A bidirectional and isolated DC/DC converter connecting mobile battery systems to a DC grid in commercial buildings

This paper introduces a novel modulation scheme for an isolated DC/DC converter in step-down direction, which enables a wide input and output voltage range. Losses in the semiconductors on the 380 V bus side are reduced due to zero voltage switching. At charging the battery, the converter works as a buck converter. In this power flow direction the discontinuous and continuous conduction mode of the bidirectional converter are discussed. For a power flow from the safety extra low voltage respectively battery side the converter works in continuous conduction mode as a boost converter. After introducing the specification of the mobile battery application, the topology and the modulation scheme are presented. The operating behavior of the DC/DC converter and the EMI spectrum with the novel modulation scheme are shown to verify the feasibility of the proposed theory. The 500 W prototype of the converter achieves a high peak efficiency of 97.7% in step-down and of 97.5% in step-up direction.