Steady-state and dynamic analysis of the LCC-type parallel resonant converter

This thesis presents the steady-state and dynamic analysis of the series-parallel resonant converter (SPRC), which is a popular configuration of the resonant power converters. The dynamic analysis includes both large and small-signal analysis. This converter is operated in variable frequency as well as fixed frequency control modes.;For the variable frequency operation, various operating modes, including the multiple conduction modes, of the converter have been identified. A generalized steady-state solution for these modes is obtained using the state-space approach. Design curves for converter gain and peak component stresses, versus the normalized load current, have been obtained. The boundaries between the various modes of operations (continuous capacitor voltage mode and discontinuous capacitor voltage mode as well as leading and lagging power factor modes) have been obtained. Experimental results obtained from a 100 W converter are presented to verify the theory.;Discrete time domain large-signal models have been derived for the converter operating in variable frequency mode for continuous and discontinuous current modes. These models have been used to study the large-signal behavior of the converter for step change in input supply voltage, step change in load, etc. The models are also used to determine the peak component stresses and discrete state response of the converter for large-signal transients. Theoretical results have been verified using SPICE simulation and experiments. It is shown by an experimental converter that most of the drawbacks of the open loop system can be overcome by operating the converter with a closed loop.;The large-signal equations for the converter operating in variable frequency and continuous current mode have been linearized about the steady-state operating point to obtain a linearized small-signal state-space model in discrete time domain. Multiple loops have been used to control the dynamics of the converter. An outer voltage feedback loop takes care of the output voltage regulation. An inner state variable feedback loop is also incorporated to improve the dynamics of the converter. The small-signal models obtained are used to study the small-signal behavior of the converter for parameters like control to output transfer function and audio-susceptibility. Experimental results are presented to verify the key theoretical results.;A small-signal equivalent circuit model has also been obtained to study the small-signal behavior of the converter. This model represents the converter dynamics in a more accessible and flexible format. It gives more physical insight into the converter dynamics and can be solved for the various transfer functions conveniently. Both exact (discrete time domain) and approximate (continuous time domain) models are obtained. When the exact model is used, the results are found to be accurate up to the switching frequency. Analytical results are verified using an experimental converter.;The different operating modes of the fixed frequency pulse-width modulated SPRC have been identified. The steady-state analysis and a discrete time domain model for the large-signal analysis are presented for the predominant mode for a capacitor ratio of 1. The large-signal model has been linearized to perform the small-signal analysis much on the same lines as for the variable frequency operation. These models have been used to study the large and small-signal dynamics of the SPRC.