The k-Q Analyze of LCLC Resonant Converter

LCLC resonant converter are often used in DC-DC energy transmission circuits, and are derived from LLC converter with higher efficiency. In the process of energy transmission, how to choose parameters reasonably is a very important issue. Fundamental harmonic approximation(FHA) was used in this paper, based on the bode diagrams analysis of different loads, the k-Q design criteria is proposed by studying the relationship among the parameters when the converter realizes zero-voltage-switching(ZVS): soft switching is implemented when the product of the square root of k1(the ratio of parallel and series resonant inductors) and Q(the quality factor) is no more than 1, there is one soft switching region when the product of the square root of the k2(the ratio of parallel and series resonant capacitors) and the inverse of Q is less than or equal to 1, and two independent soft switching regions when the product is more than 1. Satisfy this criterion will ensure converter ZVS and the criterion can be used to judge the condition of their work areas. Finally, a full-bridge LCLC resonant converter is built, simulation has proved the feasibility of the criteria.