A Soft-switching single-phase single-stage AC-to DC converter with low line current harmonic distortion
Date
1998
Authors
Venkatraman, Ramakrishnan
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Abstract
This thesis presents the steady-state and dynamic analysis of a soft-switching single phase, single-stage high frequency (HF) transformer isolated ac-to-dc converter with low line current harmonic distortion. The converter topology integrates a discontinuous conduction mode (DCM) boost converter and a soft-switching asymmetrical pulse-width-modulated (PWM) constant frequency de-to-de converter.
The steady-state operation of the converter is explained with equivalent circuits for various intervals of operation. Design curves are obtained based on steady-state analysis. The design procedure is illustrated with an example. Detailed PSPICE simulation results and experimental results obtained from a 500 W, 48 V output laboratory prototype are given to verify theory. The measured total harmonic distortion (THD) of the line current is between 9.5% to 28% for the complete operating range of load and line voltage. Zero-voltage-switching (ZVS) is maintained for the complete operating range.
Small-signal analysis of the ac-to-dc converter is done based on the state averaging technique. Control-to-output and line-to-output transfer functions are obtained. Control-to-output transfer function indicates that the duty cycle has to be restricted to 0.5 to obtain fast regulation of output voltage. PSPICE simulation results are compared with the theoretically obtained frequency response of the control-to-output transfer function. A feedback loop network is designed to regulate the output voltage. Discrete-time large signal analysis is presented to study the closed-loop behaviour of the converter for typical line and load transients. The output voltage recovers within 1 ms for 50% load transients. Theoretical results are verified with PSPICE simulation. Experimental results for load transients are given.