No abstract

Abstract-When a 'classical' current control scheme is applied, the input current of a boost power factor correction (PFC) converter leads the input voltage, resulting in a nonunity fundamental displacement factor and in important zerocrossing distortion in applications with a high grid frequency (e.g. 400Hz power systems on commercial aircraft). To resolve this problem, a current-control scheme is proposed using duty-ratio feedforward. In this paper, the input impedance of the boost PFC converter for both the classical current-loop controller and the controller using duty-ratio feedforward are derived theoretically. A comparison reveals the advantages of the proposed control scheme: a low total-harmonic-distortion (THD) of the input current, a resistive input impedance, virtually no zero-crossing distortion and a fundamental displacement power factor close to unity. The theoretical results obtained are verified using an experimental setup of a digitally controlled boost PFC converter.

Abstract-The efficiency of permanent magnet synchronous machines (PMSM) with outer rotor and concentrated windings is investigated as a function of the mass of magnets used, keeping the power, volume and mechanical air gap thickness constant. In order to be useful for electric vehicle motors and wind turbine generators, the efficiency is computed in a wide speed and torque range, including overload. For a given type and amount of magnets, the geometry of the machine and the efficiency map are computed by analytical models and finite element models, taken into account iron loss, copper loss, magnet loss and pulse width modulation loss. The models are validated by experiments. Furthermore, the demagnetization risk and torque ripple are studied as a function of the mass of magnets in the machine. The effect of the mass of magnets is investigated for several soft magnetic materials, several combinations of number of poles and number of stator slots, and for both rare earth (NdFeB) magnets and ferrite magnets. It is observed that the amount of permanent magnet material can vary in a wide range with a minor influence on the efficiency, torque density, and torque ripple and with a limited demagnetization risk. A lot of papers deal with rotor losses in the considered type of machines, and give methods to compute them. For example [6] gives a general method for several slot/pole configurations. Polinder [7] studies losses in the solid back iron of PMSM with fractional slot windings. Atallah presented an analytical model to compute magnet loss [8], and Ede proposed a computationally efficient 3D numerical method to compute the magnet loss [9]. IndexAn aspect of fractional-slot concentrated-winding PMSM's that is less investigated, is how much the amount of magnets can be reduced, and how this affects the global machine design and performance. As the price of rare earth magnets is high, PMSM's with small amount of magnets become interesting, on condition that their efficiency and torque density remain high. It is known that very powerful and light permanent magnet machines can be made when a lot of PM material can be used: for example the slotless brushless DC PMSM of [10] has two concentric rotors, both of them completely covered with a thick layer of NdFeB magnets in Halbach array. Alternatives are investigated to reduce the required amount of permanent magnets, or even to have motors without magnets [11]. Nevertheless, [12] compared caged induction, reluctance, and PM motor technologies for the more electric aircraft, concluding that three-phase permanent magnet machines may still be the favorite choice.Therefore, we investigate the impact of the amount of magnets and the magnetic material grade in the stator of the PMSM on the efficiency, keeping the machine volume and torque density constant. Here, we consider not only the efficiency at nominal speed N nom and torque T nom , but also the average efficiency in the speed range 0.25-1.50×N nom and torque range 0.25-1.50×T nom . A number of effects of reducing the amount ...

Abstract-This paper proposes a method to obtain the rotor position of switched reluctance motors by means of voltage measurements. It is shown that the combination of motor and power-electronic converter defines a resonant circuit, comprised by the motor phase inductances and the parasitic capacitance of converter switches, power cables and motor phase windings. For salient machines in general, the associated resonance frequency of the circuit depends on the rotor position. In the position estimation method, an initial voltage distribution is imposed over the impedances of the resonance circuit, after which the circuit is let to oscillate freely. During this phase of free oscillation, the induced voltage over a phase winding exhibits a damped oscillatory behaviour, from which position information can be retrieved.An overview is given of different possibilities to trigger the voltage resonance. It is shown that the proposed position estimation method has favourable characteristics such as measurement of large-amplitude voltages, robustness against temperature deviations of motor and power semiconductors, very high update rates for the estimated position and absence of sound and disturbance torque. Experimental results are given for a sensorless commutation scheme of a switched reluctance motor under small load.

No abstract