Emmanouil Dimopoulos

Comparison of the dielectric electroactive polymer generator energy harvesting cycles

The Dielectric ElectroActive Polymer (DEAP) generator energy harvesting cycles have been in the spotlight of the scientific interest for the past few years. Indeed, several articles have demonstrated thorough and comprehensive comparisons of the generator fundamental energy harvesting cycles, namely Constant Charge (CC), Constant Voltage (CV) and Constant E-field (CE), based on average theoretical models. Yet, it has not been possible until present to validate the outcome of those comparisons via respective experimental results. In this paper, all three primary energy harvesting cycles are experimentally compared, based upon the coupling of a DEAP generator with a bidirectional non-isolated power electronic converter, by means of energy gain, energy harvesting efficiency and energy conversion efficiency.

Scaling the serialization of MOSFETs by magnetically coupling their gate electrodes

More than twenty years of thorough research on the serialization of power semiconductor switches, like the Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) or the Insulated Gate Bipolar Transistor (IGBT), have resulted into several different stacking concepts; all aiming towards the establishment of a high-efficient, high-voltage, fast-switching device. Among the prevailing stacking approaches lies the gate balancing core technique, which, in its initial form, demonstrated very good performance in strings of high-power IGBT modules, by magnetically coupling their gate electrodes. Recently, a revised version of the technique, introducing an additional design specification for the employed transformer, extended its effective applicability in low and medium power MOSFETs as well. In this paper the scalability of the revised gate balancing core technique is investigated via experiments conducted on a string of three off-the-self, non-matched MOSFETs, installed in an inductively loaded step-down converter. Furthermore, during the string composition and experimental testing, all design milestones related with the scaling-up process of the revised gate balancing core concept are distinctively highlighted and discussed.

Energy harvesting cycles of Dielectric ElectroActive Polymer Generators

Energy harvesting via Dielectric ElectroActive Polymer (DEAP) generators has attracted much of the scientific interest over the past few years, mainly due to the advantages that these smart materials offer against competing technologies, as electromagnetic generators and piezoelectrics. Their higher energy density, superior low-speed performance, light-weighted nature as well as their shapely structure have rendered DEAPs candidate solutions for various actuation and energy harvesting applications. In this paper, a thoroughly analysis of all energy harvesting operational cycles of a DEAP generator, coupled to a non-isolated power electronics converter, is conducted and for the first time experimental results for each one of them are presented.

A tapped-inductor buck-boost converter for a multi-DEAP generator energy harvesting system

Interest on Dielectric ElectroActive Polymer (DEAP) generators has aroused among scientists in recent years, due to the former ones’ documented advantages against competing electromagnetic and field-activated technologies. Yet, the need for bidirectional energy flow under high step-up and high step-down voltage conversion ratios, accompanied by low-average but relatively high-peak currents, imposes great challenges on the design of the employed power electronic converter. On top of that, the shortage of commercially-available, high-efficient, high-voltage, low-power semiconductor devices limits the effective operational range of the power electronic converter. In this paper, a bidirectional tapped-inductor buck-boost converter is proposed, addressing high- efficient high step-up and high step-down voltage conversion ratios, for energy harvesting applications based on DEAP generators. The effective operational range of the converter is extended, by replacing its high-side switch with a string of three serialized MOSFETs, to accommodate the need for high-efficient high-voltage operation. Experiments conducted on a single DEAP generator - part of a quadruple DEAP generator energy harvesting system with all elements installed sequentially in the same circular disk with a 90° phase shift - validate the applicability of the proposed converter, demonstrating energy harvesting of 0.26 J, at 0.5 Hz and 60% delta- strain; characterized by an energy density of 1.25 J per kg of active material.

Serializing off-the-shelf MOSFETs by magnetically coupling their gate electrodes

While the semiconductor industry struggles with the inherent trade-offs of solid-state devices, serialization of power switches, like the Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) or the Insulated Gate Bipolar Transistor (IGBT), has been proven to be an advantageous alternative to acquire a high-efficient, high-voltage, fast-switching device. More than twenty years of research, on the serialization of solid-state devices, have resulted into several different stacking concepts. Among the prevailing ones, the gate balancing core technique, which has demonstrated very good performance in strings of high-power IGBT modules. In this paper, the limitations of the gate balancing core technique, when employed to serialize low or medium power off-the-shelf switches, are identified via experimental results. A new design specification for the interwinding capacitance of the employed transformer is derived to address those limitations, leading to a revised version of the technique. The effectiveness and the applicability of the revised gate balancing core technique are verified, via experiments conducted on a string of two off-the-shelf, non-matched MOSFETs, installed in an inductively loaded step-down converter.

An RCDD snubber for a bidirectional flyback converter

Increased usage of renewable energy sources has boosted the demand for power electronics converters. Indeed, the DC/DC flyback converter is nowadays frequently used in applications where isolation is required, due to its low component count, simple structure and high energy efficiency. One of the major challenges faced in a flyback converter is the excess voltage stress sensed by its semiconductor devices, because of the interrupted current flow through its transformer leakage inductances. In this paper, a high-efficient bidirectional flyback converter, operating in discontinuous conduction mode, is examined with an integrated RCDD snubber. Additionally, experimental comparison where the converter runs with a typical RCD and RCDD snubber network, is done. Experimental results on an IGBT-based bidirectional flyback converter validate the applicability of the RCDD snubber demonstrating energy efficiency above 90%. Furthermore, the operation of the bidirectional converter with the employed snubber is thoroughly analysed and an appropriate mathematical analysis is conducted highlighting all the design specifications of the proposed snubber.

Tvindkraft: Implementing a 500 kW 21-IGBT-based frequency converter for a 1.7 MW wind power conversion system

The 54-meter-high Tvindkraft windmill was built by a group of volunteers during 1975-1978, as an argument for renewable energy sources as well as an argument against nuclear power. At that time it was the worlds biggest windmill. So far, Tvindkraft has been running for 35 years, proving that a well-constructed wind turbine is a sustainable approach to renewable energy utilization. This paper deals with the analysis, simulation, implementation and experimental testing of a new 500 kW 21-IGBT-based frequency converter that will run in parallel with the former 12-Thyristor-based frequency converter to fully utilize the capacity of the windmill. Simulations and experimental results are presented side-by-side to verify the proper functionalities of the frequency converter described in this paper.

Simple DCM or CRM analog peak current controller for HV capacitor charge-discharge applications

This paper presents a simple analog current controller suitable for buck and boost converter topologies. The controller operates in DCM or CRM, depending on the setup. The experimental results are presented to validate the proposed controller functionality for a high voltage capacitor charge-discharge application.

An electromechanical model for a dielectric electroactive polymer generator

Smart electroactive materials have attracted much of the scientific interest over the past few years, as they reflect a quite promising alternative to conservative approaches used nowadays in various transducer applications. Especially Dielectric ElectroActive Polymers (DEAPs), which are constantly gaining momentum due to their superior low-speed performance, light-weighted nature and higher energy density when compared with competing technologies. In this paper an electromechanical model for a DEAP generator is presented, accounting for both the visco-hyperelastic characteristics of the polymer material, as well as the later ones experimentally determined stretch-capacitance dependence. Apart from the visco-hyperelastic model validation via purely mechanical experiments, the models electromechanical coupling is verified as well, via experiments conducted under all three distinct energy harvesting cycles; namely the Constant Charge (CC), Constant Voltage (CV) and Constant E-field (CE) cycles.