Energy management systems (EMSs) are an emerging set of applications aimed at optimizing the energy flow and storage between electric vehicles, photovoltaic systems, home storage batteries and the electric grid. Such flexible energy management requires that fundamental blocks like voltage regulators and chargers, connected to the EMSs, operate bidirectionally with respect to the energy flow. However, the vast majority of today’s blocks power traditional unidirectional loads like CPUs, motherboards, stationary and mobile devices. In these applications, the current and the associated energy flows unidirectionally from an input voltage source, which can have a wide range of operation, to a tightly regulated output powering a passive load. Understandably, the IC or system designer approaching this emerging field coming from such traditional applications may need some mindset adjustment with respect to bidirectionality. A designer that has thus far designed only unidirectional PWM buck converters will find himself/herself in a quite unchartered territory when asked to design an eminently bidirectional phase-shift dual active bridge (DAB) converter. Hence, designers looking to do their first bidirectional converter designs may benefit from some background on how these relate to conventional, unidirectional power converters. As we’ll see, there are already elements of bidirectional energy flow in the familiar unidirectional converters.
