Dielectric elastomer transducers (DETs) are commonly modeled by lumped-element models (LEMs), however such models do not capture the cutoff behavior that manifests at relatively low frequencies due to the high resistivity of the stretchable electrodes. Moreover, the contribution of the electrodes into the lumped series resistance is not accurately known. The aim of this work is to define the accuracy and frequency limits of the LEM and to derive the exact values of its lumped components. This is achieved by developing a detailed three-dimensional distributed-element model (DEM) of the transducer structure. Based thereon, analytical expressions are developed for the LEM components and limits are explored. Through numerical evaluation of the DEM it is found that only two-third of the single-polarity electrode resistance contributes to the lumped series resistance, which is three times lower than predicted by existing models. Comparison between the LEM and DEM further shows that the LEM is adequate for frequencies significantly below the cutoff frequency. Thereafter, capacitance and resistance fall off as a result of signal propagation limitations. This has been experimentally verified. The developed DEM and established validity range of the simple LEM allows for more accurate sensors and better optimized transducers designs, with up to three times less electrode material.

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The first generations of wave energy converters have had a number of forms, but all are essentially large steel structures concentrating the power take off onto small mechanical devices. A number of prototype devices have been installed offshore, but due to their high fabrication and installation costs, coupled with significant maintenance requirements, the production of electricity at an acceptable cost has remained elusive. To avoid the limitations of these devices, a second generation wave energy converter is being developed using electro active polymers (EAP), which are capable of generating electricity directly from wave action without the need for any mechanical power take off. The resulting system is flexible and possesses an infinite number of degrees of freedom, allowing wave energy to be captured more efficiently than with conventional devices. Deployed offshore, such a device would have no complex mechanical parts, would function silently, and would require minimal maintenance. The economics of such a system lead to predictions of a cost of electricity significantly below the levels of the first generation devices. The paper explains the principals involved in using EAP for the generation of electricity, the application of EAP to wave energy conversion, and reports key results from the ongoing development program. The paper also describes the main features of the prototype wave energy converter system presently under development for deployment offshore.@en

This paper presents an investigation on modulation modes for dual active bridge modules stacked in a 10-kV input parallel output series converter for energy extraction in dielectric electroactive polymer (DEAP) wave energy converters. The converter requirements for energy harvesting with DEAPs are derived, and the operating areas and limitations of each modulation mode are compared. A hybrid modulation strategy consisting of several variable frequency modulation modes is proposed, which is capable of operating over a wide voltage and current range at high-efficiency levels as required by the DEAP harvesting cycles. Through loss calculations using an experimentally validated loss model and by including both material and converter losses in the harvesting cycle, it is shown that the hybrid modulation method increases the energy output of low-strain cycles by 25%.@en

This paper presents a modulation strategy for wide voltage output in a bidirectional modular multilevel dc-dc power electronic converter for wave energy extraction using Electro Active Polymer Wave Energy Converters (EAPWECs). The chosen electrical power converter uses a 10 kV, low current bidirectional dc-dc modular multilevel topology with Dual Active Bridges (DABs) as a basis for each module. This paper proposes a modulation method consisting of several variable frequency DAB modulation modes and explains their operating areas and limitations. Through a simulation model it is shown how the control for the multilevel converter is implemented. Finally, loss estimation is performed using the developed loss model, which was previously validated on an experimental setup.@en

This paper introduces a separate control method for modules of the bidirectional modular multilevel dc-dc power converter in order to improve overall converter efficiency. The proposed multilevel power converter topology is based on a Dual Active Bridge (DAB) converter as elementary electrical building block - module. Using efficiency curves it is determined how the modules should be separately controlled in order to decrease the total power converter losses, thus optimizing the total efficiency. The bidirectional modular multilevel dc-dc converter finds its application in energy extraction from Electro Active Polymer Wave Energy Converters (EAPWECs). It is shown that achieved power converter efficiency improvements have significant impact on the produced power in EAPWEC systems. Efficiencies of the power converter are modeled and verified with experimental measurements on the DAB module to support loss model.@en

Over the past 4 years SBM has developed a revolutionary Wave Energy Converter (WEC): the S3. Floating under the ocean surface, the S3 amplifies pressure waves similarly to a Ruben's tube. Only made of elastomers, the system is entirely flexible, environmentally friendly and silent. Thanks to a multimodal resonant behavior, the S3 is capable of efficiently harvesting wave energy from a wide range of wave periods, naturally smoothing the irregularities of ocean wave amplitudes and periods. In the S3 system, Electro Active Polymer (EAP) generators are distributed along an elastomeric tube over several wave lengths, they convert wave induced deformations directly into electricity. The output is high voltage multiphase Direct Current with low ripple. Unlike other conventional WECs, the S3 requires no maintenance of moving parts. The conception and operating principle will eventually lead to a reduction of both CAPEX and OPEX. By integrating EAP generators into a small scale S3, SBM achieved a world first: direct conversion of wave energy in electricity with a moored flexible submerged EAP WEC in a wave tank test. Through an extensive testing program on large scale EAP generators, SBM identified challenges in scaling up to a utility grid device. French Government supports the consortium consisting of SBM, IFREMER and ECN in their efforts to deploy a full scale prototype at the SEMREV test center in France at the horizon 2014-2015. SBM will be seeking strategic as well as financial partners to unleash the true potentials of the S3 Standing Wave Tube Electro Active Polymer WEC.

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Dielectric elastomers used as generators have received considerable attention lately and several prototypes were built to demonstrate the process. The aim of the paper is to show how an innovative energy harvesting cycle can be realized to use the DEs as an efficient generator. It investigates the effects of (dis)charging instants, the current amplitude and how the parasitics of the material influences the energy gain and show what kind of trade-offs can be reached by selecting parameters carefully. Also an EAP emulator is introduced: it is able to implement a variable capacitor by a controllable power supply. It can be used for evaluating PTOs, tests, measurements; without the complexity, vulnerability and high price of the elastomer.@en

Dielectric Elastomers are well known for there performance as actuators, but these materials can be used effectively as generators. Research on this field have received considerable attention lately, several prototypes were built like wavepower and human kinetic power generators. The focus of this paper is how the dielectric elastomer can be used as generator. The paper presents a dynamic model to calculate the capacitance of the electroactive polymer according to the external loading and investigates and compares several energy harvesting cycles based on the energy gain.@en

From an electrical point of view dielectric elastomers are variable capacitors, which are frequently used as generators. The focus of this paper is to show, how the maximum energy gain can be realized by realizing an innovative current waveform to charge and discharge the polymer. Several energy harvesting cycles are introduced and their energy output compared. The most promising cycle has been optimized to increase its production while taking several limiting factors into account.

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