Energy Recovery and Efficiency Improvement of High Voltage Power Supply for Dielectric Elastomer Actuator
Dielectric elastomer actuators are soft, compliant actuators that convert electrical energy to mechanical motion through the deformation of elastomer films under electric field. The actuators require high voltage to achieve significant deformation, with voltages typically in the kilovolt range. The energy consumption includes both the energy that performs mechanical work and the energy stored in the capacitance of the actuator. Energy recovery techniques can capture and reuse the stored energy, significantly improving the efficiency of the actuator system.
Dielectric elastomer actuators consist of a thin elastomer film coated with compliant electrodes on both surfaces. When voltage is applied, electrostatic pressure compresses the film thickness and expands the area, producing mechanical deformation. The deformation can be used for various applications including soft robotics, adaptive optics, and energy harvesting. The actuation requires high voltage because the electrostatic pressure scales with the square of the electric field.
The actuator behaves as a variable capacitor, with capacitance that changes as the film deforms. When voltage is applied, the capacitance charges, storing electrical energy. When the actuator deforms, the capacitance changes, and the stored energy changes accordingly. When voltage is removed, the stored energy is discharged. The energy flow includes both the energy that performs mechanical work and the energy that charges and discharges the capacitance.
Energy consumption analysis distinguishes the mechanical work energy from the stored energy. The mechanical work equals the product of the electrostatic pressure and the deformation. The stored energy equals half the product of the capacitance and the voltage squared. During actuation, energy flows from the power supply to charge the capacitance, and some of this energy converts to mechanical work. During relaxation, energy flows from the actuator back to the power supply or is dissipated.
Conventional power supplies dissipate the recovered energy during discharge. When the actuator voltage is reduced, the stored energy must be removed from the actuator. Simple resistive discharge dissipates this energy as heat, wasting the recovered energy. The dissipation reduces the overall efficiency, particularly for actuators that cycle frequently.
Energy recovery circuits capture the stored energy during discharge and return it to the power supply or storage. The recovery circuit may use inductive elements to transfer energy from the actuator capacitance to a storage capacitor or the input supply. The energy recovery can significantly reduce the net energy consumption for cyclic actuation, improving the efficiency.
Bidirectional power converters enable energy flow in both directions between the actuator and the supply. The converter can charge the actuator from the supply and can discharge the actuator back to the supply. The bidirectional capability enables energy recovery during the discharge phase. The converter must handle the high voltage and the variable capacitance of the actuator.
Resonant energy recovery uses LC resonance to transfer energy between the actuator and a storage element. The resonant circuit oscillates, transferring energy between the actuator capacitance and an inductor or storage capacitor. The resonance enables efficient energy transfer with minimal loss. The resonant frequency must match the actuator capacitance and the desired transfer time.
Switched capacitor energy recovery uses switched capacitor circuits to transfer energy in discrete steps. The circuit switches the actuator between different voltage levels through intermediate capacitors, stepping the voltage up or down while transferring energy. The switched capacitor approach can achieve high efficiency with appropriate switching timing.
Hydraulic analogy helps understand the energy flow in dielectric elastomer systems. The actuator capacitance is analogous to a hydraulic accumulator that stores energy in compressed fluid. Charging the actuator is like pumping fluid into the accumulator. Discharging is like releasing the fluid. Energy recovery is like capturing the released fluid for reuse rather than dumping it.
Efficiency metrics for dielectric elastomer actuator systems include the energy efficiency, the ratio of mechanical work to electrical energy consumed, and the round trip efficiency, the ratio of energy recovered to energy stored. The efficiency depends on the actuator characteristics, the power supply design, and the operating conditions. Energy recovery can improve the efficiency from tens of percent to over 90 percent for cyclic actuation.
System integration of energy recovery with actuator control requires coordination of the charging, actuation, and recovery phases. The control must sequence the energy flow appropriately for the desired motion profile. The timing must account for the actuator dynamics and the energy transfer characteristics. The integrated system must achieve both the mechanical performance and the energy efficiency goals.
