Reluctance Machine Research Articles

Generic optimised torque control of marine PM propulsion machines

In recent times there has been an increased interest expressed towards the use of advanced power-dense PM (permanent magnet) motors as an alternative to traditional excited synchronous machines in terms of marine power generation and utilisation. This relates specifically to AFM and TFM (axial and transverse flux machines), since they potentially offer a higher torque per unit mass than more traditional technology. Consequently, much design work is being carried out to maximise the power to weight ratio of these machines although, in order to harness their full potential, their control also needs to be optimised. This paper describes a generalised approach to electromagnetic torque control that utilises the motor’s magnetic flux characteristic in order to ensure that maximum torque is produced for minimal input power. The method is generalised for any separately-excited synchronous, permanent magnet or reluctance machine, including AFM and TFM. A TFM motor is used to illustrate the performance of this control algorithm and was chosen because of its highly non-linear nature.

Applications and modelling of bulk HTSs in brushless ac machines

The use of high temperature superconducting material in its bulkform for engineering applications is attractive due to the large powerdensities that can be achieved. In brushless electrical machines, there areessentially four properties that can be exploited; their hysteretic nature,their flux shielding properties, their ability to trap large flux densitiesand their ability to produce levitation. These properties translate tohysteresis machines, reluctance machines, trapped-field synchronous machinesand linear motors respectively. Each one of these machines is addressedseparately and computer simulations that reveal the current and fielddistributions within the machines are used to explain their operation.

Torque from hysteresis machines with type-II superconducting segmented rotors

Electrical machines having rotors constructed from different numbers of type-II superconducting segments have been modelled numerically. The hollow cylindrical rotors are subjected to a rotating applied field that induces currents in the superconducting pieces and the resulting torque is evaluated. The mathematical technique used is based on the critical state model and solves for the current and field distributions within the superconducting pieces using the finite element method. In a two-pole rotating field, a rotor made from two half-ringed pieces is found to behave like a reluctance machine, having a larger peak torque than hysteresis type rotors constructed from other numbers of segments. In general, splitting the rotor up into more segments is advantageous when the flux penetration is small since this increases the hysteresis loss and equivalently, the torque. The modelling results indicate the number of segments which will result in the largest torque for a given rotor size, material critical current density and applied field amplitude. Such information is valuable when considering the performance optimisation of such machines.

Shunt-excited doubly salient 8/6-switched reluctance machine

The performance of a doubly salient 8/6-switched reluctance motor using a shifted fully pitched winding configuration is investigated. The self and mutual inductance characteristics of the machine windings are fundamental to torque generation and are therefore evaluated both theoretically and experimentally. Finite element analysis has been used to investigate theoretical motor-torque capability. Simulation and experimental results for different commutation schemes and their corresponding torque waveforms are investigated for low levels of torque and at low speed. Experimental results are presented for the operation of the machine up to full-load torque. A simple DC rail voltage boosting circuit is shown to enhance the current-control capabilities of an IGBT-based converter. The possibility of driving the machine using a two-switch power converter is also discussed.

Design of a Three-Phase Flux Reversal Machine

A comprehensive design of a novel doubly-salient, stator-permanent magnet (PM) three-phase flux reversal machine (FRM) is presented in this paper. FRM has a robust and easy-to-build structure and is suitable for high-speed applications. Detailed design procedures and formulae are given. All of the dimensions of the FRM are derived. Basic parameters are calculated. The most important aspect of this design is to consider the wide operating speed range. The work presented may serve as a guideline for the general principle of design on three-phase FRM. Furthermore, the methodology and formulae introduced in this paper are also applicable to other types of PM and/or reluctance machine.

Evaluation of switched-reluctance machine through generalized sizing equations

With the evolution of converter fed machines (CFMs), it becomes important to evaluate the power potential of such machines of vastly different topologies with a variety of waveforms of back emf and current. It is based on the generalized sizing equations and permits the evaluation of the main dimensions with respect to the power of those machines. In this paper, a general approach is presented to extend the evaluation method of machine power density to the switched reluctance (SR) machine, and furthermore to compare the power production capability between the SR machine and the well-known squirrel-cage induction machine.

Steady‐state analysis of three‐phase self‐excited reluctance generators

AbstractA three‐phase reluctance machine can be made to operate as a self‐excited generator when its rotor is driven at suitable speed by an external prime mover and its excitation is provided by a capacitor bank connected to the stator terminals. The reluctance generator has almost all the advantages of its counterpart induction generator and has in addition the advantages of constant frequency operation and low core and copper losses. This paper introduces an analysis of the three‐phase self‐excited reluctance generator. The developed analysis avoids the limitations of the previous works whereby the effect of the core loss is soundly taken into consideration. The analysis is suitable for variable speed, load and excitation capacitance operations. The validity of the proposed analysis is confirmed experimentally. The effect of neglecting the core loss is also studied.

Transducerless position and velocity estimation in induction and salient AC machines

This paper presents a viable transducerless rotor position and velocity estimation scheme for PWM inverter driven induction, synchronous, and reluctance machines with the capability of providing robust and accurate dynamic estimation independent of operating point, including zero and very high speeds, light and heavy loading. The injection of a balanced three-phase high frequency signal (500 to 2 kHz) generated by the inverter, followed by appropriate signal demodulation and processing combined with a closed-loop observer, enable the tracking of rotor magnetic saliencies from the machine terminals. Although rotor magnetic saliency is inherent within reluctance machines, and most synchronous machines, saliency in the induction machine is introduced via a modulation of the rotor slot leakage with minimal detrimental effects on the machine performance. Experimental verification for the induction machine is included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

CAPACITOR BRAKING OF SYNCHRONOUS RELUCTANCE MOTORS

ABSTRACT Capacitor braking, a well-known low-loss braking method of Induction ma-chines, Is described in connection with reluctance machines. To represent the main features of capacitor braking of synchronous reluc-tance motors, three dimenslonless quantities are introduced: a frequency parameter, a reactance parameter and a resistance parameter. With the load angle of the synchronous machine added, the result is a four-parameter description of the braking process. The theoretical values for speed range and braking torque are compared with the experimental results of a 22 kW 4-pole test machine. Thanks to the large difference between the d-axis and q-axis inductances of the spe-cial barrier rotor in the test machine, a sufficiently broad braking speed range can be obtained.

PERFORMANCE ANALYSIS OF SELF-EXCITED INDUCTION AND RELUCTANCE GENERATORS

ABSTRACT The paper presents a suggested method for ac power generation from a constant speed drive using capacitor excited induction and reluctance machines. The proposed arrangement is adapted to use one stator frame and two rotor types, namely, salient poles reluctance and squirrel-cage induction rotors. Operational and steady-state equivalent circuits for both types are developed and used to predict the dynamic and steadystate behaviours under load conditions. This analysis depends mainly upon the computation of the power angle for a given machine parameters, capacitor ratings, and load conditions at a constant speed. Further, stability limits of both generators are investigated by developing the active-reactive power (P-Q) diagram for each generator. Conditions required to achieve self-excitation are also given. Performances of the two generator types are evaluated theoretically and experimentally.

Elektromagnetisches Geräusch von Reluktanzmaschinen mit segmentiertem Läufer

A method is developed for the calculation of harmonic fields in reluctance machines with segmental-rotor. The influences of rotor slotting caused by squirrel-cage damper and segmentation can be determined by direct- and quadrature-axis permeance harmonics resulting in modulation of the stator-excited fields. The wider slots at the quadrature axis lead to a dense spectrum of air-gap permeance waves. In order to find out the harmonic fields due to saturation and eccentricity the influence of segmentation will be neglected

DESIGN OPTIMIZATION OF RELUCTANCE MOTORS USING A FIELD APPROACH

In order to improve performance of reluctance motors, careful design of the magnetic circuit is necessary. The machine reluctance is a determining. parameter in the design process. In this paper several techniques' for designing the magnetic circuit are proposed. A fields approach is applied and computer programs are used for numarical solutions. The proposed techniques lead to optimised values of the ratio between (Kand(Kact,) e.g. the anistropy coefficient. Theoritical prediction foraThe performance of a designed model is performed and computed results are reported.

The Reluctance Machine as a Self-Excited Reluctance Generator

ABSTRACT The test described in this paper show that the reluctance machine may be operated as an independent or isolated generator at a predetermined voltage and frequency, with sinusoidal wave form, by moans of capacitive excitation. Further, proper choice and arrangement of the capacitors will result in a practically flat external load-voltage characteristics. The performance analysis based on a developed equivalent circuit is given with experimental verification.

PRINCIPLES OF OPERATION OF THE PARAMETRIC RELUCTANCE MOTOR

ABSTRACT Although reluctance motors are classed normally as synchronous devices, the parametric motor is a reluctance machine which operates asynchronously despite the absence of any windings on the rotor. In the present paper the mechanism of torque production in the parametric motor is explained and the conditions necessary for the machine to function are determined. In addition, the operation of the parametric motor is compared to that of the conventional synchronous reluctance motor.

Optimization of Polyphase Segmented-Rotor Reluctance Motor Design: A Nonlinear Programming Approach

The advantage of the reluctance motor over that of the excited synchronous motor ia that the former does not require a separate d.c. supply for excitation of field winding. Reluctance machines are cheap, robust, and reliable. Using static frequency converters, these motors can be used in control systems and allied fields, for positioning or speed control or a combination of both. But the conventional reluctaunce motor,having ordinary sq,uirrel cage winding with saliency, has the drawback of low pover factor and output. The power factor and output are closely related to the ratio xd/xq of the motor. To obtain large power factors aid output it is necessary to make xd as large as possible and xqas smll as possible. When the ratio cf pole xarc to pole pitch of the rotor is of the order of 0.2, large value of xd/xq can be obtained but then the motor has tle drawback of having heavy magnetising current and a very low pull-in torque.

DC Standstill Torque Used to Measire Lq of Reluctance and Synchronous Machines

An experimental method for measuring the quadrature axis inductance (Lq) of polyphase synchronous machines is developed. It is based on a measurement of developed torque with the rotor at standstill and with the stator winding supplied with dc currents. While applicable to all synchronous machines, it is developed and explained for reluctance motors primarily. Special techniques are used to minimize measurement errors due to hysteresis and due to air gap permeance harmonics. Detailed results are presented for one reluctance motor which has a highly variable Lq, and correlation with other methods is found to be quite good. The effects of saturation are observed, and Lq is found to depend on quadrature axis current in the tested motor, with direct axis current having a slight effect on Lq at larger currents.

THE TRANSFER-FIELD ELECTRIC MACHINE

ABSTRACT A new kind of brushless reluctance-effect machine was described recently. This machine differs from conventional reluctance and inductor-type machines in having a segmented rotor. There is also a further difference in that there is a translation (or rotation) of the active air-gap flux in addition to the usual pulsation associated with the other reluctance-effect types. Thus, the machine is partly an electromagnetic machine and partly a magnetic machine. In the basic machine armature reaction effects pose a serious problem. It is shown in this paper how these effects may be eliminated, and it is also shown that the basic machine is the primitive form of a more general class named transfer-field machines. Like other inductor/reluctance types the machine will operate satisfactorily in the synchronous mode, but unlike them it will also operate in the asynchronous and dc modes. Some preliminary experimental results are also reported.

Synchronous performance of single-phase reluctance motors

An explanation of performance in terms of motor impedances is developed and validated by comparison with measurements on a commercially built motor. The explanation involves a significant extension of the scope of 2-axis theory to permit inclusion of the principal effects of both stator and rotor circuits. A full study of the effects of parameter variations on the performance is made and used in developing an improved machine. Torque pulsations occurring at synchronous speed and capacitor operation are both discussed. Simple relations are developed for both, and should be of value to designers of induction as well as reluctance machines. Stability of operation from a variable-frequency supply is shown to be relatable to that with a polyphase supply.

Stability of Reluctance Motors from Freely Accelerating Torque Speed Curves

The limits of stability in reluctance machines are known to be narrow, especially in machines of improved design with high reactance ratio. These stability limits can usefully be investigated with the aid of computed and measured freely accelerating torque speed curves. The machine equations are developed using a frame of reference fixed with respeot to the rotor. Machine performance is then simulated on an analogue computer. A large number of freely accelerating torque speed curves are then generated for different values of machine parameters. The model is designed to cope simply with different motors and is based on a per unit system. All parameters can be simply varied, so that their effect on performance can be demonstrated . The torque speed curves that result can be said to be characteristic. of amachine with given parameters and contain information about starting torque, transient torque dips, synchronisation ability and stability. Since changes in parameters cause marked changes in shape of the freely accelerating torque speed curve, it is possible, by matching the results obtained from a practical test with those from a computer study, to determine where the total performance of the machine lies with respect to the optimum and to decide what changes are necessary to improve design.

The goodness of a reluctance machine

The goodness of a reluctance machine