56 research outputs found

    On Deep Machine Learning Based Techniques for Electric Power Systems

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    This thesis provides deep machine learning-based solutions to real-time mitigation of power quality disturbances such as flicker, voltage dips, frequency deviations, harmonics, and interharmonics using active power filters (APF). In an APF the processing delays reduce the performance when the disturbance to be mitigated is tima varying. The the delays originate from software (response time delay) and hardware (reaction time delay). To reduce the response time delays of APFs, this thesis propose and investigate several different techniques. First a technique based on multiple synchronous reference frame (MSRF) and order-optimized exponential smoothing (ES) to decrease the settling time delay of lowpass filtering steps. To reduce the computational time, this method is implemented in a parallel processing using a graphics processing unit (GPU) to estimate the time-varying harmonics and interharmonics of currents. Furthermore, the MSRF and three machine learning-based solutions are developed to predict future values of voltage and current in electric power systems which can mitigate the effects of the response and reaction time delays of the APFs. In the first and second solutions, a Butterworth filter is used to lowpass filter the\ua0 dq\ua0 components, and linear prediction and long short-term memory (LSTM) are used to predict the filtered\ua0 dq\ua0 components. The third solution is an end-to-end ML-based method developed based on a combination of convolutional neural networks (CNN) and LSTM. The Simulink implementation of the proposed ML-based APF is carried out to compensate for the current waveform harmonics, voltage dips, and flicker in Simulink environment embedded AI computing system Jetson TX2.\ua0In another study, we propose Deep Deterministic Policy Gradient (DDPG), a reinforcement learning (RL) method to replace the controller loops and estimation blocks such as PID, MSRF, and lowpass filters in grid-forming inverters. In a conventional approach it is well recognized that the controller tuning in the differen loops are difficult as the tuning of one loop influence the performance in other parts due to interdependencies.In DDPG the control policy is derived by optimizing a reward function which measure the performance in a data-driven fashion based on extensive experiments of the inverter in a simulation environment.\ua0Compared to a PID-based control architecture, the DDPG derived control policy leads to a solution where the response and reaction time delays are decreased by a factor of five in the investigated example.\ua0Classification of voltage dips originating from cable faults is another topic addressed in this thesis work. The Root Mean Square (RMS) of the voltage dips is proposed as preprocessing step to ease the feature learning for the developed\ua0 LSTM based classifier. Once a cable faults occur, it need to be located and repaired/replaced in order to restore the grid operation. Due to the high importance of stability in the power generation of renewable energy sources, we aim to locate high impedance cable faults in DC microgrid clusters which is a challenging case among different types of faults. The developed Support Vector Machine (SVM) algorithm process the maximum amplitude and\ua0 di/dt\ua0 of the current waveform of the fault as features, and the localization task is carried out with\ua0 95 %\ua0 accuracy.\ua0Two ML-based solutions together with a two-step feature engineering method are proposed to classify Partial Discharges (PD) originating from pulse width modulation (PWM) excitation in high voltage power electronic devices. As a first step, maximum amplitude, time of occurrence, area under PD curve, and time distance of each PD are extracted as features of interest. The extracted features are concatenated to form patterns for the ML algorithms as a second step. The suggested feature classification using the proposed ML algorithms resulted in\ua0 95.5 %\ua0 and\ua0 98.3 %\ua0\ua0 accuracy on a test data set using ensemble bagged decision trees and LSTM networks

    Power Quality Improvement of Distributed Generation Integrated Network with Unified Power Quality Conditioner.

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    With the increased penetration of small scale renewable energy sources in the electrical distribution network, maintenance or improvement of power quality has become more critical than ever where the level of voltage and current harmonics or disturbances can vary widely. For this reason, Custom Power Devices (CPDs) such as the Unified Power Quality Conditioner (UPQC) can be the most appropriate solution for enhancing the dynamic performance of the distribution network, where accurate prior knowledge may not be available. Therefore, the main objective of the present research is to investigate the (i) placement (ii) integration (iii) capacity enhancement and (iv) real time control of the Unified Power Quality Conditioner (UPQC) to improve the power quality (PQ) of a distributed generation (DG) network connected to the grid or microgrid

    Novi pristup za poboljšanje karakteristika UPQC-a tijekom nesimetričnih i distorzijskih uvjeta tereta temeljen na teoriji trenutne snage

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    In order to deal with power quality problems under distortional and unbalanced load conditions, this paper presents a new control method for a four-wire three-phase unified power quality conditioner (UPQC) which is based on instantaneous power p-q theory. The proposed control approach is based on instantaneous power and is optimized by using a self-tuning filter (STF), without using any low-pass filters (LPFs) or phase locked loop (PLL), and without measuring load or filter currents. In this approach, the load and source voltages are used to generate the reference voltages of a series active power filter (APF) and source currents are used to generate the reference currents of a shunt APF. Therefore, the number of times that current is measured is reduced and system performance is improved. The performance of the proposed control approach is evaluated in terms of power factor correction, source neutral current mitigation, load balancing and mitigation of the current and voltage harmonics of distortional and unbalanced loads in a three-phase four-wire system. The results obtained by MATLAB/SIMULINK software show the effectiveness of the proposed control technique in comparison to the conventional p-q method.U ovom radu prikazana je nova metoda upravljanja za trofazni četverožični UPQC (engl. unified power quality conditioner) temeljena na teoriji trenutne vrijednosti snage koja je prikladna za upravljanje tijekom distorzijskih i nesimetričnih uvjeta na teretu. Predloženo upravljanje temelji se na teoriji o trenutnoj radnoj i jalovoj snazi i optimirano je korištenjem samopodešavajućeg fitera, bez korištenja niskopropusnih filtera ili PLL-a i bez mjerenja struje tereta i filtra. Korišteni su naponi na teretu i napon izvora kako bi se generirala referentna vrijednost napona aktivnog filtra, a struje izvora koriste se za generiranje referentne vrijednosti struje aktivnog filtra. Na taj način smanjen je broj mjerenja struje i sustav ima bolje značajke. Uz predloženi sustav upravljanja testire su mogućnosti korekcije faktora snage, smanjenja neutralne struje izvora, balansiranja tereta, smanjenje harmonika u struji i naponu. Rezultati dobiveni pomoću MATLAB/SIMULINK-a pokazuju učinkovitost predloženog sustava upravljanja

    Active Power Filters in Zero Energy Buildings

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    Master's thesis Renewable Energy ENE500 - University of Agder 2017With an increasing focus on the environment and moving from fossil to renewable energy, there has and is an increasing interest in zero energy buildings. Zero energy buildings often utilize local intermittent renewable energies such as wind and solar energy, and are going to play an important role in the smart grid development with their distributed generation and energy storage etc. In Southern Norway, the smart village Skarpnes is utilizing building integrated photovoltaic systems and is developed for studying zero energy buildings and its impact on electricity demand and power quality. Power electronic based equipment such as uninterruptible power supplies, adjustable speed drives, personal computers and more have all enhanced our daily lives by providing an efficient and reliable way of utilizing the electrical energy. Because of their non-linear behaviour, they are responsible for harmonic currents causing additional losses and harmful effects. In this thesis, a shunt active power filter based on the instantaneous power theory used for power quality improvement is studied. This involves harmonic current, reactive power and neutral current compensation, where load data is obtained from the smart village Skarpnes project. Investigating the operation of the shunt active power filter during import and export of power, during load changes and operation during distorted and unbalanced utility voltage. Based on simulations using MATLAB/Simulink the three-phase, four-wire shunt active power filter is able to compensate the harmonic currents, reactive power and neutral current. The total harmonic distortion in the source current after compensation is below limits proposed by the Institute of Electrical and Electronics Engineers Standard 519-2014 for all test case

    Mitigation of Power Quality Problems Using Custom Power Devices: A Review

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    Electrical power quality (EPQ) in distribution systems is a critical issue for commercial, industrial and residential applications. The new concept of advanced power electronic based Custom Power Devices (CPDs) mainly distributed static synchronous compensator (D-STATCOM), dynamic voltage restorer (DVR) and unified power quality conditioner (UPQC) have been developed due to lacking the performance of traditional compensating devices to minimize power quality disturbances. This paper presents a comprehensive review on D-STATCOM, DVR and UPQC to solve the electrical power quality problems of the distribution networks. This is intended to present a broad overview of the various possible DSTATCOM, DVR and UPQC configurations for single-phase (two wire) and three-phase (three-wire and four-wire) networks and control strategies for the compensation of various power quality disturbances. Apart from this, comprehensive explanation, comparison, and discussion on D-STATCOM, DVR, and UPQC are presented. This paper is aimed to explore a broad prospective on the status of D-STATCOMs, DVRs, and UPQCs to researchers, engineers and the community dealing with the power quality enhancement. A classified list of some latest research publications on the topic is also appended for a quick reference

    Online Control of Modular Active Power Line Conditioner to Improve Performance of Smart Grid

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    This thesis is explored the detrimental effects of nonlinear loads in distribution systems and investigated the performances of shunt FACTS devices to overcome these problems with the following main contribution: APLC is an advanced shunt active filter which can mitigate the fundamental voltage harmonic of entire network and limit the THDv and individual harmonic distortion of the entire network below 5% and 3%, respectively, as recommended by most standards such as the IEEE-519

    Power Electronics in Renewable Energy Systems

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    IMPROVEMENT OF POWER QUALITY BY SHUNT ACTIVE POWER FILTER IN A THREE-PHASE FOUR-WIRE DISTRIBUTION SYSTEM

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    Power quality disturbances such as harmonics, power factor and neutral conductor current in a distribution network are the major concern as utilities are moving forward to a Smart Grid. Power quality for the digital economy in a Smart Grid distribution system is a priority with a variety of quality/price options. Meanwhile, the impact of renewal sources of energy like solar, wind, wave etc., which mainly use power electronic controllers and integrated into the Smart Grid cause increased power quality problems. The main source for high current harmonics, low power factor and excessive neutral current are high power mixed non-linear loads. International standards on power quality impose a maximum limit on Total Harmonic Distortion (THD) of 5 %. In addition the power factor is to be unity and the neutral conductor current is close to zero. In many applications the electrical power is distributed through three-phase four-wire system and as a result high neutral conductor current is produced in addition to the generation of current harmonics. The presence of harmonics in the distribution lines results in greater power losses, interference with communication lines and failure of operation of sensitive equipment. A reliable and cost-effective solution to power quality disturbances is active power filtering. This thesis addresses the above issues by using two-level, five-level and seven-level three-phase four-wire Shunt Active Power Filter (SAPF) in industrial distribution network to minimize the neutral current and to mitigate the current harmonics. The line-currents which have to be injected by SAPF are shaped by controlling the two-level and multilevel Voltage Source Inverter (VSI) based SAPF. In order to control the VSI, the reference signals are computed by using three proposed control schemes based on p-q theory, d-q-0 theory and a-b-c theory. MATLAB/SIMULINK is used as a simulation tool to develop the power system models for dynamic simulation. The proposed control schemes for SAPF are analyzed and applied to three-phase four-wire system to compensate for harmonic source currents, correcting the power factor of the supply side near to unity and to improve the source current THD within the prescribed limit of 5 % as recommended by IEEE-519 standards
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