Axis Current Research Articles

Investigation of Force Generation in a Permanent Magnet Synchronous Machine

Traditional analysis of permanent magnet synchronous machines has focused upon establishing a relationship between the quadrature and direct axis stator current (or voltage) and the electromagnetic force created to establish rotation (torque). In this paper, an alternative analysis of electromagnetic force production is considered. Specifically, the influences of - and -axis stator current on both the radial and tangential components of the airgap flux densities are first evaluated. Using a Maxwell stress tensor approach, the fields are then used to evaluate both the radial and tangential component of force density created in the airgap of the machine. From this perspective several interesting observations are made. First, it is shown that the -axis current has zero influence on the average tangential force (torque), as predicted using traditional analysis, but it has a significant influence on the average radial component of force. Second, it is shown that the -axis current contributes to both the average radial and average tangential components of force. Interestingly, it is also shown that under standard operating conditions, the average radial force far exceeds that of the average tangential component of force. Therefore, one can conclude that the magnetic fields established create a significant component of force in a direction that cannot produce torque.

Current Control of Induction Machines in the Field-Weakened Region

This paper presents a novel current regulation algorithm for induction machines that enables smooth operation and maximum torque-per-ampere capability over the entire field-weakened region. The algorithm enables robust current regulation with maximum torque capability despite significant variation in voltage source and machine parameters. The algorithm identifies when the current regulator begins to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined as a function of the torque command and the d-axis current feedback. In the field-weakened region, the -axis current is monitored not to exceed the maximum -axis current. The maximum q-axis current is calculated based on the maximum slip frequency, which is a function of rotor frequency, q-axis current gesmaximum q-axis current (in motoring mode) indicates that the machine entered field-weakened region II, and the -axis current is limited to its maximum value. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation.

Maximum Efficiency Operation of Vector-Controlled Synchronous Reluctance Motors Considering Cross-Magnetic Saturation

The direct and quadrature axes inductances of flux barrier type Synchronous Reluctance Motors (SynRM) change depending on the magnitude of both direct and quadrature axes currents under the influence of the cross-magnetic saturation. This paper presents a maximum efficiency operation method of SynRMs with cross-magnetic saturation. An improved approximate equation that accurately expresses the inductance variation caused by cross-magnetic saturation is utilized for calculating the Maximum Efficiency Operation Current (MEOC, i.e., the d-axis current at maximum efficiency) at each load point. A vector control system in which the steady-state driving efficiency is maximized by selecting a d-axis current command from the obtained MEOC is shown. By considering cross-magnetic saturation the proposed method not only maximizes the efficiency but also improves the torque control accuracy. The validity of this method is demonstrated with calculated and measured results of on-load characteristics.

Fiske steps studied by flux-flow resistance oscillation in a narrow stack ofBi2Sr2CaCu2O8+δjunctions

We have experimentally investigated the fluxon dynamics in a narrow ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ stack with junction length $L\ensuremath{\sim}1.8\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. As an evidence of high-frequency excitation by a collective cavity mode, under an (in-plane) external magnetic field, the current-voltage characteristics show prominent Fiske steps with the corresponding resonance frequencies of $75--305\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. Further study of flux-flow resistance oscillation with various $c$-axis currents clarifies the correlation with Fiske steps by distinguishing two different regions, i.e., the static flux-flow region at low bias current level and dynamic Fiske step region at high bias current level.

Tracking improvement of LSRM at low‐speed operation

AbstractThis paper deals with the tracking control design of a Linear Synchronous Reluctance Motor (LSRM) drive. The modified non‐linear dynamic LSRM model with the magnetic saturation included is used in the control design and realization to improve the tracking performances at very low speed of motion. The iron core saturation is included in the modified model with the experimentally determined flux linkages given as functions of the direct and the quadrature axis currents. Experimental results show that the proposed input–output linearizing tracking control with the included saturation behaves considerably better than the one without saturation, introducing smaller position and speed errors, and better drive stiffness. Copyright © 2005 John Wiley & Sons, Ltd.

Position tracking control of saturated LSRM

This paper deals with the tracking control design of a linear synchronous reluctance motor (LSRM) drive. An extended nonlinear dynamic LSRM model with magnetic saturation included is used in the control design and practical realization, in order to improve tracking performances at very low speeds of motion. Iron core saturation is included in the extended model with the experimentally determined flux linkages given as functions of the direct and quadrature axes currents. Experimental results show that the proposed input-output linearizing tracking control with included saturation behaves considerably better than the one without saturation, introducing smaller position and speed errors and better motor stiffness, on account of the increased computational complexity.

Identification of Linear Synchronous Reluctance Motor Parameters

This paper deals with experimental methods for the identification of linear synchronous reluctance motor (LSRM) parameters. A magnetically nonlinear two-axis dynamic LSRM model is derived. This model accounts for the effects of slotting, saturation, cross-saturation, and the end effects. The parameters of the obtained model are not constant. They are given by the characteristics of the flux linkages, thrust, and friction force depending on the mover position and the direct (d) and quadrature (q) axis currents. These characteristics are determined experimentally by a controlled voltage-source inverter employing closed-loop current control in the d-q reference frame. The proposed model, experimental methods, and determined characteristics are confirmed through a comparison between the measured and calculated results. Two tests are performed: a test at the locked mover, and kinematic control at low speed. The effects of cross saturation under dynamic operating conditions and the effects of slotting can be clearly seen in the measured and calculated results.

Incremental inference of boundary forcing for a three-dimensional tidal model: tides in the Taiwan Strait

Tides in the Taiwan Strait are predominantly semidiurnal. The semidiurnal tide propagates southward along the mainland (China) coast but is a standing wave on the Taiwan coast. The tidal amplitude is large, reaching about 2 m in the middle of the strait, but diminishing rapidly towards the deeper portion of the strait. An amphidromic point is located off the southwest coast of Taiwan. Tidal currents are strong near the open ends (especially on the Taiwan side) and diminish towards the middles of the strait. A fine-resolution (3 km×3 km), three-dimensional, coastal ocean model is being developed for the Taiwan Strait. In this study, the focus is on validation of tidal sea levels and currents. The limited-area model is driven by tidal elevations on two open ends, of which amplitudes and phases are optimized through a four-dimensional variational assimilation. Specifically, the model uses an incremental approach in which misfits between model results and coastal tidal observations are reduced incrementally through repeat applications of a linear two-dimensional model and its adjoint. The incremental approach is both effective and efficient. The root-mean-squared (rms) error for the dominant M 2 tide is reduced from about 0.15 to 0.06 m, a five-fold reduction in error variance. Moreover, this is achieved with only 3–4 iterations of the three-dimensional model; for comparison, a typical four-dimensional variational assimilation will require an order of magnitude more computation effort. The predicted tidal current ellipses are also compared with the observations from six bottom-mounted Acoustic Doppler Current Profilers (ADCP). The semi-major axis currents generally agree to within 0.05 m/s. The sensitivity of vertical tidal current structure to bottom friction also is examined.

Torque and efficiency calculation of an interior permanent magnet motor considering harmonic iron losses of both the stator and rotor

A method to estimate characteristics of interior permanent magnet motors considering effects of iron loss is introduced. The equivalent circuit parameters including the iron loss resistance are calculated as functions of d-q axis currents by the finite-element method with the consideration of movement of the rotor. The characteristics of the motor are calculated from the equivalent circuit. By using this procedure, we can calculate the torque and the efficiency of the motor considering the harmonic iron losses of both the stator and rotor at any operating conditions instantaneously after parameter calculation. The results of the calculated characteristics are compared with the experimental results to examine the validity.

Development and design of an ECRF launching system for ITER

The design and development of an EC beam launcher are described for the ITER EC H&CD system for plasma heating and on/off axis current drive. The launcher in an equatorial port (an equatorial EC launcher) has three movable mirrors and can inject the EC wave beam power of 20 MW with continuous toroidal steering of 20–45° ( r=0–0.6a). The rf frequency is 170 GHz. The front shield of the equatorial EC launcher is designed, and has three narrow slots for rf injection. A 10 atm resistant torus diamond window for a vacuum and a tritium boundary is developed and introduced to the launcher design. Nuclear analysis by the two-dimensional radiation transport code, DOT3.5 for the equatorial EC launcher was carried out and showed that the present neutron radiation shield structure of the launcher could satisfy the required shielding criteria.

INTERIOR PERMANENT MAGNET MOTOR HAVING SEVERAL IMPROVED FEATURES

ABSTRACT The no-load airgap flux density distribution of most conventional permanent magnet motors is square in shape. The rotor configurations having interior magnets employed in these machines also lead to vastly different saliencies along the d- and q-axes giving a quadrature axis inductance larger than the direct axis inductance. A modified rotor configuration is presented that produces a near sinusoidal airgap flux density distribution which is achieved by shaping the rotor airgap profile while keeping the interior magnets rectangular in shape. As a result of this shaping the quadrature axis inductance is reduced significantly while there is almost no change in the direct axis inductance. It is also shown that the new rotor configuration leads to significantly reduced cogging torque and less saturation along the q-axis which assists in maintaining a linear torque versus current relationship in field oriented control employing the quadrature axis current. Airgap flux density levels, inductances and static torque characteristics obtained using the finite element simulation work are presented comparing them with those for a uniform airgap machine. There has been good agreement between the experimental and simulation results. The operational advantages gained by the improvements made are also briefly discussed.

Magneto-optical studies of magnetization of melt-processedYBa2Cu3O7−δ

Magnetization patterns on different faces of long bars cut from melt-processed YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) samples were studied using advanced magneto-optical techniques. It is shown that with an external magnetic field perpendicular to the long side of the bar the magnetization front is described by a cylindrical surface having a cross section shaped as a higher-order ellipse, i.e., the front has a sharper bending near the sample edges than a second-order ellipse. Similar to bicrystal boundaries, the boundaries of structure domains consisting of c axis-aligned crystalline plates are revealed to be weak links in a wide temperature range for misorientation angles between domains exceeding 10{degree}. The temperature dependence of the critical currents inside the domains are determined by fitting induction profiles measured across the bars. From direct flux pattern observations and measurements of the anisotropy for currents flowing along and across the crystalline plates, it follows that the crystallite boundaries also become effective weak links at higher temperatures and fields. Possible reasons for why the observed anisotropy is much less than that for c axis and ab plane currents in YBCO single crystals are discussed. {copyright} {ital 1997} {ital The American Physical Society}

Main flux‐saturation modelling in d‐q axis models of induction machines using mixed current‐flux state‐space models

AbstractMain flux saturation in induction machines is most frequently modelled by selecting either stator and rotor d‐q axis currents or stator and rotor d‐q axis flux linkages as state‐space variables. This paper deals with so‐called mixed current‐flux state‐space models where either stator or rotor current space phasor is selected as one state‐space variable. The other state‐space variable is one of the three flux‐linkage space phasors in the machine (stator, magnetizing or rotor), so that six different state‐space models are encompassed. A generalised derivation procedure for all the six models is at first presented. Models are further given in developed form. It is shown that cross‐saturation effect is explicitly present in all the models. Derivation procedure and the models are verified by simulation and experimental investigation of induction generator self‐excitation.

A unified approach to main flux saturation modelling in D-Q axis models of induction machines

Main flux saturation is most frequently modelled by selecting either stator and rotor d-q axis currents or stator and rotor d-q axis flux linkages as state-space variables. This paper attempts to unify main flux saturation modelling in d-q axis models of induction machines by presenting a general method of saturation modelling. Selection of state-space variables in the saturated machine model is arbitrary and appropriate models in terms of different state-space variables result by application of the method. A couple of models, obtainable with different selection of state-space variables, are presented. The cross-saturation effect is explicitly present in all the models, except for the one with stator and rotor flux linkage d-q axis components as state-space variables. The models are verified by simulation and experimental investigation of induction generator self-excitation. >

Modeling and vector control of synchronous reluctance motors including stator iron loss

The influence of the stator iron loss cannot be neglected since the high-speed operation and precision torque control of AC motors are required. This paper presents the modeling and vector control of synchronous reluctance motors including the stator iron loss. The stator iron loss is modeled by additional windings on the d-q axes, and is introduced as an equivalent iron loss resistance in voltage equations under the assumption that the losses in the stator core are produced in equivalent eddy current windings on d-q axes. The equivalent iron loss resistance is inserted in series with exciting inductance, and the d and q axes interfere with each other through the equivalent iron loss resistance. To achieve vector control, the d-q axis currents are decoupled by nonlinear control voltages. As a result, the instantaneous torque control scheme is equal to that of a DC machine and the torque control is simplified. >

A proposal for removing fermion doublers in lattice gauge theories

A method for removal of fermion doublers in lattice gauge theories is proposed. When applied to QCD it preserves gauge and chiral invariance and produces the usual anomalies for external axis currents.

Anisotropy in the diamagnetic properties of oriented Bi 2Sr 2CaCu 2O 8+δ polycrystalline fibers

To investigate the diamagnetic anisotropic properties of a Bi 2Sr 2CaCu 2O 8+δ fiber, which has a complex network of highly oriented platelets, low field a.c. and d.c. susceptibility, as well as magnetization, up to 5 T, measurements were performed. At 4.2 K inter-platelet critical fields, H cJ⊥ ≈(200±25) Oe and H cJ‖ ≈ (50±30) Oe, perpendicular and parallel to the fiber axis, respectively, and intra-platelet critical currents, J c⊥ =(0.5–2.)×10 5 A/ cm 2 and J c‖ =(0.8–1.5)×10 4 A/ cm 2, were derived. Finally, the results are discussed within the Biggs model framework.

Asynchronous tests for D and Qaxis subtransient time constants

The paper draws attention to difficulties in measuring the subtransient time constants, which are relatively fast in machines with rated outputs of the order of tens to hundreds of kilowatts. The frequency-response approaches, consisting of asynchronous tests with field open- and also short-circuited, are proposed as the most suitable test methods, and corrections for resistance effects are developed. A new experimental technique is used to separate the D and Q axis quantities in these asynchronous tests. The Park transformation is performed by physical means, using two 3-phase shaft-driven tachometers and Hall-effect (or quarter-square) multipliers. This results in generated voltages proportional to the hypothetical D and Q axis voltages and currents in the machine. From an ultraviolet-recorder output, one can then obtain the D and Q axis operational admittances or impedances. A curious anomaly in the measured operational impedances in the vicinity of 50% slip is explored, and is shown to be due to crosscoupling between the D and Qaxes through the stator resistance. In small machines, this effect is experimentally evident over a much wider range of slips than might be expected. It is inferred that this effect should also be present in even the largest machines provided that the stator resistance is not identically zero, although it would be evident over a much smaller range of slip. The effect depends on rotor asymmetry, either electric or magnetic, and is related to the Gorges phenomenon.

Time-domain analysis of the invertor-fed induction motor

The paper investigates induction motors running at constant speed and fed by invertors. It is based on linear 2-axis theory, and shows that an exact equivalent circuit can be drawn which includes a back e.m.f. opposed to the applied voltage, as in the synchronous motor. A rigorous analysis leads to explicit expressions in forms suitable for computation of the axis currents as time functions; samples of computed curves are given. In addition, a short approximate method is given for deriving the axis currents as time functions, including the current at commutation. Comparisons with experiments are included.