Carlo A. Borghi

Application of a multiobjective minimization technique for reducing the torque ripple in permanent-magnet motors

The main design parameters of a permanent-magnet motor, which reduce the total torque ripple, are determined. A two-step design procedure is utilized. First the geometry of the permanent-magnet rotor is derived by a one-dimensional field analysis coupled to a multiobjective minimization technique. The objective function of the minimization is defined as a combination of the electromotive force harmonic components induced in the stator and of the harmonic components of the air-gap magnet permeance. As a second step, a two-dimensional numerical model, solved through a finite element method, is adopted to further improve the analysis of the magnetic field. This allows the optimization of the magnet arc width and the minimization of the cogging torque. The method described has been used for the design of a three-phase, six-pole, permanent-magnet synchronous motor. Experimental tests have been carried out to verify the results obtained by the design procedure.

Design optimization of a microsuperconducting magnetic energy storage system

The design of a superconducting magnetic energy storage (SMES) device requires the determination of a current system that produces a magnetic field of a given magnetic energy and a low stray field outside the device. To optimize the design, the amount of conductor and the device volume is minimized. High-temperature superconductor technology is utilized. Quench conditions must be fulfilled. In order to solve the multiobjective optimization problem, two different methods have been used: the objective weighting method, which combines the two objective functions (conductor volume and device volume) into a new cost function by means of penalty coefficients, and one based on fuzzy logic. In both methods the (1+1) evolution strategy minimization algorithm has been utilized. Moreover, in order to improve the solution of the objective weighting method, the results given by the evolution strategy algorithm are used as the starting point of a deterministic method (standard SQP method). The results are compared and discussed.

Charge distribution on the surface of a dielectric barrier discharge actuator for the fluid-dynamic control

The electric potential distribution induced on the surface of an aerodynamic plasma actuator, operating by means of a surface dielectric barrier discharge (DBD), has been studied both numerically and experimentally. Three actuators made with three different dielectric materials (Teflon, Plexiglas, and glass) have been used. The geometric configuration of the three actuators is the same one. An electrode pair separated by a 2 mm thick dielectric sheet constitutes the DBD actuator. The exposed high voltage electrode has been fed by a 5 kHz a.c. electrical signal. Voltage values between 7.5 and 15 kVp have been used. Measurements of the distribution of the electrical potential in the dielectric surface, generated by the charge deposited on it, have been done. Numerical simulations allowed to evaluating the charge distribution on the dielectric surface. The discharge has been switched off after positive and negative plasma currents. The measurements have been carried out after both phases. The potential distr...

Reduction of the torque ripple in permanent magnet actuators by a multi-objective minimization technique

In this paper a minimization technique is used to reduce the torque ripple of permanent magnet actuators. In order to do this a global stochastic (1+1) evolution strategy algorithm coupled to a filled function acceleration technique is utilized. The cost function is defined as a combination of the e.m.f. harmonics induced in the stator windings and the harmonic components of the magnet permeance. The relative importance of the different contributions are taken into account by penalty coefficients. The method described is used for a 3-phase, 6-pole Permanent Magnets (PM) synchronous motor.

A combined technique for the global optimization of the inverse electromagnetic problem solution

A method for finding the global optimum of the electromagnetic inverse problem solution is presented. The problem consists in the determination of the current system which produces a given magnetic field within a domain of finite extent. An infinite class of solutions exists. In order to find the solution of the synthesis problem obtained, a global optimization technique, based on the combination of the filled function (FF) method and the evolution strategy (ES) method, is developed. The FF method is utilized to find a sequence of regions containing decreasing minima. The minimization inside this region is done by means of the ES method. The technique described has been utilized for the poloidal magnetic system of a toroidal device for thermonuclear fusion experiments and for the main coil system of a nuclear magnetic resonance (NMR) device.

Magnetohydrodynamic Interaction in the Shock Layer of a Wedge in a Hypersonic Flow

This paper describes the results of an experimental investigation on the effect of magnetohydrodynamic (MHD) interaction with the plasma of the shock layer at a test body in a hypersonic argon flow. The hypersonic flow is obtained from the high-enthalpy arc-heated wind tunnel of Alta, Pisa, Italy, on Mach 6. Tests are carried out at heating chamber stagnation pressures of 0.65, 0.85, and 1 bar and magnetic fields of 0.15-0.35 T. The experimental observations are done by means of a set of electrical probes, an optical multichannel analyzer, and a fast shutter charge-coupled device camera. In order to maximize the effect of MHD interaction, the Faraday field is shorted, and a magnetic field perpendicular to the test body surface is used. An increase of the distance between the shock front and the body, owing to the MHD interaction, is observed. The MHD interaction effect is reduced by the low conductivity of the plasma in the boundary layer at the test body surface

Numerical modeling of MHD interaction in the boundary layer of hypersonic flows

A model for the analysis of the magnetoplasmadynamic regime, devoted to magnetohydrodynamics (MHD) systems in a hypersonic flight vehicle, is presented. In the model, the discrete formulation of fluid dynamics and electrodynamics are coupled. The Navier-Stokes equations are discretized by means of a finite volume formulation. The electrodynamics is discretized by means of a finite-element method. The model has been utilized for the analysis of MHD interaction for the fluid control over a hypersonic body. Calculations have shown that MHD interaction can strongly affect the boundary layer fluid dynamic regime.

Minimizing torque ripple in permanent magnet synchronous motors with polymer-bonded magnets

The paper presents a method for determining the main design parameters of a permanent magnet (PM) motor that will reduce the total torque ripple. First, the magnet arrangement is derived by one-dimensional field analysis coupled with a multiobjective minimization technique. Then, a two-dimensional model is used to further optimize the magnet arc width and minimize the cogging torque. The analysis mainly focuses on a rotor that is completely covered by the permanent magnets. In this configuration, the permanent magnets can be made from a tube of polymer-bonded magnet, and manufacture of the motor is greatly simplified. We present experimental tests of a machine manufactured on the basis of our design procedure.

Experimental investigation on a vectorized aerodynamic dielectric barrier discharge plasma actuator array

The Electro-Hydro-Dynamics (EHD) interaction, induced in atmospheric pressure still air by a surface dielectric barrier discharge (DBD) actuator, had been experimentally studied. A plasma aerodynamic actuator array, able to produce a vectorized jet, with the induced airflow oriented toward the desired direction, had been developed. The array was constituted by a sequence of single surface DBD actuators with kapton as dielectric material. An ac voltage in the range of 0–6 kV peak at 15 kHz had been used. The vectorization had been obtained by feeding the upper electrodes with different voltages and by varying the electrical connections. The lower electrodes had been connected either to ground or to the high voltage source, to produce the desired jet orientation and to avoid plasma formation acting in an undesired direction. Voltage and current measurements had been carried out to evaluate waveforms and to estimate the active power delivered to the discharge. Schlieren imaging allowed to visualize the induc...

Study of the design model of a liquid metal induction pump

The design of an electromagnetic pump for liquid metal is optimized. The model includes both electrodynamics and fluid-dynamics of the liquid metal. End effects are included in the model, in order to take into account the finite length of the pump and consequently the decrease of efficiency. For the Electrodynamic model, the permeability of the ferromagnetic core is assumed to be infinite. A finite slot configuration of the primary windings is assumed. In the design problem considered, the optimization regards the electrical supply system, the pump dimensions and the slot configuration.