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Fuel-cell power systems comprising single-phase dc/ac inverters draw low-frequency ac ripple currents at twice the output frequency from the fuel cell. Such a 100/120 Hz ripple current may create instability in the fuel-cell system, lower its efficiency, and shorten the lifetime of a fuel cell stack. This paper presents a waveform control method that can mitigate such a lowfrequency ripple current being drawn from the fuel cell while the fuel-cell system delivers ac power to the load through a differential inverter. This is possible because with the proposed solution, the pulsation component (cause of ac ripple current) of the output ac power will be supplied mainly by the two output capacitors of the differential inverter while the average dc output power is supplied by the fuel cell. Theoretical analysis, simulation, and experimental results are provided to explain the operation and showcase the performance of the approach. Results validate that the proposed solution can achieve significant mitigation of the current ripple as well as high-quality output voltage without extra hardware. Application of the solution is targeted at systems where current ripple mitigation is required, such as for the purpose of eliminating electrolytic capacitor in photovoltaic and LED systems.

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Capacitive DC links are widely used in Voltage Source Converters (VSC) for power balance, voltage ripple limitation, and short-term energy storage. A typical solution which uses Aluminum Electronic Capacitors (E-cap) for such applications is assumed to be one of the weakest links in power electronic systems, therefore, also becoming one of the lifetime bottlenecks of power electronic systems. Various passive and active capacitive DC-link solutions have been proposed intending to improve the reliability of the DC links qualitatively, making great effort to diverting the instantaneous pulsating power into extra reliable storage components. In this publication, a generic topology derivation method for single-phase power converters with active capacitive DC link integrated has been proposed, which can derive all existing topologies, and identify a few new topologies. According to the synthesis results, the main achievements in research on capacitive DC-link solutions are reviewed and presented chronologically as well as thematically ordered. Further more, the reliabilityoriented design procedure is applied to size the chip area of active switching devices and the passive components to fulfill a specific lifetime target and system specification, as well as compare the overall capacitive energy storage, energy buffer ratio, and the cost of different solutions. The cost comparisons are performed with a scalable lifetime target and power rating. It reveals that different conclusions can be drawn with different lifetime targets in terms of cost-effectiveness.

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