An Investigation on High-Voltage-Gain Power Converters

Professor Tan, Siew Chong   (Principal Investigator (PI))

30

2013-01-01

2015-06-30

120000

An Investigation on High-Voltage-Gain Power Converters

Efficiency, High-voltage-gain, Power converters, Power electronics

Power (Obsolete)Electronics

Engineering (E)

201209159014

Seed Fund for Basic Research for New Staff

2012

Completed

In today’s energy-conscious world, new environmental-friendly energy sources, like fuel and solar cells, are becoming increasingly important. To use them as power sources, suitable DC-DC converters must be used to stabilize the variable voltage provided by these cells. The converters have to operate with high efficiency (to reduce energy wastage) and need high power density (to reduce space wastage). Most present-day consumer electronics such as cellular phones, computers, MPEG3/CDplayers/cameras/camcorders, etc., contain integrated circuits (IC) that operate at very low voltages (3.3V nowadays, with the tendency to drop to 1V soon, probably reaching a low level of 0.4V by 2016, according to ""International Roadmap for Semiconductors"". DC-DC converters with a large-step-down-voltage-conversion ratio are needed for this purpose. Portable electronic devices require a light weight for all the circuitries. The computers' modern architecture leaves a very small space for the power supply, which must be small in size. Switched-capacitor (SC) converters answer the above goals, as they have small size, light weight, and high power density. They can step-down the voltage as much as desired, with no operating impediment. They are, today, mass manufactured by companies like Maxim and National Semiconductor. But SC converters suffer from some deficiencies, which must be solved before they can be used for the above applications. The main objective of this research is to propose solutions for overcoming the inherent problems of SC converters. (1) In presence of load voltage regulation, SC converters feature a low-energy-conversion efficiency. The original solution proposed here (integration of a regulated buck converter in an unregulated SC converter, creating one stage with synchronized switches operating under a zero-current condition) eliminates a large part of the switching losses and allows the SC converter to attain its maximum possible efficiency, despite operation at very high switching frequency. The buck-cell has no conversion role. It operates at the same high switching frequency, which allows the use of very small elements in its structure. The outcome will be a small size and very efficient power supply, with high current slew-rate. 2) SC converters have (a)small power. (b)Their input current is very discontinuous (because it is given by steep capacitor charging current in a circuit formed only by small capacitors and the negligible parasitic resistances of switches and capacitors). The large di/dt provokes a large EMI (electromagnetic interference) radiation, which may affect the healthy operation of surrounding circuitries. (c)The load voltage presents large ripple that has to be attenuated by large output capacitors. To solve these problems, a paralleling system of SC modules is proposed, with both inputs and outputs interleaved. The outputs interleaving is a known technique. The interleaving of the inputs of circuits formed only by switches and capacitors is not straightforward. An original theory and solution will be presented. The outcome of the resulting continuous input current will be: (2.1) power supplies with much lesser electromagnetic radiation; and (2.2)the SC converters will become compatible with fuel or solar cells, as these cells cannot accept a pulsating drawing current which affects their lifespan and operational reliability. Moreover, a smaller output-voltage ripple would make the output capacitor redundant, simplifying the IC manufacturing of the converter. 3) The traditional design of the SC converters' control is based on small-signal approximate models. These do not work when the input voltage varies in a wide range, as typical for the fuel and solar cells. And it does not work for loads like microprocessors, which have quick large variations, requiring a quick transient response. A new original control for the interleaved SC modules integrated with the buck cell will assure quick regulation for large changes in the line voltage and load.