Energy Recovery and Efficiency Improvement of High Voltage Power Supply for Dielectric Elastomer Actuator
Dielectric elastomer actuators are a class of soft actuators that convert electrical energy into mechanical motion through the deformation of an elastomeric material under electrostatic pressure. These actuators require high voltage, typically several kilovolts, to generate sufficient electrostatic pressure for meaningful deformation. The high voltage power supply must efficiently charge and discharge the actuator capacitance, and energy recovery during discharge can significantly improve the overall efficiency.
Dielectric elastomer actuators consist of a thin elastomer film coated with compliant electrodes on both surfaces. When a voltage is applied between the electrodes, the electrostatic attraction between the opposite charges on the electrodes compresses the film thickness and expands it area. This deformation can be used to produce linear or rotary motion, depending on the actuator geometry.
The electrostatic pressure is proportional to the permittivity of the elastomer and the square of the electric field. For typical elastomers with relative permittivity around three, achieving pressures of tens of kilopascals requires electric fields of tens of megavolts per meter. For film thicknesses of tens to hundreds of micrometers, the required voltages are several kilovolts.
The actuator behaves electrically as a variable capacitor. The capacitance depends on the electrode area and the film thickness, both of which change during actuation. As the actuator deforms, the capacitance increases. The electrical energy stored in the capacitance is proportional to the capacitance and the square of the voltage.
During charging, energy is transferred from the power supply to the actuator. The actuator capacitance stores electrical energy and converts some of it to mechanical work. The mechanical work appears as the force times displacement of the actuator. The energy conversion efficiency depends on the actuator design and the driving waveform.
During discharge, the stored electrical energy must be removed from the actuator. In conventional driving, this energy is dissipated in resistors or returned to the power supply through dissipative paths. This dissipation represents a significant energy loss, particularly for applications with frequent actuation cycles. Energy recovery circuits can capture this energy and store it for reuse.
Energy recovery approaches include resonant transfer and active conversion. Resonant transfer uses an inductor to create a resonant circuit with the actuator capacitance. The energy oscillates between the capacitor and inductor, and can be transferred to a storage capacitor through appropriate switching. This approach is efficient but requires careful timing of the switches.
Active conversion uses a power converter to transform the voltage and transfer energy. A bidirectional converter can both charge the actuator from a supply and discharge the actuator back to the supply. The converter must handle the high voltage and the variable capacitance of the actuator. The efficiency of the converter determines the energy recovery efficiency.
The overall efficiency of the actuator system includes the power supply efficiency, the energy recovery efficiency, and the electromechanical conversion efficiency. The power supply efficiency affects the charging energy cost. The recovery efficiency affects the energy cost of subsequent cycles. The electromechanical efficiency affects the mechanical work output.
Optimization of the driving waveform can improve efficiency. Constant voltage driving maintains the voltage during the actuation stroke. Constant charge driving maintains the charge during the stroke, with the voltage varying as the capacitance changes. Each approach has different energy characteristics and may be preferred for different applications.
The power supply design must address the high voltage requirements, the variable capacitive load, and the bidirectional energy flow. The voltage rating must be sufficient for the maximum operating voltage with margin for transients. The current capability must be sufficient for the desired charging rate. The control must adapt to the varying capacitance during actuation. The bidirectional capability must handle both charging and discharging efficiently.
