, thus obtained, was used for estimating the increment in the inductance per unit length caused due to penetration of the magnetic flux into the conducting surfaces following Wheeler’s incremental inductance rule, which was subsequently interpreted for the attenuation constant of the propagating structure. The analysis was computationally simple and accurate, and accrues the accuracy of 3D electromagnetic analysis by allowing the use of dispersion characteristics obtainable from any standard electromagnetic modeling. The approach was benchmarked against measurement for two practical structures, and excellent agreement was observed. The analysis was subsequently applied to demonstrate the effects of conductivity on the attenuation constant of a typical broadband millimeter-wave helical slow-wave structure with respect to helix materials and copper plating on the helix, surface finish of the helix, dielectric loading effect and effect of high temperature operation – a comparative study of various such aspects are covered.

Online Modeling for Switched Reluctance Motors Using B-Spline Neural Networks

A novel online-modeling scheme for the switched reluctance motor (SRM) using a B-spline neural network (BSNN) is proposed in this paper. A 2-D BSNN is designed to learn the nonlinear-flux-linkage characteristic of an SRM online and in real-time. Torque, incremental inductance, and back-emf estimates can be derived from the BSNN after training. The scheme does not require a priori knowledge of the SRM electromagnetic characteristics. Simulation and experimental results show that the scheme has a good estimation performance and robustness at low to medium motor speed.

A Study of Inductance Computations for Transverse Flux Linear Motor Considering Nonlinearity of Magnetic Material

Inductance is an important parameter to assess electric motor characteristics. In this paper, the methods of apparent and incremental inductance calculations are introduced for a transverse flux linear motor (TFLM), which has a peculiar coil shape. To consider the nonlinearity of magnetic material, nonlinear analysis is performed by 3-dimensional equivalent magnetic circuit network (3D EMCN). The calculation method is verified by test results.

Calculation of inductances in permanent magnet type transverse flux linear motor

The design and analysis of electrical machines often require analytical models for performance assessment and system simulation. Inductance is one of important parameters of these models. In this paper, the calculation methods of apparent and incremental inductances are introduced for a transverse flux linear motor (TFLM), which has a peculiar coil shape. To consider nonlinearity of the inductances according to current and magnetic materials, nonlinear analysis is performed by 3-dimensional equivalent magnetic circuit network (3D EMCN). The calculation method has been verified by test results.

Inductance Model-Based Sensorless Control of the Switched Reluctance Motor Drive at Low Speed

A sensorless control scheme for the switched reluctance motor (SRM) drive at low speed is presented in this paper. The incremental inductance of each active phase is estimated using the terminal measurement of this phase. The estimated phase incremental inductance is compared to an analytical model, which represents the functional relationships between the phase incremental inductance, phase current, and rotor position, to estimate the rotor position. The presented sensorless control scheme requires neither extra hardware nor huge memory space for implementation. It can provide accurate rotor position information even as the magnetic characteristics of the SRM change due to aging. Combined with other inductance model-based sensorless control techniques, the proposed method can be used to develop an inductance model-based sensorless control scheme to run the SRM from standstill to high-speed. Simulation and experimental results are presented to verify the proposed scheme.

Analytical Prediction of the Incremental Inductance of the Permanent Magnet Synchronous Motors

An analytical method for calculating the incremental line inductance of a permanent-magnet synchronous motor is proposed in this paper. First, the incremental inductance is simplified as a linear combination of the slot inductance and the air-gap inductance, which are both estimated by the equivalent magnetic circuits. The reluctance of the rotor back irons and the stator back irons are ignored when the slot inductance is calculated. However, for the calculation of the air-gap inductance, the iron saturations and the perturbations of the permanent magnet are considered. The proposed method is verified by a finite-element method.

Modeling Switched-Reluctance Machines by Decomposition of Double Magnetic Saliencies

This paper presents a novel analytical model for a switched-reluctance machine (SRM) based on decomposition of its inherent double joint magnetic saliencies due to rotor and stator salient poles and saturation of magnetic field at high stator currents. With this method, the magnetic characteristics of the motor, such as flux linkage and incremental inductance, are decomposed to vector functions of rotor position and phase current. Dynamic state and torque equations for the SRM are derived on the basis of this representation. The proposed model is appropriate for online identification and for sensorless position control algorithms. It is easy to implement and computationally efficient. Comparison of the predicted motor magnetic characteristics to machine data from finite-element analysis verifies the accuracy of the model.

The Inductance Model of Coupled High-Tc Superconducting Microstrip Lines

A simple analytical model of odd and even mode external inductance and kinetic inductance for coupled high-temperature superconducting (HTS) microstrip lines is developed. The kinetic inductance model is derived with the extended incremental inductance rule which is applied in a different way for different conductor thickness. The odd and even mode inductance, self- and mutual inductance, characteristic impedance, and attenuation constant are computed with the presented model expressions and the results agree well with that in published literature.

Determination of conductor loss of multilayer‐coupled microstrip lines for CAD application

AbstractBy modifying and adopting the incremental inductance rule, in association with the variational method in the Fourier domain, and using the single layer (SLR) formulation, we present a fast and accurate method to compute the conductor loss of a multilayer‐coupled microstrip line with and without shield. The accuracy of the method has been tested against several full‐wave methods. The conductor loss of many useful structures is compared. The method is valid for conductor thickness t > 1.11 skin depth. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 409–415, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11076

A new characteristic impedance perturbation method for finding attenuation constants

AbstractA new characteristic impedance perturbation method for finding the attenuation constant α of transmission lines is presented, which not only clarifies some unclear concepts and applied limitations of the Wheeler incremental inductance rule, but which also can be extended to the TM mode transmission line in some cases. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 243–245, 2002.

Conductor loss in thin-film transmission lines

By means of the surface impedance applicable to a finite film thickness, the conductor loss of a transmission line is investigated. It is found that there exists an optimum conductor thickness at which the conductor loss becomes a minimum. This thickness is predicted to be π/2 of the skin depth. Next, by using the thin-film microstrip line with varying conductor thickness and width, the measurement of transmission loss is carried out. It is confirmed that the optimum conductor thickness is near π/2 times the skin depth. In the process of investigation, the relationship with the surface current density in the incremental inductance method, often used as a simple computation method of conductor loss, is presented. The calculation of the conductor loss of a multilayered conductor is made possible. Previously, it has been considered that the conductor loss is sufficiently small if the conductor thickness is more than three times the skin depth. It is shown in the present study that the conductor loss becomes small with a conductor thickness about one-half as great. In addition to the increased performance of a transmission line, a contribution to reduction of both the consumption of valuable interconnect materials (such as gold) and of fabrication cost is expected. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(10): 83–91, 1999

A simple evaluation of losses in thin microstrips

A simple modification of Wheeler's incremental inductance rule is presented which allows the extention of the use of this rule for the evaluation in quasi-TEM operation of losses in thin microstrips (i.e., when the Wheeler's rule is considered no longer applicable). A good agreement of the proposed formula with available numerical results is obtained when thickness is comparable with skin depth. A comparison is also made with two approximate formulas proposed by some authors. The proposed modification to Wheeler's rule should be useful for computer-aided design (CAD) of monolithic microwave integrated circuits (MMIC's).

Position estimation in solenoid actuators

This paper describes a novel method of estimating the position of a plunger inside a solenoid. The solenoid is a single-phase variable reluctance actuator, with a highly nonlinear magnetic circuit. For the proposed method, position is estimated indirectly through the solenoid's incremental inductance in the high current region. It exploits the advantage that motional electromotive force (EMF) is negligible under normal operating condition. The incremental inductance is obtained from the rate of current rise of the pulse-width modulated (PWM) waveform, which in turn, is measured by a dedicated current rise measurement circuit. Position is estimated from a two-dimensional look-up table of incremental inductance and current. The method is simulated and then implemented on a typical industrial solenoid valve. Factors which affect the accuracy of the estimation and methods of overcoming them are also described in the paper.

Quick computation of (C), (L), (G), and (R) matrices of multiconductor and multilayered transmission systems

This paper presents a general scheme to compute the four characteristic matrices, [C], [G], [L] and [R], of a multilayered and multiconductor transmission line with arbitrary cross section conductors under quasi-TEM approach and strong skin effect regime. The conductors are modeled as a set of infinitesimally thin strips following the M-strip model. An spectral domain approach (SDA) has been employed, paying special attention to the efficient computation of the spectral tails. Conductor losses are considered via the incremental inductance rule extended to the multiconductor case.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The incremental inductance rule in quasi-TEM coupled transmission lines

The application of the incremental inductance rule is described for the computation of losses in quasi-TEM coupled transmission lines. It is shown that the well-known formula valid for the single-line case can be extended to the case of normal modes travelling in general coupled structures providing one uses the power-current modal characteristic impedance definition. Numerical results are shown for several coupled lines systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Closed-form expressions for the current density on the ground plane of a microstrip line, with application to ground plane loss

In this paper closed-form expressions for the current density on the ground plane of a microstrip line are derived. The derivation is based on a quasistatic Green's function approach. These expressions are compared to both experimental and numerical values, and excellent agreement is demonstrated. The loss on a ground plane for a microstrip structure is calculated using these expressions, and comparisons with results from Wheeler's incremental inductance rule are made.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>