Analysis of Sliding-Mode Controlled Impedance Matching Circuits for Inductive Harvesting Devices

A sea-wave energy harvesting, articulated device is presented in this work. This hand-made, wooden device is made combining the coil windings of an array of three single transducers. Taking advantage of the sea waves sway, a linear oscillating motion is produced in each transducer generating an electric pulse. Magnetic fundamentals are used to deduce the electrical model of a single transducer, a solenoid-magnet device, and after the model of the whole harvesting array. The energy obtained is stored in a battery and is used to supply a stand-alone system pay-load, for instance a telecom relay or weather station. To maximize the harvested energy, an impedance matching circuit between the generator array and the system battery is required. Two dc-to-dc converters, a buck-boost hybrid cell and a Sepic converter are proposed as impedance adaptors. To achieve this purpose, sliding mode control laws are introduced to impose a loss free resistor behavior to the converters. Although some converters operating at discontinuous conduction mode, like the buck-boost converter, can exhibit also this loss free resistor behavior, they usually require a small input voltage variation range. By means of sliding mode control the loss free resistor behavior can be assured for any range of input voltage variation. After the theoretical analysis, several simulation and experimental results to compare both converters performance are given.