Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Reliability assessment of the 1964 mariner mars spacecraft

Numerical exercise of reliability model of Mariner Mars spacecraft and spacecraft subsystems reliabilit

Development of a Supercapacitor based Surge Resistant Uninterruptible Power Supply

Uninterruptible Power Supplies (UPSs) provide short-term power back-up to sensitive electronic and electrical equipments, where an unexpected power loss could lead to undesirable outcomes. They usually bridge the connected equipment between the utility mains power and other long term back-up power systems like generators. A UPS also provides a “clean” source of power, meaning they filter the connected equipment from distortions in electrical parameters of the mains power like noise, harmonics, surges, sags and spikes. A surge resistant UPS or SRUPS is one that has the capability to withstand surges, which are momentary or sustained increases in the mains voltage, and react quickly enough to offer protection to the connected equipment from the same. Usually UPSs run off battery power when the utility mains power is absent. But the SRUPS developed in this design project uses super capacitors instead of battery packs. The reason for this is that the high energy-densities and medium power-densities offered by super capacitors allow for it to serve two purposes. One is to provide the DC power to operate the UPS in the absence of mains power, as an alternative to batteries. Secondly, super capacitors can withstand heavy momentary high current/voltage surges due to its high energy-density characteristics. Also as the life-time of super capacitors is much higher than that of conventional batteries and as they do not need regular topping-up or inspection, the end result is a truly maintenance-free UPS. Most commercial UPSs do not have inherent surge protection capabilities. The UPS is one entity while a discrete surge protection module is inserted between the utility mains and the UPS to provide for transient surge suppression. In the proposed SRUPS, the super capacitor, because of their inherent capability to absorb transient surges, forms a protective front end to the actual UPS rather than needing to have the involvement of discrete protection devices

Development of a Power Factor Corrected High Current Supercapacitor Charger for a Surge Resistant UPS

The Uninterrupted Power Supplies (UPSs) provide short term power back up to electrical loads when the mains power fail. Usually UPSs employ battery packs as the energy storage device. However the limitations of battery packs can affect the UPS performance. As an alternative energy storage device, the supercapacitor (SC) technology is well developed over the past 30 years. Due to recent developments, single cell commercial supercapacitors are available up to about 5000 farads. Over the past 10 years, supercapacitor direct current (DC) voltage ratings have gradually increased to about 2.7 V/cell. New lithium based supercapacitor families have DC ratings up to 3.5 V/cell. For the high current applications, the supercapacitors have some advantages over batteries, which are the low effective series resistance (ESR), high power densities and high surge withstand capability. This thesis is a continuation of the work begun by Kozhiparambil, P. K. on Surge Resistant Uninterrupted Power Supply (SRUPS). The reason for this continual research is due to identify weaknesses in original of SRUPS work with regard to the design of the charger. To reduce the components contain, also achieve common mode transient rejection capability, a flayback mode high current charger with power factor correction has been developed for charging the SC banks. The prototype circuit includes multiple SC banks to transfer the energy from the 240 V, 50 Hz power line to the load maintaining high isolation level. The loads receive continuous and surge free power from the SC banks, and has electrical isolation from the main power line. An IGBT is used as a switch for the flyback charger, which has the advantage of high current capability. The experimental results show the design was valid for the SRUPS and it demonstrated the capability to transfer the energy through a flyback charger with power factor correction

Design of a high-performance single-phase offline UPS with reduced switching time

A high performance single phase offline UPS with reduced switching time is proposed in the present paper. The proposed UPS can protect loads from supply outage, overvoltage and undervoltage. A bidirectional DC-DC converter takes part of the presented model, in order to reduce the system size. Thus, the converter has the capability to charge the battery and to keep a regulated voltage for the inverter’s DC-link. In order to provide a regulated output voltage for any type of load, a PWM (Pulse-Width Modulation) inverter with a multi-loop control strategy, using capacitor current as feedback variable, is also developed. By using the sliding window method, to detect long period voltage disturbances in real time, the switching time between mains and UPS can be significantly reduced. Moreover, simulation and practical results in different mains conditions are analyzed.This work is funded by FEDER Funds hrough the Operational Programme Competitiveness Factors – COMPETE and by National Funds through FCT – Foundation for Science and Technology under Project: COMP-01-0124-FEDER-022674

Design of a microcontroller-based passive standby uninterruptible power suply (UPS)

Uninterruptible Power Supply (UPS) are widely used to provide emergency power to critical loads in case of utility mains failure, and as such constitutes an essential element in providing back-up power for computer networks, communication links, biomedical equipment, and industrial processes, among others. For a microcontroller-based UPS, a full hardware-based UPS are gradually being replaced by microprocessor or microcontroller-based counterparts, with significant improvement in ease of design, flexibility of the control software and overall reduction in development cost. Since a UPS incorporates a relatively large number of detection, protection and control functions, it is important to develop an organized approach to the identification and implementation of these requirements. The purpose of his project is to provide an efficient time management for users to continue their work with personal computer even though an outage had occurred. Since this project involves hardware-software co-design, so that knowledge from a number of engineering disciplines is necessary for arriving at a workable solution. This microcontroller-based Uninterruptible Power Supply will enable the users to monitor their current battery level through the installed Liquid Crystal Display. One of the advantages applying microcontroller for the Uninterruptible Power Supply is that the system is more reliable in functions compares to the conventional Uninterruptible Power Supply available in the market

Converter fault diagnosis and post-fault operation of a doubly-fed induction generator for a wind turbine

Wind energy has become one of the most important alternative energy resources because of the global warming crisis. Wind turbines are often erected off-shore because of favourable wind conditions, requiring lower towers than on-shore. The doubly-fed induction generator is one of the most widely used generators with wind turbines. In such a wind turbine the power converters are less robust than the generator and other mechanical parts. If any switch failure occurs in the converters, the wind turbine may be seriously damaged and have to stop. Therefore, converter health monitoring and fault diagnosis are important to improve system reliability. Moreover, to avoid shutting down the wind turbine, converter fault diagnosis may permit a change in control strategy and/or reconfigure the power converters to permit post-fault operation. This research focuses on switch fault diagnosis and post-fault operation for the converters of the doubly-fed induction generator. The effects of an open-switch fault and a short-circuit switch fault are analysed. Several existing open-switch fault diagnosis methods are examined but are found to be unsuitable for the doubly-fed induction generator. The causes of false alarms with these methods are investigated. A proposed diagnosis method, with false alarm suppression, has the fault detection capability equivalent to the best of the existing methods, but improves system reliability. After any open-switch fault is detected, reconfiguration to a four-switch topology is activated to avoid shutting down the system. Short-circuit switch faults are also investigated. Possible methods to deal with this fault are discussed and demonstrated in simulation. Operating the doubly-fed induction generator as a squirrel cage generator with aerodynamic power control of turbine blades is suggested if this fault occurs in the machine-side converter, while constant dc voltage control is suitable for a short-circuit switch fault in the grid-side converter.Wind energy has become one of the most important alternative energy resources because of the global warming crisis. Wind turbines are often erected off-shore because of favourable wind conditions, requiring lower towers than on-shore. The doubly-fed induction generator is one of the most widely used generators with wind turbines. In such a wind turbine the power converters are less robust than the generator and other mechanical parts. If any switch failure occurs in the converters, the wind turbine may be seriously damaged and have to stop. Therefore, converter health monitoring and fault diagnosis are important to improve system reliability. Moreover, to avoid shutting down the wind turbine, converter fault diagnosis may permit a change in control strategy and/or reconfigure the power converters to permit post-fault operation. This research focuses on switch fault diagnosis and post-fault operation for the converters of the doubly-fed induction generator. The effects of an open-switch fault and a short-circuit switch fault are analysed. Several existing open-switch fault diagnosis methods are examined but are found to be unsuitable for the doubly-fed induction generator. The causes of false alarms with these methods are investigated. A proposed diagnosis method, with false alarm suppression, has the fault detection capability equivalent to the best of the existing methods, but improves system reliability. After any open-switch fault is detected, reconfiguration to a four-switch topology is activated to avoid shutting down the system. Short-circuit switch faults are also investigated. Possible methods to deal with this fault are discussed and demonstrated in simulation. Operating the doubly-fed induction generator as a squirrel cage generator with aerodynamic power control of turbine blades is suggested if this fault occurs in the machine-side converter, while constant dc voltage control is suitable for a short-circuit switch fault in the grid-side converter