Song Xiong

A Family of Exponential Step-Down Switched-Capacitor Converters and Their Applications in Two-Stage Converters

This paper presents a family of exponential voltage step-down switched-capacitor (ESC) converters. Considering the demand of large-voltage-gain step-down converters in the market, it is difficult to achieve the step-down requirement with good efficiency for a single-stage buck converter. The two-stage converter has been an effective solution for high-voltage-step-down applications. In this paper, making use of the large-voltage-gain conversion property of the ESC converter, a two-stage ESC-buck converter is proposed. A mathematical tool for the accurate calculation of efficiency is developed. The efficiency characteristic of the proposed ESC converter is established. Experimental efficiency measurements are carried out using the ESC converter proposed and two different types of commercially available buck converter ICs. The results show that the efficiency of the ESC-buck converter is higher than that of a single buck converter for large-voltage-gain applications.

Analysis and Design of a High-Voltage-Gain Hybrid Switched-Capacitor Buck Converter

This paper presents an analysis on the effect of having different number of capacitors n in the first-stage switched-capacitor circuit of an improved hybrid switched-capacitor buck converter for high-voltage-gain conversion. Various aspects of the topology, operation, and efficiency are investigated. It is shown both analytically and experimentally that a higher n in the step-down capacitor stage does not necessarily lead to an overall improved power efficiency. A design and optimization method is thus proposed for the improved SC-buck converter.

Optimal Design of Complex Switched-Capacitor Converters Via Energy-Flow-Path Analysis

Many analytical methods of establishing accurate models of the switched-capacitor (SC) converters have been developed. These methods are applicable to simple low-order SC converters and can permit only a general efficiency calculation of SC converters. They do not provide analytical solutions that describe how individual electrical component in the circuit practically affects the SC converter at different frequencies. Such an analysis is important for the optimal design and realization of a complex (high-order) SC converter. This is particularly true for those SC converters which have more than two operating states. For complex SC converters, a constituent capacitor may have a profound effect on the converters efficiency and is dependent on the configuration of the switches and the arrangement of the energy flow paths. In this paper, the relationship of the value of capacitors and the efficiency of complex SC converters is derived and investigated using an energy-flow-path analysis. Optimal design of SC converters can be achieved through a systematic component value selection by: 1) increasing the proportion of energy flow through the most efficient paths; and 2) increasing the efficiency of the paths that have a higher energy flow. The design of complex SC converters in terms of optimizing their power efficiency is discussed using an exponential SC converter as an illustration. The results of both calculation and experimental measurement show that the approach is effective.

Family of cascaded high-voltage-gain bidirectional switched-capacitor DC-DC converters

High-voltage-gain step-up DC-DC converters are required for the applications of distributed energy resources (DERs). A family of bidirectional switched-capacitor (SC) converters with high gain ratio of any positive integer are proposed in this paper. These converters are of high efficiency, easy to control, and are with low output voltage ripple of less than 1%. The proposed converters are also capable of delivering bidirectional power, which is a key requirement for the applications with battery storage. A prototype of 9-time SC converter at 20 V input voltage, 100 W output, 75 kHz, is built and tested. Experiment results show that the maximum efficiency of the 9-time SC converter is over 98% without drivers loss and the efficiency over the entire load range between 25 W and 100 W is over 95.5% including the drivers loss.

Morphing Switched-Capacitor Converters With Variable Conversion Ratio

High-voltage-gain and wide-input-range dc-dc converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and variable and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converters structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental work on a 25-W, 6-30-V input, 3.5-8.5-V output prototype, is performed. For a single SC module, the efficiency over the entire input voltage range is higher than 98%. Applied into the two-stage converter, the overall efficiency achievable over the entire operating range is 80% including the drivers loss.

Nonisolated Harmonics-Boosted Resonant DC/DC Converter With High-Step-Up Gain

High-step-up dc/dc converters are widely required in grid-connected applications with renewable energy sources. An extremely high-ratio step-up nonisolated dc/dc converter, in the form of a harmonics-boosted resonant converter, is proposed in this paper. This proposed converter consists of a high-frequency dc/ac inverter stage that is followed by a passive ac/dc rectifier stage connected in cascade. Conventionally, such a dc/ac inverter is designed to output a pure sinusoidal ac voltage with an amplitude several times the amplitude of the input voltage. However, for the proposed converter, the harmonics-boosted inverter stage is designed to contain selected voltage harmonics that significantly boost the amplitude of its output voltage. This greatly increases the overall gain of the converter. The adopted ac/dc stage is a diode-capacitor rectifier, which is of high efficiency and easily extendable to increase the voltage gain. Importantly, the proposed converter involves only one active switch. With only one active switch, the drivers loss is minimized and the converters control is simplified. Zero-voltage switching is applied to reduce the switching loss, which also allows the converter to operate efficiently at high frequency, and thus can be designed for high power density. The optimal design of the two converter stages and their combined voltage gain is investigated and reported. Besides, a design guideline of the proposed converter is provided. A prototype of a 57-time harmonics-boosted resonant converter with 3.3 V input voltage, 500 kHz switching frequency, and 21 W output power, is built. The experimental result shows that the achieved converters efficiency is as high as 88.6%.

Non-isolated high-step-up resonant DC/DC converter

A non-isolated high-step-up resonant DC/DC converter made up of a resonant inverter and a passive switched-capacitor (SC) rectifier, is proposed in this paper. The proposed converter is free of transformer and coupled-inductor. Thus, issues related to the leakage inductance and the large volume magnetic component caused by large turns ratio of high-voltage-gain applications, are avoided. Besides, as the converter contains only one active switch, its control is simple. Second harmonic voltage across the switch is attenuated to provide low voltage stress for the active switch and a higher voltage gain of the converter. The voltage gain of the converter is not achieved by a single stage, but by the gain product of the resonant inverter and SC rectifier. A prototype with input voltage 6 V, 500 kHz switching frequency, 50% duty cycle, is constructed to validate the performance of the proposed converter. The voltage gain of the prototype is over 33 times and the achievable efficiency is close to 90% under a wide load resistance range.

Morphing switched-capacitor step-down DC-DC converters with variable conversion ratio

High-voltage-gain and wide-input-range DC-DC converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converters structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental results show that the efficiency of a single SC module is higher than 98%.

Compact modular switched-capacitor DC/DC converters with exponential voltage gain

A compact modular switched-capacitor DC/DC converter with exponential voltage gain, high efficiency, light weight, and bidirectional power flow, is proposed in this paper. The proposed converter is suitable for applications in high temperature environments since it does not contain magnetic element nor temperature-sensitive capacitor. With an output voltage that is 2N (N is the cell number) times the low-side voltage, the proposed converter has a considerably low component count and suffers from the lowest overall capacitor voltage stress as compared with other existing switched-capacitor converters. Besides, the proposed converter adopts a modular structure and simple control scheme, which enables it to be easily extended, through a repeated cascade of the same module, to achieve a higher voltage conversion. Moreover, since the load is charged via two complementary paths in an interleaved operation, the output voltage ripple is small, which is beneficial for high efficiency. Experimental results of an 8×-gain prototype at 5 V input and 70 W output power, are provided to validate the performance of the proposed converter. The achievable efficiency is up to 95.78% (including the drivers loss).