Hugo Calleja

Reliability Estimation of Three Single-Phase Topologies in Grid-Connected PV Systems

This paper presents the reliability estimation of the power stages in three grid-connected photovoltaic systems. The circuits analyzed are an integrated topology, a two-stage configuration, and a three-stage one, all commutating in the hard-switching mode. The reliability-related parameters, such as the failure rate, are calculated following the procedure outlined in MIL-HDBK 217. A comparison between the topologies is performed, and both the components and the stress factor with the highest contribution to the failure rate are identified. The methods to calculate junction temperature variations are included.

Design Strategy to Optimize the Reliability of Grid-Connected PV Systems

This paper presents a strategy, based on the design-of-experiments technique, aimed at optimizing the reliability in inverters for photovoltaic systems. The process involves designing the inverter several times, each time with different specifications, and calculating the reliability for each design. The specifications are established in a systematic manner, in such a way that the parameters with the highest impact are easily identified. The optimization procedure follows a standard reliability estimation methodology and involves modifying the stress factors in a judicious manner. The strategy is exemplified with an integrated boost inverter and a desired mean time between failures of 12 years.

Reliability-Oriented Assessment of a DC/DC Converter for Photovoltaic Applications

There is a trend toward increasing the performance of power electronics converters used in photovoltaic systems. However, parameters such as reliability, efficiency, and complexity might be in conflict. In this paper, the design of a simple DC/DC interleaved boost converter is assessed. It takes advantage of state-of-the-art power devices that have fast switching times. It is shown that requirements of low complexity, high reliability, and high efficiency can be satisfied, without resorting to switching aids, provided that the devices are selected with reliability in mind. A 1 kW prototype attained a peak efficiency as high as 98%, and a predicted mean time between failures of 100,000 hours at 80 C.

A high quality output AC/AC Cuk converter

In this paper the design of an AC-AC converter, capable of generating a high-quality output, is described It is based on the Cuk configuration and, since there are no transformers, it lends itself to a compact and lightweight implementation. An integrated circuit, developed for DC-DC applications, is used to control the converter. Tests performed show that the output exhibits a THD = 3%. The efficiency is slightly higher than 89%, and the average output regulation is 0.3%.

Reliability: A Neglected Topic in the Power Electronics Curricula

This paper presents the approach followed to develop a course that introduces reliability into the design of power electronics converters. The course is part of the curriculum of a master of science in electrical engineering program, and it is aimed at providing reliability tools that can be used in a straightforward manner, while avoiding the mathematical intricacies. The reliability calculations are performed according to the Military Handbook 217, using the evaluation version of a commercial software package which greatly reduces the computational burden usually associated with this task. The course assessment shows that, after attending the course, students were able to improve the mean time between failures in a power-electronics converter, from a minimum of 5%, up to 100%.

Harmonic Propagation Damping in Ring Power Distribution Systems using an Active Filter

This paper presents an analysis to select the best location for a shunt active power filter, aimed at damping the resonances in a ring power distribution network. The active filter, which is based on the voltage detection method, behaves as a high impedance at the fundamental frequency, and as a low resistance at harmonic frequencies. Simulation and experimental results show that the active filter can damp out harmonic propagation throughout the power distribution line.

Study of Harmonic Propagation in Ring Bus Distribution System

This paper presents an analysis of the harmonic propagation phenomenon in a ring distribution network. An actual industrial facility installation is modeled and simulated in Spice, in order to identify the nodes with the highest resonances. The simulation results are compared with experimental results obtained from a low-power test-bench. These results are used to establish a set of guidelines aimed as an aid to quickly identify the most troublesome nodes in the installation, without having to perform a complete, full analysis of the network. The guidelines were tested by modifying network parameters, such as the transformers ratings. In all the cases tested, the results were in good agreement with the guidelines

Three-Phase PWM AC/AC Cúk Converter for Voltage Sag Compensation

A three-phase PWM AC/AC Cuk converter aimed at voltage sag compensation is presented. Unlike other configurations, the converter has a modular structure, allowing individual phase compensation, and thus providing a balanced response to voltage sags. The design procedure is derived from the basic DC/DC converter analysis, and conveniently modified for AC/AC operation. The control stage is implemented using commercial analog PWM ICs along with digital logic for gating pulse distribution. The converter was tested in static and dynamic operating conditions. The tests performed show that the output voltage is kept within a ±3% range of the nominal voltage, and its THD level is below 5%, operating with an average efficiency of 89.44%. The response time to a 63% depth voltage sags is good, returning the output voltage to −10% of the nominal voltage in less than a half line cycle, in full compliance with the ITIC curve for information equipment. These performance characteristics make the converter a suitable choice for power conditioning sensitive loads.

A Review of Solutions for Harmonic Propagation Damping in Power Distribution Networks

The widespread use of non linear loads in the industry has created power-quality related problems in power distributions systems. Voltage harmonics are produced by the harmonic currents flowing through the grid. In turn, the current harmonics are generated by the non-linear loads. Voltage harmonics might be troublesome depending on the line impedance, and these harmonics can be amplified by the harmonic propagation phenomenon. The proposed solutions to this phenomenon include both active and passive approaches. This paper presents a review of passive and active solutions for this phenomenon, including the different active filters topologies, harmonic detection methods, harmonic extraction methods, control strategies and the best point connection of an active filter in power distribution networks

Design strategy to optimize the reliability of power converters

This article presents a strategy, based on the design-of-experiments technique, aimed at optimizing the reliability in power converters. The process involves designing the converter several times, each time with a different set of specifications, Afterwards, the reliability for each design is calculated using a standard procedure. The specifications are established in a systematic manner in such a way that, through a variance analysis, the factors with the highest impact on the failure rate are easily identified. Once the most failure-prone components, and the dominant failure mechanisms are identified, the design can be modified to optimize the reliability. The strategy, although is computational intensive, is a cheaper and faster approach to reliability improvement than accelerated testing. The strategy is exemplified with a DC motor drive.