High power dc-dc converter and distributed Z-source network dc-dc converter

Dc-dc converters are extensively used for various applications in industry to regulate output voltage when the input voltage of converter or output load changes. However, a lot of research activities are focused mainly on small or medium power converters, for example, less than 5 kW. High power dc-dc converters are now in great demand in many applications such as renewable energy interface systems, utility power electronics, electric vehicle system, and so on.;There are several challenging issues in designing high power and high frequency transformer isolated dc-dc converters. First, selection of the switching devices and soft switching techniques are essential to achieve high converter efficiency. Secondly, a high power and high frequency transformer design is becoming more and more important as power level of the power electronics systems increases. Thirdly, snubber or voltage clamping circuit that prevent switching devices from high voltage overshoot is also important.;In the second part of this dissertation, a 3 phase interleaved boost dc-dc converter for series hybrid electric bus system is introduced. The converter is designed to meet both 30 kW average and 120 kW peak power demand of bus. Therefore, the dc-dc converter in the HEV system plays an important role to maximize fuel efficiency. However, dominant part of the boost converter, both in terms of size and cost, belongs to the magnetic components. Consequently, better use of the magnetic content of the dc-dc converter may lead to substantial performance and cost improvements. In this section, a boost inductor using integrated magnetic approach is used to minimize inductor volume and power loss.;In order to overcome theoretical barriers of the traditional V-source or I-source converters, a novel dc-dc converter incorporating a distributed (or transmission line) Z-source network to achieve the buck (step-down) and boost (step-up) function of a transformer isolated dc-dc converter is presented in the third section. In this section, a distributed Z-source network composed of an array of inductors and capacitors is coupled between the power source and main switching devices. The great and unique feature about the distributed Z-source network dc-dc converter is that unlike the traditional V-source or I-source converters, it can be open- and short-circuited without damaging switching devices. Therefore, the desired buck and boost function can be achieved. Moreover, converter reliability can be greatly improved.