Fault tolerant drives for safety critical applications

PhD ThesisThe correct operation of adjustable speed drives, which form part of a larger system, is often essential to the operation of the system as a whole. In certain applications the failure of such a drive could result in a threat to human safety and these applications are termed 'safety critical'. The chance of a component failure resulting in non-operation of the drive can be dramatically reduced by adopting a fault tolerant design. A fault tolerant drive must continue to operate throughout the occurrence of any single point failure without undue disturbance to the power output. Thereafter the drive must be capable of producing rated output indefinitely in the presence of the fault. The work presented in this thesis shows that fault tolerance can be achieved without severe penalties in terms of cost or power to mass ratio. The design of a novel permanent magnet drive is presented and a 'proof of concept' demonstrator has been built, based on a 20 kW, 13000 RPM aircraft fuel pump specffication. A novel current controller with near optimal transient performance is developed to enable precise shaping of the phase currents at high shaft speeds. The best operating regime for the machine is investigated to optimise the power to mass ratio of the drive. A list of the most likely electrical faults is considered. Some faults result in large fault currents and require rapid detection to prevent fault propagation. Several novel fault sensors are discussed. Fault detection and identification schemes are developed, including new schemes for rapid detection of turn to turn faults and power device short circuit faults. Post fault control schemes are described which enable the drive to continue to operate indefinitely in the presence of each fault. Finally, results show the initially healthy drive operating up to, through and beyond the introduction of each of the most serious faults.EPSR

PV Array Driven Adjustable Speed Drive for a Lunar Base Heat Pump

A study of various aspects of Adjustable Speed Drives (ASD) is presented. A summary of the relative merits of different ASD systems presently in vogue is discussed. The advantages of using microcomputer based ASDs is now widely understood and accepted. Of the three most popular drive systems, namely the Induction Motor Drive, Switched Reluctance Motor Drive and Brushless DC Motor Drive, any one may be chosen. The choice would depend on the nature of the application and its requirements. The suitability of the above mentioned drive systems for a photovoltaic array driven ASD for an aerospace application are discussed. The discussion is based on the experience of the authors, various researchers and industry. In chapter 2 a PV array power supply scheme has been proposed, this scheme will have an enhanced reliability in addition to the other known advantages of the case where a stand alone PV array is feeding the heat pump. In chapter 3 the results of computer simulation of PV array driven induction motor drive system have been included. A discussion on these preliminary simulation results have also been included in this chapter. Chapter 4 includes a brief discussion on various control techniques for three phase induction motors. A discussion on different power devices and their various performance characteristics is given in Chapter 5

Digital Control of Power Converters and Drives for Hybrid Traction and Wireless Charging

In the last years environmental issues and constant increase of fuel and energy cost have been incentivizing the development of low emission and high efficiency systems, either in traction field or in distributed generation systems from renewable energy sources. In the automotive industry, alternative solutions to the standard internal combustion engine (ICE) adopted in the conventional vehicles have been developed, i.e. fuel cell electric vehicles (FCEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEV) or pure electric vehicles (EVs), also referred as battery powered electric vehicles (BEV). Both academic and industry researchers all over the world are still facing several technical development areas concerning HEV components, system topologies, power converters and control strategies. Efficiency, lifetime, stability and volume issues have moved the attention on a number of bidirectional conversion solutions, both for the energy transfer to/from the storage element and to/from the electric machine side. Moreover, along with the fast growing interest in EVs and PHEVs, wireless charging, as a new way of charging batteries, has drawn the attention of researchers, car manufacturers, and customers recently. Compared to conductive power transfer (usually plug-in), wireless power transfer (WPT) is more convenient, weather proof, and electric shock protected. However, there is still more research work needs to be done to optimize efficiency, cost, increase misalignment tolerance, and reduce size of the WPT chargers. The proposed dissertation describes the work from 2012 to 2014, during the PhD course at the Electric Drives Laboratory of the University of Udine and during my six months visiting scholarship at the University of Michigan in Dearborn. The topics studied are related to power conversion and digital control of converters and drives suitable for hybrid/electric traction, generation from renewable energy sources and wireless charging applications. From the theoretical point of view, multilevel and multiphase DC/AC and DC/DC converters are discussed here, focusing on design issues, optimization (especially from the efficiency point-of-view) and advantages. Some novel modulation algorithms for the neutral-point clamped three-level inverter are presented here as well as a new multiphase proposal for a three-level buck converter. In addition, a new active torque damping technique in order to reduce torque oscillations in internal combustion engines is proposed here. Mainly, two practical implementations are considered in this dissertation, i.e. an original two-stage bi-directional converter for mild hybrid traction and a wireless charger for electric vehicles fast charge

Design and implementation of a three-phase boost battery charger with PFC using CompactRIO control system : design, simulation and implementation of a 3-phase boost battery charger

In a plug-in hybrid electric vehicle, the utility grid charges the vehicle battery through a battery charger. For a three-phase grid supply voltage, three-phase boost rectifiers are commonly used as chargers. Bi-directional power transfer capability and unit power factor operation become desirable features due to the increasing power quality requirements on the grid-connected converters. The Voltage Oriented Control is one of the methods based on high performance dq-coordinate controllers which satisfies the increasing power quality requirements. The Voltage Oriented Control method for a three-phase boost rectifier has been designed, simulated and implemented. The system simulation is performed using Matlab/Simulink software as well as Labview. A feedforward decoupled current controller is designed along with a Pulse Width Modulation scheme to control the battery charging. The controller, consisting of a current controller and a DC-link voltage controller, is designed using a method called Internal Model Control. A National Instruments CompactRIO system is used for practical implementation. The system directly runs a Labview model to execute the control. The Labview files are developed for this purpose. A brief explanation of the system configuration is provided for the experimental system. ____________________________________________________________________________________________________________Los vehículos eléctricos e híbridos usan potencia de la red para cargar sus baterías y mientras lo hacen el sistema de tracción no está en uso. Debido a que el sistema de carga y el de tracción no están en uso al mismo tiempo, el inversor y el motor eléctrico pueden ser usados como rectificador evitando el uso redundante de componentes. Para hacer esto, un motor con dos juegos de devanados puede ser usado consiguiendo en el cargador una reducción considerable de peso, volumen y precio. El cargador propuesto en un cargador aislado de alta potencia que usa la mitad de los devanados del motor durante la carga usando el motor como si fuera un transformador. El uso de este motor especifico nos proporcionará aislamiento que será beneficioso por razones de seguridad. El objetivo principal de este proyecto fin de carrera es el diseño y la implementación de un cargador integrado para un coche eléctrico o híbrido con un nivel de potencia de 15 kW programando un control para el inversor que consiga tener un factor de potencia unitario.Ingeniería Industria

Power-electronic systems for the grid integration of renewable energy sources: a survey

The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a powerelectronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the power-system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. A review of the appropriate storage-system technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented

Study and analysis of state-of-the-art FCS-MPC strategies for thermal regulation of power converters

La degradación en los convertidores de potencia basados en silicio, enmarcados en sistemas de tracción eléctrica y fuentes de energías renovables, es un tema de estudio de especial interés para aquellas aplicaciones donde los fallos amenazan la seguridad de personas o donde el mantenimiento es particularmente costoso. Motivado por la influencia de los fallos en IGBTs sobre los fallos habituales en los convertidores de potencia comunes, este trabajo utiliza la herramienta software PLECS como marco de trabajo para la simulación de algoritmos de control predictivo basado en modelo con conjunto finito de acciones de control (FCS-MPC) que pretenden -simultáneamente a conseguir el seguimiento eléctrico- extender directa o indirectamente la vida útil de los IGBTs. El trabajo se enfoca principalmente a la simulación en ordenador de los algoritmos controlando un inversor de dos niveles conectado a una carga RL. Además, pretende también introducir la implementación de éstos sobre un microcontrolador para su estudio controlando el inversor simulado en la plataforma PLECS RT Box 1, con el fin último de poder desarrollar validaciones de los controladores basadas en técnicas Hardware-In-the-Loop.Degradation of silicon-based power electronics converters in traction and renewable energy systems is a topic of interest particularly where module failure supposes a safety threat or where maintenance becomes especially expensive. Motivated by the influence of IGBT aging in usual power converters, this work uses the software tool PLECS as framework to simulate Finite Control Set Model Predictive Control (FCSMPC) algorithms that, simultaneously to achieving a certain current tracking, aim to directly or indirectly extend IGBTs’ lifetime. Whilst the work focuses on offline simulation of the algorithms on PLECS, it also targets to pave the way to implement algorithms in a micro-controller and to study how they control a two-level inverter connected to a RL load simulated on a PLECS RT Box 1 platform. The ultimate goal is to develop validations based on Hardware-In-the-Loop techniques of the control algorithms.Universidad de Sevilla. Máster Universitario en Ingeniería Electrónica, Robótica y Automátic

Assessment of novel power electronic converters for drives applications

Phd ThesisIn the last twenty years, industrial and academic research has produced over one hundred new converter topologies for drives applications. Regrettably, most of the published work has been directed towards a single topology, giving an overall impression of a large number of unconnected, competing techniques. To provide insight into this wide ranging subject area, an overview of converter topologies is presented. Each topology is classified according to its mode of operation and a family tree is derived encompassing all converter types. Selected converters in each class are analysed, simulated and key operational characteristics identified. Issues associated with the practical implementation of analysed topologies are discussed in detail. Of all AC-AC conversion techniques, it is concluded that softswitching converter topologies offer the most attractive alternative to the standard hard switched converter in the power range up to 100kW because of their high performance to cost ratio. Of the softswitching converters, resonant dc-link topologies are shown to produce the poorest output performance although they offer the cheapest solution. Auxiliary pole commutated inverters, on the other hand, can achieve levels of performance approaching those of the hard switched topology while retaining the benefits of softswitching. It is concluded that the auxiliary commutated resonant pole inverter (ACPI) topology offers the greatest potential for exploitation in spite of its relatively high capital cost. Experimental results are presented for a 20kW hard switched inverter and an equivalent 20kW ACPI. In each case the converter controller is implanted using a digital signal processor. For the ACPI, a new control scheme, which eliminates the need for switch current and voltage sensors, is implemented. Results show that the ACPI produces lower overall losses when compared to its hardswitching counterpart. In addition, device voltage stress, output dv/dt and levels of high frequency output harmonics are all reduced. Finally, it is concluded that modularisation of the active devices, optimisation of semiconductor design and a reduction in the number of additional sensors through the use of novel control methods, such as those presented, will all play a part in the realisation of an economically viable system.Research Committee of the University of Newcastle upon Tyn

Advances in wind power generation, transmission, and simulation technology

Wind is an increasingly important piece of electricity generation portfolios worldwide. This dissertation describes advances related to the electromechanical energy conversion system of wind turbines, and the electric transmission system for offshore wind power plants. The contributions of this work are the following: (i) We propose that the power electronics topology commonly called the Vienna rectifier can be used for improved variable-speed wind energy conversion. Theoretical analysis is conducted to show how a Vienna rectifier could drive either a squirrel-cage induction generator or a permanent-magnet synchronous generator-based wind turbine. Computer simulations and experimental results demonstrate the feasibility of the proposed topology and potential improvements in energy conversion efficiency. (ii) We propose a novel low-frequency ac (LFAC) transmission system for offshore wind power plants. A system design and control method is set forth, and key system operational characteristics are illustrated via computer simulations. The LFAC system constitutes a promising option for medium- or long-distance transmission, and could be an alternative to high-voltage dc (HVDC) transmission. (iii) We develop a technique that utilizes a field programmable gate array (FPGA) as a dynamic simulation platform for wind turbines. A doubly fed induction generator-based wind turbine simulation is implemented on an FPGA board, in order to verify the effectiveness and performance advantage of this approach

Analysis of the Harmonic Performance of Power Converters and Electrical Drives

Power converters have progressively become the most efficient and attractive solution in recent decades in many industrial sectors, ranging from electric mobility, aerospace applications to attain better electric aircraft concepts, vast renewable energy resource integration in the transmission and distribution grid, the design of smart and efficient energy management systems, the usage of energy storage systems, and the achievement of smart grid paradigm development, among others.In order to achieve efficient solutions in this wide energy scenario, over the past few decades, considerable attention has been paid by the academia and industry in order to develop new methods to achieve power systems with maximum harmonic performance aiming for two main targets. On the one hand, the high-performance harmonic performance of power systems would lead to improvements in their power density, size and weight. This becomes critical in applications such as aerospace or electric mobility, where the power converters are on-board systems. On the other hand, current standards are becoming more and more strict in order to reduce the EMI and EMC noise, as well as meeting minimum power quality requirements (i.e., grid code standards for grid-tied power systems)