Jürgen Maas

Simulation model for ultrasonic motors powered by resonant converters

A rotary traveling wave type ultrasonic motor powered by a resonant converter is modeled to optimize the overall drive performance by simulation and to develop suitable control strategies for the drive. Based on mechanical approaches in modeling the stator under consideration of unsymmetries and reflecting the nonlinear stator/rotor-contact by an elastic contact model, an extended contact model of the stator/rotor interaction with closed form solutions for nonideal traveling waves is derived referring to a two-mode approximation of the stator and piezoceramic. By incorporation of a converter model into the mechanical subsystem, a proper simulation model for ultrasonic drives is presented, whereby some interesting phenomena are verified by simulations and explained by strong graphical means.

Energy harvesting cycles based on electro active polymers

Energy harvesting using dielectric elastomers is an interesting possibility to convert ambient energy into electric energy. Different small scale prototypes of energy harvesting devices, like SRIs wind- and wave-power generators have been developed so far. Nevertheless, the theoretical limits and practical implementation still have to be considered. The contribution of this paper is related to the calculation of the achievable energy gain. Different harvesting cycles are investigated theoretically and compared to each other. Based on the derived equations, several design rules for the material development are quoted. To analyze the various properties of dielectric elastomer generators an electromechanical test bench is realized. The design of an appropriate HV power electronics for energy harvesting devices is presented in the last section.

Dielectric elastomers for hydro power harvesting

Dielectric elastomers can be used as generators, converting mechanical strain energy into electrical energy using the polymer?s capacitive behavior. The amount of energy gain depends, in addition to the mechanical setup of the device, mainly on the material parameters and the energy harvesting cycle used. While the usefulness of small-scale prototypes for harvesting the energy of waves has already been demonstrated, using the capability of flow energy in rivers, based on electroactive polymers, is still a significant challenge. After introducing the basic working principle of dielectric elastomer generators, the most unique energy harvesting cycles are described, considering electrical and mechanical losses. To harvest the energy of flowing waters, a novel flow energy converter based on a simple and environmentally sustainable mechanical design has been developed, consisting of an elastomeric tube with a closing mechanism on the outlet. The stationary stretch of such a tube is comparably small, but the resonant operation offers large tube deformations. The basic mechanisms of the flow energy converter are modeled, and confirmed on the basis of a FSI simulation, and a control concept is proposed. The expected mechanical behavior of the tube is demonstrated with a small-scale prototype. It can be concluded that a very efficient, resource-saving, scalable and lightweight energy harvesting system can be realized at comparably low frequencies in the infrasonic range.

Real-time HIL-simulation of power electronics

In modern vehicles, electrical drives and power electronics are used to control a large variety of different applications. To operate these components electronic control units have to be designed and tested. To validate the software of the electronic control units hardware-in-the-loop simulation is a todaypsilas standard method. Hardware-in-the-loop simulation always comprises a real-time simulation of the plant, including actuator and sensor models. In case of an electronic circuit the plant consists of passive components like capacitors and inductors, usually assumed to be linear, and semi-conductors with nonlinear and discontinuous behavior. The following paper suggests classification criteria and compares different methods for real-time simulations of electronic circuits considering switching events. For evaluation theoretical considerations as well as simulation results are presented concerning differences in approaches.

Cascaded bidirectional flyback converter driving DEAP transducers

For the control of Dielectric Elastomer Generators (DEGs) a special high voltage power-electronic (HVPE) is necessary, driving this kind of novel generators at high voltages and typically low currents. In order to supply the generator with initial charges and to harvest the generated energy, the HVPE must also enable a bidirectional energy transfer. After introducing the functional principle of DEGs and significant equations for the energy gain, the requirements to the HVPE are derived. The HVPE is based on a bidirectional flyback converter concept, which is cascaded to achieve the necessary voltage level. The converter is analyzed and modeled to describe the average current, which is used for the controller design. The performance of the converter is demonstrated based on simulations.

Averaged model of inverter-fed ultrasonic motors

An averaged model for the most advanced traveling wave type ultrasonic motor drive is presented using a generalized averaging method. The modeling approach reflects the interesting dynamic behavior of the drives ultrasonic vibrations by time-varying fundamental Fourier coefficients and coincides with the realized measurement system. Hence, the novel model is predestined for optimized control schemes of the drive using two-phase vector-modulation concepts for the feeding resonant converter. Since the describing function method is applied for the nonlinear blocks of inverter and stator/rotor-contact, first the switching behavior is eliminated reducing the simulation time compared with the original drive model and second an appropriate contact model is derived combining the partial models of stator and rotor.

Optimized energy harvesting based on electro active polymers

Energy harvesting using dielectric elastomers is an interesting possibility to convert ambient energy into electric energy. Different small scale prototypes of energy harvesting devices, like SRIs wind- and wave-power generators have been developed so far. Nevertheless, the theoretical limits and practical implementation still have to be considered. In a previous paper the achievable energy gain for different harvesting cycles was investigated theoretically. When using the cycles for energy harvesting also losses occur due to the behavior of the material. In this paper detailed loss mechanisms are taken into account to derive design rules for the material development and for the optimization of the overall system setup.

Online identification algorithms for integrated dielectric electroactive polymer sensors and self-sensing concepts

Transducers based on dielectric electroactive polymers (DEAP) use electrostatic pressure to convert electric energy into strain energy or vice versa. Besides this, they are also designed for sensor applications in monitoring the actual stretch state on the basis of the deformation dependent capacitive–resistive behavior of the DEAP. In order to enable an efficient and proper closed loop control operation of these transducers, e.g. in positioning or energy harvesting applications, on the one hand, sensors based on DEAP material can be integrated into the transducers and evaluated externally, and on the other hand, the transducer itself can be used as a sensor, also in terms of self-sensing. For this purpose the characteristic electrical behavior of the transducer has to be evaluated in order to determine the mechanical state. Also, adequate online identification algorithms with sufficient accuracy and dynamics are required, independent from the sensor concept utilized, in order to determine the electrical DEAP parameters in real time. Therefore, in this contribution, algorithms are developed in the frequency domain for identifications of the capacitance as well as the electrode and polymer resistance of a DEAP, which are validated by measurements. These algorithms are designed for self-sensing applications, especially if the power electronics utilized is operated at a constant switching frequency, and parasitic harmonic oscillations are induced besides the desired DC value. These oscillations can be used for the online identification, so an additional superimposed excitation is no longer necessary. For this purpose a dual active bridge (DAB) is introduced to drive the DEAP transducer. The capabilities of the real-time identification algorithm in combination with the DAB are presented in detail and discussed, finally.

Simulation model for electro active polymer generators

Energy harvesting using dielectric elastomers is an interesting possibility to convert ambient energy into electric energy. Different small scale prototypes of energy harvesting devices, like wave-power generators, have been developed so far. Nevertheless, the theoretical limits and practical implementation still have to be considered. To analyze and optimize the design of the dielectric elastomer generator, the material parameters and the energy harvesting cycles, a validate electromechanical model is necessary. Further on, the simulation model can also be used to optimize the Energy Harvesting Cycle. This paper presents a model for dielectric elastomer generators, combining the electrostatic properties of the electrical part with the nonlinear elastic behavior and damping of the polymer material, validated with measurement results of a test bench.

Analytical modeling and optimization of DEAP-based multilayer stack-transducers

Transducers based on dielectric electroactive polymers (DEAP) use electrostatic pressure to convert electrical into mechanical energy or vice versa. To scale up the actuation or the energy gain, multilayer transducers like DEAP stack transducers are appropriate. Within this contribution, a model of such a stack transducer is derived and experimentally validated. The model is based on a multi-domain approach to describe the mechanical dynamics and the electrical behavior of the DEAP. Since these two domains influence each other they are coupled afterwards by a novel approach using interchanging power flows. To parametrize this model, tensile and compression tests for different polymer materials were performed under static and transient considerations. The results of these experiments show that the parameters obtained from the tensile test sufficiently describe the compression mode and can therefore be used for the model. Based on this transducer model the overall energy and the different parts of the multi-domain are analytically determined for arbitrary operating points. These expressions for the energies are finally used to optimize well-defined coupling coefficients, by which a maximum part of the electrical input energy is converted to mechanical energy, especially mechanical work.