Single-carrier phase-disposition PWM techniques for multiple interleaved voltage-source converter legs

Interleaved converter legs are typically modulated with individual carriers per leg and phase-shifted PWM (PS-PWM) as it facilitates current balancing amongst the legs. Phase-disposition PWM (PD-PWM), despite the better harmonic performance, cannot be directly used due to the resulting current imbalance that may damage the converter. This paper addresses the current sharing issue and proposes a single-carrier PD-PWM technique for multiple leg two-level converters based on a hierarchy scheme derived from current sorting algorithms. An extension of the proposed algorithm through a switching state feedback loop, limiting the average switching frequency, is also developed. In both cases, the load current is shared amongst the legs and the high-quality of the output voltages and currents is maintained while the circulating currents amongst the converter legs are kept to a minimum. Simulation results demonstrate the method for multiple interleaved legs as well as its current sharing capabilities for high-power applications. Experimental results from a low-power laboratory prototype validate the operation of the proposed approach.Peer ReviewedPostprint (published version

Comparison of bipolar sub-modules for the alternate arm converter

© 2016 IEEE.Research on dc-fault tolerant multilevel converters has gained noticeable attention over recent years. The alternate arm converter (AAC) is one of such emerging multilevel converter topologies, and a hybrid topology of the two-level converter and the modular multilevel converter (MMC). Bipolar sub-modules (SMs) that can produce both positive and negative voltages are the building blocks of the AAC. This paper analyses the operation of an AAC with the full-bridge SM (FB-SM) and the cross-connected SM (CC-SM). The conduction and switching losses of the two SM configurations are evaluated and compared, in order to identify the suitability of CC-SM for AACs and its performance compared to the FB-SM. The CC-SM with identical semiconductor devices has reduced losses compared to the CC-SM with higher rated devices in the cross-connected path. It is concluded that the CC-SM does not offer advantages in the losses, construction, and application to the AAC, compared to FB-SM

Grid sequence detector based on a stationary reference frame

This paper proposes a new three-phase positive sequence detector. The scheme is based on a stationary reference frame and a Moving Average Filter (MAF) that guarantees the complete cancellation of harmonics and grid imbalances. The performance of the MAF is mathematically analyzed and a proper selection of the optimal filter’s window width is realized. The proposed detector operates in open loop and there is no PI controller to be tuned. Thus, the dynamic response and simplicity is improved compared to other solutions. Performance of the proposed detector is verified through simulation and experiment. It shows very good performance under extreme grid voltage conditions, allowing fast detection of the grid voltage positive sequence (within one grid voltage cycle).Postprint (published version

Capacitor voltage balance limits in a multilevel-converter-based energy storage system

This paper studies an energy storage system based on a three-level DC-DC converter and a gridconnected neutral-point-clamped inverter. The main advantages of this multilevel power conversion system are highlighted and the neutral-point voltage oscillations are analyzed. A modulation algorithm for the DC-DC converter which includes the neutral-point voltage balance control is used to improve the voltage balancing capabilities of the inverter. Some figures are presented to show the extended operating areas without neutral-point voltage oscillations thanks to the contribution of the DC-DC converter to the voltage balance. Finally, some guidelines to size the DC-link capacitors are given for a practical application.Peer ReviewedPostprint (published version

A Universal Formulation for Multilevel Selective Harmonic Elimination - PWM with Half-Wave Symmetry

Selective harmonic elimination - pulse width modulation (SHE-PWM) can be utilized to improve the efficiency of multilevel voltage source converters due to its ability to provide low switching frequency and tight control of low-order harmonics. In addition, SHE-PWM with half-wave (HW) symmetry provides a higher number of solutions than quarter-wave (QW) symmetry and therefore, the waveform design can be improved. This work proposes a universal formulation, which can be utilized with HW symmetry, that provides a unique system of equations valid for any possible multilevel waveform. Thereby, without using predefined waveforms, this formulation provides the ability to search simultaneously both the firing angles and the switching patterns, simplifying significantly the search process and providing a high number of solutions. With the aim of selecting the optimum sets of firing angles, the solutions provided by HW and QW symmetries are compared, based on several metrics of harmonic performance, for particular test cases. Experimental results also validate the universal formulation with HW symmetry.Eusko Jaurlaritza; Secretaria de Estado de Investigacion Desarrollo e Innovacio

Parallel-connected legs in a grid-tied inverter system for distributed generation

Grid-connected high-power inverters are often used in distributed generation and power quality systems. Those inverters have to handle high currents in order to achieve high power values without resorting to higher voltages. Connecting inverter legs in parallel is a proper way to achieve such high currents. Such parallel connection is made by means of inductors and achieving balanced currents among the legs becomes a critical issue. Circulating currents may produce additional losses and stress to the converter’s power devices. Therefore, they should be controlled and minimized. An efficient technique to achieve such balance is presented in this paper. The proposed strategy has been developed on a gridconnected three-phase system. Each phase of the inverter is made up of three legs in parallel. Besides, the control implemented in this work allows full regulation of the power factor. This way, any desired power factor value can be achieved in order to meet grid-connection requirements. Simulation and experimental results are shown in this paper.Peer ReviewedPostprint (published version

Management control in Radiopharmacy Hospital Units: Review of the variables to consider using Balanced Scorecards In

Objetivos: Listar las variables imprescindibles en los cuadros de mando integrales para abarcar todas las áreas básicas de trabajo en una Unidad de Radiofarmacia hospitalaria, cuya adecuada gestión puede ser clave para optimizar los recursos disponibles. En segundo lugar, enumerar los beneficios que redundan en la práctica de trabajo diario tras su integración. Métodos: Revisión de la bibliografía publicada sobre cuadros de mando integrales, seleccionando las variables para que el radiofarmacéutico asuma un papel activo en la mejora de su área de trabajo. Se utilizan programas construídos en Microsoft Access para la gestión integral. Se administran en varios módulos toda la información desde la prescripción y citación de los pacientes (asignándoles un código) hasta que se les realiza la exploración. Se recogen también variables como: fecha y hora límites de tramitación de radiofármaco al proveedor; fecha prueba médica; gestión de eluciones de generadores y kits fríos; turnos de trabajo del personal; registro de incidencias tipificadas y de datos de recepción, marcaje, control de calidad y dispensación de cada radiofármaco (asegurando la trazabilidad); detección de desviaciones entre actividad calibrada y medida; la actividad dispensada y la disponible a tiempo real; gestión de eliminación de residuos radiactivos, de existencias y caducidades; fechas de próximas revisiones de equipos; archivado de PNT; sistemas conversores de unidades y registro de informes clínicos. Resultados: Los programas especializados gestionan la información que se maneja en la Unidad de Radiofarmacia, facilitando tomar decisiones coste-efectivas. Los parámetros analizados son: número de preparaciones elaboradas y actividad manejada; posibles incidencias en cualquiera de los procesos cotidianos; porcentaje de resolución satisfactoria sin que derive en falta de disponibilidad; correcta trazabilidad de los radiofármacos; porcentaje de controles de calidad satisfactorios; evolución en el consumo por tipo de radiofármaco, etc. La mejora en la gestión de pedidos asegura la presencia del radiofármaco necesario para cada exploración. Conclusiones: Estos nuevos cuadros de mando integrales son útiles para optimizar pedidos y radiofármacos, asegurar trazabilidad, gestionar inventario, informes clínicos, residuos radiactivos y para evaluar la eficiencia de la Unidad de radiofarmacia, permitiendo la integración de estos datos con otros softwares de gestión sanitaria. Esta metodología puede aplicarse en Centros Sanitarios de Atención Primaria para enfocar al personal en sus funciones asistenciales y operativas.Objetives: We list the essential variables in Balanced Scorecards to cover all basic areas of work in a Radiopharmacy Hospital Unit, whose proper management can be key in optimizing the resources that are available. Secondly, to list the benefits in the practice of daily work that result after integration. Methods: A review of the published literature about Balanced Scorecards, selecting the variables to be collected for the radiopharmaceutical to take an active role in improving his work area. Applications built in Microsoft Access for comprehensive management are used. They are administered in various modules all the information from the prescription and citation patients (assigning a code) until they perform medical test. Also collected variables such as date and time limits for processing radiopharmaceutical supplier; medical test date; management elutions of generators and cold kits; staff work shifts; typified record incidents and receive data, labeling, quality control and dispensing of each radiopharmaceutical (ensuring traceability); detecting deviations between calibrated and measured activity; to know the dispensed activity and available in real time; management of radioactive waste disposal, inventory and expiration dates; dates of upcoming reviews of equipment; SOP filed; converter systems units and registration of clinical reports. Results: These specialized software manage the information handled in daily practice in Radiopharmacy Hospital Unit, facilitating cost-effective decisions. These parameters analyzed are usually: number of elaborate preparations and managed activity; possible incidents in any of the everyday processes; percentage of satisfactory resolution without resulting in unavailability; correct traceability of radiopharmaceuticals; percentage of satisfactory quality controls; evolution in consumption by type of radiopharmaceutical, etc. The improved order management ensures the presence of the radiopharmaceutical needed for each medical test. Conclusions: These new Balanced Scorecards are useful to optimize orders and radiopharmaceuticals, ensure traceability, inventory management, clinical reports, radioactive waste and to evaluate the efficiency of the Radiopharmacy Hospital Unit, allowing the integration of these data with others software health management. This methodology can be applied in Primary Care Health Centers to focus on its healthcare staff and operational functions

Marco para evaluar las condiciones institucionales de la docencia en línea.

The purpose of the paper is to present a validated analytical framework for assessing the institutional conditions of online teaching in higher education. A descriptive study was performed using content analysis techniques, interviews and focus groups. The method included theory, fieldwork, and academic teamwork, and an intersubjective consensus was sought between various teams of participants (expert researchers, basic and specialized users of online teaching) who assessed the clarity, relevance, coherence, and adequacy of dimensions and indicators. As a result, a framework was developed including seven dimensions: institutional policy, institutional organization, institutional regulations, institutional plans and programs, online educational model, teachers’ working conditions, and infrastructure and equipment. The work concludes by supporting the use of the proposed framework as a guide for self-assessment of institutional conditions that further the quality of online teaching