Encoderless direct torque controller for limited speed range applications of brushless doubly-fed reluctance motors

Presents the experimental verification of a new sensor-less control algorithm for direct torque (and flux) control (DTC) of the BDFRM in low variable frequency applications (e.g. wind energy conversion systems) where the low cost potential of the machine can be best exploited by using partially-rated power electronics. Brings a significant contribution to knowledge in the subject field as the proposed scheme has many important advantages over its counterparts in the target applications. Represents one of the main achievements of the aforementioned EPSRC project

General Torque Enhancement Approach for a Nine-Phase Surface PMSM with Built-in Fault Tolerance

The paper investigates maximum possible torque improvement in a two-pole surface permanent magnet synchronous machine (PMSM) with a reduced magnet span, which causes production of highly non-sinusoidal back-EMF. It contains a high third and fifth harmonics, which can be used for the torque enhancement, using stator current harmonic injection. Optimal magnet span is studied first and it is shown that with such a value the machine would be able to develop an insignificantly lower maximum torque than with the full magnet span. Next, field-oriented control (FOC) algorithm, which considers all non-fundamental EMF components lower than the machine phase number, is devised. Using maximum-torque per Ampere (MTPA) principles, optimal ratios between fundamental and all other injected components are calculated and then used in the drive control. The output torque can be in this way increased up to 45% with respect to the one obtainable with fundamental current only. Alternatively, for the same load torque, stator current RMS value can be reduced by 45%. Last but not least, a method for position sensor fault mitigation is introduced. It is based on the alternative use of a back-EMF harmonic for rotor position estimation, instead of the torque enhancement. Experimental verification is provided throughout for all the relevant aspects

Number of switching state vectors and space vectors in multilevel multiphase converters

Expressions to calculate the number of switching state vectors and the number of space vectors in multilevel multiphase voltage-source converters are given.Ministerio de Educación y Ciencia | Ref. ENE2006-0293

A simple braking method for six-phase induction motor drives with unidirectional power flow in the base-speed region

Induction motor drives supplied from diode front-end rectifiers are commonly used in industrial applications due to their low cost and reliability. However, the two-quadrant operation of such a topology makes the regenerative braking impossible. Braking resistors can be used to dissipate the braking power and provide enhanced braking capability, but additional hardware is then necessary. Alternatively, the braking power can be dissipated within the inverter/motor by control software reconfiguration. In this scenario, the additional degrees of freedom of multiphase drives can be used to increase the system losses without disturbing the flux and torque production. Experimental results confirm the possibility to enhance the braking capability of six-phase drives with only few changes in the control scheme

Fault-tolerant Operation of Six-phase Energy Conversion Systems with Parallel Machine-side Converters

The fault tolerance provided by multiphase machines is one of the most attractive features for industry applications where a high degree of reliability is required. Aiming to take advantage of such postfault operating capability, some newly designed full-power energy conversion systems are selecting machines with more than three phases. Although the use of parallel converters is usual in high-power three-phase electrical drives, the fault tolerance of multiphase machines has been mainly considered with single supply from a multiphase converter. This study addresses the fault-tolerant capability of six-phase energy conversion systems supplied with parallel converters, deriving the current references and control strategy that need to be utilized to maximize torque/power production. Experimental results show that it is possible to increase the postfault rating of the system if some degree of imbalance in the current sharing between the two sets of threephase windings is permitted.Ministerio de Ciencia e Innovación ENE2014-52536-C2–1-R DPI2013-44278-RJunta de Andalucía P11-TEP-755

Multidimensional two-level multiphase space vector PWM algorithm and its comparison with multifrequency space vector PWM method

A multilevel multiphase space vector pulsewidth modulation (SVPWM) algorithm has been introduced recently, in which the reference is separated into an integer part and a fractional part. The fractional part is, in essence, a two-level multiphase space vector algorithm. This paper shows that, with appropriate adaptations, the fractional part of the general space vector multilevel multiphase PWM can be applied as a stand-alone PWM method in conjunction with two-level voltage-source converters with any number of phases. Simulation results of the five- and six-phase cases are shown, and the new algorithm is compared with another recent multifrequency SVPWM algorithm, which follows the standard approach of selecting the switching vectors and calculating their application times using planes. The experimental verification is provided using a five-phase two-motor series-connected induction motor drive, supplied from a custom-designed five-phase voltage-source inverter.Ministerio de Ciencia e Innovación | Ref. DPI2009-0700

Hiding and Confining Charges via "Tube-like" Wormholes

We describe two interesting effects in wormhole physics. First, we find that a genuinely charged matter source may appear neutral to an external observer - a phenomenon opposite to the famous Misner-Wheeler "charge without charge" effect. This phenomenon takes place when coupling a bulk gravity/nonlinear-gauge-field system to a charged lightlike brane as a matter source. The "charge-hiding" effect occurs in a wormhole solution which connects a non-compact "universe", comprising the exterior region of Schwarzschild-(anti-)de-Sitter (SdS) or purely Schwarzschild black hole beyond the Schwarzschild horizon, to a Levi-Civita-Bertotti-Robinson-type (LCBR) "tube-like" "universe" via a wormhole "throat" occupied by the brane. In this solution the whole electric flux produced by the brane is expelled into the "tube-like" "universe" and the brane is detected as neutral by an observer in the non-compact "universe". Next, we find a truly charge-confining wormhole solution when we couple the bulk gravity/nonlinear-gauge-field system to two oppositely charged lightlike branes. The latter system possesses a "two-throat" wormhole solution, where the "left-most" and the "right-most" "universes" are two identical copies of the exterior region of SdS black hole beyond the Schwarzschild horizon, whereas the "middle" "universe" is of LCBR "tube-like" form with geometry dS_2 x S^2. It comprises the finite-extent intermediate region of dS_2 between its two horizons. Both "throats" are occupied by the two oppositely charged lightlike branes and the whole electric flux produced by the latter is confined entirely within the middle "tube-like" "universe". A crucial ingredient is the special form of the nonlinear gauge field action, which contains both the standard Maxwell term as well as a square root of the latter. This theory was previously shown to produce a QCD-like confining dynamics in flat space-time.Comment: 26 pages, 2 figures; v.2 several references added, missing constant factors in few equations inserted, acknowledgement added, results unchanged; v.3 28 pages, several clarifying remarks, references and acknowledgements added, version to appear in International Journal of Modern Physics

Dynamical Couplings, Dynamical Vacuum Energy and Confinement/Deconfinement from R^2-Gravity

We study within Palatini formalism an f(R)-gravity with f(R)= R + \alpha R^2 interacting with a dilaton and a special kind of nonlinear gauge field system containing a square-root of the standard Maxwell term, which is known to produce confinement in flat space-time. Reformulating the model in the physical Einstein frame we find scalar field effective potential with a flat region where the confinement dynamics disappears, while in other regions it remains intact. The effective gauge couplings as well as the induced cosmological constant become dynamical. In particular, a conventional Maxwell kinetic term for the gauge field is dynamically generated even if absent in the original theory. We find few interesting classes of explicit solutions: (i) asymptotically (anti-)de Sitter black holes of non-standard type with additional confining vacuum electric potential even for the electrically neutral ones; (ii) non-standard Reissner-Nordstroem black holes with additional constant vacuum electric field and having non-flat-spacetime "hedgehog" asymptotics; (iii) generalized Levi-Civitta-Bertotti-Robinson "tube-like" space-times.Comment: 16 page

Asymptotically de Sitter and anti-de Sitter Black Holes with Confining Electric Potential

We study gravity interacting with a special kind of QCD-inspired nonlinear gauge field system which earlier was shown to yield confinement-type effective potential (the "Cornell potential") between charged fermions ("quarks") in flat space-time. We find new static spherically symmetric solutions generalizing the usual Reissner-Nordstroem-de-Sitter and Reissner-Nordstroem-anti-de-Sitter black holes with the following additional properties: (i) appearance of a constant radial electric field (in addition to the Coulomb one); (ii) novel mechanism of {\em dynamical generation} of cosmological constant through the non-Maxwell gauge field dynamics; (iii) appearance of confining-type effective potential in charged test particle dynamics in the above black hole backgrounds.Comment: 9 pages, v2 12 pages, many additional clarifying remarks, references added, v3 minor typos corrected, to appear in Physics Letters B, v4 missing line in Eqs.(10) and missing constant factors in Eqs.(12),(17) inserted, acknowledgement added, results unchange

Interplane cross-saturation in multiphase machines

The use of electrical machines in electric vehicles and high-power drives frequently requires multiphase machines and multiphase inverters. While appropriate mathematical models under the linear magnetic conditions are readily available for multiphase machines, the same cannot be said for the models of the saturated multiphase machines. This paper examines the saturation in an asymmetrical six-phase induction machine under different supply conditions and addresses the applicability of the existing saturated three-phase machine models for representation of saturated multiphase machines. Specifically, the mutual coupling between different sequence planes in the vector space decomposed model under saturated conditions is analyzed. The paper relies on analytical considerations, finite element analysis and experimental results. It is shown that the saturation of the main flux path is influenced by the current components in the orthogonal (non-fundamental) sequence plane. This implies the need to develop new multiphase machine models which take this effect into account