Real-time impedance measurement and frequency control in an automotive plasma ignition system

Abstract

We describe a method for optimizing plasma matching in a pulsed 2.45 GHz automotive plasma ignition system. The large-signal impedance into the spark plug feed network is continuously monitored, and the frequency for optimal match is estimated and changed in less than 100 μs to accomodate changes in gas pressure. This method is also used to “learn” the frequency response of the system to compensate for initial manufacturing variations, ageing, and temperature-related changes in the feed network and spark plug. We describe the performance of a system using a modified coaxial transmission line resonator (CTLR) spark plug operating at pressures from 0.1 to 1 MPa, and discuss a low-cost implementation.