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This article presents a control linearization technique for a single-phase single-stage inverter with multiple modulation strategies. The power topology is based on an flying capacitor multi-level (FCML) inverter, and the control is based on the plant inversion. The proposed technique allows decoupling the control of the input current and the output voltage, which simplifies the control in two ways: first, the control of both variables is independent and second, the controllers are independent of the modulation applied, thanks to the plant inversion. This control is implemented in an field-programmable gate array. Since the converter operates at variable frequency, two different data acquisition alternatives are explored: sampling at variable frequency (once per switching cycle) or sampling at constant frequency (higher than the switching frequency).The proposed control is validated by simulation and experimental results with a 1-kVA prototype.

Web APIs have been adopted as the de facto standard for exchanging data on the Web. However, engineering applications that orchestrate the invocation of multiple APIs and the data flow among them are still mostly manual and labor intensive. In fact, as the number of the potentially relevant APIs increases, compositions become opaque, difficult to maintain, and practically impossible to reuse. The recent advances around linked data formalisms have the potential to provide “usable” semantics, to enable automatic API composition methods. In this paper, we formalize a simplified description model, based on SPARQL graph patterns, for capturing the semantics of Web APIs. Based on this model, we propose a methodology for a fully automated process that produces semantically valid composition chains, using iterative subgraph isomorphism. We have validated the usefulness and accuracy of our approach, using a collection of publicly available Web APIs relevant to a real-world use cases.

Background High frequency alternating current (HFAC) stimulation have been shown to produce a peripheral nerve conduction block. Currently, all the studies applying HFAC stimulation in clinical studies, have employed frequencies below 10 kHz. The main aim of this work was to investigate the neuromodulatory effect of transcutaneous 20 kHz stimulation on somatosensory and pain thresholds, and maximal handgrip strength. Methods A randomized, crossover, single-blinded, placebo-controlled trial was conducted following recruitment of fourteen healthy volunteers. Transcutaneous stimulation at 20 kHz and sham stimulation were applied over the ulnar and median nerves of fourteen healthy volunteers for 20 min. Maximal handgrip strength (MHS), mechanical detection threshold (MDT) and pressure pain threshold (PPT) were registered prior to, during (15 min), immediately after the end (20 min), and 10 min following stimulation. Results The 20 kHz stimulation showed a lower MHS during the stimulation at the 15 min (30.1 kgs SE 2.8) and at 20 min (31.8 kgs, SE 2.8) when compared to sham stimulation (35.1 kgs, SE 3.4; p p = 0.03, respectively). The 20 kHz stimulation resulted in a slight increase in MDT at 15 min (0.25 mN; 0.25–2.00) when compared to the sham stimulation (0.25 mN; 0.25–0.25; p = 0.02), and no effects were showed for PPT. Conclusions High-frequency stimulation at 20 kHz suggests a partial block of nerve activity. Studies in subjects with neurological disorders characterized by nerve hyperactivity are needed to confirm the clinical impact of this non-invasive electrical stimulation technique. Trial registration NCT, NCT02837458. Registered on 12 April 2017.

Background. Epidural spinal electrical stimulation at the lumbar spinal level evokes rhythmic muscle activation of lower-limb antagonists, attributed to the central pattern generator. However, the efficacy of noninvasive spinal stimulation for the activation of lower-limb muscles is not yet clear. This review aimed to analyze the feasibility and efficacy of noninvasive transcutaneous spinal cord stimulation (tSCS) on motor function in individuals with spinal cord injury. Methods. A search for tSCS studies was made of the following databases: PubMed; Cochrane Registry; and Physiotherapy Evidence Database (PEDro). In addition, an inverse manual search of the references cited by the identified articles was carried out. The keywords transcutaneous, non-invasive, electrical stimulation, spinal cord stimulation [Mesh term], and spinal cord injury were used. Results. A total of 352 articles were initially screened, of which 13 studies met the inclusion criteria for systematic review. The total participant sample comprised 55 persons with spinal cord injury. All studies with tSCS provided evidence of induced muscle activation in the lower and upper limbs, and applied stimulation at the level of the T11-T12 and C4-C7 interspinous space, respectively. All studies reported an increase in motor response measured by recording surface electromyography, voluntary movement, muscle strength, or function. Conclusions. Although this review highlights tSCS as a feasible therapeutic neuromodulatory strategy to enhance voluntary movement, muscle strength, and function in patients with chronic spinal cord injury, the clinical impact and efficacy of electrode location and current intensity need to be characterized in statistically powered and controlled clinical trials.

Transcutaneous electrical spinal cord stimulation (tSCS) is a non-invasive technique for neuromodulation and has therapeutic potential for motor rehabilitation following spinal cord injury. The main aim of the present study is to quantify the effect of a single session of tSCS on lower limb motor evoked potentials (MEPs) in healthy participants. A double-blind, sham-controlled, randomized, crossover, clinical trial was carried out in 15 participants. Two 10-min sessions of tSCS (active-tSCS and sham-tSCS) were applied at the T11-T12 vertebral level. Quadriceps (Q) and tibialis anterior (TA) muscle MEPs were recorded at baseline, during and after tSCS. Q and TA isometric maximal voluntary contraction was also recorded. A significant increase of the Q-MEP amplitude was observed during active-tSCS (1.96 &plusmn, 0.3 mV) when compared from baseline (1.40 &plusmn, 0.2 mV, p = 0.01) and when compared to sham-tSCS at the same time-point (1.13 &plusmn, 0.3 mV, p = 0.03). No significant modulation was identified for TA-MEP amplitude or for Q and TA isometric maximal voluntary isometric strength. In conclusion, tSCS applied over the T11-T12 vertebral level increased Q-MEP but not TA-MEP compared to sham stimulation. The specific neuromodulatory effect of tSCS on Q-MEP may reflect optimal excitation of this motor response at the interneuronal or motoneuronal level.

This work presents a non-isolated hybrid topology targeting at 4:1 fixed ratio and high output current applications. This topology can be regarded as a compact integration of switched capacitor and autotransformer. The switched capacitors are soft charged and the two winding currents in the autotransformer are auto balanced. The transformer has quasi-DC current with negligible AC winding losses. To further study the performance of the transformer in the proposed circuit, the transformer is simulated with different current waveforms, and the results show that with quasi-DC current the winding losses do not increase with switching frequency, and they are at least two times lower than the losses generated from sinusoidal or square current. The proposed circuit is measured at 24V-6V step-down and up to 25A output current, achieving 96.7% peak efficiency. The same transformer is also tested in a full bridge testbench to compare winding losses with square current by measuring its temperature.

This paper presents a methodology to derive power converters when a single inductor is used. Given the current and voltage in the different ports, the modulation that minimizes the power processed in the inductor (indirect power) is obtained. The indirect power is associated with the energy stored and delivered by reactive components and the switching frequency. Therefore, it should be minimized to reduce volume and losses in the inductor. The methodology consists in the analysis of the indirect power on the possible operation modes of a converter, where operation modes are sequences of switching states. This methodology, when applied to DC-DC two-port conversion shows that the Buck or Boost converters are optimal in terms of power processed. Nevertheless, this methodology is more interesting when applied to three-port converters. In this work, it is applied to a three-port single-phase inverter where the third port is the capacitor used for power decoupling. The result is a complex topology that operates in several modes in different sectors of the line cycle with very reduced indirect power in the inductor. Finally, a simplified structure is described and implemented, providing experimental results.

Numerous neurological dysfunctions are accompanied by an undesirable increase of nerve activity, such as neuropathic pain or spasticity. There have been several studies over the last years on peripheral nerve block using high-frequency alternating currents, which could become a therapeutic alternative for such nerve hyperactivity. The main aim of this systematic review was to determine the optimal parameters of the electrical currents for producing peripheral nerve conduction block, the underlying neurophysiological mechanisms, and their possible adverse effects. Of the 49 included studies, 30 were animal experiments, 13 were computer simulations, and six were clinical trials. High-frequency alternating currents using frequencies of >4–5 kHz effectively block nerve conduction. However, depending on the type of axon or nerve diameter, the minimum frequency required to produce the nerve block could be >20kHz. Electrodes design, electrode-axon distance, and temperature are variables that affect the block threshold. There is no consensus about the block mechanism, although it has been showed that the frequency is a key factor to produce K+ channels activation or Na+ channels inactivation. The nerve block produced by currents quickly reverts without causing further damage to the nerve. Studies in humans are necessary to further validate what preclinical studies have already shown.

In modern aircraft designs, following the More Electrical Aircraft (MEA) philosophy, there is a growing need for new high-power converters. In this context, innovative solutions to provide high efficiency and power density are required. This paper proposes an unregulated LLC full-bridge operating at resonant frequency to obtain a constant gain at all loads. The first harmonic approximation (FHA) model is not accurate enough to estimate the voltage gain in converters with high parasitic resistance. A modified FHA model is proposed for voltage gain analysis, and time-based models are used to calculate the instantaneous current required for the ZVS transition analysis. A method using charge instead of current is proposed and used for this ZVS analysis. Using this method, an auxiliary circuit is proposed to achieve complete ZVS within the whole load range, avoiding a gapped transformer design and increasing the efficiency and power density. A 28 Vdc output voltage prototype, with 10 kW peak output power, has been developed to validate the theoretical analysis and the proposed auxiliary circuit. The maximum efficiency (96.3%) is achieved at the nominal power of 5 kW.

Very compact, highly efficient, hybrid DC/DC topology, consisted of a standard interleaved boost converter followed by a multilevel Resonant Switched Capacitor Converter (RSCC), that employs 900V Silicon-Carbide (SiC) devices, for use in emerging, two-stage, grid connected 1500V Photo-Voltaic (PV) systems is presented in this paper. Operation principle of this topology is described: controllability of its output voltage and power processing distribution among its stages in function of input voltage. Depending on operating region, certain amount of input power is not processed, but it is transfered directly to the output. This behaviour increases significantly efficiency of the analyzed topology, compared to the solutions presented in literature. The presented topology obtains full ZVS transitions in all operating conditions, even without load. ZVS transitions and employed SiC MOSFETs are the key elements for the high converter efficiency. Triangular Conduction Mode (TCM) in boost stage and resonant switching technique in RSCC part are used to obtain ZVS transitions in all the switches under wide range of loads and PV voltages. Results of multivariable optimization (pareto front) for the presented topology are provided. Previousely described theoretical analysis is fully experimentally confirmed by building and measuring a 10kW prototype of 8.26kW/kg of specific power and 404.6cm3 of volume occupied only by power stage components. Euro efficiency of 99.48% in nominal input/output voltage conditions is achieved.

In this paper, we present a highly efficient and compact voltage doubler based on a resonant switched-capacitor converter implemented with GaN FETs. Two possible approaches for its implementation are analyzed and compared. In the first approach, the resonant inductor is placed in series with a resonant capacitor, conducting a sinusoidal current, while in the second, it is placed in series with the input source, conducting rectified sinusoidal current. Both resonant converters have the same voltage gain, and although the change in the position of the resonant inductor is, at the first glance, of minor importance, the analysis and results show that it has huge impact on the capability to achieve zero-voltage switching (ZVS) transitions at low output power. The experimental results clearly show that at low loads when the resonant inductor is in series with the resonant capacitor, the switching frequency can be significantly higher than the resonant frequency and that it is, practically, impossible to achieve ZVS transitions, forcing the implementation of cycle skipping. The prototype implemented for the experiments can provide up to 4.5-kW losing between 20 and 22 W. In the case of light load (500 W), the power losses were only 2–3 W. Its power density is higher than 65 kW/dm3. The same resonant converter was tested with Si CoolMOS devices as well and the impact of the semiconductor technology on the overall power losses was verified. Due to higher $C_{\mathrm {oss}}$ capacitance, the Si-based converter has 40% higher power losses at full power than its GaN-based counterpart. The components of the GaN-based converter occupy only 65 cm3, which opens a possibility to obtain a design with extremely high power density

This paper describes a simple methodology to generate “continuous power models” (CPM), based on VA area interpretation of the power flowing through the ports of multiport converters. These models enable the calculation of the minimum indirect power to be processed by power converters based on their electrical specifications. It is especially useful to compare power architectures with multiple building blocks or multiple ports, such as stacked sources (PV cells) or loads (digital cores) and energy buffered converters such as single-phase inverters, power factor correction circuits and three phase rectifiers and inverters. The synthesis of circuits that minimize the figure of merit $P_{ind}/P_{diff}$ is also illustrated in the paper.

In this paper we compare two different approaches to control an inverter operating at variable frequency with multiple operation modes along the line cycle. The first methodology is to control at constant sampling frequency higher than the switching frequency. Over sampling techniques seems promising in reducing the phase lag, but inject high frequency disturbance and may produce limit cycle oscillations. The other approach is to control at variable sampling frequency, equal to the switching frequency. The main drawback is how to discretize the regulator.

The scope of this paper is to describe how to achieve and optimize Zero-Voltage Switching (ZVS) in an energy buffered single-phase inverter. The inverter can be described as a three-port system in which the third port is the storage capacitor. Several operation modes are used along the line cycle, depending on the required voltages and currents in the three ports. The operation modes shape the inductor current and control the power balance among ports. Operation modes are selected to ensure ZVS in every transition and minimum power precessed by the inductor. The energy in the inductor is used to obtain ZVS. ZVS is not only important to reduce dramatically switching losses, but also to limit dv/dt in switching nodes. GaN transistors require low current in the inductor to perform ZVS compared to Silicon devices since they feature around four times lower parasitic capacitance. This paper describes a methodology to calculate the minimum current in the inductor required to perform ZVS in all transitions, and the trade-off between $\boldsymbol{R_{ds}}$ and $\boldsymbol{C_{oss}}$ of switching devices. Results obtained are applied and validated in the prototype.

The number of Web APIs for accessing information and services is continuously increasing, and yet, no tools exist to automate the process of invoking these APIs and composing their responses, which can be time consuming and error prone. In our previous work, we described LRA (Linked REST APIs) [1], a middleware that enables the automatic composition of REST APIs. Although this automation represents a great opportunity to systematize and improve the quality of the process of using Web APIs, LRA's reliance on SPARQL as the user-interaction model may hinder its adoption. Hence, based upon previous work on Linked Data query systems, in this paper we present a tool that takes advantage of the emergent schema of Web API descriptions, in order to simplify the formulation of LRA-compliant queries.

In this paper we compare two resonant switched capacitor converters in which the resonant inductor can be placed in series with a resonant capacitor (AC side), conducting a sinusoidal current, or it can be placed in series with the input source (DC side), conducting rectified sinusoidal current. Both resonant converters have the same voltage gain, and although the change in the position of the resonant inductor is, at first glance, of minor importance, the analysis and results show that it has huge impact on the capability to achieve ZVS transitions at low output power and on the inductor design and power losses. The experimental results show that for circuit with the resonant inductor in the AC side, the ZVS transitions produce an effective switching frequency significantly higher than the resonant frequency which forces the implementation of cycle skipping at light loads. The difference between the power losses in these two approaches is between 3W and 5W. The prototype implemented for the experiments provides up to 4.5kW with 33.3W power loss (99.3% efficiency). In the case of light load (1.5kW) power losses are only 8.25W (η=99.45%). Its power density is higher than 65kW/dm3.

In this paper we propose the mode selection strategy of a multi-mode single-stage single-phase inverter and the associated mode selection scheme for double-line-frequency power pulsation decoupling between the input an the output port for PV (photovoltaic) panel applications. Multiple modulation strategies are used along the line cycle to optimize the overall efficiency of the converter. The proposed topology uses several modulations for the inductor current waveform, such that the power handled internally by the elements in the converter is minimized at any time, while performing the output voltage control and power decoupling. The evaluation and selection of the most appropriate modulation in real-time represents a challenge for the control. This work allows to reduce the computational cost of evaluating the decision metric. A mode selection scheme is proposed and validated in a hardware prototype.

This work proposes a control linearization technique for a single phase 3 level-flying capacitor multi-level (FCML) inverter with multiple modulation strategies along the line period, based on the plant inversion. Multiple modulation strategies are used along the line cycle so that the overall size and efficiency of the converter are optimized. This benefit from the point of view of the energy processing generates a design challenge for the control. The proposed technique allows decoupling the control of the input current and the output current, which simplifies the control of the output voltage and the storage capacitor voltage in two ways: first, the control of both variables is independent and second, the controller parameters will be independent on the modulation strategy due to the plant inversion. These advantages are critical for the successful control of this highly non-linear time-varying system.

Over the last decade, an exponentially increasing number of REST services have been providing a simple and straightforward syntax for accessing rich data resources. To use these services, however, developers have to understand "information-use contracts" specified in natural language, and, to build applications that benefit from multiple existing services they have to map the underlying resource schemas in their code. This process is difficult and error-prone, especially as the number and overlap of the underlying services increases, and the mappings become opaque, difficult to maintain, and practically impossible to reuse. The more recent advent of the Linked Data formalisms can offer a solution to the challenge. In this paper, we propose a conceptual framework for REST-service integration based on Linked Data models. In this framework, the data exposed by REST services is mapped to Linked Data schemas, based on these descriptions, we have developed a middleware that can automatically compose API calls to respond to data queries (in SPARQL). Furthermore, we have developed a RDF model for characterizing the access-control protocols of these APIs and the quality of the data they expose, so that our middleware can develop "legal" compositions with desired qualities. We report our experience with the implementation of a prototype that demonstrates the usefulness of our framework in the context of a research-data management application.

In this paper we review some of the fundamental limits of dc-dc power converters described in 1966 and 1969 and generate an averaged power model that is useful to perform high-level comparison of power converters and architectures. The model is extended to 3 port power converters, which is used to calculate the minimum possible internal power to be processed by the components of the power stage of energy buffered converters. Finally, a single stage inverter/rectifier with energy storage capability that meets the fundamental limit is synthesized.

Nowadays, the Web of Data contains a myriad of structured information sources on a large number of domains. Nevertheless, most of the information is available through Web APIs that act as isolated silos of data that cannot interoperate automatically with other resources and services on the Web. My dissertation aims at synthesizing semantic web technologies over Web APIs, in order to combine the easy data integration techniques offered by semantic web, with the flexibility and availability of web services. This paper discusses the two main aspects of the envisioned thesis: (a) a description language to semantically describe functional and non-functional components of web services, and the relationships among those components, and (b) a middleware that plans composition chains, based on user’s specifications, optimizing their trade-offs.

The emergence of cloud computing and the Internet of Things (IoT) have given rise to a wealth of new opportunities for integrating heterogeneous systems and collecting massive data sets, whose analysis may lead to new information, insight, and knowledge. Building a scalable architecture for urban IoT environments is a complex task, primarily because of the massive amounts of data generated by sensor devices, and the variety of data sources. And yet it is a compelling application area, given the number of potential municipal services that can be improved using these technologies. In this paper, we describe our study of how cloud-computing and big-data management technologies can assist decision making for transportation systems in smart cities. More specifically, this paper presents and discusses a proof-of-concept prototype, based on open-source technologies and publicly available data for the city of Edmonton.

Nowadays, exoskeletons have been introduced for empowering walking in military, industrial and rehabilitation settings. Several companies are commercializing these devices, but there is a lack of understanding of their effects on muscle activations and coordination. The objective of this article is to investigate the impact on muscle activation and user effort during ambulatory, robotic-assisted walking. Compared with free walking, our results suggest that robotic assistance with the Exo-H2 lower limb exoskeleton may result in increased muscle activation. Muscular timing experienced unspecific changes with respect to unassisted walking. Further research is needed to unveil the mechanical interaction between the robot and the lower limbs and the underlying motor adaptations in response to robot-assisted walking.

Mobile video streaming becomes increasingly useful in a variety of contexts (social interaction, education, and entertainment) and increasingly feasible with the rapid advancement of wireless networks and mobile technologies. In this paper, we present, Kaleidoscope, a cloud platform for multimedia streaming on mobile devices, enhanced with textual and touch-display interactions for a rich user experience. We evaluate the Kaleidoscope system on two different clouds at different locations, testing the streaming quality, and CPU and memory usage, using different numbers of clients.