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Three-phase four-leg voltage-source converters by virtue of the fourth leg connected to the neutral points of the wye-connected loads effectively handle the zero-sequence currents and voltages occasioned by connected load impedance imbalances and/or nonlinearity of loads. This paper develops a generalized carrier-based pulsewidth-modulation scheme for this converter which with a natural reference-frame control scheme that directly controls the actual load currents ensures current regulation irrespectively of the nature of the load. The proposed modulation and control schemes are effectively validated by computer simulation and experimental results for the converter operation in the linear and overmodulation regions.

Home appliances and comfort conditioners are yet to benefit from the recent developments in power electronics because of cost constraints. In this paper, a speed-sensorless induction motor drive system using converters with reduced device counts (minimalist, sparse converters) and actuated from a single-phase system is proposed for such low-cost applications. The analysis, control, dynamic, and steady-state characteristics of the proposed drive are experimentally illustrated.

A three-phase synchronous reluctance machine having an axially laminated rotor structure and an auxiliary DC source fed single-phase control winding has utility as either as a high-speed generator or a high-torque, low-speed motor. This paper provides an understanding of its operation using electric circuit and electromagnetic field concepts in the process of which some insights are provided into the design of the windings, conditions for torque production and generation of electric power when operating in the motoring or generating modes. Some confirmatory experimental results of analytical developments are provided showing performance characteristics of an experimental machine.

Non-relaxational magnetic hysteresis loops of (YBCO) thin films have been measured by an improved a.c. magnetization measurement with a.c. external field amplitude up to 1000 Oe and frequency range from 30 Hz - 10 kHz at 77 K. Above a certain frequency , the width of the magnetization hysteresis loop does not change with frequency, indicating that the magnetization can maintain a saturated state, namely the critical state. Experiments show that the critical current density deduced from the non-relaxational magnetic hysteresis loops is quite close to the value obtained by the four-probe measurement.

The analysis and high performance control of an induction motor drive actuated with a rectifier/inverter system having a reduced count of switching devices is explained in the paper. The input factor of the single-phase voltage source is controlled to have unity displacement factor using pulsewidth modulation control. The technique for determining the expressions, for the modulation signals for the generation of the PWM pulses, is presented with a unique single-phase current control scheme in the natural reference frame. Confirmatory experimental results are presented in the paper to show unity displacement factor and fast motor speed response.