Current Balancing Cells Based IPOP LLC Resonant Converter Modules

The input-parallel output-parallel(IPOP) DC-DC converters are very suitable for low voltage and high current applications, especially using high-frequency isolation instead of traditional line-frequency transformer for AC-DC converters in DC distribution, which focus on how to ensure input-current sharing(ICS) and output-current sharing(OCS) among the constituent modules, all the existing methods are closed-loop control schemes. The LLC resonant converter is a kind of practical soft-switching DC-DC converter. The LLC resonant converter can be used as a high-frequency isolation DC transformer under the quasi-resonant mode which can achieve zero voltage switching(ZVS) for the inverter side and zero current switching(ZCS) for the rectifier side that ensure high power density and high efficiency.In this paper, the IPOP LLC resonant converter modules are developed based on current balancing cells. Through the magnetic-coupling effect of current balancing cell, the LLC resonant converter modules can achieve ICS and OCS that guarantee the IPOP system work stably. Employing current balancing cell instead of traditional control schemes to solve the unequal current-sharing problem of IPOP system have the following advantages. All the LLC resonant converters LLC converters’ system can work under the quasi-resonant mode without the variable frequency control and other control strategies having the DC transformer function. The auxiliary sampling and control circuits can be avoided, thus the number of components can be decreased significantly to reduce the cost. Without the complicated multi-loop control scheme to achieve ICS and OCS, the whole IPOP converter system has higher reliability. The IPOP DC converter system can be used in the DC transmission applications to increase the power rating of the isolated DC converters for higher power level.In this paper, from the current balancing cell magnetic model, its electrical model can be built, and the simulations of current balancing cell steady-state and dynamic-state current-sharing performance show the working principle. Finally, a current balancing cell based IPOP LLC resonant converter modules hardware prototype is designed and built up to verify the validity and performance of the proposed solution.