Abstract:
This thesis is subdivided into two parts. The first part deals with single phase switched capacitor AC-DC step down converters for improved power quality and the second part deals with non-isolated single stage PFC based LED driver with THD minimization using Cúk converter.
In the first part, two novel topologies for single-phase AC-DC buck converter using switched capacitor network has been proposed. The first proposed topology modified the conventional two stage buck converter by introducing a switched capacitor network in between stages whereas the second topology introduced two switched capacitor networks, one for each half cycle of line frequency of operation. The proposed converters offered better efficiency, reduced total harmonic distortion (THD) and improved input power factor (PF) using suitable power factor correction (PFC) control. Converters offered best performances in simulation have been implemented in laboratory experiment. These highly efficient proposed schemes can be used in the lighting application of new generation LEDs.
The second part proposed a utility supply driven single stage PFC based LED driver using Cúk converter. For low DC voltage output requirement of LED driver, Cúk converter is a convenient choice due to its topological suitability for PFC application and stepping the voltage down at a desired level unlike the Boost Converter. A hysteresis current control scheme is adopted to operate the converter in Continuous Conduction Mode (CCM) and fast enough to follow the current reference causing power factor to approach near unity. Although the converter operates at variable switching frequency, the response is very fast and independent of the converter dynamics. At the same time the converter ensures a constant current drive at the output side to operate the LED. Theoretical analysis, design calculation and simulation results confirm that the proposed single stage control scheme operates with an improved THD and performs better compared to the commercially available controller because the same converter is used for both PFC and LED Driver. As it diminishes one stage of power conversion, the efficiency of the driver is increased whereas the complexity in controller design and implementation is decreased.
