Time Domain Simplified Equations and its Iterative Calculation Model for LLC Resonant Converter

Abstract

LLC resonant converters can achieve soft switching and loss reduction. However, the analysis methods of wide frequency range LLC converters generally have problems with incomplete working condition analysis at non-resonant frequencies and there is always a tradeoff between the accuracy and the simplicity. These problems will affect the loss calculation, synchronous rectification and so on. The research objective of this paper focuses on the full-bridge LLC resonant converter. In this paper, three conditions are analyzed in time-domain including switching frequency lower than the resonant frequency at heavy load, switching frequency lower than the resonant frequency at light load, and switching frequency larger than the resonant frequency. Based on proper assumption and simplification, the approximate equivalent of the trigonometric function is used to simplify the complex time-domain equations. The simplified equations are obtained with the resonant capacitor voltage and resonant inductor current as the key variables. In order to make the simplified equations easy to use, an iterative calculation model is proposed with more simplicity than sophisticated software to solve nonlinear equations. The simplified equations and the model proposed in this paper are verified by comparison with the fundamental analysis methods, the simulation, and the experiments. By using the iterative calculation model, the voltage, current, time and other variables of switching points can be obtained with the relative error less than 3% to theoretic values, which can be used in loss calculation, synchronous rectification and so on. And the iterative calculation model can be realized on DSP or other processors in real-time.

Inductor-Aid Step-Up LLC Resonant Wireless Power Transfer

“…6, the normal lines are the Mgfsw curve with secondary consideration while the dash line is regardless. Apparently, the resonant frequency of the circuit with secondary resonant tank consideration 𝑓 𝑐 is slightly lower than the neglected analysis of (17). Hence, it ensures the inductive operation and ZVS of primary inverter switches.…”

“…Many LLC circuit analysis methodologies raised in the past, covered the circuit gain analysis derivation from the conduction angle of rectifier diode, Lagrandian dynamics model analysis, modified fundamental harmonic approximation (FHA), and the time-domain simplified equations with iterative calculation model [14][15][16][17]. Among them, the FHA is straightforward and accurate enough to conduct the LLC design by the comparison of FHA and frequency domain analysis with time-domain partial or complete correction, and the operation mode-based analysis presented in [18].…”

A High Step-Up Interleaved Current-Fed Resonant Converter for High-Voltage Applications

“…The LLC resonant converter is widely used in practice in many applications such as renewable energy systems [40], [41], on-board chargers [42], [43], light-emitting diodes (LEDs) [44], [45], and power factor correction (PFC) [46]. To regulate the output voltage of the LLC-based resonant converters, several methods such as Pulse Frequency Modulation (PFM), Phase Shift Modulation (PSM), Pulse Width Modulation (PWM), Asymmetric PWM (APWM), or hybrid modulation strategies like PFM+PWM and PFM+PSM can be utilized [26]. In the PFM strategy that operates based on the resonant tank impedance modification, a wide frequency range is used to regulate the output voltage.…”