Steady-state analysis of the bidirectional CLLLC resonant converter in time domain

Abstract

In this paper, the operating modes of the bidirectional CLLLC resonant converter are analyzed in time domain to determine the steady-state operating point. The operating mode boundaries, mode transitions and mode distribution are discussed and the dependencies of modes on voltage transfer ratio, inductor ratio and switching frequency are illustrated. Based on the mode analysis results, normalized equations and characteristics for the resonant tank currents and voltages are presented, which support the designer selecting the optimal operating point. A prototype system is built and it is shown that the calculations predict the resonant current, voltage behavior, and output power characteristic very well

Design of an Isolated Bidirectional Symmetric Resonant Converter

“…For obtaining the voltage gain and its relationship with respect to frequency, the fundamental harmonic approximation method (FHA) [19] was used to build the equivalent circuit model of the forward charging mode as illustrated in Figure 7 [20]. Here, V DC_Grid_FHA is the fundamental component of the square voltage waveform at the primary side.…”

Influence of the junction capacitance of the secondary rectifier diodes on output characteristics in multi-resonant converters

“…4) as this will be important for the following discussion. For a more detailed description please refer to [16] for the LLC and to [17] for the CLLLC topology. Within one C add =0pF…”

“…The step-up operation mode at f sw = 85 kHz for the SiC SBD in Fig. 5(a) starts with the power transferring subinterval P at t = t 0 and is followed by subinterval N at t = t 1 , in which the power transfer to the secondary side diminishes and energy is stored in the resonant tank [17]. The rising edge of v sec is very steep due to the very small diode junction capacitance and thus the state of the output rectifier abruptly changes.…”

“…As rather straightforward approach resonant converters can be analyzed theoretically by the first harmonic approximation (FHA) method, assuming that only sinusoidal current waveforms are applied on the resonant tank and only ideal components are utilized [15]. A more detailed and advanced analysis is the calculation of the time domain solution (TDS) for steady-state [16], [17]. But it has been shown that there is still a deviation between measurement and TDS calculation [17], which is merely not explainable with resistive losses and/or dead time of the primary inverter.…”

“…A more detailed and advanced analysis is the calculation of the time domain solution (TDS) for steady-state [16], [17]. But it has been shown that there is still a deviation between measurement and TDS calculation [17], which is merely not explainable with resistive losses and/or dead time of the primary inverter. Both methods, FHA and TDS, have the disadvantage that they do not account for the secondary side rectifier diodes junction capacitances and their significant influences on converter output characteristic, which represents the most important point for design considerations.…”