Projects in Power Electronics

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1. Pentium III power supply-- adaptive converter for 12 V to 1.6 V at 20 W. The Pentium family processors try to minimize power consumption by a digital feedback power supply process. This uses a switching dc-dc converter, operating from either a 12 V or 5 V systems bus, to step down to a low voltage level for the processor. Initially, a "high" voltage (such as 3.3 V or 5 V) is applied. Then the processor requests reduction of the voltage until an on-board test circuit begins to report errors. Since power consumption in a digital chip is roughly proportional to V^2, this feedback scheme saves significant power and keeps the chip as cool as possible.
2. High-performance network converter: 28 V to 5 V isolated, with 90% efficiency into a 0.25 W load. In a high-performance communications network (such as ISDN and others), there is a need for local power a every node. In a satellite system, it is usual to provide electrical isolation at every node as well to prevent ground loops and electrical problems. A modern satellite can have several hundred communication nodes, and each one consumes a small amount of power (perhaps 50-250 mW). However, commercial power converters suitable for this purpose are not designed for efficient operation at such low power levels. One satellite designer uses more than 100 dc-dc converters, each designed for 5 W load, and simply operates them into a 100 mW load. The efficiency is less than 50%, and the cost is very high (>$300 per node). There are better ways to design a converter to meet this need, and this project involves a design and implementation suitable for a low-power network node.
3. 1 V, 100 A converter for future microprocessor. Microprocessor voltage levels drop about 30% each generation, to meet objectives for power reduction and to be consistent with reduced feature size on the dies. Intel is already discussing a future processor that runs at 1 V -- with a load current as high as 100 A. This project involves a study of the design considerations for such a converter, as well as a working design and demonstration that approaches it (perhaps at 20-40 A). Efficient power at 1 V and 100 A is a difficult challenge, and this project will lead to an understanding of parasitic effects, packaging methods, thermal considerations, and other high-current issues.
4. Lithium-ion cell monitor and protection circuit. New lithium-ion rechargeable batteries require internal protection and monitoring circuits. In this project, the team is asked to research these needs and design a circuit that meets them. Can a design smaller than those in production be achieved? Can extra features, such as charge management or life-cycle monitoring, be added?
5. State-of-charge monitoring for lead-acid string. A meter for "state of charge" of a working battery is needed. The meter needs to be accurate to within about +-5% over an interval of at least 20 charge and discharge sequences. This type of metering is needed for electric and hybrid cars.
6. Fast charging system. Most battery chemistries support high charging rates -- under certain very specific conditions. In this design, you are asked to select a battery technology (lead-acid, nicad, or nickel-metal-hydride), and design a charger that will bring the battery up to 100% charge as fast as possible with minimum stress on the battery.
7. Power maximizing solar-powered water pump for remote villages. There is a new (patented) control technology for automatically maximizing the power drawn from a set of solar cells. This project involves a demonstration of the project in a realistic context -- an electric water pumping station for a remote African village with lots of sun but no electricity. The pumping station will lift water from a well into a holding tank and simple system of pipes, and will save the village their backbreaking daily chores pumping the well be hand and lugging water. The designer should determine how to make the best use of the energy, and also design float switches and other accessories to make the system automatic and maintenance free. See the PESC'96 paper on automated power maximization by Midya, Krein, et al.
8. Human-powered electronic communications gear. The military has long used hand-cranked generators to provide communications power in the field. Similar technology could be very valuable for hikers, forest rangers, and anyone who needs portable electronics without the cost and hassle of batteries. The project engineers should measure human energy potential (and find out how much energy and power a person can reasonable produce). The specifications call for a 1 W radio load to be supported for one hour after a person turns a hand crank for a minute or so. The team should decide how the energy should be extracted (a crank generator, for instance), stored (a capacitor, for example), and converted for use by the electrical load.
9. Automated maximum power conversion system with a lighting load. This demonstration project is intended to show how maximum power transfer applies in modern power systems. A power system has internal inductance, and power transfer is maximized when the load resistance matches the reactance of the inductance. The team should design an automatic system suitable for demonstrating this concept to freshman engineering students. The system might be based on a lighting load, for example, and could show that the lights actually dim when one tries to add more light "beyond" the maximum power point. Feedback control should be set up either to hold the maximum point, or to slowly adjust near it to illustrate the effects.
10. Class D amplifier for 100 W stereo system. Class D amplifiers use switching technology to achieve very high efficiencies. They are common in portable telephone applications, but can even apply to high-fidelity stereo equipment. The objective is to use a Class D circuit and achieve 90% efficiency for a 100 W audio amplifier, yet fit the entire amplifier into a volume on the order of 5 cubic inches. the team should try to obtain very low THD (distortion).
11. Audio modulation of motor drive for noise cancellation. Noise cancellation is an important current topic in controls. Modern electronic motor drives tend to generate acoustic noise because they create audio-frequency vibrations within a motor. However, the acoustic noise actually represents an added degree of freedom for the system. In this project, the objective is to use the acoustic "noise" deliberately to cancel out bearing noise, fan noise, and other audio interference from the motor. This would result in a "self-cancelling" motor noise system, and a very quiet motor without the need for separate loudspeakers or amplifiers.
12. High-fidelity personal amplifier powered by a single battery. In this project, a high-efficiency class-D amplifier suitable for driving either stereo headphones or a small pair of computer speakers is to be built. The primary objective is high efficiency, so that the amplifier will operate as long as possible. The circuit should work from a single 1.5 V supply, in order to allow a single AA battery to do the job.
13. Uninterruptible battery backup for personal computer. In this project, a converter is to be designed to take energy from a 12 V battery and convert it to a dc level suitable for direct connection just after the input rectifier in a PC power supply. It is connected through a diode, and provides power whenever the input ac line drops or is lost.
14. Dc-dc converter for automotive power of certain electronics. This seeks to convert power from an autonotive source (at about 10 to 15 V) to isolated high-quality power suitable for a camcorder or a laptop computer. Typical camcorder specs are 10 V +- 2% with low ripple. Isolation is important, since it prevents any grounding problems.
15. Universal ac converter. This project seeks to help interface international products. The input can be switched for either 220 V, 50 Hz or 120 V, 60 Hz. The output also can be either of these, at levels up to 500 W. A rectifier-inverter architecture is suggested.
16. Multi-output power supply for a combined electronic application. This is a power supply with multiple isolated outputs for use in circuit design. Suggested output levels are 5 V at up to 20 W, +12 V at up to 12 W, -12 V at up to 12 W, -5 V at up to 5 W, 24 V at up to 6 W, +5 V at up to 10 W, 48 V at up to 10 W, and 13.8 V at up to 15 W for battery charging. The input can either be rectified from an ac line or developed from a 12 V battery.

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