High-Voltage-Gain DC-DC Power Electronic Converters -- New Topologies and Classification

This dissertation proposes two new high-voltage-gain dc-dc converters for integration of renewable energy sources in 380/400V dc distribution systems. The first high-voltage-gain converter is based on a modified Dickson charge pump voltage multiplier circuit. The second high-voltage-gain converter is based on a non-inverting diode-capacitor voltage multiplier cell. Both the proposed converters offer continuous input current and low voltage stress on switches which make them appealing for applications like integration of renewable energy sources. The proposed converters are capable for drawing power from a single source or two sources while having continuous input current in both cases. Theoretical analysis of the operation of the proposed converters and the component stresses are discussed with supporting simulation and hardware results. This dissertation also proposes a family of high-voltage-gain dc-dc converters that are based on a generalized structure. The two stage general structure consists of a two-phase interleaved (TPI) boost stage and a voltage multiplier (VM) stage. The TPI boost stage results in a classification of the family of converters into non-isolated and isolated converters. A few possible VM stages are discussed. The voltage gain derivations of the TPI boost stages and VM stages are presented in detail. An example converter is discussed with supporting hardware results to verify the general structure. The proposed family of converters can be powered using single source or two sources while having continuous input current in both cases. These high voltage gain dc-dc converters are modular and scalable; making them ideal for harnessing energy from various renewable sources offering power at different levels --Abstract, page iv

Advanced topologies of high step-up DC-DC converters for renewable energy applications

This research is focused on developing several advanced topologies of high step-up DC-DC converters to connect low-voltage renewable energy (RE) sources, such as photovoltaic (PV) panels and fuel cells (FCs), into a high-voltage DC bus in renewable energy applications. The proposed converters are based on the combinations of various voltage-boosting (VB) techniques, including interleaved and quadratic structures, switched-capacitor (SC)-based voltage multiplier (VM) cells, and magnetically coupled inductor (CI) and built-in-transformer (BIT). The proposed converters offer outstanding features, including high voltage gain with low or medium duty cycle, a small number of components, low current and voltage stresses on the components, continuous input current with low ripple, and high efficiency. This research includes five new advanced high step-up DC-DC converters with detailed analyses. First, an interleaved converter is presented, which is based on the integration of two three-winding CIs with SC-based VM cells. Second, a dual-switch converter is proposed, which is based on the integration of a single three-winding CI with SC-based VM cells. Third, the SC-based VM cells are utilized to present three new Z-source (ZS)-based converters. Fourth, two double-winding CIs and a three-winding BIT are combined with SC-based VM cells to develop another interleaved high step-up converter. Finally, two double-winding CIs and SC-based VM cells are adopted to devise an interleaved quadratic converter with high voltage gain. The operating and steady-state analyses, design considerations, and a comparison with similar converters in the literature are provided for each converter. In addition, hardware prototypes were fabricated to verify the performance of the proposed converters --Abstract, page iv

Design and implementation of two non-isolated high gain DC-DC converters

In most solar energy systems, the output voltage of a photovoltaic panel is usually between 20 to 40 Vdc. In order to interface the panels to a 400 Vdc bus, a high voltage gain dc-dc converter is required. This thesis starts with analyzing and simulating several topologies that have been already introduced for this application. The voltage gain and efficiency are investigated analytically. A hardware prototype of one of the existing topologies, the interleaved boost converter with voltage multiplier cell, has been developed. Finally, a new topology with a higher voltage transfer ratio is proposed and its experimental results are compared with former topologies. Simulations are used to verify the design and predict the performance of each topology --Abstract, page iii

An Interleaved High Step-Up DC-DC Converter with Built-In Transformer-Based Voltage Multiplier for DC Microgrid Applications

This paper proposes a high step-up DC-DC converter with a built-in transformer (BIT)-based voltage multiplier (VM) that is suitable for integrating low-voltage renewable energy sources into a DC microgrid. A three-winding BIT is combined with the switched-capacitor (SC) cells to extend the voltage gain and reduce the voltage stress on the switches. The current-falling rates of the diodes are controlled by the leakage inductances of the BIT, alleviating the reverse-recovery problem of the diodes. The operating modes and steady-state analysis are presented. Additionally, the validity of the proposed converter is confirmed by the simulation and experimental results of a 400 W converter with an input voltage of 20 V and output voltage of 400 V. Moreover, a comparison study is presented to verify the superiority of the proposed converter over the closest existing topologies in the literature

A Three Phase Interleaved Boost Converter with L & C Voltage Extension Mechanism

In this paper a high step-up dc-dc voltage converter is proposed. The proposed converter employs coupled inductors and voltage extension capacitors for obtaining a high voltage gain. The coupled inductors and extension capacitors are merged in traditional interleaved boost converters to get the additional advantage of high step-up voltage conversion ratio and reduced voltage stress on switches along with existing features of interleaved boost converters. The main operating principle of the proposed converter is discussed and the key principle waveforms and equations are analysed. A simulation in PSIM is carried out for the proposed converter as well as traditional interleaved boost converter for the same parameters which shows that the proposed converter has better performance as compared to the traditional interleaved boost converter. Finally, an experiment is carried on a 32 W, 20 V input, 160 V output prototype in the laboratory for experimental validation of the proposed converter. Important future directions have also been given for future research on the proposed topology

A Non-Isolated High Step-Up Interleaved DC-DC Converter with Diode-Capacitor Multiplier Cells and Dual Coupled Inductors

In this paper, a non-isolated high step-up dc-dc converter is presented. The proposed converter is composed of an interleaved structure and diode-capacitor multiplier cells for interfacing low-voltage renewable energy sources to high-voltage distribution buses. The aforementioned topology can provide a very high voltage gain due to employing the coupled inductors and the diode-capacitor cells. The coupled inductors are connected to the diode-capacitor multiplier cells to achieve the interleaved energy storage in the output side. Furthermore, the proposed topology provides continuous input current with low voltage stress on the power devices. The reverse recovery problem of the diodes is reduced. This topology can be operated at a reduced duty cycle by adjusting the turn ratio of the coupled inductors. Moreover, the performance comparison between the proposed topology and other converters are introduced. The design considerations operation principle, steady-state analysis, simulation results, and experimental verifications are presented. Therefore, a 500-W hardware prototype with an input voltage of 30-V and an output voltage of 1000-V is built to verify the performance and the theoretical analysis.Comment: 2020 North American Power Symposiu

Analysis and comparison of two high-gain interleaved coupled-inductor boost converters

The main objective of this thesis is to compare and analyze two different high-gain dc-dc power electronic converters based on coupled inductors and capacitor-diode multiplier cells. The idea of these converters is to integrate the solar energy with a 400V DC microgrid. DC microgrids are more efficient, less expensive, and more reliable compared to AC microgrids. They also favor the integration of renewable energy sources. With the growing need for the utilization of more renewable sources of energy, photovoltaic panels have become one of the trending technologies which convert the energy from the sun to a useable electrical power. But these panels produce a low dc output voltage which cannot directly be connected to the high voltage dc distribution of the grid. They require high-gain dc-dc converters suitable for converting the output voltage of the solar panels to the dc distribution grid voltage. The topologies studied in this thesis provide a high dc voltage gain suitable for this application. The other significant advantage of these topologies is a continuous input current which increases the effective utilization of the source. These converters can also be used in applications involving high gain dc-dc conversion such as fuel cells, and energy storage applications like ultracapacitors. In this thesis, the different operating modes of the two high-gain dc-dc converters are explained in detail. Also, the voltage and current stresses seen by the components have been derived and power loss analysis is carried out for both the topologies. Recently, GaN switches have gained popularity for their higher efficiencies at higher switching frequencies, so this thesis also makes an attempt to compare Si to GaN devices in terms of efficiency improvements for the studied converters --Abstract, page iii

A Family of Interleaved High Step-Up DC-DC Converters by Integrating a Voltage Multiplier and an Active Clamp Circuits

A family of interleaved current-fed high step-up dc-dc converters are introduced and analyzed here by combining a voltage multiplier (VM) and an active clamp circuit for high-voltage high-power applications. Low input currents and output voltages ripples values and high voltage-gains characteristics of these converters make them suitable for lots of dc-dc applications. All power devices operate entirely under soft switching conditions, even when wide load and input voltage variations are applied. Thus, they can be designed at high switching frequencies to reduce passive components sizes to achieve high-power density, one of the main targets of the power electronics researches. Also, their input and output ports common ground simplifies the gate-drives and control circuits. To verify the given analyses and simulations, a 120-320 V to 1 kV, 50-1300 W three-stage two-leg prototype converter has been implemented at 100 kHz. Based on the experimental results, maximum efficiency of 96.5% is achieved.Comment: 14 pages, 15 figure

High gain - high power (HGHP) DC-DC converter for DC microgrid applications: design and testing

The use of green energy sources to feed DC microgrids is gaining prominence over traditional centralised AC systems. DC microgrids are characterised by the use of intermediate DC-DC converter which acts as power conditioning units. Hence, the choice of an appropriate DC-DC converter becomes significant as the overall system efficiency is strongly dependent on the converter’s performance. This paper proposes a novel high gain high power (HGHP) DC-DC converter for DC microgrid, which is of one of the significant step forward in the development of DC microgrids. The suitability of the proposed HGHP DC-DC converter is demonstrated by experimental tests of the 60V/1.1kV, 3kW converter; test results validate the converter’s suitability for DC distribution. A significant number of performance parameters of the proposed converter is compared with state of the art converter topologies demonstrating the superior capabilities of the proposed converter. This paper also portrays the potential benefits that could be reaped by trending towards DC instead of existing AC system. The advantages and challenges to be confronted in the foreseeable future while implementing sustainable DC microgrids are also highlighted. Finally, this paper encapsulates renewable energy fed DC microgrid system as an appropriate, technically feasible, economically viable and competent solution for efficiently utilising the sustainable energy sources

A NON-ISOLATED HIGH STEP-UP CONVERTER WITH LOW RIPPLE INPUT CURRENT AND REDUCED VOLTAGE STRESS

In this paper a new non-isolated high step-up interleaved cascade converter is presented. In comparison with the conventional cascade boost converter, the proposed converter has a higher voltage gain, lower input current ripple and reduced voltage stress for the switches and diodes. Besides, unlike the conventional cascade boost converter, in the proposed converter the input current is shared between inductors and hence the converter can be implemented with lower current rated inductors. Thus, the converter size and conduction losses are reduced and the efficiency is increased. The proposed converter is analyzed and experimental results of a 200W laboratory prototype are presented