High step-up boost converters with coupled inductor have attracted much attention in the fuel cell or photovoltaic grid-connected generation system, however, there are few literatures elaborated on the construction ideas and derivation methods of them. Accordingly, in order to obtain a clear roadmap on the derivation and inner connection of these converters, a comprehensive review and analysis are presented in this paper. First, the basic boost converter with coupled inductor is regarded as the basic topology, and its merits and demerits are analyzed in detail. Then, in order to address these demerits, various step-up techniques are introduced, such as the rectifier circuit, the active-clamped circuit, the multi-winding coupled inductor, and the voltage doubler rectifier; and numerous new topologies are continuously proposed by combinations and equivalent simplifications. In addition to a detailed synthesis of each topology, a comparative and quantitative analysis among some important converters is presented, and the optimal one is chosen to build a 250 W prototype. Finally, based on comparisons and analysis, the main characteristics and inner connections of these high step-up boost converters with coupled inductor are identified and clarified.

The LLC resonant converters have been widely used in many applications due to their features such as wide input voltage range, high efficiency, and high power density. Therefore, the analysis methodology for the LLC resonant converter is of great importance. Based on the existing literature, there are mainly four analysis methodologies: (i) fundamental harmonic analysis; (ii) frequency domain with time domain partial correction; (iii) frequency domain with time domain complete correction; (iv) time domain analysis or operation mode-based analysis. However, there is no systematic view and study on different LLC analysis methodologies. Therefore, the main purpose and contribution of this study are to make a comprehensive study and comparison of these analysis methodologies and to provide guidance on analysing and designing of the LLC resonant converter to the readers. In this study, the principles of these four analysis methodologies are introduced briefly. Then, by introducing gain error and peak gain frequency error as definitions, comprehensive comparison studies on these four different methodologies for different conditions are implemented. Recommended applications for each methodology are summarised; finally, an experimental prototype is built to verify the theoretical analysis, and a conclusion is drawn.

The DC distributed power systems (DPS) have attained much attention because of its characteristics of high efficiency, high power density and flexible configuration. However, interactions between converters may cause stability issues. Currently, research mainly focuses on the DPS with a DC voltage bus, including the stability analysis and the approaches to improve the system stability. This paper is to establish stability criteria for DPS with a DC current bus. Firstly, basic current type DC/DC converters and their small signal models are introduced. Then, the current bus DPS is derived, discussed, and the stability criteria is obtained by using two-port small signal model. The proposed criteria is verified by comparing theoretical calculations and simulations of a DC current bus DPS. Finally, an experimental prototype is built to validate the theoretical analysis and simulations.

In this paper, a high efficiency single stage bi-directional battery charger for light electric vehicles (LEVs) is proposed. In Grid-to-Vehicle (G2V) mode, single stage operation is achieved by sharing switches between totem-pole bridgeless power factor correction circuit (PFC) and bi-directional half-bridge LLC resonant converter; in Vehicle-to-Grid (V2G) mode, by turning off the mode selection switch, the proposed topology changed into the form of a half-bridge LLC resonant converter and a full-bridge inverter. Meanwhile, the magnetic control instead of the widely used frequency control is adopted to achieve a better performance. The control circuit and EMI design is simplified, and constant frequency operation is achieved. By carefully designing resonant tank, zero voltage switching (ZVS) and zero current switching (ZCS) operation for switches are guaranteed. Experimental results about variable inductor are presented and analyzed. A simulation case is introduced to verify the feasibility and validity of the proposed topology.

An interleaved high step-up zero-voltage-switching boost converter is proposed in this study. The operating principle and voltage gain ratio of the proposed converter are presented. The variable inductor control method is used to regulate the output voltage and to achieve a high-voltage gain. The design procedure of the variable inductor with a double E core is also presented in detail. Finally, a 40 W prototype with a 12 V input and 100 V output is built to verify the consistency of the theory analysis. The highest efficiency measured is 84.5%.

A kind of interleaved non-isolated high step-up DC/DC converter is presented in this study. The converter consists of two basic Boost cells and some diode-capacitor multiplier (DCM) cells as needed. Because of the DCM cells, the voltage conversion ratio is enlarged and the extreme large duty ratio can be avoided in the high step-up applications. Moreover, the voltage stress of all the power devices is greatly lower than the output voltage. As a result, lower-voltage-rated power devices can be employed, and higher efficiency can be expected. Since the two basic Boost cells are controlled by the interleaving method, which means the phase difference between the two pulse width moderlation (PWM) signals is 180 degrees and the input current is the sums of the two inductor currents, the input current ripple is decreased and the size of the input filter could be reduced, which make it a suitable choice in the photovoltaic power generation system and hybrid electric vehicles, etc. Finally, the experimental results from a 300 W, 30-400 V laboratory prototype are presented to validate the effectiveness of the proposed converter.