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A hybrid power system consists of a combination of two or more power generation technologies to make best use of their operating characteristics and to obtain efficiencies higher than that could be obtained from a single power source. Since fuel cells directly convert fuel and an oxidant into electricity through an electrochemical process, they produce very low emissions and have higher operating efficiencies. Hence, combining fuel cells with other sources, the efficiency of the combined system can be further increased or extend the duration of the available power to the load as a backup power. In this paper, different types of fuel-cell hybrid systems and their applications are presented. An analysis of the combined cycle operation of a solid oxide fuel cell (SOFC)--microturbine is presented. A strategy for combining the thermophotovoltaic power generation unit and SOFC to obtain the hybrid power system that would have higher efficiency is proposed. The hybrid operation of wind power and solar power system with proton exchange membrane fuel cell is also presented. Index Terms--Fuel cell, hybrid power systems, solar power, thermophotovoltaic (TPV) system, wind power.

This paper traces the efforts by General Motors in the area of electric and hybrid propulsion systems. Propulsion systems developed for different vehicles are described and performance achieved is presented. The present activities to commercialize the electric vehicles are briefly examined. The paper concludes with recommendations of technologies to be applied in propulsion systems to bring the performance of the electric vehicles to the state that is viable for mass acceptance.

This paper proposes a new vector-based dead-time compensation method for three-level T-type converters. The origins and effects of the dead-time voltage errors are analyzed in detail for different switching commutations and load conditions. In order to eliminate the dead-time distortion in each phase, a dead-time error voltage vector is introduced to adjust the reference voltage vector depending on load current polarity. The proposed vector-based dead-time compensation scheme has several advantages. First, it can be applied to multilevel converters with any number of voltage levels using any modulation schemes. Second, the pulse loss issue which is common in conventional pulse-based compensation strategies can be eliminated. In addition, the pulse saturation can be mitigated by operating the converters in overmodulation regions. All of these advantages and effectiveness of the proposed vector-based dead-time compensation method are verified through both simulation and experimental studies. [ABSTRACT FROM AUTHOR]