New modifications of a Bennet doubler circuit-based electrostatic vibrational energy harvester

In this work, theoretical and experimental studies of the conditioning circuit based on the Bennet doubler with a power source in a variable capacitor branch having one, two and three variable capacitors are carried out for electrostatic vibrational energy harvesters (e-VEHs). Analytical expressions for evaluation of the e-VEH conditioning circuit main parameters are derived. All three modifications of the conditioning circuit have two operation modes: autostabilization and the mode of unlimited capacitors charge and voltage growth. The change between the operation modes for one-, two- and three-capacitor circuits with switches takes place when the maximal-to-minimal capacitance ratio eta is equal to 2, 1.618 and 1.414, respectively. For e-VEHs with switches in the autostabilization regime, a three-capacitor circuit will be the most efficient when the capacitance modulation depth eta is less than 1.414, a two-capacitor circuit will be the most efficient when 1.414 < eta < 1.618, and, for 1.618 < eta < 2, the most efficient will be a one-capacitor circuit. In the steady-state autostabilization mode, the saturation voltage will be greater than the primary voltage source V-0 if the capacitance modulation depth eta is greater than 1.5, 1.366 and 1.302 for the circuit with one, two and three variable capacitors, respectively. The use of diodes instead of switches in the circuits results in the decrease of saturation voltage and leads to the increase of the critical values of eta(cr) when the change between the operation modes occurs. As the diode inverse currents increase, the effect of the saturation voltage reduction in the autostabilization mode becomes stronger and can even lead to the circuit nonoperabilities. The employment of the Bennet doubler based conditioning circuit modifications considered here enables solving its two main problems: operation only for the capacitance modulation depth more than 2 and the uncontrolled capacitors charge and voltage growth. It should be noted that the observed two conditioning circuit operation regimes will be also inherent for electret vibrational microgenerators and for microgenerators based on using electrodes with materials having different work functions. In addition, the considered two- and three-capacitor circuits make it possible to use e-VEHs at lower values of an external mechanical force or with greater stiffness of spring suspensions minimizing the pull-in effect probability. (C) 2019 Elsevier B.V. All rights reserved.