Analysis of the time‐domain model of the LLC series resonant converter with frequency and single phase shifted control

Abstract

LLC series resonant converter (LLC‐SRC) has attracted much attention due to its simple circuit structure and easy realization of soft‐switching. To get a better efficiency, rectifier stage can be realized by the active switches instead of the diodes. Meanwhile, more control variables can be selected besides the switching frequency, such as single phase shifted (SPS) angle, dual phase shifted (DPS) angle, and extended phase shifted (EPS) angle. Considering the simplicity of the implementation of the control strategy, this paper focused on the converter model with frequency and SPS control. Different from the common modelling method with the Fundamental Harmonic Approximation (FHA), the precise time‐domain mathematic model is built. By a comparison between the two modelling results, it can be proved the FHA model may be failure in some operating condition while the proposed time‐domain model can still show a good accuracy. According to the proposed model, two simple fixed‐frequency SPS control strategies are proposed. The first one can realize infinite soft‐switching margin with no restrictions on the transformer magnetizing inductance. The second one can greatly improve the efficiency of the converter. All the theoretical results are verified by a 1‐kW experiment prototype.

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“…The resonant parameters of inductance L r1 , capacitance C r1 , impedance Z 01 , and magnetizing inductance L m1 with equivalent resistance R ac1 as well mentioned in following Equations (13)(14)(15)(16)(17),…”

“…Over the years, many control methods are proposed to improve soft switching, tight regulation, and reduce the circulating current. [16][17][18] All these control methods can be utilized at various converter operating regions like f s < f r , f s = f r , and f s > f r which it effects the regulation. 19,20 This article also, proposes a hybrid control strategy which it operates at predefined current value in ZCS or ZVS operating region, the entire strategy named it as variable frequency + phase shift modulation scheme (VFPSM).…”