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

Lesnicar and Marquardt introduced a modular multilevel converter (MMC) topology back in 2003. Although this topology has received a great deal of attention in recent years by both the research community and industry, hitherto no steady-state model has been developed which accurately captured all the relevant power losses while being computationally light. Hence, the aim of this paper is to introduce a fast MMC loss model which captures the key sources of power losses in steady-state operation. The proposed model was compared to a loss model developed by Marquardt. Both models presented similar results under the same assumptions. However, the proposed model captures the switching losses more realistically and considers the temperature of operation of the electronics, as well as the losses of the inductors and cooling system, in the overall efficiency of the MMC. To validate these new additions, the proposed steady-state model was compared to a dynamic model. Once again, the proposed model was able to capture the different sources of power losses. Nonetheless, results demonstrated that the balancing strategy greatly influences the efficiency of the MMC. Therefore, information regarding the envisioned control strategy is necessary to accurately calculate the efficiency curve of the MMC.@en

This thesis deals with the new approach for harvesting renewable energy from sea waves. The main research problem is finding a way to efficiently extract the energy of the sea waves with the S3 concept using power electronics converter. The required operational high voltage of the generator limits the choice of possible power electronic converter topologies that can be employed, while a wide converter’s power range is imposed with the pulsed character. A large amount of energy is circulating in the system, consequently, power electronics conversion losses are making a substantial impact on the produced power. Therefore, the efficiency of the power converter has to be optimized over the whole operating area to reduce overall losses... @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