Simulation and experiment of algorithm and circuit design for UPQC

Power quality issues have become one of the most important issue for researchers to concern. In this paper, simulation and experiment of algorithm and circuit design of Unified Power Quality Conditioner (UPQC) are provided. Control algorithm and topology design of one UPQC which includes active power filter (APF) and dynamic voltage restorer (DVR) are introduced. Stability condition of the filter unit is deduced and proved by Routh stability criterion. Simulation for APF and DVR is carried out in PSCAD to show the proposed control strategy. Experiments such as current tracking, harmonic detection and compensation and voltage drop compensation are provided in details. Experimental results show that the proposed control method and the designed topology are effective and practical

Active power filter control strategy with novel dual-repetitive controller and neural network adaptive PI control

U ovom je radu analizirana konfiguracija karakteristična za razdjelni aktivni filtar snage (SAPF) s dvodijelnim kondenzatorom kao i njegov glavni dijagram i upravljački modul. U svrhu poboljšanja dinamičke performanse upravljačkog sustava i pojačanja dinamičkog odziva, predstavljena je kombinirana strategija zasnovana na dvostruko-ponavljajućem kontrolnom uređaju (DRC) i adaptivnom PI upravljanju. U DRC-u jedan ponavljajući kontrolni uređaj je za osiguranje točnosti strujnog toka, a drugi za poboljšanje dinamičkog odziva. Prihvaćeno je PI upravljanje neuronskom mrežom da bi se poboljšala brzina odziva prilagođavanjem PI parametara, postavljajući parametre K\u27x i K\u27y online. Takva je strategija upravljanja primijenjena na simulaciju industrijskog prototipa i terensko ispitivanje. U usporedbi s uobičajenom strategijom upravljanja, eksperimentalni rezultat pokazuje da bi se kompenzacijom sustava mogle učinkovito smanjiti vrijednosti ukupne harmonijske distorzije (THD) od 26,02 %, 27,76 % i 27,60 % do 4,25 %, 4,57 % i 4,35 % za svaku fazu struje. A i puno vrijeme odziva je manje od 10 ms te u potpunosti zadovoljava standard IEEE-519.In this paper, the configuration characteristic of shunt active power filter (SAPF) with split-capacitor was analysed, as well as its principle diagram and control module. In order to improve the dynamic performance of a control system and elevate dynamic response, a combination strategy based on dual-repetitive controller (DRC) and adaptive PI control is presented. In DRC, one repetitive controller is for ensuring the current tracking accuracy and the other one is for enhancing dynamic response. The neural network PI control is adopted to improve response speed by turning the PI parameters adaptively, setting parameters K\u27x and K\u27y online. This control strategy was applied on industrial prototype simulation and field test. Comparing with the conventional control strategy, the experimental result shows that system compensation could effectively reduce the total harmonic distortion (THD) values from 26,02 %, 27,76 % and 27,60 % to 4,25 %, 4,57 % and 4,35 % for each phase of the current. And the full response time is all less than 10 ms, fully meeting the standard of IEEE-519

Power quality improvement through a UPQC and a resonant observer-based mimo control strategy

Performance degradation is, in general, regarded as a power quality problem. One solution to recover grid performance is through the application of a unified power quality conditioner (UPQC). Although these devices are multi-input/multi-output (MIMO) systems, the most common control strategies consist of two decoupled controllers, which neglect the coupling effects and add uncertainty to the system. For this reason, this paper proposes a multivariable resonant observer-based control strategy of a UPQC system. This method includes all significant coupling effects between this system and the grid. This strategy results in a stability-based compensator, which differs from recently proposed strategies that are based on signal calculation and cannot assure closed-loop stability. In addition, this paper introduces a simplified controller tuning strategy based on optimal conventional methods without losing closed-loop performance. It implies that the controller can be easily tuned, despite the complexity of the MIMO dynamic model. The UPQC with the resonant observer is verified on an experimental setup for a single-phase system, obtaining three relevant results for power quality improvement: (1) harmonics compensation tested with a total harmonic distortion limit of 5%; (2) sags and swells mitigation; and (3) power factor correction, achieving a unitary value on the grid side.Peer ReviewedPostprint (published version

Design and Assessment of a Grid Connected Industrial Full-SiC Converter for 690 V Grids

Die Bedeutung von Leistungshalbleitern mit großem Bandabstand (Wide Band Gap, WBG) nahm in den letzten drei Jahrzehnten kontinuierlich zu. Diese Bauelemente haben das Potenzial, Silizium (Si) - Bauelemente in bestimmten Anwendungen sowie Leistungs- und Frequenzbereichen zu ersetzen. Siliziumkarbid (SiC)-Leistungshalbleiter sind die gegenwärtig am Weitesten entwickelten WBG-Leistungshalbleiter. Dank besonderer Materialeigenschaften zeichnen sich SiC-Leistungshalbleiter im Vergleich zu Si-Bauelementen durch einen geringeren spezifischen Widerstand, eine höhere Schaltgeschwindigkeit, geringere schaltverluste sowie eine höhere maximale Sperrschichttemperatur aus. Die deutlich erhöhten Herstellungskosten limitieren den Einsatz von SiC-Leistungshalbleitern auf Anwendungen, in denen die Vorteile dieser Bauelemente die höheren Kosten überkompensieren und Systemvorteile ermöglichen. Heute werden SiC-Leistungshalbleiter z.B. in Solarwechselrichtern oder in Elektrofahrzeugen verwendet. Für Stromrichter industrieller elektrischer Antriebe ist die Kosten-Nutzen-Bilanz des Einsatzes von SiC-Leistungshalbleitern gegenwärtig nicht bekannt. Diese Fragestellung motiviert diese Arbeit. Die Auslegung sowie die daraus resultierenden Vor- und Nachteile eines Stromrichters mit SiC-Leistungshalbleitern für elektrische Industrieantriebe ist der Untersuchungsgegenstand dieser Arbeit. Zu diesem Zweck wurde unter Einhaltung industrieller Auslegungskriterien ein 240 kVA SiC-basierter Stromrichterdemonstrator als aktiver Gleichrichter am dreiphasigen 690 V Niederspannungsnetz untersucht. Auf der Basis einer Stromrichterauslegung für SiC- und Si-Leistungshalbleiter wurde ein theoretischer Vergleich von Kosten, Effizienz, Größe und Gewicht durchgeführt. Die Arbeit stellt zunächst den Stand der Technik für SiC-Leistungshalbleiter dar. Anschließend wird ein geeignetes SiC-MOSFET Module für den industriellen Stromrichter ausgewählt und bezüglich des Schaltverhaltens sowie der Parallelschaltung charakterisiert. Der Auslegung des Stromrichterleistungsteils liegen industrielle Anforderungen zu Grunde. Ein realisierter Demonstrator für einen netzseitigen Stromrichter (Active Front End) ist durch eine symmetrische Parallelschaltung von zwei SiC-Modulen, geeignete Ansteuerschaltungen (Gate Drive Units), eine niedrige Streuinduktivität im Kommutierungskreis sowie ein LCL-Filter mit Standard-Kernmaterialien gekennzeichnet. Der Stromrichtervergleich zeigt, dass der betrachtete Stromrichter mit SiC-Leistungshalbleitern im gesamten Betriebsbereich geringere Verluste verursacht als ein vergleichbarer Stromrichter mit Si-Leistungshalbleitern. Der SiC - basierte Stromichter ermöglicht auch eine deutliche Gewichtsreduktion bei ca. 89% der Systemkosten. Somit stellen SiC-Leistungshalbleiter eine attraktive technische Lösung für die untersuchte Anwendung eines aktiven Gleichrichters für industrielle elektrische Antriebe dar.Wide bandgap (WBG) power semiconductors have drawn steadily increasing interest in power electronics in the last three decades. These devices have shown the potential of replacing silicon as the default semiconductor solution for several applications in determined power and frequency ranges. Among them the most mature WBG semiconductor material is silicon carbide (SiC), which presents several characteristics at the crystal level that translate in the potential of presenting lower resistivity, be able to switch faster with lower switching loss, and present both higher characteristics to tolerate and dissipate heat when com pared with silicon. However, the same characteristics that make it great also present a different set of drawbacks to be considered, which aligned with its increased cost make it challenging to assess if its advantages are justified for a particular application. Applications that highly value efficiency and/or power density are the most benefited, and converter solutions featuring the technology have already breached into these application markets. However in other applica tions, the line from which silicon carbide starts making sense in the cost/benefits/drawbacks balance is not clear. This is typically the case of industrial applications, which were the main focus and motivation of this work. Hence, in this work the main goal has been to determine the basic characteristics, advantages and limitations that SiC technology designs for industrial low voltage high power grid connected converters present. To that end, a 690 V, 240 kVA SiC-based grid-tied converter demonstrator following industrial design criteria has been developed. Then, based on this design procedure a theoretical comparison between a 690 V, 190 kVA SiC-based converter against a silicon-based converter designed for the same power output has been performed to compare them regarding cost, efficiency, size and weight. This work also comprises a thorough revision of the state of art of SiC devices, which led to the selection of the switching device. Additionally, a characterization of both single and parallel-connected operation of the semiconductor modules was performed, to determine the module characteristics and its suitability to build the SiC converter demonstrator. Results show that the converter demonstrator operates as designed, proving that is possible with the corresponding precautions to achieve: a low inductive power loop, balanced parallel connection of SiC modules, adequate driving circuits for the parallel-connected modules and an adequate filtering solution in compliance with grid-codes based on standard core materials for the selected switching frequency. Finally, the theoretical comparison between the two designed power converters shows that, attained to the conditions of the comparison, the SiC converter solution presents efficiency gains over the whole operating range, while presenting substantial weight savings at 89% of the costs of the Si-IGBT design, presenting itself as the cost-effective solution for the presented application requirements under the given design constraints

Optimal model reference control design for grid connected voltage source converters

Texto en inglés y resumen en inglés y españolEsta tesis se centra en el diseño de controladores H∞ basados en modelos de referencia para su aplicación en el control de convertidores electrónicos de potencia en fuente de tensión (VSC). Se persiguen dos objetivos: el conformado de la admitancia de entrada de un VSC controlado en corriente y el óptimo amortiguamiento activo de filtros resonantes.El diseño de controladores óptimos H∞ aporta ciertas ventajas con respecto al diseño clásico. La principal técnica de diseño H∞ utilizada en la literatura se centra en la minimización de la función de sensibilidad. Ésta permite lidiar con diferentes problemas de compromiso en el diseño de controladores de forma sencilla, como el conformado de la función de lazo, el seguimiento de referencias, la estabilidad del sistema o la limitación del ancho de banda de control. Sin embargo, esta técnica carece de la habilidad de conformar la fase de funciones en lazo cerrado. La técnica H∞ basada en modelos de referencia soluciona este problema.La principal contribución de esta tesis es la aplicación de esta técnica para el moldeado de la admitancia en lazo cerrado de VSCs, la cual juega un importante papel tanto en la estabilidad de sistemas complejos como en la mejora de la calidad de energía en la red. Utilizando la técnica propuesta, el diseñador podrá especificar, en un gran ancho de banda y en un solo marco de diseño, tanto la admitancia del convertidor del convertidor (en modulo y en fase), como el comportamiento del seguimiento de referencias. El proceso de diseño finaliza con la síntesis de un controlador discreto ejecutable en una plataforma digital (DSP).Las posibilidades que presenta esta nueva metodología de diseño son amplias. La presente propuesta se ilustra con el control de un rectificador activo conectado a la red, pero es lo suficientemente flexible como para aplicarse en otros esquemas de control y topologías de convertidor. Se considerarán tres aplicaciones del control de admitancia: el diseño de aplicaciones resistivas en un gran ancho de banda, las cuales mejoran la robustez en la conexión estable a red débiles, el diseño de aplicaciones con una admitancia baja, las cuales mejoran el rechazo de (sub/inter)armónicos de la tensión de red en el control de corriente, y el diseño de aplicaciones con una admitancia alta, que al conectarse en paralelo a la red actúan como estabilizadores de ésta. La metodología de diseño de cada controlador, así como sus limitaciones, implementación y los resultados experimentales obtenidos son detallados.De forma complementaria, se explora la técnica de diseño basada en modelos de referencia para el amortiguamiento óptimo de resonancias en filtros LCL. La idea es diseñar un amortiguador activo que, una vez conectado, moldee la dinámica del filtro LCL de tal manera que este se comporte como un filtro L. Esto permitirá el posterior uso de sencillos controladores de corriente diseñados para filtro L, evitando la complejidad del diseño de controladores para filtros LCL, sin renunciar con ello a su gran capacidad de filtrado. La metodología de diseño es lo suficientemente general como para presentar diferentes estructuras de entrada/salida para el amortiguador. Los resultados obtenidos demuestran la mejora en la robustez del sistema

Control of voltage source converters connected to variable impedance grids

The increase in new renewable energy resources is key to achieving carbon reduction targets, however it also introduces new grid integration challenges. The best renewable resource in Scotland is found in remote parts of the country, and as a result new renewable based generation is increasingly subjected to high and variable levels of impedance. Impedances that cause resonances are also increasingly common, given the higher order characteristics of impedance when transformers, filters, subsea cables, compensators and so on are present in the network. For a better understanding of impedance related stability issues, the estimation of the grid impedance using both Thévenin equivalent and wide spectrum techniques is studied in this thesis and integrated into the converter’s control. These estimations inform the controller of the grid conditions, allowing for controller adaptation. In instances where weak grid conditions are severe and the local grid impedance is dominant, a disturbance rejection mechanism called the pre-emptive voltage decoupler (PVD) is proposed. The PVD feeds forward the active current reference and measured voltage, and adapts the reactive current reference as a function of the impedance estimation, to pre-emptively compensate the local voltage for changes in active power transfer. This is justified through small signal analysis using linearised state space models and validated in the laboratory using large inductors and a converter. The control is also made more resilient with an instability detector, proposed to prevent instability when significant grid disturbances occur. Through early detection of sudden power angle changes, stability can be maintained. This is achieved by momentarily reducing the power reference and re-establishing grid parameters. The implementation of the proposed changes improves the steady state stability region from -0.75 – 0.55 pu to -0.85 – 0.75 pu. Further, the nonlinear transient performance is much more resilient, and uninterrupted power flow can be maintained. When the local grid is not dominant, and higher order grid impedances cause undesired resonances, a detection of the resonant frequency allows for an adaptation of the outer loop gains, thus damping the resonances and improving stability. Such grids are also prone to instability, but a reduction of the power reference does not improve stability, on the contrary the reduction of the power reference shifts eigenvalues into the right hand plane. A better preventative measure is to reduce the outer loop gains, and once the frequency of the problematic resonances is identified, final decisions on outer loop tuning can be taken. With this implementation, the stability of the system is maintained and the power output can be recovered within about 1 second.The increase in new renewable energy resources is key to achieving carbon reduction targets, however it also introduces new grid integration challenges. The best renewable resource in Scotland is found in remote parts of the country, and as a result new renewable based generation is increasingly subjected to high and variable levels of impedance. Impedances that cause resonances are also increasingly common, given the higher order characteristics of impedance when transformers, filters, subsea cables, compensators and so on are present in the network. For a better understanding of impedance related stability issues, the estimation of the grid impedance using both Thévenin equivalent and wide spectrum techniques is studied in this thesis and integrated into the converter’s control. These estimations inform the controller of the grid conditions, allowing for controller adaptation. In instances where weak grid conditions are severe and the local grid impedance is dominant, a disturbance rejection mechanism called the pre-emptive voltage decoupler (PVD) is proposed. The PVD feeds forward the active current reference and measured voltage, and adapts the reactive current reference as a function of the impedance estimation, to pre-emptively compensate the local voltage for changes in active power transfer. This is justified through small signal analysis using linearised state space models and validated in the laboratory using large inductors and a converter. The control is also made more resilient with an instability detector, proposed to prevent instability when significant grid disturbances occur. Through early detection of sudden power angle changes, stability can be maintained. This is achieved by momentarily reducing the power reference and re-establishing grid parameters. The implementation of the proposed changes improves the steady state stability region from -0.75 – 0.55 pu to -0.85 – 0.75 pu. Further, the nonlinear transient performance is much more resilient, and uninterrupted power flow can be maintained. When the local grid is not dominant, and higher order grid impedances cause undesired resonances, a detection of the resonant frequency allows for an adaptation of the outer loop gains, thus damping the resonances and improving stability. Such grids are also prone to instability, but a reduction of the power reference does not improve stability, on the contrary the reduction of the power reference shifts eigenvalues into the right hand plane. A better preventative measure is to reduce the outer loop gains, and once the frequency of the problematic resonances is identified, final decisions on outer loop tuning can be taken. With this implementation, the stability of the system is maintained and the power output can be recovered within about 1 second

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics

Ultra-low losses SiC based shunt active power filter for harmonics mitigation and harmonics power recovery in industrial power systems

The classical method to suppress resonances in power systems is by installing passive dampers in parallel to the loads. However, observations indicate significant power losses due to harmonic currents flowing over passive dampers. Certainly, passive dampers absorb harmonic active power and dissipate this power as heat on their resistive elements leading to energy waste. On the other hand, the passive damper counterpart is the active damper. The latter is also known in technical literature as Voltage driven shunt active power filter (VSAPF). The active damper is a power-electronics-based system that emulates a virtual resistance at harmonic frequencies. Truly, very little was known about the harmonic power absorption on active dampers. Therefore, this dissertation delves into a profound analysis of the capability of an ultra-low losses active damper based on SiC semiconductor technology to process the harmonic power intake and perform harmonic power recovery. Harmonic power recovery in this context is understood as the process of transforming the harmonic active power absorbed into fundamental power that is injected back into the power system. The next topic that is addressed is the reduction in the fundamental power demanded by an industrial facility due to the recovery of harmonic active power. To this end, this dissertation analyzes the power balance flow of a distribution power system (e.g., industrial grid) that includes an ultra-low losses active damper. Arising out of the power balance flow analysis, it was found that the active damper with harmonic recovery function achieves a 1.4% reduction on the fundamental power demanded compared to a passive damper. Naturally, the lower the active damper´s power losses, the higher will be the amount of harmonic active power\ud that can be recovered from the power system. Therefore, during this research work, various power electronics converters topologies are analysed to find the best possible design for the active damper with harmonic power recovery functionality. Arising out of this investigation, it was found that the conventional three-level neutral point piloted converter (3L-TNPC) and the asymmetrical three-level converter (3L-ASYM) are the most suitable power circuit topologies for the ultra-low losses active damper. The former topology, the 3L-TNPC, exhibits the lowest power losses for switching frequencies up to 60 kHz. And then, the 3L-ASYM topology presents the lowest losses among all the studied power circuits for switching frequencies beyond 70 kHz. Furthermore, as an active damper forms a closed loop between harmonic voltages and compensating currents, its stability must be ensured. Thus, a careful design of the VSAPF control system and its inner current controllers is essential. On account of this, this dissertation proposes using the Ragazzini method to design the VSAPF’s inner current controllers. Furthermore, the direct design of the inner current controllers on the discrete domain using the Ragazzini method increases the current controllers’ bandwidth by a factor of three compared to the controllers’ design with conventional methods. Consequently, the increased current controller’s bandwidth achieved through the Ragazzini method pushes the stability limit of the active damper forward compared with traditional current controller designs

Robust Control of Wide Bandgap Power Electronics Device Enabled Smart Grid

abstract: In recent years, wide bandgap (WBG) devices enable power converters with higher power density and higher efficiency. On the other hand, smart grid technologies are getting mature due to new battery technology and computer technology. In the near future, the two technologies will form the next generation of smart grid enabled by WBG devices. This dissertation deals with two applications: silicon carbide (SiC) device used for medium voltage level interface (7.2 kV to 240 V) and gallium nitride (GaN) device used for low voltage level interface (240 V/120 V). A 20 kW solid state transformer (SST) is designed with 6 kHz switching frequency SiC rectifier. Then three robust control design methods are proposed for each of its smart grid operation modes. In grid connected mode, a new LCL filter design method is proposed considering grid voltage THD, grid current THD and current regulation loop robust stability with respect to the grid impedance change. In grid islanded mode, µ synthesis method combined with variable structure control is used to design a robust controller for grid voltage regulation. For grid emergency mode, multivariable controller designed using H infinity synthesis method is proposed for accurate power sharing. Controller-hardware-in-the-loop (CHIL) testbed considering 7-SST system is setup with Real Time Digital Simulator (RTDS). The real TMS320F28335 DSP and Spartan 6 FPGA control board is used to interface a switching model SST in RTDS. And the proposed control methods are tested. For low voltage level application, a 3.3 kW smart grid hardware is built with 3 GaN inverters. The inverters are designed with the GaN device characterized using the proposed multi-function double pulse tester. The inverter is controlled by onboard TMS320F28379D dual core DSP with 200 kHz sampling frequency. Each inverter is tested to process 2.2 kW power with overall efficiency of 96.5 % at room temperature. The smart grid monitor system and fault interrupt devices (FID) based on Arduino Mega2560 are built and tested. The smart grid cooperates with GaN inverters through CAN bus communication. At last, the three GaN inverters smart grid achieved the function of grid connected to islanded mode smooth transitionDissertation/ThesisDoctoral Dissertation Electrical Engineering 201