The parity-time (PT) symmetric principle has been increasingly adopted in inductive power transfer (IPT) systems to enhance their misalignment tolerance. To extend the transfer distance in this region, relay coil is introduced between primary and secondary coils. Currently, the existing three-coil IPT systems are usually modeled by coupled mode theory, whose simplification is available only in weak coupling conditions. To solve it, this paper employs electric circuit theory to analyze the PT-symmetric based three-coil IPT systems with series-series-series (SSS) and parallel-parallel-parallel (PPP) compensations. The coupling-independent transfer characteristics and exact PT-symmetric region, including PT frequency, critical coupling coefficient and load range, are derived in detail for both compensation methods. A fair comparison between series and parallel compensation is carried out and shows that the proper topology should be selected and designed according to application specifications. Finally, a PPP compensated IPT prototype is built and works at PT-symmetric frequency to verify the above analysis.

Grid-following (GFL) inverters exhibit stable operation in strong grids but may encounter instability in weak grids, whereas grid-forming (GFM) inverters exhibit the reverse behavior. Stability analysis of grid-connected AC systems with a single inverter typically uses an impedance-ratio criterion that requires distinguishing between the source and load converters. When multiple inverters are connected to the AC grid, it is difficult to distinguish between source and load converters. To evaluate the small-signal stability of grid-connected AC systems integrating both GFL and GFM inverters, this paper proposes an impedance-based stability criterion. This criterion eliminates the need to define the impedance ratio, and the system is considered stable if and only if the Nyquist plot of the proposed composite bus port impedance does not encircle the point (−1, j0). Moreover, the effects of grid strength and control parameters on system stability are thoroughly examined. The theoretical framework is validated through both comprehensive simulations and experimental results.

Negative reactance does not exist in the real world, which creates a unique challenge for electrical systems design. Due to the absence of the negative reactance, the only way to counteract any undesired reactance is to exploit resonance to null the positive reactance for a limited range of frequency, i.e., capacitance counteracting inductance. In this paper, we present a practical realization of negative reactance for power processing applications that will change the way electrical systems will be designed. We show that by using two DC-DC power converters and the appropriate control, we can obtain a standalone negative inductance that can directly cancel an existing positive inductance or any portion of it, opening up an entirely new direction for electrical systems design.

In this paper, a novel four-switch buck-boost (FSBB) integrated bridge is put forward for the bidirectional inductive power transfer (BIPT) system. By integrating a FSBB topology with the full-bridge (FB), the dc voltage utilization of the proposed FSBB integrated bridge as inverter is improved from $2\sqrt 2 /\pi $ to $\sqrt 2 $, and the resistance conversion ratio range of the FSBB integrated bridge as active rectifier is extended from [0,8/π2] to [0, 2]. Therefore, the BIPT system with FSBB integrated bridges can output more active power, maintain the rated power at larger coil misalignment, and guarantee impedance matching over a wider load range. A 100W experimental prototype is provided to verify the effectiveness of the proposed bridge.

Fast screening of drug molecules based on the ligand binding affinity is an important step in the drug discovery pipeline. Graph neural fingerprint is a promising method for developing molecular docking surrogates with high throughput and great fidelity. In this study, we built a COVID-19 drug docking dataset of about 300,000 drug candidates on 23 coronavirus protein targets. With this dataset, we trained graph neural fin-gerprint docking models for high-throughput virtual COVID-19 drug screening. The graph neural fingerprint models yield high prediction accuracy on docking scores with the mean squared error lower than 0.21 kcal/mol for most of the docking targets, showing significant improvement over conventional circular fin-gerprint methods. To make the neural fingerprints transferable for unknown targets, we also propose a transferable graph neural fingerprint method trained on multiple targets. With comparable accuracy to target-specific graph neural fingerprint models, the training and data efficiency of the transferable model is several times higher. We highlight that the impact of this study extends beyond COVID-19 dataset, as our approach for fast virtual ligand screening can be easily adapted and integrated into a general machine learning-accelerated pipeline to battle future bio-threats.

Inductive power transfer (IPT) technologies have gained a wide acceptance in onboard battery charging applications due to some significant advantages over traditional plug-in systems. An IPT battery charger is expected to provide a configurable charging profile consisting of an initial constant current (CC) and a subsequent constant voltage (CV) efficiently. With a wide load range during the charging process, two sets of IPT topologies with the inherent load-independent CC and CV at the same zero-phase angle (ZPA) frequency are commonly combined into a hybrid topology to avoid sophisticated control schemes, while maintaining nearly unity power factor and soft switching of power switches simultaneously. However, the load-independent CC and CV are usually constrained by parameters of a loosely coupled transformer (LCT), making the LCT hard to design. To solve it, this paper systematically presents a method to derive such effective hybrid IPT converters, which starts from some existing topologies having the configurable CC or CV output and cascades a general T network for mode transition. Design principles with fewer mode switches and compensation components are proposed and some available hybrid topologies regardless of the constraint of LCT parameters are given in this paper. Control logic and sensitivities of compensation parameters to the input impedance and the load-independent output are also discussed. Finally, a 1 kW hybrid IPT battery charger prototype based on LCC-LCC and LCC-S topologies is built to verify the theoretical analysis.

The lifetime prediction of LED lighting system is important to guide the designers to fulfill the design specifications and to benchmark the cost-competitiveness of different lighting technologies. Currently, the lifetime of LED system is usually predicted from the source part and the driver part separately, and then the thermal design is also optimized independently. In practice, the LED source and driver are usually compacted in a single fixture. The heat dissipated from LED source and driver will be coupled together and affect the heat transfer performance, which may degrade the whole system and accelerate the failure. In this paper, a new thermal model concerning the thermal coupling is proposed with Finite Element Method (FEM) simulation for parameter acquirement. The proposed model has a better estimation of the thermal stresses of key components in the LED lamps and therefore an improved lifetime prediction of the LED systems. Moreover, with a given lifetime requirements, this method can be used to guide the thermal design of the LED system. A case study of an outdoor lighting application is then demonstrated by both FEM simulations and experimental verifications in this digest.

Summary This paper introduces FireWorks, a workflow software for running high‐throughput calculation workflows at supercomputing centers. FireWorks has been used to complete over 50 million CPU‐hours worth of computational chemistry and materials science calculations at the National Energy Research Supercomputing Center. It has been designed to serve the demanding high‐throughput computing needs of these applications, with extensive support for (i) concurrent execution through job packing, (ii) failure detection and correction, (iii) provenance and reporting for long‐running projects, (iv) automated duplicate detection, and (v) dynamic workflows (i.e., modifying the workflow graph during runtime). We have found that these features are highly relevant to enabling modern data‐driven and high‐throughput science applications, and we discuss our implementation strategy that rests on Python and NoSQL databases (MongoDB). Finally, we present performance data and limitations of our approach along with planned future work. Copyright © 2015 John Wiley & Sons, Ltd.

The Electronically Controlled Pneumatic (ECP) brake system is being applied to the heavy-haul trains for its control accracy and real time performance. A high power supply with high efficiency and reliability is essential to the safe operation of the ECP brake system. In this paper, a push-pull forward converter with a secondary full bridge rectifier is proposed for the ECP power supply. The voltage stress of the rectifier diodes can be reduced by a modified nodissipative snubber. Furthermore, hybrid control methods and criteria are utilized to improve the converter performance, including forced flux balancing circuit design, power supply output impedance and noise requirements. Finally, A 2.5kW prototype of the converter with efficiency up to 93% verifies the proposed circuit and theoretical analysis.

The current imbalance in driving LED strings will cause fast degradation or even failure in some LEDs that should be avoided in LED applications. This paper presents a current balancing method based on the pulse-width modulation of a common bus voltage to each LED string to achieve the intended averaged current. For the balance of a common averaged current, a small duty cycle will necessitate a large LED turn-on current amplitude, which may cause temporal overheat and low luminous efficacy of LEDs. An optimal feedback control scheme is proposed to maximize the duty cycles and minimize the bus voltage. As a result, at lease one of the LED string is operating at a unity duty cycle. The analysis, implementation and verification are detailed in this paper.

Light-emitting-diode (LED) light sources, which are more compact, capable to change color in real time, less dissipative and more durable, are finding more applications in domestic, commercial and industrial environments. However, requirements such as high power factor, long lifetime, accurate current control and high efficiency pose challenges to the design of LED ballast circuits. This paper proposes an LED ballast with a first-stage isolated current-fed power factor correction (PFC) pre-regulator that puts the short-lifetime high-voltage storage capacitor to the secondary, thus extending the overall system lifetime. Furthermore, the high voltage stress on the main switch, which is typical in current-fed converters, is reduced substantially by appropriately exploiting the transformer leakage inductance. The design uses two secondary transformer windings and an LED current driver to form a non-cascading structure to improve efficiency. Multiple non-cascading structures can be used for LED lamps for instant independent brightness control. Analysis, design example and prototype verification are given for the LED ballast.