Analysis and design of asymmetric CLLC resonant DC-DC converter

With the global climate deterioration and the increase of energy demands, distributed generation was used to converse the clean energy to electricity. Direct current-direct current (DC-DC) converter has been widely applied in many fields such as uninterruptible power supply (UPS) DC power distribution system, electric vehicles, and small photovoltaic power generation. Most of the CLLC resonant converters are of symmetric structures. However, asymmetric CLLC resonant converters are drawing more and more attention for higher voltage gain. But the operation characteristics of asymmetric CLLC resonant converters are more difficult to analyze, and the calculating method of the key parameters is also too complex. This paper analyzes the structure composition, operation principle, DC voltage gain, and frequency characteristics of the topology and then presents a method of parameter design to solve the key problem encountered in the asymmetric structure resonant converter design. By adopting the method of parameter design, it could be ensured that the converter has similar operation characteristics and a high transmission efficiency in both directions. Moreover, an asymmetric CLLC resonant DC-DC converter that connects 300-to-300-V DC and with a power rating of 1 kW is designed and built up to verify validity and correctness of this parameter design method.