Distributed power generation systems (DPGSs) integrate power sources that tend to be smaller than the typical utility scale, such as for renewable energy sources and other applications. Storage systems that incorporate supercapacitors (SCs) have been proposed to extend the life of batteries and to increase the power capacity of the DPGSs, guaranteeing maximum efficiency. The extraction of energy in SCs is more demanding than in the case of batteries; when SCs have delivered only 75% of their energy, their voltage has already decreased to 50%. Beyond this value, the banks fail to meet the requirements demanded by loads that require a minimum voltage to operate correctly, leaving 25% of the energy unused, thereby limiting the deep charge/discharge cycles that occur. This paper presents a model of a switching matrix applied in a bank of SCs. The model allows the use of a simpler circuit to achieve a large number of serial/parallel-configuration connections (levels), improving the utilization of energy to obtain deep discharge cycles in each SC; therefore, by increasing the average energy extracted from each SC, it extends the power delivery time in the storage bank. The efficiency was verified by experimental results obtained using a bank of six SCs.
Power transistors are the most vulnerable components in switching converters, and derating is usually applied to increase their reliability. In this paper, the effectiveness of derating guidelines is experimentally assessed using a push-pull DC-DC converter as a case study, operating in three different environments. After measuring the electrical variables and temperature, reliability was predicted following the guidelines in MIL HDBK 217F. The sensitivity analysis performed indicates that temperature has the largest impact on reliability, followed by environment and device quality. The results obtained demonstrate that a derating procedure based solely on DC ratings does not ensure an adequate performance. Therefore, additional guidelines are suggested to help increase the overall reliability obtained from a power circuit.
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