Dynamic Impedance Matching for a Variable Reluctance Energy Harvesting Application with Constrained Space

Variable Reluctance Energy Harvesters (VREH) are scavenging devices that provide a sinusoidal voltage of variable frequency and have an inductive output impedance. Thus, to maximize power extraction, a variable capacitor is required to perform impedance matching at each frequency. For space-constrained applications, the technology of the capacitor plays an important role, since it determines the physical size and possible capacitance deviations in the presence of high voltages. In this paper, an adaptive capacitance circuit based on a custom capacitor array is designed for VREH applications with space constraints. A modeling methodology that considers the capacitance changes of class II ceramic capacitors under high voltages is proposed. With this technology, a 91% reduction in capacitor volume is achieved when compared to solutions that use film capacitors. The system is tested in a real setup obtaining output power levels that are in accordance with the simulated model.