A controlled filtering method for estimating harmonics of off-nominal frequencies

The increasing use of power electronics in power systems causes a high injection of harmonic components which can in turn interfere with utility equipment and customer loads. Therefore, the correct estimation and measurement of harmonics have become an important issue. If the power frequency of the signal is steady and near the nominal value, the discrete Fourier transform (DFT) can be used and good estimation performance is achieved. However, there are considerable power frequency variations on isolated systems such as shipboard power systems, micro-grids and smart-grids. When these variations occur there may be significant errors in the estimates using the DFT. In order to deal with this problem, this work presents a novel technique based on demodulation of the power line signal and subsequent filtering for harmonics estimation. The main features of the proposed harmonic estimation technique are: precise and accurate estimation of harmonics of off-nominal frequencies and fast estimation of harmonics (about two cycles of the fundamental component). Simulation results show that the proposed technique performs well in comparison with the DFT and can be a good candidate to replace it in cases where the power frequency is subject to considerable variations

Research and development of diagnostic algorithms to support fault accommodating control for emerging shipboard power system architectures

The U.S. Navy has proposed development of next generation warships utilising an increased amount of power electronics devices to improve flexibility and controllability. The high power density finite inertia network is envisioned to employ automated fault detection and diagnosis to aid timely remedial action. Integration of condition monitoring and fault diagnosis to form an intelligent power distribution system is anticipated to assist decision support for crew while enhancing security and mission availability. This broad research being in the conceptual stage has lack of benchmark systems to learn from. Thorough studies are required to successfully enable realising benefits offered by using increased power electronics and automation. Application of fundamental analysis techniques is necessary to meticulously understand dynamics of a novel system and familiarisation with associated risks and their effects. Additionally, it is vital to find ways of mitigating effects of identified risks. This thesis details the developing of a generalised methodology to help focus research into artificial intelligence (AI) based diagnostic techniques. Failure Mode and Effects Analysis (FMEA) is used in identifying critical parts of the architecture. Sneak Circuit Analysis (SCA) is modified to provide signals that differentiate faults at a component level of a dc-dc step down converter. These reliability analysis techniques combined with an appropriate AI-algorithm offer a potentially robust approach that can potentially be utilised for diagnosing faults within power electronic equipment anticipated to be used onboard the novel SPS. The proposed systematic methodology could be extended to other types of power electronic converters, as well as distinguishing subsystem level faults. The combination of FMEA, SCA with AI could also be used for providing enhanced decision support. This forms part of future research in this specific arena demonstrating the positives brought about by combining reliability analyses techniques with AI for next generation naval SPS.The U.S. Navy has proposed development of next generation warships utilising an increased amount of power electronics devices to improve flexibility and controllability. The high power density finite inertia network is envisioned to employ automated fault detection and diagnosis to aid timely remedial action. Integration of condition monitoring and fault diagnosis to form an intelligent power distribution system is anticipated to assist decision support for crew while enhancing security and mission availability. This broad research being in the conceptual stage has lack of benchmark systems to learn from. Thorough studies are required to successfully enable realising benefits offered by using increased power electronics and automation. Application of fundamental analysis techniques is necessary to meticulously understand dynamics of a novel system and familiarisation with associated risks and their effects. Additionally, it is vital to find ways of mitigating effects of identified risks. This thesis details the developing of a generalised methodology to help focus research into artificial intelligence (AI) based diagnostic techniques. Failure Mode and Effects Analysis (FMEA) is used in identifying critical parts of the architecture. Sneak Circuit Analysis (SCA) is modified to provide signals that differentiate faults at a component level of a dc-dc step down converter. These reliability analysis techniques combined with an appropriate AI-algorithm offer a potentially robust approach that can potentially be utilised for diagnosing faults within power electronic equipment anticipated to be used onboard the novel SPS. The proposed systematic methodology could be extended to other types of power electronic converters, as well as distinguishing subsystem level faults. The combination of FMEA, SCA with AI could also be used for providing enhanced decision support. This forms part of future research in this specific arena demonstrating the positives brought about by combining reliability analyses techniques with AI for next generation naval SPS

Design and implementation of hybrid series compensators for smart grid applications

The vision of future modern grids goes through the increase of renewable énergies penetration while providing an efficient, reliable and sustainable power supply to consumers. According to the recent report on climate challenging the way electrical energy is produced and because of the rapid emerging of power electronics based equipment; some serious actions should be engaged. In order to achieve such promoting visions, all power grids are required to become smarter especially at the distribution level. Increasing the application of renewable energy sources and distributed generations assist these vision in the development of a modern power grid where modern equipment are becoming highly sensitive to the supplied voltage quality. Moreover, in this paradigm of design, the traditional power systems based on large concentrated power plants should be able to deal with these unpredictable sources of energy at distribution level. Under these circumstances, considerable activities were carried out aiming to render the grid more flexible and intelligent while taking the power efficiency and its environmental impacts into account. In this way, the power quality issues should be considered for the development of new type of smart grids which are more efficient and sustainable with regards to environmental constraints. Available active and passive compensators are widely involved to improve major power quality issues. Recent trends towards realization of multitasking devices which can solve several power quality issues simultaneously, propose Hybrid active filters or Unified power quality conditioners. These versatile devices should threaten both voltage and current related issues in one place for compensation. They can significantly improve power quality issues, such as voltage distortions, voltage sags, voltage swells, voltage unbalances, and ensure a constant and reliable voltage supply to the load. On the other hand, they compensate for current problems of linear and non-linear loads, such as current harmonics, unbalances, neutral current, and load reactive power. The Hybrid series active filter (HSeAF) is among the most versatile and efficient power electronics based active power compensators. Without the shunt passive filter, the active part could operate solely to rectify for voltage problems and is commonly known as Dynamic voltage restorer. A conventional HSeAF, targeting three-phase system, consists of a three separate series isolation transformer connected to a three-phase converter sharing a common DC link bus. The device is controlled as a variable voltage source in similar but duality manner as of Shunt active power filter. A shunt passive filter tuned for harmonic frequencies is installed to produce an alternative path for load current harmonics and reducing voltage distortions at the load terminals. The existing literature suggests utilizing the hybrid active power filters to compensate for load current related issues only, while due to the complexity and implementation outlays of such devices, it shows a significant drawback of under usage of series compensation to address such power quality problems. The present doctoral research is based on the philosophy of optimal utilization of the available resources in the most efficient way to enhance the product efficiency and to reduce the overall cost. This work proposes a novel control approach for three-phase system in which both the grid’s voltage and load current issues are treated in a co-ordination between the series active and the shunt passive filters without affecting the basic voltage or current compensation capabilities. This eventually results in a better utilization of the series active filter, reduction of the shunt passive filter rating to some extent, and ultimately in the reduction of the overall cost for a unified compensator. Moreover, this thesis also introduces a novel transformerless topology in which the threephase configuration is split into separate devices. It is then possible to extent the Series active power compensation based for three-phase systems with three or four wires to single-phase or bi-phase systems. This newly transformerless hybrid series active filter (THSeAF) is first hosted for single-phase system where appropriate developed controllers ensure adequate operation under low profile power quality systems. The developed single-phase THSeAF concept is successfully validated through digital simulations as well as real-time extensive experimental investigations. The experimental results show that for a given laboratory test conditions with highly polluted nonlinear loads, the active compensator ride of the bulky transformer is capable of compensating load current and correcting the power factor. Moreover, the performance of the THSeAF under polluted grid supply with voltage harmonics, sags, and swells, demonstrates regulated and reduced voltage distortions at the load’s terminals. Following this successful transformerless configuration, and to integrate the series compensation concepts dedicated for power quality improvement of distribution network, the three-phase configuration is anticipated. Three-phase control strategies developed previously for the HSeAF are applied to the proposed topology to make the point of common coupling (PCC) smarter and to decentralize the control of the distribution network. This affordable solution increases the efficiency and sustainability of modern smart power systems and help higher penetration of renewable fluctuating power into the network. The off-line simulations demonstrate that the three-phase THSeAF is capable of healing voltage problems and load current issues simultaneously. The real-time experimental results, carried out on a laboratory prototype, validate successfully the proposed configuration