In the last few years, the LLC converter, consisting of two inductors and a capacitor in the resonant path, became very popular. Among the advantages of the LLC converter is the rather narrow frequency span that is needed to cope with variable loads and zero voltage switching, when operated above the resonance frequency. On the other hand, the LCC converters which are sort of a complementary to the LLC have not gained much popularity even though they have been introduced just about the same time when the LLC was revealed. The LCC possess some interesting characteristics such as better coping with variable output voltage and better performance in very high output voltage applications. And yet, the LCC is less knows, not that much explored, and as far as I can tell, not that popular in commercial products. LLC and LCC are not rivals, but rather, they complement each other and hence, sticking to the LLC for all applications may be a mistake.
A comparison between the LCC and the LLC converters will be covered in a forthcoming series of tutorials in my “sam ben-yaakov” YouTube channel. The first installment deals with the basics and the issue of linearization.
Linearization is a powerful tool for the analysis of switch mode and resonant converters in general and the LCC converter in particular. Switch mode converters are nonlinear and therefore cannot be handled by phasor analysis, which is the most easy and intuitive tool to apply (many thanks and appreciation to Steinmetz). As it turns out, the linearization of the LCC converter with an output capacitor filter is not simple. This is due to the highly clamped and nonlinear current and voltage which is a result of the fact that the output filter capacitor is connected to the parallel capacitor only during part of the cycle. This problem was investigated and reported in a paper published in 1999:
G. Ivensky, A. Kats and S. Ben-Yaakov, "An RC load model of parallel and series-parallel resonant DC-DC converters with capacitive output filter," in IEEE Transactions on Power Electronics, vol. 14, no. 3, pp. 515-521, May 1999.
The paper can be down loaded from:
http://www.ee.bgu.ac.il/~pel/pdf-files/jour105.pdf
It was shown that in this case, the linear equivalent of the output section includes both a resistor and a capacitor. The analytical method and results are explained in the first part of the tutorial sequence: “LCC versus LLC converters. Part I. Basics and linear models.” The accuracy of the proposed approach is then demonstrated in the tutorial by comparing a time domain simulation of the full converter to the results obtained by the RC model. The link to the first part:
Comments and discussion are welcomed.
