Estado periodontal de los segundos molares, posterior a exodoncia de terceros molares inferiores incluidos, comparando dos diseños de colgajos

78 p.Introducción: La exodoncia de terceros molares es un procedimiento frecuente en odontología, la evidencia es contradictoria con respecto al efecto de la cirugía sobre los tejidos periodontales del segundo molar. La utilización de colgajos marginales provoca daño directamente sobre el ligamento periodontales del segundo molar, y por otra parte se ha descrito que la confección de colgajos mucoperiosticos produce la activación osteoclastica con la consiguiente pérdida de hueso alveolar de la zona. Estudios han comparado la influencia de un colgajo marginal y uno paramarginal en la salud periodontal del segundo molar, se han presentado resultados favorables pero que han hecho la diferencia a lo largo del tiempo. Objetivo: Establecer si existen diferencias en el estado de salud periodontal de los segundos molares, tres meses posterior a la cirugía de terceros molares, comparando el colgajo triangular con el paramarginal triangular modificado (PTM). Materiales y Métodos: 29 pacientes, entre 15 y 30 años, lo que contabilizo un total de 43 terceros molares con indicación de extracción, se constituyeron dos grupos uno de 21 y otros de 22 terceros molares, en un grupo se realizo la cirugía con el diseño de colgajo triangular y en el otro el diseño PTM. La salud periodontal del segundo molar fue evaluada preoperatorio y tres meses posterior a la cirugía. Luego se realizo la comparación de los parámetros medidos. .Resultados: En cuanto al PSR, no mostros diferencia estadísticamente significativas, la presencia de recesión mostró resultados favorables para el colgajo PTM pero no estadísticamente significativos, en los índices gingival y la profundidad del sondaje presentaron cambios estadísticamente significativos a favor del colgajo PTM, por último el nivel de inserción clínica presento resultados estadísticamente significativos para todos los sitios, excepto el mesiovestibular, a favor del colgajo PTM. Conclusión: Existe evidencia respecto a que el colgajo PTM posee mejores resultados postoperatorios sobre la salud periodontal del segundo molar en los sitios vestibular y distovestibular, no presentando diferencias estadísticamente significativas para los otros sitios. *Palabras claves: Salud Periodontal; Diseños de Colgajos; Terceros Molares

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

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).Peer ReviewedPostprint (author’s final draft

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

Variable-Frequency Grid-Sequence Detector Based on a Quasi-Ideal Low-Pass Filter Stage and a Phase-Locked Loop

This paper proposes a filtered-sequence phase-locked loop (FSPLL) structure for detection of the positive sequence in three-phase systems. The structure includes the use of the Park transformation and moving average filters (MAF). Performance of the MAF is mathematically analyzed and represented in Bode diagrams. The analysis allows a proper selection of the window width of the optimal filter for its application in the dq transformed variables. The proposed detector structure allows fast detection of the grid voltage positive sequence (within one grid voltage cycle). The MAF eliminates completely any oscillation multiple of the frequency for which it is designed; thus, this algorithm is not affected by the presence of imbalances or harmonics in the electrical grid. Furthermore, the PLL includes a simple-frequency detector that makes frequency adaptive the frequency depending blocks. This guarantees the proper operation of the FSPLL under large frequency changes. The performance of the entire PLL-based detector is verified through simulation and experiment. It shows veryPeer ReviewedPostprint (published version

Study and comparison of discontinuous modulation for modular multilevel converters in motor drive applications

Discontinuous modulation applied to modular multilevel converters is an effective method for reducing the capacitor voltage ripples. In this paper, the discontinuous modulation is adapted and used in a motor drive application. For proper operation of the converter, a new energy controller is presented, which is suitable for operation with nonsinusoidal reference signals. Experimental results comparing the discontinuous modulation with other techniques operating at low motor speeds are shown. The results demonstrate the effectiveness of the discontinuous modulation on reducing capacitor voltage ripples and power losses.Postprint (published version

Current balancing strategy in parallel-connected legs of power inverters

The parallel connection of inverter legs is a way to increase the output currents and thus the converter rated power. The connection is made by inductors and a critical issue is to achieve balanced currents among the legs. Circulating currents produce additional losses and stress to the power devices of the converter. Therefore, they should be controlled and minimized. An efficient technique to achieve such a balance is presented in this paper. The proposed strategy does not include proportional-integral (PI) controllers and parameter tuning is not required. The exact control action to achieve current balance is straightforward calculated and applied. Simulation and experimental results are shown in this paper to verify efficiency of the proposed balancing method.Postprint (author’s final draft