Fakultät für Elektrotechnik Feinwerktechnik Informationstechnik
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Embedded permanent magnets are widely used for electrical machines with interior-rotor. This provides better protection of the magnets and enables the use of an additional reluctance torque for torque density improvements. For external rotors, the use of surface-mounted permanent magnets is common. The following paper analyses the application of inserted magnets at exterior-rotors with segmentation to achieve an increase in torque density.High pole electrical machines are often designed with a fractional-slot concentrated winding which leads to field harmonics. Therefore, an analytical method for qualitative comparison of different winding configurations for using reluctance torque with consideration of stator field harmonics is applied. Besides rotor saliency, the magnetic flux concentration is a positive effect of interior permanent magnets. Here, the flux leakage along mechanical necessary iron bridges is crucial. With the segmented rotor geometry, these iron bridges can be avoided for interior placed magnets. This allows a flux concentration for electrical machines with a high number of pole-pairs. The paper presents a simplified geometry-based approach to describe these improvements. The method is validated with a finite element analysis (FEA) and a prototype with a segmented rotor is built.
Because of the absence of rare earth magnets, the reluctance synchronous machine has a more favourable sustainability balance compared to the permanent magnet synchronous machine with NdFeB magnets. Additional advantages include the absence of copper in the rotor and the ease of manufacture of the non modified rotor. A clear disadvantage of the reluctance synchronous machine is the relatively high torque ripple if no measures such as skewing are taken. Therefore, the machine is mainly used in applications such as fans where the torque ripple is not critical for the operation. The paper makes a contribution to addressing the problem of torque pulsation. For the reduction of torque harmonics, the usage of various rotor designs as well as asymmetric rotor geometry are presented. In addition, the aspect of torque harmonics, which is predicted by the finite element analysis is discussed and possibilities of torque ripple reduction for further investigations are shown. The description of a reluctance network of the machine is addressed with a semi-analytical approach for this purpose. Finally, the results of the preliminary calculation are validated by finite element analysis (FEA) and the quantities are verified with measurements on a device under test. The deviations between the methods are shown and discussed.
This paper presents a current control approach for permanent magnet synchronous machines (PMSMs) using the deep reinforcement learning algorithm deep deterministic policy gradient (DDPG). The proposed method is designed by examining different training setups regarding the reward function, the observation vector, and the actor neural network. In doing so, the impact of the different design factors on the steady-state and dynamic behavior of the system is assessed, thus facilitating the selection of the setup that results in the most favorable performance. Moreover, to provide the necessary insight into the controller design, the entire path from training the agent in simulation, through testing the control in a controller-in-the-loop (CIL) environment, to deployment on the test bench is described. Subsequently, experimental results are provided, which show the efficacy of the presented algorithm over a wide range of operating points. Finally, in an attempt to promote open science and expedite the use of deep reinforcement learning in power electronic systems, the trained agents, including the CIL model, are rendered openly available and accessible such that reproducibility of the presented approach is possible.
In this paper, the influence of temperatures up to
250 °C on core losses and magnetization demand of electrical
steel sheets is illustrated. Therefore, measurements are made
using an adopted high-temperature Epstein frame and a stator
core as a ring probe. Three different electrical steel sheet grades,
M330-50A, M530-50A and NO20-15, and a stator core are
tested. Magnetic property measurements are performed at
various frequencies from DC to 1.2 kHz with a defined
sinusoidal waveform of magnetic polarization. This covers a
wide range of electric motor applications from industrial drives
to electric vehicle drives. With increasing temperature,
magnetization demand rises significantly in medium
polarization range. For specific core losses, a loss separation is
performed using the Jordan approach, separating specific
hysteresis and specific eddy current losses to determine the
temperature influence on each loss component. The
temperature behavior of the specific electrical resistivity of
electrical steel sheets is measured and used to calculate the
physical specific eddy current losses. After separation, specific
hysteresis losses also show a significant temperature influence.
Control of multi-phase machines is a challenging topic due to the high number of controlled variables. Conventional control methods, such as field-oriented control (FOC), address this issue by introducing more control loops. This, however, increases the controller design complexity, while the tuning process can become cumbersome. To tackle the above, this paper proposes a deep deterministic policy gradient algorithm based controller that fulfills all the control objectives in one computational stage. More specifically, the proposed approach aims to learn a suitable current control policy for six-phase permanent magnet synchronous machines to simplify the commissioning of the drive system. In doing so, physical limitations of the drive system can be accounted for, while the compensation of imbalances between the two three-phase subsystems is rendered possible. After validating the training results in a controller-in-the-loop environment, test bench measurements are provided to demonstrate the effectiveness of the proposed controller. As shown, favorable steady-state and dynamic performance is achieved that is comparable to that of FOC. Therefore, as indicated by the presented results, reinforcement learning-based control approaches for multi-phase machines is a promising research area.
Energy-saving potential for centrifugal pump storage operation using optimized control schemes
(2021)
AbstractIn this paper, we present the energy-saving potential of using optimized control for centrifugal pump–driven water storages. For this purpose, a Simulink pump-pipe-storage model is used. The equations and transfer function for steady-state and transient system behavior are presented and verified. Two different control strategies — optimum constant flow rate and level guided speed control — are compared to an allegedly optimal-driven pump with constant rotational speed. Twelve centrifugal pumps between 1 and 120 kW nominal power are evaluated to analyze the influence of different system parameters. The system characteristics, which are the static head, dynamic head factor, and maximum filling head, are varied 25 times for each pump in consideration of the pump’s best efficiency point. Thus, 300 different systems are optimized for each control strategy and compared to the constant speed control. The results are analyzed and the relevant system’s parameters, which have the most significant impact on energy savings, are shown. This theoretical energy–saving potential is verified with measurements, which show the high impact of the part load losses of the frequency converter and the electric motor. A law for identifying and estimation potential energy savings is developed using this information. Four use cases are analyzed with this law. It is shown that for a cost-minimal operation, not only the savings potential but also the operating time is decisive.
In laboratory practicals (labs), students actively investigate technical and scientific phenomena and thus experience autonomy, competence, and social embedding, factors that promote motivation. However, labs mostly rely on highly structured and instructive concepts and often require costly equipment. Therefore, the research question in this paper is: How can learner-centered teaching methods and learning formats be improved by rethinking the digitization of lab practicals?
The implementation of a reliable vision system for a human-robot environment is a key issue for the collaborative production industry. The core challenge of human-robot collaboration is to ensure safety. Furthermore, a flexible safety system is required for frequently changing applications and work areas. This paper focuses on the development and application of a workspace monitoring system for safeguarding using radar sensors. The human-robot collaboration cell is designed to enable a flexible integration regardless of the work location. This results in higher productivity. Since no separating protective devices are provided for the cell, safety-oriented monitoring and control by suitable safety sensors is required. The methods to minimize the size of the necessary safety distance will be presented. The experimental validation shows that this safety system with radar sensors performs a reliable workspace monitoring system. The high robustness, reactivity and flexibility of the safet y concept makes this system usable for collaborative tasks in a real industrial environment.
In the research project AVerdi the influence of photonic sintering methods on the resulting electrical conductivity, sintering duration and adhesion of digitally printed silver nanoparticle inks was investigated and compared to convective sintering. Conductor paths with film thicknesses below 1 μm were applied on flexible polymer substrates via inkjet printing. Aerosoljet printing was used to generate thicker lines up to 11 μm on injection molded substrates. Photonic sintering was carried out with near infrared emitters or ultraviolet light emitting diodes. For inkjet printed structures on polyimide a conductivity up to 24 % relative to bulk silver was achieved after a sintering duration of 2 s and 5 s for the near infrared and the ultraviolet light source, respectively. Oven sintered samples showed an electrical conductivity of 14 % after 1 h at 200° C. On polyethylene terephthalate a conductivity around 7 % was achieved after irradiation with near infrared light for 1 s, whereas convectively sintered samples showed a conductivity around 4 %. All material combinations sintered by the different methods showed good adhesion. The overall results of long-term behavior after thermal-cycling, regarding electrical conductivity and adhesion, show that the photonically sintered structures achieve similar results compared to the reference. The photonically sintered structures generated with the aerosoljet on polyamide 6 achieved conductivity values up to 19 %, which were comparable to the furnace sintered reference samples. On liquid crystal polymer substrates conductivity values reached up to 35 % after sintering with ultraviolet light emitting diodes for 60 s. Oven sintered samples showed a conductivity around 25 % after 1 h at 150° C. The adhesion of the silver nanoparticle ink on liquid crystal polymer and polyamide 6 substrates is better than with the reference samples. The reliability tests show fewer failures with alternative sintered samples. In this study only the results for inkjet printed structures are presented.
The integration of SMT components is necessary to produce more complex assemblies within the framework of conformable electronics. During High-Pressure-Forming (HPF) and subsequent overmolding electronic components must withstand high amounts of stress. In this study 0402- as well as 0603-sized chip resistors were mounted on different common polymer substrates using conductive adhesive paste followed by electrical and mechanical evaluation. Prior to HPF electronic components were positioned in areas of different local deformation. After HPF the specimen were characterized by shear force testing and electrical resistance measurements. In a similar manner, electronic components were tested to assess the mechanical behavior during injection molding. To examine different melt induced stress scenarios, electronic components were arranged parallel as well as perpendicular to the flow direction of the melt at different positions. Additionally, three different injection speeds were evaluated to assess the influence on the electrical conductivity and functionality of the assemblies. It was found that meandering of conductors is necessary for higher deformations. El. components (without additional nonconductive adhesives) can be placed in areas of up to 15% deformation, smaller package sizes seem to be advantageous for HPF. Regarding overmoulding, it was found that larger components (larger bonding area) is beneficial. Also, placement near the injection point, as well as low injection speeds should be avoided. Overall, el. components should be protected (using globtops / underfills etc.) to withstand consecutive HPF and overmoulding.