High frequency high efficiency bidirectional dc-dc converter module design for 10 kVA solid state transformer

This paper presents the development of modular dual-half-bridge (MDHB) bidirectional dc-dc converter as the dc-dc stage of 10 kVA single phase solid state transformer (SST) for future renewable electric energy distribution and intelligent power management systems. The dc-dc converter, connected to 12 kV DC bus generated by an ac-dc rectifier interfacing with 7.2 kV electric utility grid, is to provide galvanic isolation function as well as 400 V DC bus for DC loads. The dc-dc converter consists of multiple low-voltage modules connected in input-series and output-parallel mode so that low-voltage commercial silicon MOSFETs, which usually have low conduction losses and high switching speed, can be adopted. Besides bidirectional power flow capability, the phase-shift dual-half-bridge (DHB) can realize zero-voltage-switching for all the switching devices without auxiliary switch devices, which enables the high switching frequency operation with low switching losses. As a result, high efficiency and high power density can be achieved. Other advantages of DHB topology have also been investigated for this application. A planar transformer adopting printed-circuit-board (PCB) winding is designed to realize high voltage solid isolation and identical parameters in multiple modules. The power loss of each main component has been analyzed for DHB converter under high frequency operation. Finally, the experimental results of two modules operating at 50 kHz switching frequency are presented with 97% efficiency.