High efficiency power conditioner employing low voltage dc bus and buck and boost converters

Abstract

A power conditioner interfaces a load to a fuel cell that produces a low voltage that varies with the load. A dc-to-ac inverter operates with a low voltage input provided by a dc bus . When a positive step load change occurs, a low voltage battery provides power equal to the step change until the fuel cell is able to provide enough power to support the entire load. The power from the battery is supplied to the varying dc bus through a boost converter . When very large positive load step changes occur, the battery can feed power to the dc bus through diode D , rather than through the boost converter. Diode D does not need to be used, but its use allows the boost converter to be sized for common load changes rather than for the maximum possible load change (such as might be seen during a faulted output). A buck converter converts the variable voltage on the dc bus to the appropriate float charging voltage of the battery. The buck converter also supplies power for auxiliary equipment when available from the fuel cell. If the fuel cell is unable to provide the auxiliary power (such as during startup or load transients), then the auxiliary power can come directly from the battery.