Microelectromechanical-Systems-Based Switches for Power Applications

A new system for switching electrical power using microelectromechanical 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 amperes of current and switch hundreds of volts. Such current and voltage handling capability deliver 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 μs, 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 °C . The switches also have a vibration tolerance in excess of 1000 G. 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 enables 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 that the devices may be used to provide protection and control within electrical systems will also be presented.

I. Introduction

Today's fault protection systems use breakers or switches that open circuits after a fault is detected; however, the rapidly rising current is only interrupted after significant energy has already traveled through the fault interrupter. Such power surges often damage generators, distribution systems, conductors, and loads and create hazard to personnel. Very fast fault current detection and interruption is needed to mitigate the damage caused by excessive fault currents. The microelectromechanical-systems (MEMS)-based microsecond arcless interruption can deliver the interruption speed required to mitigate damage to conductors and loads, as well as to the switching device. Electrical discharge or arcing across opening mechanical contacts, a phenomenon studied since the advent of electricity [1]–[5], is eliminated through the use of an electronic protection system combined with an ultrafast microscale electrical relay based on MEMS switch [6]–[9] technology. When fault situations occur in electrical power distribution systems, conventional power circuit protection devices, even current-limiting ones, can react too slowly to adequately limit destructive energy dissipation that damages electronic equipment downstream from the fault interrupter. Additionally, even normal-interruption-related discharge plasmas and arc energy can eventually damage the contacts used in breakers and contactors, thereby rendering the devices inoperable.