Control of current ripple in dc-dc converters

• Main Author: Wang, Jing
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8573

An investigation is conducted into the analysis of power converters from the ripple point of view. In short, the thesis is about a deep understanding of the basic dc-dc converter from the ripple viewpoint and thus develops a family of converters with ripple free input current or output current by using coupled inductors, which may achieve reduced component count, reducing the amount of material and increasing the energy density. Based on the existing ripple free converter topologies, a synthesis method for ripple free current converters is summarized and studied. Five elements are found to be the minimum requirement to achieve ripple free current topology by using coupled inductors and the LCL structure is found important for ripple free current converters. Several modified converters are developed from the synthesis analysis which is presented in this thesis. A pair of generated modified Boost topologies are compared with the well-known Cuk and Sepic converters and found to have several advantages, such as low switch and diode voltage stress, low switch and diode current stress and low voltage and current stresses on capacitor Cs. In particular, the developed Boost converters can achieve ripple-free input current while keeping the properties of the conventional Boost converters when they operate in both continuous and discontinuous conduction modes. The modified Boost converters operating in discontinuous conduction mode are investigated for the application of power factor correction. They can keep the input current continuous or even ripple free, but be proportional to the input line voltage. An almost unity power factor can be achieved when the switching frequency and switching duty ratio are fixed. This indicates that the pair of modified Boost topologies have the same "voltage follower" property as the conventional Boost topology, but with a continuous and ripple free input inductor current, which is the same as the Cuk and Sepic converters. As the reverse circuits of the modified Boost topologies, a pair of modified Buck topologies are developed and analyzed. They are found to have continuous and ripple free output current, in both continuous conduction mode and discontinuous conduction mode. The modified Buck topologies can keep the same properties as the conventional Buck topology while they maintain the output current continuous and ripple free. In addition, the modified Buck topology 1 is found to have high input impedance which can limit the input in-rush current effectively. All modified topologies can use coupled inductors to decrease the converter size and weight, which is very desirable. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate