  This paper addresses the problem of output voltage regulation for multiple
DC-DC converters connected to a grid, and prescribes a robust scheme for
sharing power among different sources. Also it develops a method for sharing
120 Hz ripple among DC power sources in a prescribed proportion, which
accommodates the different capabilities of DC power sources to sustain the
ripple. We present a decentralized control architecture, where a nested
(inner-outer) control design is used at every converter. An interesting aspect
of the proposed design is that the analysis and design of the entire
multi-converter system can be done using an equivalent single converter system,
where the multi-converter system inherits the performance and robustness
achieved by a design for the single-converter system. Another key aspect of
this work is that the voltage regulation problem is addressed as a
disturbance-rejection problem, where {\em unknown} load current is viewed as an
external signal, and thus, no prior information is required on the nominal
loading conditions. The control design is obtained using robust optimal-control
framework. Case studies presented show the enhanced performance of prescribed
optimal controllers.
