High Efficient Power Electronic Converter for new Generator Technology

This PhD dissertation summarizes the experience accumulated over three-years of research on Dielectric ElectroActive Polymer (DEAP) generators; conducted within the seventh Work-Package (WP7) framework of Innovation Fund Denmark e15 million project ‘Highly efficient low cost energy generation and actuation using disruptive DEAP technology ’ (Højteknologifonden J.nr. 009-2011-2). In particular, WP7 primary goal was to investigate the degree of high-efficient, cost-effective, large-scale, potential applicability of Danfoss PolyPower R © A/S DEAP generators to wave energy harvesting applications, due to the latter one’s direct energy conversion feature and prominent low-speed performance. To that end, and after a brief introduction of Danfoss PolyPower R © A/S DEAP technology, a meticulous and precise electromechanical model of a DEAP generator, accounting for both the visco-hyperelastic characteristics of the elastomer as well as the latter one’s stretch-dependent capacitance, was designed, tuned via merely mechanical experiments and assessed via direct juxtaposition with actual experimental data, under all distinct energy harvesting cycles; namely the Constant Charge (CC), Constant Voltage (CV) and Constant E-field (CE). In addition, a first complete energy harvesting system, i.e. demo#0, was build to facilitate the conduction of experimental work on several mechanically inphase co-cycled DEAP generators. Post the establishment of an appropriate comparative benchmark, the DEAP generators energy harvesting cycles were, for the first time, experimentally outlined and compared, by means of energy gain, energy harvesting efficiency and energy conversion efficiency, by employing a typical non-isolated bidirectional half-bridge buck-boost converter. In a nonpareil demo#0 energy harvesting experiment, mechanical energy was successfully converted into electrical one with a 3.5 % energy conversion efficiency. Yet, and as demonstrated in demo#0 experiments, great challenges are imposed on the power electronic converter design, by the necessity for bidirectional energy flow in an energy harvesting cycle, under high step-up and high step-down voltage conversion ratios, accompanied by low-average but relatively high-peak currents; let alone that the effective operational range of the latter one is usually limited by the lack of commercially-available, high-efficient, high-voltage, low-power switches. Hence, and towards the establishment of such a prominent power semiconductor device, the gate balancing core stacking technique was revisited and a new design specification for its transformer interwinding capacitance was derived, enabling the serialization of low-power MOSFETs. Assuredly, besides enabling the out-of-phase co-cycling of several DEAP generators, increasing the utilization factor of the infrastructure input mechanical energy by 86.8 %, demo#1 drove the DEAP generators at high E-field strength values, by employing a power electronic converter prototype, based on a i string of three (3) off-the-shelf non-matched non-thermally-coupled MOSFETs. Demo#1 achieved energy conversion efficiency of 7 %, characterized by energy density of 2 J/kg of active material, which was at date a world-first for an active power electronic converter coupled to such a sizeable DEAP generator. Unfortunately, all voluminous DEAP generators, designed to accommodate the operation of the final demonstrator, i.e. demo#2, towards the scaling-up of the energy harvesting system, experienced early destructive electrical breakdowns and they were thus rendered inoperative. However, new, smaller scale DEAP generators were manufactured, validating the applicability of demo#2 novel converter to DEAP-generator-based energy harvesting systems. Indeed, founding its up to 3000 V operation on the revised gate balancing core technique, the corresponding tapped-inductor buck-boost converter demonstrated highefficient bidirectional energy flow, above 94 % for the buck function and 92 % for the boost function, under high step-up and high step-down voltage conversion ratios, accompanied by low-average but relatively high-peak currents. Finally, this PhD dissertation is concluded with a judicious perspective analysis on the DEAP technology and its potential large-scale commercialization, highlighting key activities in areas such as the DEAP film research and development and the DEAP film production, as well as trends in modern power electronic converters and semiconductors; materializing WP7 years of experience and collaboration with seven (7) industrial partners and three (3) universities.