Power quality improvement utilizing photovoltaic generation connected to a weak grid

Microgrid research and development in the past decades have been one of the most popular topics. Similarly, the photovoltaic generation has been surging among renewable generation in the past few years, thanks to the availability, affordability, technology maturity of the PV panels and the PV inverter in the general market. Unfortunately, quite often, the PV installations are connected to weak grids and may have been considered as the culprit of poor power quality affecting other loads in particular sensitive loads connected to the same point of common coupling (PCC). This paper is intended to demystify the renewable generation, and turns the negative perception into positive revelation of the superiority of PV generation to the power quality improvement in a microgrid system. The main objective of this work is to develop a control method for the PV inverter so that the power quality at the PCC will be improved under various disturbances. The method is to control the reactive current based on utilizing the grid current to counteract the negative impact of the disturbances. The proposed control method is verified in PSIM platform. Promising results have been obtaine

Design and Control of Virtual Synchronous Machine Based Energy Systems

Conventionally, the operation and stability of power systems have been governed by the dynamics of large synchronous generators (SGs) which provide the inertial support required to maintain the resilience and stability of the power system. How-ever, the commitment of the UK to drive a zero-carbon economy is accelerating the integration of renewable energy sources (RESs) into the power system. Since the dynamics and operation of RESs differs from SGs, the large-scale integration of RESs will significantly impact the control and stability of the power system.This thesis focuses on the design of grid-friendly control algorithms termed virtual synchronous machines (VSMs), which mimic the desirable characteristics of SGs. Although several VSM topologies have been proposed in literature, most of them require further modifications before they can be integrated into the grid. Hence, a novel VSM algorithm for permanent magnet synchronous generator based wind turbines has been proposed in this thesis.The proposed VSM performs seamlessly in all operating modes and enables maxi-mum power point tracking in grid-connected operation (assuming strong grid), load following power generation in islanded mode and fault ride-through during faults. To ensure optimal performance of the VSM in all operating modes, a comprehensive stability analysis of the VSM was performed in the event of small and large per-turbations. The result of the analysis was used to establish design guidelines and operational limits of the VSM.This thesis further evaluates the impact of VSMs on the power systems low-frequency oscillations (LFOs). A detailed two-machine test-bed was developed to analyze the LFOs which exists when VSMs replace SGs. The characteristics of the LFO modes and the dominant states was comprehensively analyzed. The LFO modes which exists in an all-VSM grid was also analyzed. Further, the role of the power system stabilizers in an all-VSM grid was comprehensively evaluated. An IEEE benchmark two-area four-machine system was employed to validate the results of the small-signal analysis.The analysis and time-domain simulations in this thesis were performed in the MAT-LAB/SIMULINK environment

Electromechanics of an Ocean Current Turbine

The development of a numeric simulation for predicting the performance of an Ocean Current Energy Conversion System is presented in this thesis along with a control system development using a PID controller for the achievement of specified rotational velocity set-points. In the beginning, this numeric model is implemented in MATLAB/Simulink® and it is used to predict the performance of a three phase squirrel single-cage type induction motor/generator in two different cases. The first case is a small 3 meter rotor diameter, 20 kW ocean current turbine with fixed pitch blades, and the second case a 20 meter, 720 kW ocean current turbine with variable pitch blades. Furthermore, the second case is also used for the development of a Voltage Source Variable Frequency Drive for the induction motor/generator. Comparison among the Variable Frequency Drive and a simplified model is applied. Finally, the simulation is also used to estimate the average electric power generation from the 720 kW Ocean Current Energy Conversion System which consists of an induction generator and an ocean current turbine connected with a shaft which modeled as a mechanical vibration system

Electromechanics of an Ocean Current Turbine

The development of a numeric simulation for predicting the performance of an Ocean Current Energy Conversion System is presented in this thesis along with a control system development using a PID controller for the achievement of specified rotational velocity set-points. In the beginning, this numeric model is implemented in MATLAB/Simulink® and it is used to predict the performance of a three phase squirrel single-cage type induction motor/generator in two different cases. The first case is a small 3 meter rotor diameter, 20 kW ocean current turbine with fixed pitch blades, and the second case a 20 meter, 720 kW ocean current turbine with variable pitch blades. Furthermore, the second case is also used for the development of a Voltage Source Variable Frequency Drive for the induction motor/generator. Comparison among the Variable Frequency Drive and a simplified model is applied. Finally, the simulation is also used to estimate the average electric power generation from the 720 kW Ocean Current Energy Conversion System which consists of an induction generator and an ocean current turbine connected with a shaft which modeled as a mechanical vibration system

Power system control for large-disturbance stability : security, robustness and transient energy

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 223-228).by Jeffrey Wayne Chapman.Ph.D

Converse Magnetoelectric Resonators for Biomagnetic Field Sensing

Contact-less biomagnetic sensing constitutes the next frontier for advanced healthcare, bringing novel diagnostic abilities using multichannel magnetocardiography (MCG) and magnetoencephalography (MEG) either as a single source of information for rapid patient screening or in combination with established methods such as electrocardiography (ECG) and electroencephalography (EEG) as a source for additional patient information. The combination of established electrical with magnetic patient information potentially leads to novel tools for deep knowledge generation towards pathologies and early prevention of such. The main obstacle towards biomagnetic diagnosis using magnetic imaging techniques is the lack of easy applicable sensor technology which offers extremely low magnetic noise floors; realtime MCG measurements demand for lower than 10 pT/sqrt(Hz), reaching below 100 fT/sqrt(Hz) enables even MEG signal acquisition. Such extremely minute amplitudes that are six to seven orders lower than earth's permanent magnetic field, demand lowest noise sensor technology as the low frequency signal regime below about 1 kHz is strongly affected by omnipresent 1/f-noise. Magnetoelectric (ME) thin film composites consisting of a sputtered piezoelectric (PE) and an amorphous magnetostrictive (MS) layer are usually employed for measurements of magnetic fields passively, i.e. an AC magnetic field directly generates an ME voltage by mechanical coupling of the MS deformation to the PE phase. In order to achieve high field sensitivities, a magnetic bias field is required to operate at the maximum piezomagnetic coefficient of the MS phase. Additionally using mechanical resonances further enhances this direct ME effect size. Despite being able to directly detect very small field amplitudes on the order of 1 pT/sqrt(Hz) for magnetic fields of a frequency exactly matching mechanical resonances comes at the expense of available signal bandwidth, because of rather high resonator quality factors. Strong 1/f noise prevalent in the low frequency regime, makes DC or low frequency magnetic fields tedious to record in that regime using direct ME detection scheme. In the presented work the PE phase is actively excited, thus exploiting the converse ME effect, remedying the shortcomings of the direct effect. ME composites are demonstrated for use as precision sensors, capable of magnetic signal detection in the low frequency, low amplitude biomagnetic regime. The combination of the converse ME effect with high frequency acoustic resonances leads to high piezoelectric stresses generated within the composite, leading to large inverse magnetostriction and thus high sensitivity. A limit of detection (LOD) of 70 pT/sqrt(Hz) at 10 Hz is obtained with composites based on amorphous films of Iron-Cobalt-Silicon-Boron (FeCoSiB). Exploiting advanced magnetoelectric composites based on exchange biased FeCoSiB films (EB-FeCoSiB) LOD values reaching down to 17 pT/sqrt(Hz) at 10 Hz are demonstrated. A trial recording a healthy subjects human MCG signal using an advanced ME composite demonstrates the practical feasibility of biomagnetic measurements and paves the way for routine, realtime biomagnetic measurements in the future.Kontaktlose biomagnetische Diagnostik stellt die nächste Generation von Patientenmonitoring und bildgebender Diagnostik dar, sie ist in der Lage einen schnellen, kontaktlosen Überblick der Vitalfunktionen zu liefern. In Kombination mit etablierten Methoden wie Elektrokardiografie (EKG) und Elektroenzephalografie (EEG) entsteht ein zusätzliches Werkzeug zur Erlangung tieferer Informationen über Pathogenesen und ermöglichen somit eine frühzeitige Erkennung solcher. Die größte technische Hürde der biomagnetischen Diagnose stellt die Entwicklung einer anwenderfreundlichen, wartungsarmen Sensortechnologie dar. Diese Technologie muss über ein extrem niedriges magnetisches Rauschen von kleiner als 10 pT/sqrt(Hz) für Echtzeit Magnetokardiografie (MKG) und bis unter 100 fT/sqrt(Hz) für Magnetoenzephalografie (MEG) verfügen. Derartige Feldstärken von biomagnetischem Niveau sind etwa sechs bis sieben Größenordnungen geringer als das statische Erdmagnetfeld und dabei ebenfalls stets niederfrequent, unterhalb etwa 1 kHz. Damit liegen die relevanten Magnetfelder im Bereich des omnipräsenten 1/f-Rauschens. Magnetoelektrische Dünnschicht-Komposite werden üblicherweise passiv betrieben, indem ein magnetisches Wechselfeld direkt zu einer proportionalen ME-Spannung führt. Dies geschieht mittels magnetostriktiver Dehnung welche durch mechanische Kopplung auf ein Piezoelektrikum übertragen wird und dort eine elektrische Spannung über den direkten piezoelektrischen Effekt erzeugt. Um den größtmöglichen piezomagnetischen Koeffizienten zu erhalten, kommt zusätzlich ein statisches magnetisches Haltefeld zum Einsatz. Durch die Ausnutzung mechanischer Resonanzen wird die Oszillation verstärkt, diese Verstärkung führt in gleichem Maße zu einer Verstärkung des ME-Effekts. Auf diese Weise ist es möglich, magnetische Detektionsgrenzen von etwa 1 pT/sqrt(Hz) zu erreichen, weit im erforderlichen Bereich für Echtzeit MKG Messungen. Diese direkte Ausnutzung mechanischer Resonanzen von hohem Gütefaktor, bringt den wesentlichen Nachteil, dass die Bandbreite des ME Oszillators auf wenige Herz beschränkt ist, welches einer praktischen, breitbandigen Signalerfassung entgegen steht. In dieser Arbeit wird die piezoelektrische Materialphase direkt elektrisch angeregt, es wird der inverse ME-Effekt ausgenutzt. Dieser inverse ME Effekt stellt sich als vorteilhaft im Bezug auf den direkten ME-Effekt heraus, da eine rauscharme Operation ermöglicht wird. Magnetoelektrische Dünnschicht-Komposite werden als Präzisionssensoren zur Detektion von niederfrequenten magnetischen Kleinstsignalen untersucht. Die Kombination aus inversem ME-Effekt und der Ausnutzung hochfrequenter mechanischer Oszillationen führt zu starken mechanischen Verspannungen in der magnetostriktiven Phase und dadurch zu hoher Empfindlichkeit des Sensor-Komposites. Eine Detektionsgrenze von 70 pT/sqrt(Hz) bei einer Frequenz von 10 Hz wird unter Verwendung von magnetostriktiven Einfachlagen erreicht. Die Verwendung fortgeschrittener Mehrlagen-Materialsysteme führt zu einer weiteren Verringerung der Detektionsgrenze auf 17 pT/sqrt(Hz) bei 10 Hz. Schließlich wird in einer Feldstudie am gesunden Probanden eine Machbarkeit zur Detektion humaner MKG Signale gezeigt

Modelling, dynamics and control of a permanent magnet generator for wind power applications.

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN014115 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Electromagnetic fast-transients in LV networks with ubiquitous small-scale embedded generation

Small-scale embedded generation projects rated below 16A per phase are being integrated into low-voltage distribution networks in ever increasing numbers. Seen from the network operator's perspective as little more than negative load, the commissioning of such generators is subject to compliance with the Fit and Forget connection requirements of ENA Engineering Recommendation G83/1. This thesis has sought to quantify the electromagnetic switching transient implications of integrating very large volumes of embedded generation into the UK's low-voltage supply networks. Laboratory testing of a converter-interfaced PV source has been undertaken to characterise typical switching transient waveshapes, and equivalent representative source models have been constructed in EMTP-ATP. A detailed frequency-dependent travelling wave equivalent of the DNO-approved Generic UK LV Distribution network model has been developed and, by means of extensive statistical simulation studies, used to quantify the cumulative impact of geographically localised generators switching in response to common network conditions. It is found that the magnitude of generator-induced voltage and current transients is dependent on the number of concurrently switched generators, and on their relative locations within the network. A theoretical maximum overvoltage of 1.72pu is predicted at customer nodes remote from the LV transformer terminals, for a scenario in which all households have installed embedded generation. Latent diversity in switch pole closing and inrush inception times is found to reduce predicted peak transient voltages to around 25-40% of their theoretical maxima.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Electronic identification systems for asset management

Electronic identification is an increasingly pervasive technology that permits rapid data recovery from low-power transponders whenever they are placed within the vicinity of an interrogator device. Fundamental benefits include proximity detection not requiring line-of-sight, multiple transponder access and data security. In this document, electronic identification methods for asset management are devised for the new target application of electrical appliance testing. In this application mains-powered apparatus are periodically subjected a prescribed series of electrical tests performed by a Portable Appliance Tester (PAT). The intention is to enhance the process of appliance identification and management, and to automate the test process as far as possible. Three principal methods of electronic identification were designed and analysed for this application: proximity Radio Frequency Identification (RFID), cable RFID and power- line signalling. Each method relies on an inductively coupled mechanism that utilities a signalling technique called direct-load modulation. This is particularly suited to low- cost passive transponder designs. Physical limitations to proximity RFID are identified including coil size, orientation and susceptibility to nearby conducting surfaces. A novel inductive signalling method called cable RFID is then described that permits automatic appliance identification. This method uses the appliance power cable and inlet filter to establish a communication channel between interrogator and transponder. Prior to commencing the test phase, an appliance is plugged into the PAT and identified automatically via cable RFID. An attempt is made to extend the scope of cable RFID by developing a novel mains power-line signalling method that uses direct-load modulation and passive transponders. Finally, two different implementations of RFID interrogator are described. The first takes the form of an embeddable module intended for incorporation into electronic identification products such as RFID enabled PAT units. Software Defined Radio (SDR) principles are applied to the second interrogator design in an effort to render the device reconfigurable