A multi-frequency induction heating system for a thermally triggered gel polymer dynamic vibration absorber

Abstract

Since its invention in the early part of the twentieth century, the dynamic vibration absorber (DVA) has played an important role in vibration suppression. In its simplest form, a dynamic vibration absorber is a mechanical network consisting of a spring, a mass and sometimes a damping element. These networks have been used to successfully reduce vibrations in buildings, bridges and imbalances in rotating machinery. Because these absorbers are most effective at attenuating disturbance near or at their self-resonant frequency, there is on-going research to develop semi-active DVA's capable of adjusting their natural frequency in real time. A new semi-active DVA is described that can modify its moment of inertia, and therefore its natural frequency, by using a collection of thermo-responsive gel polymers. This thesis develops an induction heating system that is suitable for noncontact heating of these gel polymers. The proposed heating system addresses the more general problem of controllable power delivery to multiple induction targets driven by a single induction coil. The focus of this work divides neatly between the design of the induction heating targets and the necessary power electronics. Targets that have preferential heating characteristics at particular frequencies are developed and analyzed. These targets include both resonant RLC circuits as well as conductors whose critical dimensions are much smaller than their associated skin depth. Extensive modeling of these targets is carried out and experimental results are presented. The ability to "selectively" heat these induction targets requires a power supply that can generate a sinewave with enough purity to not excessively heat unwanted targets.

(cont.) A 1 kW multilevel inverter topology is presented as an excellent compromise between total harmonic distortion and efficiency for this application. Referred to as the Marx inverter, this circuit can maintain its multilevel nature during real power transfer without the need for an external voltage balancing circuit or complicated control- unlike more traditional multilevel topologies. In addition to the gel vibration damper, portions of this work stand to benefit both medical and industrial venues where a desired temperature profile must be generated in a noncontact manner.