John G. Kassakian

Distributed interleaving of paralleled power converters

This paper introduces a distributed approach to interleaving paralleled power converter cells. Unlike conventional methods, the distributed approach requires no centralized control, automatically accommodates varying numbers of converter cells, and is highly tolerant of subsystem failures. A general methodology for achieving distributed interleaving is proposed, along with a specific implementation approach. The design and experimental verification of a 50 kHz prototype system is presented, and quantitative performance comparisons are made between synchronized clocking, independent clocking, and interleaved clocking of the converter cells. The experimental results corroborate the analytical predictions and demonstrate the tremendous benefits of the distributed interleaving approach.

Automotive electrical systems circa 2005

Demands for better fuel economy and more electric power are driving cars to multiple higher voltages. In the next 10 years the electrical systems in some luxury automobiles will be so changed as to be almost unrecognizable. Although they will doubtless employ the old reliable 12 V lead-acid battery, their loads will be driven by a variety of voltages, both AC and DC, perhaps derived from a single AC distribution network. Designers will be able to match voltages to individual loads for best efficiency and performance-lights perhaps at 6 V AC, electronics at 5 V DC, active suspension at 350 V DC, and motors and actuators at 42 V DC. The digital signals controlling those loads will be carried by a separate communications network. The enabling technology for these advances are semiconductors. The authors discuss the future development of automobile electrical systems.

Automotive electrical systems-the power electronics market of the future

The automobile is undergoing a revolution in the design of its electrical system. This is the result of increasingly sophisticated engine and body controls, as well as the introduction of new, electrically controlled functions. The main electrical bus of the future will be 42 V, and it will be buffered by a 36 V battery. As many devices and electronic control units require voltages different from 42, conversion from the 42 V bus to these other voltages will be necessary. Some anticipated features, such as electromechanical engine valves, will demand both conversion and sophisticated control at power levels in the 2 kW to 10 kW range. These, and other developments in automotive engineering, are promising to create a vital and challenging new market for power electronics in the next decade.

Issues related to 1-10-MHz transformer design

Issues related to the design of high-frequency transformers are discussed. An analysis of skin and proximity effects in the conductors and measurements of permeability and hysteresis loss in the magnetic material are combined in a computer-assisted study of the relationships between size, efficiency, and frequency. Experimental data are presented for a prototype transformer. >

High-frequency high-density converters for distributed power supply systems

The technical challenges of developing very-high-power-density power supplies operating of switching frequencies in the vicinity of 10 MHz are considered. Primary applications are in the computer, telecommunications, and automotive industries. It is shown that a successful development requires simultaneous considerations of topologies, materials, devices, control, electromagnetic interference, manufacturing, and packaging. Some results of work being done at MIT are presented, including a new integrated power MOSFET/driver, high-field frequency magnetic material characterizations, and high-frequency synchronous rectifiers. The design and performance of a 50-W 3.5-MHz converter is described. >

Two-dimensional tungsten photonic crystals as selective thermal emitters

This paper presents theory, design, fabrication, and optical characterization of two-dimensional (2D) tungsten (W) photonic crystals (PhC) as selective thermal emitters. We use the photonic band gap of a 2D W PhC, radiating out of a plane of periodicity, to design a selective infrared thermal radiation source that exhibits close to blackbody emittance near the the band gap wavelength and relatively sharp cutoff for wavelengths above the band gap. In addition, we present simple design rules and detailed simulation results for several representative geometries. Microfabrication steps are also presented. Finally, we present detailed experimental results of the optical characterization of three fabricated prototypes that exhibit good agreement with simulation results.

The future of electronics in automobiles

The present 14 V automotive electrical system will soon become 42 V. New electrical features and electrification of present mechanically driven functions will provide commercial opportunities for a new high volume application of power electronics. Cost and the thermal environment present difficult challenges to device designers. SiC is shown as a promising material for this environment. A new high efficiency power supply design using the existing automotive alternator is presented.

Automotive electronics power up

People are spending increasing amounts of time in their cars. As a result, automakers are equipping vehicles with more and more power-draining creature comforts as selling points. Cup holders have given way to navigational systems, separate driver and passenger climate controls, and surround sound and compact disk players. But performance and handling improvements under the hood, such as dynamic stability controls, electronic suspensions, and precision-controlled fuel injection, also need power from the 14-V system featured in todays cars. To handle the situation, automotive manufacturers and suppliers are embracing a 42-V standard for system voltage as they design new products. The challenge for designers, however, is that the cost of the new electronics cannot prohibit the economic production of automobiles. This hurdle must be cleared before cars with 42-V systems will become available to consumers. The paper discusses why 42 Volts was chosen, how many batteries will be needed, control systems, start/stop operation, and the influence of silicon devices on cost.

Sampled-data modeling and digital control of resonant converters

A sampled-data model to describe the dynamics of large signals and of small perturbations away from a cyclic steady state is developed. Associated transfer functions are obtained. The application of the model is illustrated by correlating the analysis with simulation results obtained for a series resonant DC/DC power converter. A discrete-time microprocessor-based controller, designed using the aforementioned dynamic model, has been built and tested using a simulation for a series-resonant DC/DC converter set up on the Massachusetts Institute of Technology Parity Simulator. The control methods implemented are state feedback and periodic output feedback, each designed to achieve a specified set of closed-loop poles. The controller has been implemented using the Parity Simulator generalized controller. Results of the closed-loop response showed an improvement over the open-loop response. In addition, the effect of the microprocessor computation delay on the closed-loop dynamics of the converter is investigated. >

Analysis of three-phase rectifiers with constant-voltage loads

This work presents a quantitative analysis of the operating characteristics of three-phase diode bridge rectifiers with AC-side reactance and constant-voltage loads. We focus on the case where the AC-side currents vary continuously (continuous AC-side conduction mode). This operating mode is of particular importance in alternators and generators, for example. Simple approximate expressions are derived for the line and output current characteristics as well as the input power factor. Expressions describing the necessary operating conditions for continuous AC-side conduction are also developed. The derived analytical expressions are applied to practical examples and both simulations and experimental results are utilized to validate the analytical results. It is shown that the derived expressions are far more accurate than calculations based on traditional constant-current models.