Grid-connected inverters have wide application in the field of distributed generation and power quality. As the power level demanded by these applications increase, the design and performance evaluation of these converters become important. In the present work, a 50 kVA three-phase back-to-back connected inverter with output LCL filter is built to study design and performance evaluation aspects of grid-connected inverters. The first part of the work explores the split-capacitor resistive-inductive (SC-RL) passive damping scheme for the output LCL filter of a three-phase grid-connected inverter. The low losses in the SC-RL scheme makes it suitable for high power applications. The SCRL damped LCL filter is modelled using state space approach. Using this model, the power loss and damping are analysed. A method for component selection that minimizes the power loss in the damping resistors while keeping the system well damped is proposed. Analytical results show the losses to be in the range of 0.05-0.1% and the quality factor to be in the range of 2.0-2.5. These results are validated experimentally. In the second part of the work, a test method to evaluate the thermal performance of the semi-conductor devices of a three-phase grid-connected inverter is proposed. The method eliminates the need for high power sources, loads or any additional power converters for circulation of power. Only energy corresponding to the losses is consumed. The capability of the method to evaluate the thermal performance of the DC bus capacitors and the output filter components is also explored. The method can be used with different inverter configurations -three-wire or four-wire and for different PWM techniques. The method has been experimentally validated at a power level of 24kVA. In the third part of the work, the back-to-back connected inverter is programmed as a hardware grid simulator. The hardware grid simulator emulates the real-time grid and helps create grid disturbances often observed at the point of common coupling in an ac low voltage grid. A novel disturbance generation algorithm has been developed, analysed and implemented in digital controller using finite state machine model for control of the grid simulator. A wide range of disturbance conditions can be created using the developed algorithm. Experimental tests have been done on a linear purely resistive load, a non-linear diode-bridge load and a current-controlled inverter load to validate the programmed features of the grid simulator.

This Master of Applied Science thesis presents an inverter control system design and implementation with active damping of LCL filter resonance for a single phase grid-connected Distributed Power Generation (DPGS). The focus of the thesis is to actively damp the LCL filter resonance while keeping inverter control variables well regulated. The mathematical model of the LCL filter is analyzed and the filter is designed. Then, a PLL, and a PI compensator in the synchronous reference frame, and a PR compensator in stationary reference frame along a notch filter in cascade are designed and implemented. System level simulation and implementation are conducted. The idea of systematic applying the low loss power conversion topology, effective grid condition detection, grid synchronization, and advanced signal processing theory provides some advantages for single phase grid-connected inverter control design to meet the standard specifications of the interaction between the DPGS and utility grid. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2014-06-26 17:06:03.693

abstract: This thesis addresses the design and control of three phase inverters. Such inverters are used to produce three-phase sinusoidal voltages and currents from a DC source. They are critical for injecting power from renewable energy sources into the grid. This is especially true since many of these sources of energy are DC sources (e.g. solar photovoltaic) or need to be stored in DC batteries because they are intermittent (e.g. wind and solar). Two classes of inverters are examined in this thesis. A control-centric design procedure is presented for each class. The first class of inverters is simple in that they consist of three decoupled subsystems. Such inverters are characterized by no mutual inductance between the three phases. As such, no multivariable coupling is present and decentralized single-input single-output (SISO) control theory suffices to generate acceptable control designs. For this class of inverters several families of controllers are addressed in order to examine command following as well as input disturbance and noise attenuation specifications. The goal here is to illuminate fundamental tradeoffs. Such tradeoffs include an improvement in the in-band command following and output disturbance attenuation versus a deterioration in out-of-band noise attenuation. A fundamental deficiency associated with such inverters is their large size. This can be remedied by designing a smaller core. This naturally leads to the second class of inverters considered in this work. These inverters are characterized by significant mutual inductances and multivariable coupling. As such, SISO control theory is generally not adequate and multiple-input multiple-output (MIMO) theory becomes essential for controlling these inverters. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2015

Rozptýlená výroba elektrické energie využívající obnovitelné zdroje, jako je sluneční energie, přispívá ke snížení emisí skleníkových plynů. Z hlediska provozu distribuční soustavy je také výhodné, aby energie byla primárně spotřebována v místě výroby. To je částečně možné přizpůsobením spotřeby, ale především využitím akumulačních systémů. V této práci je představen hybridní systém složený z fotovoltaické elektrárny, akumulátoru elektrické energie a akumulátoru tepelné energie. Výběr a parametry všech částí hybridního systému jsou popsány v práci. Akumulátor elektrické energie je navržen a sestaven z LiNiMnCoO2 článků a řídícího systému zajišťujícího bezpečný provoz. Řídicí systém akumulátoru (BMS) zajistí odpojení baterie, pokud je překročen některý z provozních parametrů baterie. Návrh baterie i sestavy je popsán v práci. Akumulátor tepelné energie sestává z výkonového spínače a nádrže na teplou vodu s topnou patronou pro odporový ohřev vody. Na základě rešerše komerčně používaných zařízení pro regulaci příkonu byly definovány jejich nedostatky a na základě nich bylo navrženo optimální řešení. Řešení spočívá v použití komerčního polovodičového spínacího prvku. Pro tento výkonový spínací prvek byla vytvořena zpětnovazební řídící smyčka s regulátorem výkonu, který byl implementován v prostředí softwaru LabVIEW. V práci je také uveden postup návrhu chladiče spínacího prvku a LCL filtru, který je klíčový pro splnění požadavků elektromagnetické kompatibility. V druhé části práce je popsán návrh nadřazeného řídícího algoritmu, jehož úkolem je řídit výkonové toky v hybridním systému tak, aby byly splněny požadavky definované jak uživatelem, tak i okamžitým stavem akumulátorů. Algoritmus byl implementován v prostředí LabVIEW. Funkčnost celého systému byla ověřena měřením v laboratorních podmínkách. Z výsledků plyne, že nadřazený řídící algoritmus funguje správně. Řídící smyčka tepelného akumulátoru je stabilní a reguluje zátěž na požadovanou hodnotu. Přidanou hodnotou je kratší reakční doba na změnu toku výkonu oproti hybridnímu měniči a díky tomu dochází k minimalizaci přetoků elektrické energie do distribuční sítě. Na práci je možné navázat rozšířením stávajícího algoritmu o možnost řízení/ovládání více typů akumulačních jednotek a generátorů nebo implementováním odlišných strategií řízení.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This thesis addresses the design of adaptive current controllers applied for voltagesource grid-connected converters with LCL-filter. Due to the grid equivalent impedance uncertainty and/or variation at the point of connection, the current controller of such converters may become unstable or have a poor performance with fixed-gain controllers because the grid impedance is part of the dynamic model. So, adaptive control techniques are proposed to ensure stability and performance of current controllers for grid-connected converter with LCL-filter even without knowledge of the grid equivalent impedance. Continuous time adaptive control, from the theoretical point of view, is a well established control technique. However, in this application, a discrete-time current controller is implemented. There are some differences between discrete-time and continuous-time adaptive controllers. When the controlled variable is the converter current, a model reference adaptive state feedback is proposed. The adaptation algorithm, responsible to update the gains in real-time, consists on a recursive least-squares (RLS) algorithm. When the controlled variable is the grid current, a model reference adaptive state feedback is also used. However, the RLS algorithm has some modifications to keep the controller robust under unmodeled dynamics. The RLS algorithm is used because it has better parametric convergence characteristics compared to other algorithms. The grid voltage disturbance is rejected making some small modifications on the controller structure. Simulation results are validated by experimental results in a 5,5kW three-phase grid-connected converter, which shows good convergence and steady state stability of the adaptive controllers. Finally, some comparisons with fixed gain current controllers are presented to show de advantages and disadvantages of each controller. / Esta tese trata do projeto de controladores adaptativos aplicados a conversores estáticos alimentados em tensão conectados à rede elétrica através de filtro LCL. Devido às características incertas e/ou variantes da impedância equivalente da rede no ponto de conexão de conversores estáticos, o controle da corrente de tais conversores pode se tornar instável ou o desempenho pode ser degradado com a utilização de controladores com ganhos fixos, pois a característica da rede faz parte do modelo dinâmico. Com base nisso, é proposto o uso de técnicas de controle adaptativo para garantir a estabilidade e o desempenho do controlador de corrente de conversores conectados à rede mesmo sem o conhecimento da sua impedância equivalente. Controle adaptativo em tempo contínuo, no ponto de vista teórico, é uma técnica de controle bem consolidada. No entanto, na aplicação em questão, o controlador de corrente é implementado em tempo discreto. Controle adaptativo em tempo discreto apresenta algumas diferenças quanto aos controladores em tempo contínuo. Quando a variável de controle é a corrente do conversor, é proposta a utilização de uma retroação de estados adaptativa por modelo de referência cujo adaptador, responsável por atualizar os ganhos em tempo real, consiste em um algoritmo recursivo por mínimos quadrados (RLS). Quando a variável de controle é a corrente da rede, também é utilizada uma retroação de estados adaptativa por modelo de referência, porém o algoritmo RLS apresenta modificações para torná-lo robusto à dinâmicas não modeladas. O algoritmo RLS é utilizado por ter melhores características de convergência paramétrica se comparado a outros algoritmos. O distúrbio de tensão da rede é rejeitado fazendo-se algumas modificações na estrutura da lei de controle. Os resultados de simulação são validados através de resultados experimentais em um conversor de potência nominal de 5,5kW, os quais mostram as características promissoras dos controladores de corrente adaptativos. Por fim, são apresentadas comparações com controladores de corrente de ganhos fixos, mostrando as vantagens e desvantagens de cada uma dos controladores.

The high penetration of renewable energy and the emerging concept of micro-grid system raises challenges to the high power conversion techniques. Multilevel converter plays the key role in such applications and is studied in detail in the dissertation. The topologies and modulation techniques for multilevel converter are categorized at first by a thorough literature survey. The pros and cons for various multilevel topologies and modulation techniques are discussed. The 3-level neutral point clamped (NPC) topology is selected to build a 200kVA, 20 kHz power conversion system. The modularized phase leg building block of the converter is carefully designed to achieve low loss and stress for high frequency and high power operation. The switching characteristics for all the commutation loops of 3-level phase leg are evaluated by double pulse tests. The switching performance is optimized for loss and stress tradeoff. A detailed loss model is built for system loss distribution and loss breakdown calculation. Loss and stress for the phase leg and 3-phase system are quantified at all power factors. The space vector modulation (SVM) for 3-level NPC converter is investigated to achieve loss reduction, neutral voltage balance and noise reduction. The loss model and simulation model provides a quantitative analysis for loss and neutral voltage ripple tradeoff. An improved SVM method is proposed to reduce NP imbalance and switching loss simultaneously. This method also ensures an evenly distributed device loss in each phase leg and gives a constant system efficiency under different power factors. Based on the improved modulation strategy, a new modulation scheme is then proposed with largely reduced conduction loss and switching stress. Moreover, the device loss and stress distribution on a phase leg is more even. This scheme also features on the simplified implementation. The improved switching characteristics for the proposed method are verified by double pulse tests. Also the system loss breakdown and the phase leg loss distribution analysis shows the loss reduction and redistribution result. The harmonic filter for the grid interface converter is designed with LCL topology. A detailed inductor current ripple analysis derives the maximum inductor current ripple and the ripple distribution in a line cycle. The inverter side inductor is designed with the optimum loss and size trade-off. The grid side inductor is designed based on grid code attenuation requirement. Different damping circuits for LCL filter are evaluated in detail. The filter design is verified by both simulation and hardware experiment. The average model for the 3-level NPC converter and its equivalent circuit is derived with the consideration of damping circuit in both ABC and d-q frame. The modeling and control loop design is verified by transfer function measurement on real hardware. The control loops design is also tested and verified on real hardware. The interleaved DC/DC chopper is introduced at last. The different interleaving methods and their current ripple are analyzed in detail with the coupled and non-coupled inductor. An integrated coupled inductor based on 3-dimentional core structure is proposed to achieve high power density and provide both CM and DM impedance for the inductor current and output current. / Ph. D.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Master Thesis presents the development of a grid-connected transformerless three-phase photovoltaic inverter. The Neutral Point Clamped (NPC) three-level inverter was chosen for implementation. The grid connection is made with a modified LCL filter (MLCL), where the common point of the output filter capacitors is connected directly to the dc bus central point (neutral point). The MLCL filter reduces the leakage current of photovoltaic system and attenuates the current harmonics injected in the grid. A passive damping of MLCL filter resonance peak was employed in order to avoid instability in the grid connection. In this sense, this Master Thesis contributes proposing a passive damping design method which is based not only on the stability requirement, but also considers the leakage current of photovoltaic system, once that passive damping impacts on the high frequency components of voltage on parasitic capacitance. Therefore, based on leakage current limit and current loop stability, a range for the damping resistance was obtained. The control system of the threephase inverter was developed in a synchronous reference frame (dq0), where the proper alignment with the grid voltage reference vector allows the independent control of active and reactive power inject in the grid. Simulation and experimental results are shown to evaluate the inverter performance and to validate the theoretical analysis. / Esta Dissertação de Mestrado apresenta o desenvolvimento de um inversor fotovoltaico trifásico não isolado conectado à rede. A topologia desenvolvida foi a de um inversor trifásico três níveis com ponto neutro grampeado (NPC Neutral Point Clamped). A conexão com a rede é feita através de um filtro LCL modificado (LCLM), que possui o ponto comum dos seus capacitores conectado ao ponto central do barramento CC do inversor. O filtro LCLM possui a finalidade de reduzir a corrente de fuga do sistema fotovoltaico ao mesmo tempo em que atenua os harmônicos de corrente injetados na rede. De modo a evitar problemas de instabilidade da malha de corrente do inversor, um sistema de amortecimento passivo do pico de ressonância do filtro LCLM foi empregado. Neste sentido, esta Dissertação de Mestrado contribui propondo um método de projeto do amortecimento passivo que se baseia não somente no critério de estabilidade, mas que também considera a corrente de fuga do sistema fotovoltaico, uma vez que o amortecimento impacta na atenuação das componentes de alta frequência da tensão sobre a capacitância parasita dos módulos fotovoltaicos. Com isso, uma faixa de valores para a resistência de amortecimento foi obtida a partir do limite permitido para a corrente de fuga e da estabilidade da malha de corrente. O sistema de controle do inversor trifásico foi desenvolvido com base no sistema de coordenadas síncronas dq0, cujo correto alinhamento com o vetor de referência das tensões da rede permite o controle independente das potências ativa e reativa injetadas na rede. Resultados experimentais e de simulação são apresentados de modo a comprovar o desempenho do inversor trifásico.

Made available in DSpace on 2016-12-12T17:38:38Z (GMT). No. of bitstreams: 1 JULIO KENDI NISHIOKA.pdf: 8294340 bytes, checksum: 28a4178bb0ec559b2db43a1aa6676188 (MD5) Previous issue date: 2011-08-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This dissertation proposes a digital control system for a three-phase four-wire high input power factor PWM rectifier with LCL filter. The proposed control system includes an inner control loop for active damping of the LCL filter peak resonance, which uses a lead-lag compensator. In addition, the control system presents an independent current loop for each rectifier phase, which employs resonant compensators tuned at the fundamental frequency of the utility grid voltage. Finally, other two outer loops are used to maintain the voltages across the dc bus capacitors regulated and balanced. This work also proposes a design methodology to obtain the parameter of the LCL filter, which is based on maximum harmonic currents allowed by technical standards and on the minimization of the reactive energy of the LCL filter capacitors. Simulation and experimental results are presented to validate the developed analysis and demonstrate the performance of the proposed controllers. / Esta Dissertação de Mestrado propõe um sistema de controle digital para um retificador PWM trifásico a quatro fios com filtro LCL e elevado fator de potência de entrada. O sistema de controle proposto inclui uma malha interna de amortecimento ativo do pico de ressonância do filtro LCL, fazendo uso de um compensador em avanço. Além da malha de amortecimento ativo, o sistema de controle apresenta uma malha de corrente independente para cada fase do retificador, as quais empregam compensadores ressonantes sintonizados na frequência fundamental da tensão de entrada. Por fim, outras duas malhas externas são utilizadas para manter as tensões dos capacitores que compõem o barramento CC reguladas e equilibradas. Este trabalho também propõe uma metodologia de projeto para os parâmetros do filtro LCL, a qual é baseada nos limites máximos de harmônicos de corrente permitidos pelas normas e na minimização da energia reativa do capacitor do filtro LCL. Resultados de simulação e experimentais são apresentados para validar as análises desenvolvidas e demonstrar o desempenho dos controladores propostos.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This Thesis deals with the development of a novel robust model reference adaptive controller (RMRAC), in discrete-time applied to grid-connected systems using LCL filter. This controller uses a modified robust parameters identifier based on a recursive least-squares algorithm. Two control structures are analyzed: state feedback approach and input-output approach. The robust stability analysis of the controller is presented including unmodeled dynamics. Thus, through these analyses, constraints design, in discrete-time, are obtained. For the validation of the proposed control algorithm, simulation and experimental results of a grid-connected power converter with LCL-filter, with current control, are presented. / Esta Tese de Doutorado apresenta o desenvolvimento de um novo controlador adaptativo por modelo de referência, totalmente desenvolvido em tempo discreto, aplicado a sistemas conectados à rede de energia elétrica empregando filtro LCL. Este controlador utiliza um identificador de parâmetros modificado robusto baseado no método dos mínimos quadrados recursivos. Em relação à estrutura do controlador, a abordagem por realimentação de estados e a abordagem entrada-saída são utilizadas. A análise de estabilidade robusta do controlador é apresentada incluindo dinâmicas não-modeladas. Por meio destas análises, restrições de projeto (em tempo discreto) são obtidas. Para a validação do algoritmo proposto, resultados de simulação e experimentais do sistema de controle de corrente em um conversor conectado à rede de energia elétrica com filtro LCL são apresentados.

Using alternating current in order to heat batteries at sub-zero temperatures is a method,which is investigated in-depth by an increasing number of study groups. The thesis considersthe resonance phenomenon with the intention to use alternating current amplificationand battery’s impedance in order to induce power dissipation inside the battery, and in thisway increase its temperature. A battery cell is thereby modelled as an impedance transferfunction, estimated from electrochemical impedance spectroscopy measurements, whichare taken for a LiNi 13Mn13Co13O2 cell. Note that at 1 kHz and room temperature (20 ◦C),the ohmic resistance of the selected cell amounts to only 0.76m. Five resonant circuitsare investigated and one of them is selected for further investigation, and as a basis for afilter design. The chosen resonant circuit lead to an LCL filter with current magnification.The experimental setup used for conducting practical experiments, offers the possibilityof operating the voltage source converter both as a Full-bridge and as a Half-bridge, withand without current control. For each possible configuration, an LCL filter and a currentcontroller are designed, taking into account the corresponding limitations in frequency,current and controller voltage. The filter design is based on a multiobjective optimizationmethod used to determine filter components that yield the highest gain value for everyconfiguration. The method minimizes two objective functions in order to find an optimalsolution. The first objective is the reversed absolute value of the gain, whereas thesecond one is the absolute impedance of the circuit, consisting of the filter and batterycells. The gain is thereby defined as the ratio between the induced cell current and thecurrent entering the circuit. The obtained results of the proposed method are experimentallyvalidated. Depending on how the filters were physically designed and taking intoaccount the corresponding voltage source converter configuration, gains of 16 were experimentallyachieved. Finally, the three investigated configurations are compared againstthe reference case (Half-bridge voltage source converter with current control and a singleinductor) regarding their power efficiencies. The power measurements showed that despitehigh obtained gains, the overall filter power losses remained approximately in thesame range, compared to the power losses of the reference case. This is due to the factthat stray resistances of the designed LCL filters easily reached values of around 40m,which hindered an efficient power transfer with the chosen voltage source converter andthe used battery cells. This further indicates the importance of building filters with lowstray resistances and in this thesis, it represents a primary source of improvement. / Användandet av växelströ m fö r att värma upp batterier är en metod som fö r närvarande undersö ks av ett flertal forskargupper. Detta examensarbete fokuserar kring hur resonans kan nyttjas fö r att ö ka strö mfö rstärkningen och, pådetta sätt, ö ka effektutvecklingen i batteriet (av LiNi1/3Mn1/3Co1/3O2-typ). Battericellens impedans modelleras som en ö verfö ringsfunktion vars parametrar estimerats från tidigare genomfö rda impedansspektroskopimätningar. Vid 1 kHz och rumstemperatur är den cellens ohmska resistansen endast 0.76 mΩ. Fem mö jliga resonanta kretsar har undersö kts och en av dem valts ut fö r vidare undersö kningar. The utvalda kretsen är ett LCL-filter med vilken strö mfö rstärkning åstadkoms. Den experimentella uppställningen, i vilken praktiska test har genomfö rts, medger mö jligheten att nyttja den tillhö rande omriktaren både som en helbrygga och en halvbrygga, med och utan strö mreglering. Fö r varje mö jlig omriktarkonfiguration har ett LCL-filter och en strö mreglering tagits fram, med hänsyn tagen till uppställningens begränsningar i termer av frekvens, strö moch dc-spänningsnivå. Filtren är framtagna med hjälp av en multiobjektiv optimering vilken åstadkommer hö gsta strö mfö rstärkning mö jlig fö r varje omriktare och strö mregleringsval. Metoden minimerar tvåfunktioner fö r att finna en optimal lö sning. Den fö rsta funktionen beskriver inversen påströ mfö rstärkningen och den andra lastens (bestående av filter och tillhö rande battericell) impedans absolutbelopp. Den resulterande ö har validerats experimentellt och en strö mfö rstärkningsnivåpå 16 uppnåddes. Slutligen har de olika konfigurationerna jämfö rts i termer av verknings-grad. De genomfö rda effektmätningarna visar att trots att hö ga strö mfö rstärkningsnivåer var mö jliga såresulterade de associerade filterfö rlusterna till liknande verkningsgrader fö r alla studerade konfigurationer. Resultaten understryker fö rdelarna med hö geffektiva filtervilka representerar en mö jlig väg fö r vidare undersö kningar.