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Summary Organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) have developed very fast in recent years. A proper balance among power conversion efficiency (PCE), stability, and production cost needs further elaboration. Here we investigate the industrial viability of highly efficient OSCs based on several representative NFAs. The most stable OSCs exhibit PCE of ∼8% along with extrapolated T80 lifetime (80% of the initial PCE) of over 11,000 hr under equivalent 1 sun illumination, which would lead to a very impressive operational lifetime approaching 10 years. Photo-stability is strongly dependent on the end-group and side-chain engineering of the NFAs. Breaking of conjugation during photo-aging leads to increased energetic traps. Fluorination of the end-group stabilizes molecules against light soaking, while adding methyl groups shows an opposite trend. Side-chain modification can significantly influence the morphological stability. Reducing synthetic complexity of this class of NFAs will ultimately push the organic photovoltaics technology into real-life applications.

The operational stability of organic solar cells (OSCs) is the essential barrier to commercialization. Compared to thermally-induced degradation, photo-stability of OSCs is far away from being resolved. Here, we demonstrate that the thermal- and photo-degradation of metastable bulk-heterojunction OSCs are governed by the same mechanism. Understanding the fundamental principles behind this mechanism is of significant importance to fully address the instability issues. Structural incompatibilities between the donor and acceptor molecules are identified as the main origin of the instability. Further, we introduce a top-down approach mainly based on their melting temperature and interaction parameters to rationally screen molecular phase stabilizers from a database with more than 10 000 small molecules. Eventually, five chemicals were selected to validate our concept and tested in unstable organic solar cells. 1,4-Piperazine, which possesses a high melting point, good miscibility with polymers and the capability of forming inter-molecular hydrogen bonding, can indeed stabilize the mixed amorphous phases, leading to significantly improved stability of otherwise metastable OSCs.

There is a strong market driven need for processing organic photovoltaics from eco-friendly solvents. Water-dispersed organic semiconducting nanoparticles (NPs) satisfy these premises convincingly. However, the necessity of surfactants, which are inevitable for stabilizing NPs, is a major obstacle towards realizing competitive power conversion efficiencies for water-processed devices. Here, we report on a concept for minimizing the adverse impact of surfactants on solar cell performance. A poloxamer facilitates the purification of organic semiconducting NPs through stripping excess surfactants from aqueous dispersion. The use of surfactant-stripped NPs based on poly(3-hexylthiophene) / non-fullerene acceptor leads to a device efficiency and stability comparable to the one from devices processed by halogenated solvents. A record efficiency of 7.5% is achieved for NP devices based on a low-band gap polymer system. This elegant approach opens an avenue that future organic photovoltaics processing may be indeed based on non-toxic water-based nanoparticle inks., Water-based semiconducting polymer nanoparticles are eco-friendly and non-toxic but their performance suffers from the surfactants. Here Xie et al. design an approach to minimize the amount of residual surfactant in these nanoparticles and make high-efficiency and stability solar cells.

The preparation of a highly ordered nanostructured transparent electrode based on a combination of nanosphere lithography and anodization is presented. The size of perfectly ordered pore domains is improved by an order of magnitude with respect to the state of the art. The concomitantly reduced density of defect pores increases the fraction of pores that are in good electrical contact with the underlying transparent conductive substrate. This improvement in structural quality translates directly and linearly into an improved performance of energy conversion devices built from such electrodes in a linear manner.

Small cooling fan failures are attributed to bearings. If a propeller rotates without any contact by magnetic levitation technology, high-speed rotation and long durability can be achieved. Thus, the authors are developing a small size maglev type motor. The Axial force/Torque Motor (AFTM) can generate axial bearing force and drive torque force in one unit. To increase the filling rate and manufacturing accuracy of winding, we used flex Printed Circuit Board (PCB) technology for AFTM. Coils are formed by winding the flex PCB around the back yoke. To higher manufacturable and improve the performance of AFTM, it is desirable to make flex PCB patterns correctly and increase the occupation ratio of copper. In this paper, we investigated the manufacturable layer configuration of special flex PCBs. Several prototypes with a different cover and copper thickness were manufactured and evaluated. We succeeded in producing a printed pattern with a copper thickness of 50 µm and a polyimide thickness of 5 µm. We could obtain a high filling factor.

A possible combination of a magnet gear and a high-speed bearingless motor has been investigated. The high-speed side is driven by magnetically suspended bearingless motor, which is integrated in the magnetic gear. The initial study has shown that, the eddy current loss increases at high speed due to the influence of harmonic flux. In order to improve the efficiency, several structures are proposed and compared with the sintered and bonded NdFeB permanent magnets. The proposed magnetic geared bearingless motor is formed to be compact light weighted, and high efficiency to the IE3 isdustrial motor with an output of 550W and 3,000rpm.

Great attention has been paid to developing low bandgap non-fullerene acceptors (NFAs) for matching wide bandgap donor polymers to increase the photocurrent and therefore the power conversion efficiencies (PCEs) of NFA organic solar cells, while pyrene-core based acceptor–donor–acceptor (A–D–A) NFAs have been mainly reported via the 2,9-position connection due to their bisthieno[30,20-b']thienyl[a,h]pyrene fused via a five-membered ring bridge at the ortho-position of pyrene as the representative one named FPIC5, which has prohibited further narrowing their energy gap. Herein, an acceptor FPIC6 was exploited by creating the 1,8-position connection through fusing as bisthieno[30,20-b0]thienyl[f-g,m-n]pyrene linked at the bay-position via a six-membered bridge, with enhanced push–pull characteristics within such A–D–A structure. As a structural isomer of FPIC5, FPIC6 exhibited a much lower bandgap of 1.42 eV (1.63 eV for FPIC5). Therefore, the photocurrent and PCE of PTB7-Th:FPIC6 cells were improved to 21.50 mA cm2 and 11.55%, respectively, due to the balanced mobilities, better photoluminescence quenching efficiency and optimized morphology, which are both40% better than those of PTB7-Th:FPIC5 cells. Our results clearly proved that a pyrene fused core with 1,8-position connection with electron-withdrawing end groups instead of 2,9-position connection is an efficient molecular design strategy to narrow the optical bandgap and improve the photovoltaic performance of NFA based OSCs.

This paper studies the modeling and field-oriented control (FOC) for hysteresis motors, with the goal of achieving position control of hysteresis motors for servo applications. Hysteresis motors include a wide range of machines with solid cylindrical or ring-shaped steel rotors, which generate torque primarily via the magnetic hysteresis effect of the rotor material. Previously, hysteresis motors have been mainly used under open-loop operation. However, they are also attractive for position control in some special applications such as in-vacuum operation or when smooth running and high speed is required. In this paper, an equivalent circuit model for hysteresis motors that describes the motor's transient-time dynamics is introduced, and a state-space model for hysteresis motors is developed. This model is used to construct a rotor flux orientation observer for the FOC for hysteresis motors. Three methods for estimating the rotor field angle are introduced. The proposed FOC-based position control method was tested with three hysteresis motors, including two custom-made motors of different rotor materials and one off-the-shelf hysteresis motor. Experimental results show that position control for all three hysteresis motors can reach a bandwidth of 130 Hz with the proposed methods. To the authors’ best knowledge, this is the first experimental study on FOC and position control for hysteresis motors.

Magnetlager sind aus etlichen industriellen Anwendungen nicht mehr wegzudenken, in anderen erscheint ein Einsatz in Zukunft vielversprechend. Durch die Magnetlagertechnik werden Effizienzsteigerungen unterschiedlicher Art ermoglicht – sowohl auf direkte Weise durch Verringerung der Lagerverluste im Vergleich zu mechanischen Lagerungen, als auch durch Verbesserungen im industriellen Prozess, die erst durch die besonderen Eigenschaften der Magnetlagerung erzielt werden konnen. Im ersten Teil dieses Beitrags werden die unterschiedlichen zur Verfugung stehenden Topologien der Magnetlagertechnik vorgestellt. Der zweite Teil stellt effizienzsteigernde Masnahmen in der Magnetlagertechnik anhand eines lagerlosen Hochgeschwindigkeitsmotors vor. Im abschliesenden, dritten Teil, werden Moglichkeiten zur Effizienzsteigerung durch die Magnetlagertechnik prasentiert. Dies geschieht anhand von vier Anwendungsgebieten, in denen Magnetlager bereits wesentlich zur Performance des Gesamtsystems beitragen, gewisse Prozessschritte erst ermoglichen oder dies in Zukunft tun konnten.

High-performance electrical drives, typically comprised of permanent magnet synchronous motors (PMSMs), generally require correct values of electrical parameters for the tuning of controllers. Those parameters are also required for the estimation of the electromagnetic torque together with the magnetic flux linkages in the direct torque control (DTC) as well as for observers of the angular position and speed of the rotor in sensorless applications of the field-oriented control (FOC). In this paper, nonlinearities imposed by the voltage source inverter (VSI) that prevent direct measurements of electrical parameters are circumvented by a method based on quotients of secants as approximations of gradients of reference voltages and measured currents. While each measurement is performed without a position sensor at a standstill, the rotor has to be able to move to align itself with a required angular position. The novelty of the proposed method is the use of currents generated by the VSI for the alignment and the locking of the rotor. The proposed method is presented analytically and its functionality demonstrated by experiments.

This paper deals with modeling of bearingless synchronous reluctance motors with a combined winding. A method to link an existing model used for the separated windings structure to the combined winding structure is proposed. A dynamic model applicable for the purposes of time-domain simulation, model-based control design, and real-time control is presented. The finite-element method (FEM) is used to validate the proposed model and to show the feasibility of the considered slice motor type, including passive stability of axial movement and tilting, force and torque production, and ripple. Applicability of the developed model in control design is demonstrated. The model is validated by means of experiments.

Worldwide research efforts have been devoted to organic photovoltaics in the hope of a large-scale commercial application in the near future. To meet the industrial production requirements, organic photovoltaics that can reach power conversion efficiency (PCE) of over 10% along with promising operational device stability are of utmost interest. In the study, we take PCE11:PCBM as a model system, which can achieve over 11% PCE when processed from nonhalogen solvents, to deeply investigate the morphology–performance–stability correlation. We demonstrate that four batches of PCE11 with varying crystalline properties can achieve similar high performance in combination with PCBM. Careful device optimization is necessary in each case to properly address the requirements for the quite distinct microstructures. The bulk-heterojunction (BHJ) microstructure is comprehensively investigated as a function of the macromolecular weight and crystallinity. It is demonstrated that small differences in morphology significantly affect the kinetics and thermodynamic equilibrium of the BHJ microstructure as well as the photostability and thermal stability of the PCE11:PCBM solar cells.

Bearingless motors are very compact magnetically levitated systems. In addition to their technological benefits like no friction, no mechanical wear and long lifetime they can be simplified regarding their mechanical composition and electronic hardware demand. Under these constraints typically a one degree of freedom actively positioned system is preferable. Passive stabilization is used for the other degrees of freedom due to simplicity. In this manuscript such a system, the bearingless axial-force/torque motor, is implemented in a small fan application. The manufactured prototype is outlined and its hard- and software are explained. Static and dynamic measurements with the bearingless fan prove the concept and show its operation feasibility.

In this work design and implementation of a bearingless high-speed motor are presented. Several different rotor and stator topologies are discussed and simulated to determine their suitability for high-speed operation. Finally, the most promising concept is implemented as a prototype. To the author's best knowledge for the first time a bearingless high-speed slice motor with slotted stator is manufactured. The slotted stator features the advantage of reduced magnetic air gap compared to motors with toroidal air-gap windings and slotless stator. The smaller air gap leads to increased air-gap bias flux and increased stiffness values as well as higher force and torque constants. Additionally a damper winding is included to suppress tilt motions.

Alongside technical performance features, low system costs are the highest priority in the field of low-power electric drives. This makes adoption of magnetic bearing technologies difficult in applications with higher production volumes. Since published literature on cost-saving measures in this field is scarce, we present in this paper some ideas and stimuli using three selected examples: 1) a highly integrated hybrid bearing that provides active stabilization in 3 degrees of freedom (DOF); 2) a brushless permanent magnet motor with additional axial bearing capability; and 3) a bearingless flux-switching motor. We describe their particular designs and operational features, and compare the additional mechanical and electrical costs of these and similar systems with those of standard motor technologies. This paper concludes with a stability analysis of example 2), since it features passive permanent magnetic bearings, which are inherently only weakly attenuated.

This article focuses on the operational behaviours of two novel bearingless reluctance slice motor prototypes. After a brief introduction of the two systems, we present our experience with both bearingless drives. On this basis, commonalities and differences in terms of construction, geometric constraints, winding systems, force-to-torque ratio, power electronic utilization and efficiency are outlined in order to demonstrate the suitability of the reluctance slice motor concepts for industrial applications.

As the power conversion efficiency (PCE) of organic solar cells (OSCs) has surpassed the 17% baseline, the long-term stability of highly efficient OSCs is essential for the practical application of this photovoltaic technology. Here, the photostability and possible degradation mechanisms of three state-of-the-art polymer donors with a commonly used nonfullerene acceptor (NFA), IT-4F, are investigated. The active-layer materials show excellent intrinsic photostability. The initial morphology, in particular the mixed region, causes degradation predominantly in the fill factor (FF) under illumination. Electron traps are formed due to the reorganization of polymers and diffusion-limited aggregation of NFAs to assemble small isolated acceptor domains under illumination. These electron traps lead to losses mainly in FF, which is in contradistinction to the degradation mechanisms observed for fullerene-based OSCs. Control of the composition of NFAs close to the thermodynamic equilibrium limit while keeping adequate electron percolation and improving the initial polymer and NFA ordering are of the essence to stabilize the FF in NFA-based solar cells, which may be the key tactics to develop next-generation OSCs with high efficiency as well as excellent stability.

Several bearingless flux-switching motors have been implemented recently. These magnetically levitated drives create radial suspension forces and drive torque. They represent permanent-magnetic excited synchronous machines but feature rotors without any permanent-magnetic but salient rotor poles. A heteropolar air-gap field is excited by stator permanent magnets, which are located in-between the stator teeth. The rotor teeth change the permanent-magnetic flux paths and switch the magnetic flux linked with the stator coils, which are concentrically wound around the stator teeth. Typical bearingless flux-switching motors feature twelve stator teeth and ten salient rotor poles. However, all the presented designs up to now feature interior rotors. In this work an exterior rotor composition is considered for the first time in bearingless flux-switching motors. Design rules for a proper selection of the rotor tooth number are given using an analytic motor model considering suspension force and drive torque generation. To verify the theoretical results a prototype flux-switching motor with exterior rotor is optimized and manufactured. Its characteristic data is measured and compared to the referring 3D finite-element simulation results.

The magnitude of the rotor magnetic flux linkage and its spatial orientation within a permanent magnet synchronous motor directly define the angular position of the rotor and are thus used in many sensorless applications as the governing variables. The rotor magnetic flux linkage in the stator reference frame is represented by two orthogonal sinusoids whose amplitudes and phases are determined by the integration of the orthogonal components of the corresponding voltage, which, due to DC offsets and initial conditions at transient states, result in an integrational drift. This paper proposes a solution to the problem of such integrational drift in the form of a compensation based only on orthogonal properties of waveforms in the stator reference frame. That makes it completely independent of electrical parameters of the motor. As a result, the proposed compensation of the integrational drift does not require any optimization by the user and it is functional from a standstill. The effectiveness of the proposed compensation is demonstrated analytically, by a simulation, and an experiment on a real motor by a simple observer for the sensorless field-oriented control based on the voltage model in the stator reference frame.

Field-oriented control has become a standard method to generated drive torque in permanent magnet excited synchronous drives with high efficiency. In this work, a similar control approach is proposed for radial suspension force generation in bearingless drives with combined winding system. Combined windings sets generate both motor torque and suspension force in each phase depending on the rotor angle. This allows increased efficiency, simpler manufacture and higher compactness compared to separated winding systems. However, in this case the decoupling of force and torque, which is necessary for proper bearingless operation, has to be achieved in the control scheme. Using transformations into two different rotating coordinate systems is proposed in this work to solve this issue. Hence, for full bearingless motor operation, two different field-oriented control schemes of the same structure have to work in parallel, one for force generation and the other for torque generation. The necessary phase currents are finally superposed. Thus, well proven and state-of-the-art industrial procedures can be used to implement the control scheme for a bearingless permanent magnetic motor, similar to a standard electric motor.

The axial force/torque motor (AFTM) can generate axial bearing strength and drive torque simultaneously with a conventional 2-phase winding system. Since the end windings provide the active axial suspension forces, there is no necessity of additional windings to control the axial position. Passive magnetic ring bearings stabilize the remaining four degrees of freedom. It is crucial to achieving a high fabrication precision and filling factor of the winding to reach a high efficient AFTM. Therefore, we utilize the technique of directly printing the winding on a flexible printed circuit board (flex-PCB). The focus of this paper lies in the underlying design of the AFTM and the configuration of the flex-PCB windings. Analytic models that describe the influence of the motor dimensions on its force and torque generation capability are presented and validated by finite element method (FEM) analysis. Based on these results, a detailed experimental setup was designed to achieve performance validation.

Disturbance or resonance effects can cause axial vibrations in bearingless slice motors. Typically, these vibrations are only very poorly dampened, as the passive restoring force due the permanent magnets is proportional to the axial deflection (rather than to the axial speed). In this paper, a strategy to actively reduce axial vibrations is presented. In addition to reluctance forces for passive stabilisation, axial damping force is generated by modulating the permanent magnetic air-gap field. To model the rotor’s behaviour the equation of motion is set up and analysed. It is shown, that applying field current, which is proportional to the axial velocity, leads to an improved dampening behaviour. Several static and dynamic measurements are conducted to proove the function of the proposed vibration dampening strategy with a bearingless flux-switching slice motor. Finally, also the case without gravitational force is considered, which leads to a different operational behaviour.

In a recent paper, the authors have introduced the concept of a novel bearingless (slice) motor topology, the bearingless permanent magnet Vernier motor intended for low speed and high torque applications. It features an exterior rotor typical for direct drives. The feasibility of this new motor topology was proven by finite element simulations. Based on the results of these simulations, a prototype was manufactured and successfully put into operation. This paper, therefore, presents the control scheme that comprises the measurement of active and passive forces, including the active torque generation, as well as the performance of this bearingless permanent magnet Vernier motor prototype.

We present a new concept of bearingless slice motor that levitates and rotates a ring-shaped solid rotor. The rotor is made of a semi-hard magnetic material exhibiting magnetic hysteresis, such as D2 steel. The rotor is radially biased with a homopolar permanent-magnetic flux, on which the stator can superimpose two-pole flux to generate suspension forces. By regulating the suspension forces based on position feedback, the two radial rotor degrees of freedom are actively stabilized. The two tilting degrees of freedom and the axial translation are passively stable due to the reluctance forces from the bias flux. In addition, the stator can generate a torque by superimposing six-pole rotating flux, which drags the rotor via hysteresis coupling. This six-pole flux does not generate radial forces in conjunction with the homopolar flux or two-pole flux, and therefore the suspension force generation is in principle decoupled from the driving torque generation. We have developed a prototype system as a proof of concept. The stator has 12 teeth, each of which has a single-phase winding that is individually driven by a linear transconductance power amplifier. The system has four reflective-type optical sensors to differentially measure the two radial degrees of freedom of the rotor. The suspension control loop is implemented such that the phase margin is 25 $^\circ$ at the cross-over frequency of 110 Hz. The prototype system can levitate the rotor and drive it up to about 1730 r/min. The maximum driving torque is about 2.7 mNm.

This work presents a novel bearingless (slice) motor concept, the bearingless Vernier motor. It is intended for low speed and high torque applications, as typical for direct drives. Design criteria are deduced by the help of an analytic model describing single phase force and torque generation. The feasibility of the model is also proven by finite element simulations. Based on these results the performance of several bearingless permanent magnetic Vernier motor topologies with exterior rotor is evaluated. After that a bearingless Vernier motor prototype is optimized by 3D finite element simulations, designed and manufactured.

We present a low-cost position sensing module based on a commercial Inductance-to-Digital Converter (LDC) that is applied to bearingless motor suspension control. The sensing module uses four LDC evaluation boards to differentially measure the x- and y-positions of the rotor. Each of the evaluation boards consists of an LDC chip, a sensing coil, and an on-board capacitor. The LDC chip drives the sensing coil and the capacitor to their resonance, and streams out the instantaneous frequency values. As a conductive target approaches the sensing coil, the apparent inductance of the coil decreases due to the induced eddy-current, thereby increasing the resonance frequency. This frequency shift can be used for estimating the distance to the target. The sensing module exhibits a position resolution of 0.37 micrometers with the standard deviation of 0.31 micrometers at a sampling rate of 2 kH. We have implemented this sensing module to our homopolar-biased hysteresis bearingless slice motor that drives a ring-shaped rotor made of D2 steel.

This work introduces a novel bearingless slice motor design: the bearingless flux-switching slice motor. In contrast to state-of-the-art bearingless slice motors, the rotor in this new design does not include any permanent rotor magnets. This offers advantages for disposable devices, such as those used in the medical industry, and extends the range of bearingless slice motors toward high-temperature applications. In this study, our focus is on the analytical modeling of the suspension force torque generation of a single coil and the bearingless motor. We assessed motor performance in relation to motor topology by applying performance factors. A prototype motor was optimized, designed, and manufactured. We also presented the state-of-the-art nonlinear feedback control scheme used. The motor was operated, and both static and dynamic measurements were taken on a test bench, thus successfully demonstrating the functionality and applicability of the novel bearingless slice motor concept.