Analysis, Dimensioning and Robust Control of Shunt Active Filter for Harmonic Currents Compensation in Electrical Mains

In this chapter some results related to Shunt Active Filters (SAFs) and obtained by the authors and some coauthors are reported. SAFs are complex power electronics equipments adopted to compensate for cur-rent harmonic pollution in electric mains, due to nonlinear loads. By using a proper "floating" capacitor as energy reservoir, the SAF purpose is to inject in the line grid currents canceling the polluting har-monics. Control algorithms play a key role for such devices and, in general, in many power electronics applications. Moreover, systems theory is crucial, since it is the mathematical tool that enables a deep understanding of the involved dynamics of such systems, allowing a correct dimensioning, beside an effective control. As a matter of facts, current injection objective can be straightforwardly formulated as an output tracking control problem. In this fashion, the structural and insidious marginally-stable internal/zero dynamics of SAFs can be immediately highlighted and characterized in terms of sizing and control issues. For what concerns the control design strictly, time-scale separation among output and internal dynamics can be effectively exploited to split the control design in different stages that can be later aggregated, by using singular perturbation analysis. In addition, for robust asymptotic output tracking the Internal Model Principle is adopted.Comment: Paper presented at the AUTOMATICA_IT 2011 conference, Pisa, Italy, September 201

Recent Advances in Robust Control

Robust control has been a topic of active research in the last three decades culminating in H_2/H_\infty and \mu design methods followed by research on parametric robustness, initially motivated by Kharitonov's theorem, the extension to non-linear time delay systems, and other more recent methods. The two volumes of Recent Advances in Robust Control give a selective overview of recent theoretical developments and present selected application examples. The volumes comprise 39 contributions covering various theoretical aspects as well as different application areas. The first volume covers selected problems in the theory of robust control and its application to robotic and electromechanical systems. The second volume is dedicated to special topics in robust control and problem specific solutions. Recent Advances in Robust Control will be a valuable reference for those interested in the recent theoretical advances and for researchers working in the broad field of robotics and mechatronics

Effective Design of STATCOM Considering Fundamental Frequency Current, Active Harmonic Filtering and Zero Sequence Current

The main objective of this thesis was to investigate the effect of parallel reactive power compensation (RPC) and active harmonic filtering (AHF) operation on a STATCOM design, in terms of needed number of submodules (SMs), DC link voltage capacity, MV busbar voltage, zero sequence current demand, transformer and coupling inductor reactance. To achieve this objective, two design scenarios were carried out. In the first scenario, fundamental reactive current of studied STATCOM was prioritized over its current for active harmonic voltage filtering. In the second scenario, studied STATCOM was required to produce the nominal fundamental reactive power and perform active harmonic voltage filtering simultaneously. The problem was studied in PSCAD based simulation environment. In all simulations, q-component current was supplied manually to enable the RPC operation of studied STATCOM. To enable AHF operation, harmonic current control mode was used, and the reference value of the desired harmonic filtering current was supplied accordingly. However, before proceeding with any simulation, first, the system limitations based on the studied STATCOM technology were studied and adequate majors were placed inside the simulation mode accordingly. Thereafter, simulations providing information on the basic STATCOM design operating in RPC mode only (and without AHF functionality) were carried out so that it can be compared later with the aforementioned scenarios of parallel RPC and AHF operations. In the first design scenario, it was found out that additional AHF operation affects the STAT-COM design in three ways. First was the magnitude of AHF current where an increment in the needed number of SMs w.r.t basic design was noticed with increasing magnitude of AHF current. The second was the phase angle references of AHF current where if phase angle references of AHF current are chosen such that peaks of produced voltage source converter’s (VSC’s) fundamental and harmonic voltages are aligned then the amount of needed SMs to produce the same VSC voltage was increased. But, if phase angle references of AHF current are such that the peaks of VSC voltages are opposite to each other, then fewer SMs are required to produce the same VSC voltage. The third effect on STATCOM design was based on the harmonic order of AHF current produced. It was noticed that when harmonic order of AHF current was high, then the amount of needed SMs to produce the same magnitude of AHF current was increased. In the second design scenario, it was found that maximum fundamental reactive current and maximum filtering current cannot be achieved at the same time with a geometrical summation principle of these currents, but possible with an arithmetical summation principle with a trade-off between optimum utilisation of current capacity and extra hardware cost. Hence, an optimum design to achieve the maximum of RPC and AHF current simultaneously exists between economical (based on the geometrical summation principle) and conservative (based on the arithmetical summation principle) design, but rather close to the economical one. In last, it was also noticed that the maximum demand of zero sequence current occurred when STATCOM was producing fundamental reactive current and negative sequence AHF current simultaneously in the maximum capacitive operation point, with an unbalanced network. And, peaks of positive and negative sequence network voltage and peaks of produced VSC voltages (fundamental and harmonic) were aligned

Dynamic performances of the shunt active power filter control system

Гармонічні спотворення в електричних мережах є добре відомими та достатньо вивченими явищами. Силовий активний фільтр визнано ефективним засобом для задоволення вимог нормативних документів, що регулюють якість електроенергії. Незважаючи на цей факт, їхня практична реалізація досі пов’язана зі значними складностями. Зокрема, в існуючих системах для оцінювання гармонічного складу струму мережі, як правило, використовуються методи на основі швидкого перетворення Фур’є або методи на основі теорії миттєвої потужності. Проте використання швидкого перетворення Фур’є вимагає високої обчислювальної здатності системи керування з однієї сторони, а застосування теорії миттєвої потужності значно підвищує вимоги до силової частини активного фільтра. Застосування іншого підходу – селективної компенсації гармонік, дає можливість зменшити вимоги до обчислювальної потужності та значно спростити технічну реалізацію активного фільтра і при цьому досягти прийнятного рівня компенсації спотворень. В статті представлено результати розробки та дослідження системи керування силовим активним фільтром. Запропонована система керування складається із селективного спостерігача гармонік, лінеаризуючого зворотним зв’язком регулятора струмів, регулятора напруги ланки постійного струму фільтра та спостерігача напруги мережі. Спостерігач гармонік, який налаштовано відповідно до спрощеної процедури, забезпечує селективне виявлення вищих гармонік струму мережі та формує завдання на струм компенсації, яке відпрацьовується регуляторами струмів. Нелінійний регулятор напруги забезпечує асимптотичне регулювання середнього значення напруги ланки постійного струму САФ, розв’язане з процесом компенсації струмів. Адаптивний спостерігач напруги мережі надає інформацію про амплітуду, частоту обертання та положення вектора напруги мережі. Запропоновану систему керування реалізовано на цифровому сигнальному процесорі TMS320F28335 та досліджено експериментально. Результати експериментальних досліджень разом із результатами моделювання підтверджують ефективність запропонованого рішення. Розроблена система керування може бути використаною для реалізації силових активних фільтрів.Harmonic pollution of the electrical mains is well known and well-studied phenomena. Active power filter being a powerful tool to meet the requirements of regulatory documents regulating the electricity quality. Despite this fact, practical implementation of the active power filter is still connected with significant difficulties. In particular, existing systems typically use fast Fourier transform methods or instantaneous power theory to estimate the harmonic composition of the mains current. However, the use of fast Fourier transform requires high computing power of the control system, and the implementation of the theory of instantaneous power significantly increases the requirements for the power part of the active filter. The application of another approach - selective compensation of harmonics, makes it possible to reduce computational requirements and significantly simplify the technical implementation of the active filter and at the same time to achieve an acceptable level of distortion compensation. In this paper, the shunt active power filter control system is designed and investigated. Proposed control system consist of selective harmonics observer, feedback-linearizing current controller, dc-link controller and mains voltage observer. Harmonics observer is tuned according to simplified approach, provides selective estimation of the load current harmonics and produce the compensation current reference for the current controller. Nonlinear dc-link voltage controller guarantees decoupled from current compensation process asymptotic regulation of the average dc-link voltage. Mains voltage vector adaptive observer provides magnitude, angular position and frequency estimation. Proposed control system is implemented on digital signal processor TMS320F28335 end verified experimentally. Results of experimental investigations together with results of simulations confirm effectiveness of proposed solution. Developed control system can be used for shunt active filters implementation.Гармонические искажения в электрических сетях – хорошо известные и достаточно изученные явления. Силовой активный фильтр признано эффективным средством для удовлетворения требований нормативных документов, регулирующих качество электроэнергии. Несмотря на этот факт, их практическая реализация все еще связана со значительными сложностями. В частности, в существующих системах для оценки гармонического состава тока сети, как правило, используются методы на основе быстрого преобразования Фурье или методы на основе теории мгновенной мощности. Однако использование быстрого преобразования Фурье требует высокой вычислительной способности системы управления с одной стороны, а применение теории мгновенной мощности значительно повышает требования к силовой части активного фильтра. Применение другого подхода - селективной компенсации гармоник, дает возможность уменьшить требования к вычислительной мощности и значительно упростить техническую реализацию активного фильтра и при этом достичь приемлемого уровня компенсации искажений. В статье представлены результаты разработки и исследования системы управления силовым активным фильтром. Предложенная система управления состоит из селективного наблюдателя гармоник, линеаризующего обратной связью регулятора токов, регулятора напряжения звена постоянного тока фильтра и наблюдателя напряжения. Наблюдатель гармоник, который настроен в соответствии с упрощенной процедурой, обеспечивает селективное обнаружение высших гармоник тока сети и формирует задания на ток компенсации, которое отрабатывается регуляторами токов. Нелинейный регулятор напряжения обеспечивает асимптотическое регулирования среднего значения напряжения звена постоянного тока САФ, развязанное от процесса компенсации токов. Адаптивный наблюдатель напряжения сети предоставляет информацию об амплитуде, частоте вращения и положении вектора напряжения. Предложенную систему управления реализовано на цифровом сигнальном процессоре TMS320F28335 и исследовано экспериментально. Результаты экспериментальных исследований вместе с результатами моделирования подтверждают эффективность предложенного решения. Разработанная система управления может быть использована для реализации силовых активных фильтров

Power Quality

Electrical power is becoming one of the most dominant factors in our society. Power generation, transmission, distribution and usage are undergoing signifi cant changes that will aff ect the electrical quality and performance needs of our 21st century industry. One major aspect of electrical power is its quality and stability – or so called Power Quality. The view on Power Quality did change over the past few years. It seems that Power Quality is becoming a more important term in the academic world dealing with electrical power, and it is becoming more visible in all areas of commerce and industry, because of the ever increasing industry automation using sensitive electrical equipment on one hand and due to the dramatic change of our global electrical infrastructure on the other. For the past century, grid stability was maintained with a limited amount of major generators that have a large amount of rotational inertia. And the rate of change of phase angle is slow. Unfortunately, this does not work anymore with renewable energy sources adding their share to the grid like wind turbines or PV modules. Although the basic idea to use renewable energies is great and will be our path into the next century, it comes with a curse for the power grid as power fl ow stability will suff er. It is not only the source side that is about to change. We have also seen signifi cant changes on the load side as well. Industry is using machines and electrical products such as AC drives or PLCs that are sensitive to the slightest change of power quality, and we at home use more and more electrical products with switching power supplies or starting to plug in our electric cars to charge batt eries. In addition, many of us have begun installing our own distributed generation systems on our rooft ops using the latest solar panels. So we did look for a way to address this severe impact on our distribution network. To match supply and demand, we are about to create a new, intelligent and self-healing electric power infrastructure. The Smart Grid. The basic idea is to maintain the necessary balance between generators and loads on a grid. In other words, to make sure we have a good grid balance at all times. But the key question that you should ask yourself is: Does it also improve Power Quality? Probably not! Further on, the way how Power Quality is measured is going to be changed. Traditionally, each country had its own Power Quality standards and defi ned its own power quality instrument requirements. But more and more international harmonization efforts can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and even directly embedded into sensitive loads. But work still has to be done. We still use Power Quality standards that have been writt en decades ago and don’t match today’s technology any more, such as fl icker standards that use parameters that have been defi ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct. Almost all experts are in agreement - although we will see an improvement in metering and control of the power fl ow, Power Quality will suff er. This book will give an overview of how power quality might impact our lives today and tomorrow, introduce new ways to monitor power quality and inform us about interesting possibilities to mitigate power quality problems. Regardless of any enhancements of the power grid, “Power Quality is just compatibility” like my good old friend and teacher Alex McEachern used to say. Power Quality will always remain an economic compromise between supply and load. The power available on the grid must be suffi ciently clean for the loads to operate correctly, and the loads must be suffi ciently strong to tolerate normal disturbances on the grid

Nonlinear constrained and saturated control of power electronics and electromechanical systems

Power electronic converters are extensively adopted for the solution of timely issues, such as power quality improvement in industrial plants, energy management in hybrid electrical systems, and control of electrical generators for renewables. Beside nonlinearity, this systems are typically characterized by hard constraints on the control inputs, and sometimes the state variables. In this respect, control laws able to handle input saturation are crucial to formally characterize the systems stability and performance properties. From a practical viewpoint, a proper saturation management allows to extend the systems transient and steady-state operating ranges, improving their reliability and availability. The main topic of this thesis concern saturated control methodologies, based on modern approaches, applied to power electronics and electromechanical systems. The pursued objective is to provide formal results under any saturation scenario, overcoming the drawbacks of the classic solution commonly applied to cope with saturation of power converters, and enhancing performance. For this purpose two main approaches are exploited and extended to deal with power electronic applications: modern anti-windup strategies, providing formal results and systematic design rules for the anti-windup compensator, devoted to handle control saturation, and “one step” saturated feedback design techniques, relying on a suitable characterization of the saturation nonlinearity and less conservative extensions of standard absolute stability theory results. The first part of the thesis is devoted to present and develop a novel general anti-windup scheme, which is then specifically applied to a class of power converters adopted for power quality enhancement in industrial plants. In the second part a polytopic differential inclusion representation of saturation nonlinearity is presented and extended to deal with a class of multiple input power converters, used to manage hybrid electrical energy sources. The third part regards adaptive observers design for robust estimation of the parameters required for high performance control of power systems

Planning and Management of a solar power-based distribution system

This thesis is aimed at the response of the power system network to the integration of solar photovoltaic (PV) generation and battery energy storage systems (BESS). Any solar power–based system integrated into a grid has voltage fluctuations that must be controlled through adaptive and robust control algorithms. The siting of battery in a distribution system affects system performance, including voltage regulation, system losses and cost minimization. In particular, here the aim is to analyse how the present-day schemes and technologies affect voltages, and their control, in the network. Another focus is on the optimal placement of BESS to facilitate system loss minimisation and cost reduction in the system. The battery placement optimisation is achieved through the minimisation of the losses in, and the cost of, the system. The voltage regulation is achieved through two control algorithms: Synchronous Reference Frame theory (SRFT) and adaptive linear neural network (ADALINE), which are subsequently modified by incorporation of fuzzy logic into the control system. Both battery placement optimisation and improvements to voltage regulation are shown to improve performance of the system. A further aim of this work is to improve cooperation between present day grid regulation equipment and schemes and the conventional methods through advancements in the control techniques. The aims of this thesis are as follows: 1. It is essential to place BESSs optimally. The aim of the thesis is to study and enhance the method of the optimal siting of battery energy storage in the presence of renewable energy–based power generating sources (RES)– such as solar PV – in a low-voltage power system network. A model for optimisation is developed to potentially find the battery site that enhances the hosting capability of the RES of the power system network. Among the essential points of this technique are its accuracy and robust nature. The fitness function includes the minimisation of the cost of operation and of system losses. 2. The second research objective is to examine the power control techniques of the inverter that might be leading to the voltage quality issues during unbalanced voltage scenarios, especially with solar PV–based generation in the power system. As such, after the implementation of the suggested coordination of the control mechanism into the grid under study, the variations in the voltage due to the solar PV variability dynamics are regulated more quickly and more precisely compared with the control schemes employed in the past. This substantially minimises the voltage fluctuations in time and amplitude, helps in mitigating hunting phenomena in voltage and provides alternative to the unnecessary control operations existing in the system

Technical solutions for low-voltage microgrid concept

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Development of Robust Control Schemes with New Estimation Algorithms for Shunt Active Power Filter

The widespread use of power electronics in industrial, commercial and even residential electrical equipments causes deterioration of the quality of the electric power supply with distortion of the supply voltage. This has led to the development of more stringent requirements regarding harmonic current generation, as are found in standards such as IEEE-519. Power Quality is generally meant to measure of an ideal power supply system. Shunt active power filter (SAPF) is a viable solution for Power Quality enhancement, in order to comply with the standard recommendations. The dynamic performance of SAPF is mainly dependent on how quickly and how accurately the harmonic components are extracted from the load current. Therefore, a fast and accurate estimation algorithm for the detection of reference current signal along with an effective current control technique is needed in order for a SAPF to perform the harmonic elimination successfully. Several control strategies of SAPF have been proposed and implemented. But, still there is a lot of scope on designing new estimation algorithms to achieve fast and accurate generation of reference current signal in SAPF. Further, there is a need of development of efficient robust control algorithms that can be robust in face parametric uncertainties in the power system yielding improvement in power quality more effectively in terms of tracking error reduction and efficient current harmonics mitigation. The work described in the thesis involves development of a number of new current control techniques along with new reference current generation schemes in SAPF. Two current control techniques namely a hysteresis current control (HCC) and sliding mode control (SMC) implemented with a new reference current generation scheme are proposed. This reference generation approach involves a Proportional Integral (PI) controller loop and exploits the estimation of the in phase fundamental components of distorted point of common coupling (PCC) voltages by using Kalman Filter (KF) algorithm. The KF-HCC based SAPF is found to be very simple in realization and performs well even under grid perturbations. But the slow convergence rate of KF leads towards an ineffective reference generation and hence harmonics cancellation is not perfect. Therefore, a SMC based SAPF is implemented with a faster reference scheme based on the proposed Robust Extended Complex Kalman Filter (RECKF) algorithm and the efficacy of this RECKF-SMC is compared with other variants of Kalman Filter such as KF, Extended Kalman Filter (EKF) and Extended Complex Kalman Filter (ECKF) employing simulations as well as real-time simulations using an Opal-RT Real-Time digital Simulator. The RECKF-SMC based SAPF is found to be more effective as compared to the KF-HCC, KF-SMC, EKF-SMC and ECKF-SMC. Subsequently, predictive control techniques namely Dead Beat Control (DBC) and Model Predictive Control (MPC) are proposed in SAPF along with an improved reference current generation scheme based on the proposed RECKF. This reference scheme is devoid of PI controller loop and can self-regulate the dc-link voltage. Both RECKF-DBC and RECKF-MPC approaches use a model of the SAPF system to predict its future behavior and select the most appropriate control action based on an optimality criterion. However, RECKF-DBC is more sensitive to load uncertainties. Also, a better compensation performance of RECKF-MPC is observed from the simulation as well as real-time simulation results. Moreover, to study the efficacy of this RECKF-MPC over PI-MPC, a comparative assessment has been performed using both steady state as well as transient state conditions. From the simulation and real-time simulation results, it is observed that the proposed RECKF-MPC outperforms PI-MPC. The thesis also proposed an optimal Linear Quadratic Regulator (LQR) with an advanced reference current generation strategy based on RECKF. This RECKF-LQR based SAPF has better tracking and disturbance rejection capability and hence RECKF-LQR is found to be more efficient as compared to RECKF-SMC, RECKF-DBC and RECKF-MPC approaches. Subsequently, two robust control approaches namely Linear Quadratic Gaussian (LQG) servo control and H∞ control are proposed in SAPF with highly improved reference generation schemes based on RECKF. These control strategies are designed with the purpose of achieving stability, high disturbance rejection and high level of harmonics cancellation. From simulation results, they are not only found to be robust against different load parameters, but also satisfactory THD results have been achieved in SAPF. A prototype experimental set up has been developed in the Laboratory with a dSPACE-1104 computing platform to verify their robustness. From both the simulation and experimentation, it is observed that the proposed RECKF-H∞ control approach to design a SAPF is found to be more robust as compared to the RECKF-LQG servo control approach in face parametric uncertainties due to load perturbations yielding improvement in power quality in terms of tracking error reduction and efficient current harmonics mitigation. Further, there is no involvement of any voltage sensor in this realization of RECKF-H∞ based SAPF resulting a more reliable and inexpensive SAPF system. Therefore, superiority of proposed RECKF-H∞ is proved amongst all the proposed control strategies of SAPF