Frequency Domain Modelling of Series LC- Parallel LC Resonant Converter with Capacitive Output Filter
Multi-element DC-DC resonant converters have been a topic of interest over the past several years. The need for reduced sizes of passive components in the converter, has stimulated substantial research towards the high- frequency operation of these converters, specifically pertaining to high voltage applications. Hence, the series LC-parallel LC (LCLC) resonant converter with capacitive output filter is an emerging favorite for high frequency, high voltage applications. The use of the capacitive output filter ensures reduced peak voltage stress of the rectifier diodes, which is equal to the clamped output voltage. Although the topology exhibits various modes of operation, it predominantly operates in one mode with a lagging power factor. Existing literature utilizes conventional fundamental harmonic approximation (FHA) due to its simplicity. However, FHA has accuracy limitations when applied on low quality factor (Q<2) tuned resonant circuit since higher order harmonics are neglected. To resolve this issue, this thesis presents an improved frequency domain-based analysis of the LCLC resonant converter with a capacitive output filter, considering the harmonics of both the input and load side of the converter. The proposed analysis can be extended to study converter operational characteristics under variable frequency and fixed- frequency PWM control. Closed- form expressions for the performance characteristics such as voltage gain, resonant tank RMS current, and ZVS angle (β) were derived from the nth harmonic equivalent circuit. The proposed model is validated using simulation studies performed on PSIM (Power Simulation) and by using a hardware prototype. This model improves the accuracy over conventional FHA by 4%.
URI for this recordhttp://hdl.handle.net/1974/28796
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