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In this paper, a method is presented to reduce electromagnetic (EM) emissions in ac drives. This method is applicable to many ac drives. It is proposed to dither the switching frequency of the power devices of an inverter in a pseudorandom way to spread out the emitted RF energy over a larger frequency range. The proposed method requires only software changes. Practical constraints to implement the frequency dithering approach are discussed. Simulation and measurement results show an improvement of more than 10 dB. The proposed method also converts specific spikes in the long-wave range from narrowband to broadband noise, which results in less stringent EM emission requirements for many applications. Index Terms--AC drives, electromagnetic interference (EMI), inverter, RF noise.

This paper examines the torque ripple and cogging torque variation in surface-mounted permanent-magnet synchronous motors (PMSMs) with skewed rotor. The effect of slot/pole combinations and magnet shapes on the magnitude and harmonic content of torque waveforms in a PMSM drive has been studied. Finite element analysis and experimental results show that the skewing with steps does not necessarily reduce the torque ripple but may cause it to increase for certain magnet designs and configurations. The electromagnetic torque waveforms, including cogging torque, have been analyzed for four different PMSM configurations having the same envelop dimensions and output requirements. Index Terms--Back-EMF (BEMF) harmonics, phase advancing, phase lagging, step skew, torque ripple.

An improved version of a single-ended primary inductor converter (SEPIC) is presented. The converter consists of a conventional SEPIC converter plus an additional high-frequency transformer and diode to maintain a freewheeling mode of the dc inductor currents during the switch on state. The voltage conversion ratio characteristics and semiconductor device voltage and current stresses are characterized. The main advantages of this converter are the continuous output current, smaller output voltage ripple, and lower semiconductors current stress compared with the conventional SEPIC converter. The design and simulation of the concept is verified by an experiment with a 48-V input and 12-V/3.75-A output converter. Index Terms--Active clamp, continuous conduction mode (CCM), dc-dc power conversion, ripple reduction, single-ended primary inductor converter (SEPIC).

A new family of a single-switch three-diode dc-dc pulsewidth-modulated '(PWM) converters operating at constant frequency and constant duty cycle is presented in this paper. The proposed converters are different from the conventional de-de step-up converters, and they posses higher voltage gain with small output voltage ripples. Other advantages of the proposed converters include lower voltage stress on the semiconductor devices, simple structure, and control. Moreover, the reduced voltage stress on the diodes allows using Schottky diodes for alleviating the reverse-recovery current problem, as well as decreasing the switching and conduction losses. The principle of operation, theoretical analysis, and experimental results of one prototype rated 40 W and operating at 94 kHz are provided in this paper to verify the performance of this new family of converters. Index Terms--DC-DC power conversion, pulsewidth-modulated (PWM), step-up converter, switched-mode power supplies.

Phase windings of switched reluctance machines are modeled by a nonlinear inductance and a resistance that can be estimated from standstill test data. During online operation, the model structures and parameters of SRMs may differ from the standstill ones because of saturation and losses, especially at high current. To model this effect, a damper winding is added into the model structure. This paper proposes an application of artificial neural network to identify the nonlinear model of SRMs from operating data. A two-layer recurrent neural network has been adopted here to estimate the damper currents from phase voltage, phase current, rotor position, and rotor speed. Then, the damper parameters can be identified using maximum likelihood estimation techniques. Finally, the new model and parameters are validated from operating data. Index Terms--Modeling, neural network, parameter identification, switched reluctance motor.

This paper describes the design of high-efficiency, electronically commutated, permanent-magnet machine (ECPM) drives based on the finite-element/difference method, and the solution of the ensuing differential equations with the Simulation Program with Integrated Circuit Emphasis (SPICE). The permanent-magnet motor model includes the computation of load-dependent components of the motor-equivalent circuit (e.g., induced voltages and inductances). A new SPICE metal-oxide semiconductor field-effect transistor (MOSFET) model reflecting the reverse-recovery current phenomenon - which is very important for the design of variable-speed drives operating in the pulse-width-modulated (PWM) mode - is introduced. Results of this new model are compared with measurements. Since ECPM's lend themselves well to vehicle propulsion due to their inherent high efficiencies at light weight, it is desirable to have a very high output-power-to-weight ratio for such applications. In addition, high ECPM drive efficiencies are important for recovery of the braking energy.