Current-Limiting Control Strategies in Variable Capacitance Electrostatic Energy Harvesters

Electrostatic energy harvesters (EEHs), especially those employing electroactive polymers, show significant potential to be scaled up into real-world technologies for ambient energy harvesting. Conventional EEH cycles involve rapidly charging and discharging a variable capacitor at specific instants corresponding to maximum and minimum capacitance values. This approach poses two major challenges in practical operation: 1) the precise detection of these extrema is difficult under stochastic inputs, and 2) instantaneous charging demands high peak currents and power, creating significant cost and complexity burdens for large-scale applications. This work proposes control strategies that enable charging and discharging under stochastic excitations while also evaluating the impact of limiting the peak current on the maximum convertible energy. Traditional peak-triggered controls are compared with newly proposed smooth current control methods that use continuous AC-like driving voltages, whose phase is bound to the capacitance. Modelling and experimental results on elastomeric generators show that smooth voltage controls can be implemented in a real-time prediction-free fashion, while competing in performance with peak-triggered controls even under realistic stochastic ambient energy harvesting conditions.