Multiport resonant DC-DC converter

Abstract

Abstract-This paper presents a multiport galvanically isolated LLC resonant DC-DC converter suitable for DC applications. A three-port structure is analyzed, with full bidirectional power flow capabilities, simple control and behavior similar to that expected from a DC transformer. Each port is equipped with half-bridge modules accompanied with tuned resonant tank, partly realized with elements of a multiwinding high frequency transformer. With some restrictions that are explained in the paper, each port can be a sink or a source of power, depending on the presence of switching action on the half-bridge stage. To maximize the efficiency of the system, no active control is applied and the system operates at fixed switching frequency, below the resonant frequency of the system.

A multiport isolated DC-DC converter

“…This paper is an extension of the previous work [7] and it presents a novel multi-port topology and its operation in section II. Design considerations and sizing of main components are presented in section III, while the control scheme is provided in section IV.…”

“…The design of the resonant part is based on a methodology presented in [7]. The aim is to determine the resonant parameters in such a way that ensures the ZVS of the primary switches (active port), soft commutation of rectifier diodes (passive port) and minimize the amount of circulating energy (conduction losses).…”

A multiport medium voltage isolated DC-DC converter

“…When the port is active, its semiconductors are modulated with a constant switching frequency f sw,res , below the resonant frequency (f sw,res /f res = f n ≤ 1), and with a fixed duty cycle of around 50%. There are several possible operating modes based on the power flow direction [13]. To avoid large current transients during startup or change of mode of operation from passive to active, the duty cycle follows a ramp from 0 to 50%.…”

“…The components of the inner resonant stage are sized following the methodology developed in [13]. The principle is to design the transformer and the elements of the distributed resonant tank for the soft switching conditions on all the three ports.…”

“…Each submodule is composed by a three winding MFT and additional capacitors creating a distributed LLC resonant tank. The resonant components are tuned on the three sides following [13], in order to allow an extended soft switching operation range, compared to solutions based on the multiple active bridge structure. As the MFT provides a galvanic isolation between the ports and the different submodules, the storage elements (ES) can be freely selected for each port, allowing a hybrid combination of batteries and ultracapacitors, in an optimal configuration.…”