Switch-mode High Voltage Drivers for Dielectric Electro Active Polymer (DEAP) Incremental Actuators

Abstract

Actuators based on dielectric electro active polymers (DEAPs) have attracted special attention in the recent years. The unique characteristics of DEAP are large strain (5-100%), light weight (7 times lighter than steel and copper), high flexibility (100,000 times less stiff than steel), low noise operation, and low power consumption. DEAP actuators require very high voltage (2-2.5 kV) to fully elongate them. In general, the elongation or stroke length of a DEAP actuator is of the order of mm. DEAP actuators can be configured to provide incremental motion, thus overcoming the inherent size-to-stroke implications of conventional linear actuators, where the stroke is limited by their size. In incremental mode, DEAP actuators are several orders of magnitude shorter in their length compared to the stroke/elongation they provide. The dissertation presents design, control and implementation of switch-mode high voltage DC-DC converters for driving the DEAP based incremental actuators. The DEAP incremental actuator technology has the potential to be used in various industries, e.g., automotive, space and medicine. The DEAP incremental actuator consists of three electrically isolated and mechanically connected capacitive actuators. To accomplish the incremental motion, each capacitive actuator needs to be independently charged (from 0 V to 2.5 kV, within 40-60 ms) and discharged (from 2.5 kV to 0 V, within 40-60 ms) by a high voltage bidirectional DC-DC converter. This thesis investigates a low input voltage (24 V) and high output voltage (0-2.5 kV) bidirectional flyback converter toplology for driving the capacitive actuators. Due to very high step-up ratio requirement, the transformer design becomes very complex for charging and discharging the capacitive load at very high voltage. Hence, the thesis particularly focuses on design and optimization of high voltage flyback transformer. The energy efficiency of the bidirectional flyback converter is optimized using a proposed new automatic winding layout (AWL) technique and a comprehensive loss model. Different transformer winding architectures such as noninterleaved and non-sectioned, interleaved and non-sectioned, non-interleaved and sectioned, and interleaved and sectioned have been investigated and implemented. A digital control technique to achieve the valley switching (variable frequency control) during both charge and discharge operations in a bidirectional flyback converter, has been proposed and implemented. Using the proposed digital control scheme, the converter achieved good charge and discharge energy efficiencies in the entire output voltage range, and was able to charge and discharge the capacitive load with in a minimum time period. This digital control scheme is very useful to control and change the charging and discharging profiles of the three high voltage drivers. The DEAP incremental actuator concept has been designed, built and tested. It is demonstrated that the DEAP is feasible for providing incremental motion with variable speed and bidirectional motion. The system integration has been performed by driving the three capacitive actuators (each having a capacitance of 400 nF) up to a maximum voltage of 1.8 kV. Each high voltage driver is able to charge and discharge the 400 nF capacitive actuator within 23 ms and 36 ms, respectively. Finally, a new bidirectional flyback converter topology with multiple series connected outputs is proposed. A theoretical comparison showed that the proposed converter could improve the overall energy efficiency, lower the cost and reduce the volume of high voltage driver. Key words: high voltage, switch-mode power converters, capacitive loads, flyback, transformer design, energy efficiency, dielectric electro active polymer actuators, digital control.