Roberto Leidhold

The efficiency of vertical-axis cross-flow turbines can be significantly improved by actively adjusting the pitch during each rotation cycle. This continuous pitching of the blade demands a high dynamic actuator, which in turn should not perturb the flow, for instance, by embedding it into the blade. These requirements and conditions make the design challenging. The usual approach using conventional servo motors with a gearbox has the disadvantage of wear, increased by frequent changes in motion direction, and backlash, which may lead to inaccurate position control or even instability. To avoid this, in the present work, a direct-driven actuator with a form factor suited to embed it into a blade profile is proposed. A parametric FEM model was developed and a prototype was implemented to validate the proposal. A cascaded position control algorithm was also designed and implemented. It can be seen that, although the torque characteristic varies with the angle, it still meets the requirements for the expected pitch span. Finally, using the proposed controller, the ability to track the pitch angle with expected high accuracy and dynamics has been demonstrated.

Experimental research of the processes of magnetization and demagnetization for the motionless vector-controlled induction motor was performed, according to a linear law with a variation in the duration of these processes. The methodology of research during which the orthogonal components of the stator and rotor currents were recorded in the rotor flux reference frame, the rotor flux module and the energy of the total losses in the stator and rotor copper is described. The main characteristics and parameters of laboratory equipment and facilities are given. From the point of view of minimizing copper losses, the existence of the optimal duration of the investigated transient processes has been experimentally proven. The results of experimental studies with high accuracy coincide with calculations based on previously obtained analytical dependencies, which confirms the admissibility of the assumptions made during theoretical studies. References 10, figures 7, tables 2.

Up to now bio-inspired fish-mimicking robots fail when competing with the swimming performance of real fish. While tail motion has been studied extensively, the influence of the head motion is still not fully understood and its active control is challenging. In this experimental study, we show that head yawing strongly impacts on the propulsion force and determines the optimal fin actuation amplitude and tail beat frequency when aiming for a maximal propulsion force. In a parametric experimental study on a tethered 367 mm long fish robot the pivot point location of the head yaw has been varied along with tail beat frequency and actuation amplitude. The experiments took place in a still water tank and the swimming force has been measured with a single axis load cell. The robot is actuated with non-conventional area actuators based on micro fiber composites. 105 parameter sets have been investigated while the highest pivot point distance of roughly 0.36 body length from the nose tip provided the highest propulsion force of 500 mN with the lowest actuation frequency of 2.5 Hz and the highest head motion amplitude of a magnitude of 0.18 body length. Even though the pivot point location on a free swimming robot is a consequence of the complex fluid-structure interactions of fish and fluid, the results provide valuable information for the design of fish mimicking robots and questions the paradigm that head yaw is a simple recoil effect from tail motion and has to be minimized for an effective propulsion.

This chapter provides a comprehensive review of the advanced manufacturing of hard magnetic material. An overview of the fundamental science of hard magnetic material, their various classes and computer-aided tools for design and modeling will be given. The mainstream sintering and bonding techniques will also be summarized along with applicable materials. Four most popular research directions for hard magnetic material for applications in (i) grain boundary regulation, (ii) grain boundary diffusion, (iii) rapid quenching and (iv) and temperature resistance and (BH)max will be identified. The most currently updated research trends, achievements, challenges faced and future prospects in these fields will be analyzed and discussed in detail.

This article describes the design method for an electrical machine for a free-piston linear generator. As with other applications for linear machines, defining a steady-state operating point as the basis for the design proved infeasible. To overcome the challenge of optimizing for an alternating motion cycle with accelerations and dynamic load forces, a previously established design methodology was implemented. In addition to the experimental validation of the optimization approach, each research step was presented, beginning with the preliminary choices for the machine topology. This was followed by the optimization of the linear machine and lastly the measurements of its characteristics for comparison with the simulation. A control strategy was determined and a machine prototype constructed that achieved the desired operating cycle, matching the simulated behavior remarkably.

Internal combustion engines with a crankshaft have been successfully developed for many years. They are lacking in the fact that the piston trajectory, i.e., position as a function of time, is limited by the crankshaft motion law. Position-controlled electric linear machines directly coupled to the piston allow to realize free-piston engines. Unlike the crankshaft-based engines, they allow for a higher degree of freedom in shaping the piston trajectory, including adaptive compression ratios, which enables optimal operation with alternative fuels. The possibility of adapting the stroke course results in new degrees of freedom with which the combustion process can be optimized. In this work, four-stroke trajectories with different amplitudes and piston dynamics have been proposed and analyzed regarding efficiency. A simulation model was created based on experimental measurements for testing the proposed trajectories. It could be proved that the variation of the trajectory resulted in an improvement of the overall efficiency. The trajectories were described analytically so that they can be used for a prototype in a future work.

Two optimized filter topologies for four-wire electric drive systems (EDSs) are proposed with smaller size, lower power loss, and larger common-mode (CM) current reduction than the usual filter topologies. It has been previously shown that using a four-wire topology reduces the CM current in a wide frequency range, when compared with the three-wire one. However, there still exist low- and high-frequency resonances in the transfer function between neutral and inverter output voltage, resulting in the increase of CM current. By means of the transfer function analysis, two types of optimized filter topology specified for the four-wire EDS are proposed. Unlike conventional CM filter (CMMF), the design of these two new filters also requires a serious consideration of the characteristics of motor and cable impedance. Based on the design procedure, these two filters are built with excellent performance of CM current reduction in the whole frequency range. Besides, compared with conventional CMMF used for three-wire EDS, they also show benefits, such as lower power loss and less implementation space. All theoretical analyses are validated by the experimental measurements and can benefit further studies.

Zusammenfassung: Die genaue Kenntnis der Zahnstangenkraft ist in einem Steer-by-Wire-Fahrzeug unablässlich, um dem Fahrer am entkoppelten Handaktuator ein realistisches Gefühl über die Fahrbahnbeschaffenheit zu generieren. Aus wirtschaftlichen Gründen wird oftmals auf eine Schätzung zurückgegriffen. Mögliche Ansätze werden in dieser Untersuchung aufgegriffen, ihre Tauglichkeit analysiert, steuergerättauglich in Fixpoint modelliert, Programmlaufzeiten auf einem Entwicklerboard ermittelt, auf einem Steer-by-Wire-Steuergerät implementiert und ihre Genauigkeiten im Fahrzeug nachgewiesen.

A signal-based strategy for static eccentricity (SE) detection in permanent magnet synchronous machines (PMSM) is proposed in this work. The effects of SE are analyzed from a model developed using a finite element method (FEM). SE detection is realized by evaluating the residual voltages (RV) obtained from the midpoint voltages measured in the middle of the windings of each phase. Unlike the methods based on motor current or voltage signature analysis (MCSA/MVSA), RVs allow to detect only the effects of an SE against other external problems that are usually found in industrial applications. Experimental laboratory results are presented which were obtained using bearings with eccentric bushings to generate different degrees of SE in the PMSM. The proposed strategy is validated by comparing the results obtained by FEM with the experimental tests for PMSM in different operating conditions, guaranteeing the correct diagnosis of SE.