Nihal Kularatna

Rechargeable batteries and their management

With the consumer electronics, electric vehicles (EVs) and portable product markets growing, design of battery packs can challenge the designer because they are no longer a simple configuration of cells. They could contain many safety features, intelligence, energy aware models and selective batteries feeding the host product, serial data communication, and even recycling suggestions. In all these situations, a simple concept which should be kept in mind by designers is that batteries are like human beings, and they need care and intelligence.

Surge Capability Testing of Supercapacitor Families Using a Lightning Surge Simulator

Supercapacitors (SCs) are capable of storing energy in the range of fractional joules to several thousands of joules despite their lower dc voltage ratings. Farad-order capacitances combined with milliohm-order equivalent series resistances provide time constants ranging from fractional seconds to seconds. Given these time constants, compared to the time durations of power line transients in the range of a few microseconds to several hundreds of microseconds, these devices may be able to withstand short-duration surges with energy values specified in IEEE C62-XX series, IEC 61400-4-5, and similar standards. However, there is little or no manufacturer datasheet information on these aspects. This paper provides details of an automatic tester interfaced with a lightning surge simulator, a test procedure, and summarized test data on three different families of SCs. The test data set provides some valuable insight in estimating the capabilities of these new SC families to withstand surges and transients, which, in turn, could lead to nontraditional applications.

A low frequency supercapacitor circulation technique to improve the efficiency of linear regulators based on LDO ICs

Linear regulators have output specifications far superior to switch-mode techniques, except for the overall efficiency. This efficiency limitation can be overcome by applying a very low frequency supercapacitor circulation technique at the input side of a low dropout regulator IC. The technique was proven in 12V to 5 V versions, and, can be easily applied to other power supplies such as 5 to 3.3V or 5 to 1.5V versions required by various processors. The paper outlines the concepts and experimental results related to this technique. With the commercial LDO chips available with output current ratings up to 10A, and, thin profile supercapacitors available are with DC voltage ratings from 2.3V to 5.5V, the technique assists developing medium current linear regulators which could compete with present day switch-mode power supplies in efficiency and compactness, maintaining the superior output specifications of a linear regulator.

Design approaches to supercapacitor based surge resistant UPS techniques

Time constants of supercapacitors are in the range of 100mS to tens of seconds compared to the time durations of power line transients, which are usually within a few hundred microseconds. Therefore supercapacitors should withstand short duration surges with energy values specified in IEEE C62-41 series and IEC 61400-4-5 and similar standards. After experimentally confirming this useful property of supercapacitors, new topologies for supercapacitor based surge-resistant uninterruptible power supplies were developed. Paper summarizes the approach to developing suitable topologies for surge-resistant UPS systems based on supercapacitor energy circulation techniques, despite the lower continuous DC voltage ratings of commercial supercapacitors.

Analysis and Design Aspects of a Series Power Semiconductor Array with Digital Waveform Control Capability for Single Phase AC Voltage Regulators and Other Applications

A series connected power semiconductor array, with digital control capability could be used for developing single phase AC regulators or other applications such as AC electronic loads. This technique together with an ordinary gapless transformer could be used to develop a low cost AC voltage regulator (AVR) to provide better or comparable specifications with bulky ferro-resonant AVR types. One primary advantage of the technique is that digital control can be used to minimize harmonics. Commencing with a review of AC voltage regulator techniques for single phase power conditioning systems, an analysis and design aspects of this technique is presented with experimental results for AVRs. Guidelines on how to utilize the technique in a generalized basis is also summarized together with a summary of a technique for achieving harmonic control.

Protection Systems for Low Voltage, Low Power Systems

Utilities realize that different types of customers require different levels of reliability, and make every effort to supply disturbance-free power. However, normal occurrences, most of which are beyond control (such as adverse weather, vehicles running into poles and equipment malfunction) make it impossible to provide disturbance-free power 100 percent of the time. In addition to these external disturbances, sources within buildings, such as switching of heavy equipment loads, poor wiring, overloaded circuits, and inadequate grounding, can cause electrical disturbances. Many of these power disturbances can be harmful to electronic equipment. Power disturbances can cause altered or lost data and sometimes equipment damage which may, in turn, result in lost production, scheduling conflicts, lost orders, and accounting problems. There are methods and devices available to prevent these disasters from happening. Protective devices range from those providing minimal protection to those that construct a new power source for critical loads, converting the standard “utility grade power,” which is adequate for most equipment, into “electronic grade power” required by some critical loads.

Off-the-Line Switchmode Power Supplies

The rapid advancement of microelectronics in recent decades has created a necessity for the development of sophisticated, efficient, light weight power supplies which have a high power-to-volume (W/in 3 ) ratio with no compromise in performance. The high-frequency switching power supply meets these demands. Recently it has become the prime powering source in the majority of modem electronic systems. The trends associated with the switchmode power supplies for the electronic products and systems are to reach direct off-the-line design approach, higher frequencies be utilized, and output rating/volume being increased and minimizing the components and increasing reliability. This chapter discusses the basic blocks of direct off line SMPS units and the newer trends in technology such as distributed DC power. Introduction to magnetic components, use of magnetic amplifiers, and the modem trends in high frequency capacitors, are also introduced.

Power Integrated Circuits, Power Hybrids, and Intelligent Power Modules

From their humble beginnings as audio amplifiers, Power Integrated Circuits (PIC) are now moving towards a more prominent role in many power electronic systems. Today an increasing number of applications make use of these devices. Usually power integrated circuits are designed for specialized applications in the lower power range. Their concept represents the natural continuation of IC evolution, realizing a complete system on one chip. The power limit arises from the amount of heat that can be dissipated by a silicon surface of approximately one square centimeter in size. When most of the silicon real estate is devoted to power devices, the chips are usually called “smart power.” However, the terminology applied is more often based upon institutional rather than technical reasons. What constitutes a power integrated circuit varies from manufacturer to manufacturer, depending on their product portfolios and point of view; that is, whether they approach the market from a discrete-transistor or an IC perspective. Some define power ICs by their functions—whether the IC actually includes the power transistor itself; others, by the ICs voltage and current levels, and still others by the ICs general involvement in controlling power.