A Quadratic-Programming Approach to the Design Optimization of Fractional-Slot Concentrated Windings for Surface Permanent-Magnet Machines

Fractional-slot concentrated windings (FSCW) are becoming more and more popular in the design of permanent magnet electric machines. A well-known drawback of their adoption is the occurrence of large magneto-motive force (MMF) harmonics, which produce eddy-current losses in rotor permanent magnets. The use of a multi-layer design, with coils of different phases wound around the same tooth, is a possible countermeasure to mitigate the problem. In this paper, a new general systematic methodology is proposed to optimize the multilayer FSCW design in the form of a multi-objective quadratic programming problem. The maximization of the MMF fundamental and the minimization of total rotor losses are taken as properly weighed objective functions. Constraints are imposed to guarantee the physical feasibility and the electric symmetry of the winding. An application example to a 9-slot 8-pole machine is presented, together with extensive validations by comparison with finite element analysis (FEA) simulations, to prove the effectiveness of the proposed technique

Motori Elettrici Lineari ad Elevata Spinta per Applicazioni Navali

Gli attuatori oleodinamici usati per timonerie e pinne stabilizzatrici sviluppano elevate coppie a basse velocit\ue0. Viene presentato, in alternativa, un innovativo motore elettrico lineare ad elevata spinta alimentato da inverter per azionamenti diretti a bordo nave, che offre grandi vantaggi in termini di compattezza, manutenzione, efficienza, e tolleranza al guasto

Analytical Computation of End-Coil Leakage Inductance of Round-Rotor Synchronous Machines Field Winding

3noThe computation of end coil leakage inductances of electric machines is a challenging task due to the complicated leakage flux 3D distribution in the winding overhang region. In this paper the problem is addressed of computing the field circuit leakage inductance of round-rotor synchronous machines. The proposed method is fully analytical and descends from the symbolical solution of Neumann integrals applied to the computation of self and mutual inductances combined with the method of mirror images to account for core effects. With respect to existing analytical approaches, the methodology requires neither numerical integral solutions nor discretizing the end-coil geometry into small straight elements. The accuracy of the proposed technique for computing the mutual inductance between two single end turns is assessed against measurements on a dedicated experimental set-up. The extension of the method to the computation of the entire field-circuit end-coil leakage inductance is assessed by comparison with 3D finite element analysis (FEA).Pubblicato online nel settembre 2015 e pubblicato su carta nel febbraio 2016partially_openopenBortolozzi, Mauro; Tessarolo, Alberto; Bruzzese, ClaudioBortolozzi, Mauro; Tessarolo, Alberto; Bruzzese, Claudi

Modeling, Analysis and Testing of a Novel Spoke-Type Interior Permanent Magnet Motor with Improved Flux Weakening Capability

Spoke-type interior permanent magnet (IPM) machines are an attractive topology for high performance electric motors, especially designed for vehicle traction applications. In this paper, a special design for a spoke-type IPM motor is presented to enhance motor flux-weakening capability in the operation over a wide speed range. The proposed design consists of a simple and robust mechanical device that includes radially-displaceable rotor yokes, connected to the shaft by means of springs. At high speed, the centrifugal force prevails over the elastic one due to springs, causing the mobile yokes to displace radially and to establish a partial magnetic short circuit between permanent magnets. This increases permanent magnet leakage flux and consequently reduces the air-gap field. As a result, a mechanical flux weakening effect is achieved at high speed, which helps significantly reduce the demagnetizing d-axis current to be injected by the inverter, along with the related copper losses and demagnetization issues. The proposed design is investigated in the paper using an analytical model whose parameters are computed by finite-element analysis (FEA). The effectiveness of the solution being set forth is successfully proven by some testing on a laboratory prototype. Experimental results are compared to analytical predictions showing a satisfactory accordance

A New Method for Determining the Leakage Inductances of a Nine-Phase Synchronous Machine From No-Load and Short-Circuit Tests

The accurate determination of stator leakage inductances is presently an open issue in the analysis and testing of multi- phase electric machines. Calculation methods are available, which involve complicated and often poorly precise three-dimensional (3-D) analyses. Experimental determination techniques, using measurements on the wound stator with the rotor removed, are also possible, but quite impractical, as they need to be performed during machine manufacturing or require rotor withdrawal. In this paper, a new approach is proposed to determine all the stator self- and mutual leakage inductances of a nine-phase synchronous machine based on a minimal set (a couple) of magnetostatic finite- element (FE) simulations, and on the measurements taken during no-load and short-circuit routine tests. The procedure is applied to a wound-field salient pole nine-phase synchronous generator for validation, showing good accordance with the results obtained from measurements on the machine with the rotor removed. A discussion is also proposed on the possibility to extend the presented procedure to other multiphase topologie

Steady-State Simulation of LCI-Fed Synchronous Motor Drives Through a Computationally Efficient Algebraic Method

Wound-field synchronous motors (WFSMs) fed by load-commutated inverters (LCIs) are widely used for high-power applications in many fields like ship propulsion, oil and gas industry, and pumped-storage hydropower generation. Several design architectures exist for LCI drives, depending on the number of LCIs and their dc-link connection as well as on the number of WFSM phase count. The prediction of LCI drive performance at steady state is important in the design stage, especially in regard to the prediction of the torque pulsations, which can give rise to serious mechanical resonance issues. This paper proposes an algebraic method to simulate the steady-state behavior of LCI drives in all their configurations of practical interest. Compared to conventional dynamic simulation approaches based on differential equation solution, the method is much more computationally efficient and requires a very limited knowledge of system parameters. Its accuracy is experimentally assessed by comparison against measurements taken on a real LCI drive arranged according to various possible schemes. Furthermore, the advantages of the proposed algebraic method over the dynamic simulations are highlighted by comparison against the simulation results on a high-power LCI-fed WFSM drive in MATLAB/Simulink environment

Distributed speed control for multi-three phase electrical motors with improved power sharing capability

This paper proposes a distributed speed control with improved power sharing capability for multi-three phase synchronous machines. This control technique allows the speed to be precisely regulated during power sharing transients among different drives. The proposed regulator is able to control the time constant of the current within the dq0 reference frame to a step input variation. If compared to current set-point step variations, the proposed droop controller minimises device’s stress, torque ripple, and thus mechanical vibrations. Furthermore, since distributed, it shows improved fault tolerance and reliability. The design procedure and the power sharing dynamic have been presented and analysed by means of Matlab/Simulink and validated in a 22kW experimental rig, showing good agreement with the expected performances

Optimal Selection of Rotor Bar Number in Multiphase Cage Induction Motors

Rules for the selection of rotor bar numbers which minimize current and torque ripples are derived in this paper for a general symmetrical multiphase cage induction machine with prime phase number and integral slot winding. Analytically obtained expressions for optimal rotor bar number selection are validated by means of totally independent simulations, one based on a parameterized winding function (PWF) model of the induction machine and the other employing time-stepping finite element analysis (TSFEA). As a case study, five-phase four-pole cage induction motors with forty stator slots and different number of rotor bars are comparatively analyzed. Results obtained from the PWF model are in excellent accordance with those independently obtained by TSFEA and both confirm the correctness of the proposed selection criteria. The practical motivation of the study is that an incorrect selection of rotor bar number can lead to parasitic torques of significant amplitude and, presently, there are no general rules available in the literature which may guide designers towards an optimal design choice for a general number of phases

The effect of manufacturing mismatch on energy production for large-scale photovoltaic plants

In the literature, the effect of the mismatch due to manufacturing tolerances on PV plant productivity has been investigated under the hypothesis of plant operation in Standard Test Conditions (STC). In this paper, mismatch impacts are evaluated in more realistic terms taking into account various possible operating conditions. Results are illustrated through the study case of a 1 MWp solar park for which module datasheets as well as flash test data are available. The plant production is evaluated assuming operating conditions that comply with the European efficiency standards. It is shown how the effect of a given mismatch on the annual productivity estimation can significantly change depending on the operating conditions

An Algebraic Algorithm for Motor Voltage Waveform Prediction in Dual-LCI Drives With Interconnected DC-Links

Load-commutated inverters (LCI's) are often used to supply dual-three-phase synchronous motors in high-power variable-speed applications. A pair of LCIs is used in this arrangement to feed the two motor three-phase winding sets. In order to cope with inter-harmonic issues, a drive configuration with an interconnection of the two LCI dc-links has been proposed. In this paper, such a drive design is shown to produce an increased voltage stress on motor windings compared with traditional configurations. The problem is investigated in the paper by proposing an algebraic algorithm capable of predicting the steady-state voltage waveform applied to the motor terminals and arising between the star points of the two winding sets. Unlike conventional dynamic simulations, the proposed approach gives practically instantaneous results, making it possible to quickly investigate a wide number of possible operating conditions. Furthermore, it requires a limited knowledge of system parameters, which are often hardly available. Its reliability and accuracy are assessed by comparison with measurements on a test drive system and examples are given of the method application to the sizing of motor insulation system