John Norton Park

A dual mode forward/flyback converter

This paper presents a single transistor dc-dc converter that combines both forward and flyback action. The resulting circuit is ohmically isolated and can operate over a wide range of input-to-output voltage ratios. An analysis of the circuit indicates that the forward and flyback portions of the circuit interact to produce three distinct regions of operation. With the design information presented, the circuit can be tailored to utilize the desirable characteristics of either converter action for a specific application. The dynamics of the dual mode circuit are modeled by means of the state-space averaging technique. An ac-dc regulator that takes advantage of the wide operating range of the dual mode circuit operating off the ac line, with only a small input filter, is described.

Micro-Electromechanical-System (MEMS) based switches for power applications

A new system for switching electrical power using Micro-Electromechanical-Systems (MEMS) is presented. The heart of the system utilizes custom designed MEMS switching device arrays that are able to conduct current more efficiently and can open orders of magnitude faster than traditional macroscopic mechanical relays. Up to now, MEMS switches have been recognized for their ability to switch very quickly due to their low mass, but have only been used to carry and switch very low currents at extremely low voltage. However, recent developments have enabled suppression of the arc that normally occurs when the MEMS switch is opened while current is flowing. The combination of the arc suppression with the MEMS switch arrays designed for this purpose enables a breakthrough increase in current and voltage handling capability. The resultant technology has been scaled to handle many Amps of current and switch 100s of volts. Such current and voltage handling capability delivers improved energy efficiency and the capacity to handle fault current levels that are encountered in typical AC or DC power systems. Fault current interruption takes place in less than 10 microseconds, almost regardless of the prospective fault current magnitude. The properties of the MEMS switch arrays allow the switching mechanism to operate at temperatures in excess of 200 deg. C. The switches also have a vibration tolerance in excess of 1000G. The combination of fast MEMS switching speed, optimized current and voltage handling capacity of the switch arrays, the arc suppression circuitry and optimized sensing and control enable a single sensing, control and switching system to operate in a small fraction of a millisecond. This paper will present the basic physics of the MEMS switches together with recent advances that enable the technology. Some illustrative examples of the ways the devices may be used to provide protection and control within electrical systems will also be presented.

Power switch system based on Microelectromechanical switch

A power switching system combining a MEMS (Microelectromechanical systems) switch and an arc suppression circuit has been developed. The system, using a single 3mm × 3mm MEMS switch die coupled with protection electronics, has been demonstrated to switch both resistive loads and inductive loads to a peak power of around 800W. The entire opening and closing operations are completed in a few microseconds, orders of magnitude faster than mechanical relays and nearly as fast as solid state devices. The MEMS switch is an array of microscale cantilevered relays that are electrostatically opened and closed in microseconds. A pulsed diode bridge protection circuitry is used in conjunction with the MEMS switch to open and close the energized contacts without damaging the contacting surface and without generating an arc. This MEMS based power switching system is scaled in both series and parallel to increase the switched voltage and current capability respectively. MEMS switch based power switching has the capability to enable both current limiting and arc free switching, characteristics that can significantly reduce dangerous downstream fault energy for AC and DC protection and distribution applications.

A chopper converter for electric vehicle propulsion battery charging and propulsion motor field excitation

A dual mode chopper power converter circuit capable of providing the separate functions of on-board propulsion battery charging and propulsion motor field excitation under microcomputer command is described. Normal charge mode delivers 24 A until a predetermined voltage is reached (when connected to an appropriate 115 V service outlet) whereupon current is tapered at constant battery voltage. Underway, the chopper circuitry supplies propulsion motor field current in the range of 2 to 11 A (field weakening). The chopper power circuit employs a fast power Darlington transistor and diode packaged in modular form specifically developed for the electric vehicle application and driven by a special isolated proportional base drive circuit, providing minimum storage time and high efficiency. The power circuit uses two diodes and a field reversing relay to satisfy the topology requirements for both the battery charging and field excitation modes. The selection of modulation schemes and control strategy particular to the present application are discussed.