Soft-switched high-frequency power converters for energy systems

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With increased energy demand and environmental concerns, alternate energy sources (fuel cell, wind, photovoltaic and ocean) are becoming popular. The outputs of these energy sources vary widely including some operational limits. Some examples are: (1) Fuel cells generate widely varying low voltage dc (e.g., 22 to 41 V) having slow transient response for load changes and has degraded performance with ripple currents. (2) Permanent magnet synchronous generators used with wind turbines generate varying voltage and varying frequency ac output demanding power factor (pf) corrected ac/dc converters to get a regulated dc bus. For all these sources, an additional dc/ac converter is required for stand alone or utility interface to augment power generation. In addition, when different energy sources are connected to a dc bus, a bidirectional dc-to-dc converter is needed for battery charging as well as to supply the dc bus and an electrolyser used to generate hydrogen for fuel cells requires a dc/dc converter. Therefore, all these energy sources require low cost, highly efficient dc/dc, dc/ac and ac/dc power electronic converters while satisfying the constraints imposed by the energy sources. This is possible using soft-switching (including resonant) converters operating with low losses and high switching frequencies. These converters have a number of advantages, e.g., high efficiency, small size, light weight, reduced EMI, low component stresses, etc.