5,788 research outputs found

    Architecture of a network-in-the-Loop environment for characterizing AC power system behavior

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    This paper describes the method by which a large hardware-in-the-loop environment has been realized for three-phase ac power systems. The environment allows an entire laboratory power-network topology (generators, loads, controls, protection devices, and switches) to be placed in the loop of a large power-network simulation. The system is realized by using a realtime power-network simulator, which interacts with the hardware via the indirect control of a large synchronous generator and by measuring currents flowing from its terminals. These measured currents are injected into the simulation via current sources to close the loop. This paper describes the system architecture and, most importantly, the calibration methodologies which have been developed to overcome measurement and loop latencies. In particular, a new "phase advance" calibration removes the requirement to add unwanted components into the simulated network to compensate for loop delay. The results of early commissioning experiments are demonstrated. The present system performance limits under transient conditions (approximately 0.25 Hz/s and 30 V/s to contain peak phase-and voltage-tracking errors within 5. and 1%) are defined mainly by the controllability of the synchronous generator

    DESIGN OF REAL-TIME FUZZY LOGIC PSS BASED ON PMUs FOR DAMPING LOW FREQUENCY OSCILLATIONS

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    Poorly damped low frequency oscillations is one of the main problems threatening safe and stable operation of the interconnected power systems and reducing the capability of transmission the power. The generator's excitation system has been supplemented with the Power System Stabilizer (PSS) in order to improve the damping of these low oscillations. In the latest smart power grids, the Phasor Measurement Units (PMUs) become a fundamental element in the monitoring, protection and control applications as PMU signals are more accurate than the conventional measurement units and real time GPS stamped. In this study, Fuzzy Power System Stabilizer (FPSS) has been designed and its performance in damping inter-are oscillations compared with the conventional PSS (CPSS) based on the simulation with MATLAB/Simulink model. The results of the simulation with the Simulink model proved that the performance of the designed FPSS in damping inter-area oscillation is better than the CPSS. One of the main features of fuzzy controller is that it doesn't require mathematical modeling as it is designed based on the time-domain and the operator experience while, in contrast, the conventional PSS requires to be designed in the frequency domain. Real Time Digital Simulator (RTDS) has been used to develop the real-time models of the test systems. The time-domain simulations with the RTDS model when the system subjected to the large disturbance (three-phase to ground fault) have been performed to show that the designed FPSS improved the damping of the oscillations effectively. The simulation results have been verified by modal analysis

    Small-Signal Modelling and Analysis of Doubly-Fed Induction Generators in Wind Power Applications

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    The worldwide demand for more diverse and greener energy supply has had a significant impact on the development of wind energy in the last decades. From 2 GW in 1990, the global installed capacity has now reached about 100 GW and is estimated to grow to 1000 GW by 2025. As wind power penetration increases, it is important to investigate its effect on the power system. Among the various technologies available for wind energy conversion, the doubly-fed induction generator (DFIG) is one of the preferred solutions because it offers the advantages of reduced mechanical stress and optimised power capture thanks to variable speed operation. This work presents the small-signal modelling and analysis of the DFIG for power system stability studies. This thesis starts by reviewing the mathematical models of wind turbines with DFIG convenient for power system studies. Different approaches proposed in the literature for the modelling of the turbine, drive-train, generator, rotor converter and external power system are discussed. It is shown that the flexibility of the drive train should be represented by a two-mass model in the presence of a gearbox. In the analysis part, the steady-state behaviour of the DFIG is examined. Comparison is made with the conventional synchronous generators (SG) and squirrel-cage induction generators to highlight the differences between the machines. The initialisation of the DFIG dynamic variables and other operating quantities is then discussed. Various methods are briefly reviewed and a step-by-step procedure is suggested to avoid the iterative computations in initial condition mentioned in the literature. The dynamical behaviour of the DFIG is studied with eigenvalue analysis. Modal analysis is performed for both open-loop and closed-loop situations. The effect of parameters and operating point variations on small signal stability is observed. For the open-loop DFIG, conditions on machine parameters are obtained to ensure stability of the system. For the closed-loop DFIG, it is shown that the generator electrical transients may be neglected once the converter controls are properly tuned. A tuning procedure is proposed and conditions on proportional gains are obtained for stable electrical dynamics. Finally, small-signal analysis of a multi-machine system with both SG and DFIG is performed. It is shown that there is no common mode to the two types of generators. The result confirms that the DFIG does not introduce negative damping to the system, however it is also shown that the overall effect of the DFIG on the power system stability depends on several structural factors and a general statement as to whether it improves or detriorates the oscillatory stability of a system can not be made

    Modeling, Control, and Optimization for Diesel-Driven Generator Sets

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    Coordination of Generator Protection and Control in the Over and Under Excited Regions

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    This thesis deals with the coordination of protection and control functions associated with the synchronous generators. The excitation control functions are a key component in maintaining the stability of machines and the network. The overall objective of coordination is simple; to allow excitation control functions, the automatic recovery from excursions beyond normal limits, and only take protective action as a last resort. This thesis focuses on four areas of generator control and protection : a) Loss of excitation protection, b) Dynamic underexcitation coordination, c) Dynamic Overexcitation coordination, and d) a generic protective relay development platform for hardware and software development. Loss of excitation (LOE) is a condition in the underexcited region that presents a risk of severe damage to a generator. The state of the art in the detection of a loss of excitation condition is based on the principle that, for a zero Thevenin voltage, the generator becomes a reactance as seen from the power system. The difficulty in detecting a loss of excitation is that several other disturbances may temporarily present a similar behavior, for instance a fault followed by a power swing. In this part of the work, a new algorithm for the detection of a loss of excitation condition is proposed by using the Support Vector Machine (SVM) classification method and a careful design of the necessary feature vectors. The proposed method is robust to changes in conditions including initial load, fault types, line impedance, as well as generator parameter inaccuracies. Coordination in the underexcited region presents difficulties due to the commonly used static characteristics instead of dynamic simulation. The underexcited limit presents an overload characteristic that is not normally known or used. Once the limit is exceeded, the limiting control action is a control loop that presents a dynamic behavior not typically represented in studies in the current industry practice. It is also important to properly model and include dynamic performance of protection functions. An important consideration not typically taken into account is the actual stability limit, which depends on the characteristics and the mode of excitation control used. This thesis includes all the above considerations necessary to achieve the required coordination using the more accurate dynamic simulations. Specific scenarios that present risk to the machine or the system are included to assess the coordination achieved. A real generator from the Alberta power system is used as a case study to demonstrate the proposed coordination methodology. Coordination in the overexcited region again presents practical difficulties due to static characteristics instead of dynamic simulation of conditions that exercise the overexcitation limits. The problems observed relate to coordination methodology and modeling methods for both protection and control limits. Once the limit boundary characteristic is exceeded, the limiting action is a control loop that presents dynamic behavior that needs to be represented. Similar considerations need to be made with the protection function protecting against rotor overload. Current modeling methods mostly use low bandwidth simulations, i.e., transient stability studies. A modeling methodology as well as specific model improvements to the IEEE ST1A excitation control model are proposed to achieve the required coordination. The ST1A type is one model that can represent a wide variety of system models from different manufacturers. The proposed modeling methodology applies to high bandwidth simulations such as electromagnetic simulations. Specific important scenarios, such as severe temporary reactive overload or severe power swing conditions, where the protection and control are required to coordinate but that present risk to the machine or the system are proposed as part of the coordination considerations. The detection of LOE conditions by the proposed SVM method and by traditional methods was implemented in hardware by using a digital signal processor (DSP) platform and tested using real time power system simulations. A new platform for real time protective relay development was designed and used for the purpose of implementation. In the proposed platform, a processor independent code is used so that development can be performed using native host computer development tools. By using the proposed platform-independent code, off line testing can be performed either interactively or in batch mode for evaluating multiple cases

    Dynamický model dvou synchronních generátorů propojených dlouhou přenosovou linkou

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    Due to the large desire to utilize transmission networks for more flexible power interchange transactions, the high requirement for power system dynamic analysis has grown significantly in recent years. While dynamics and stability have been studied for years in a long term planning and design environment, there is a recognized need to perform this analysis in a weekly or even daily operation environment. The dynamic performance of power systems is important to both the system organizations, from an economic viewpoint, and society in general, from a reliability viewpoint. The analysis of power system dynamics and stability is increasing daily in terms of number and frequency of studies, as well as in complexity and size. Dynamic phenomena have been discussed according to basic function, time-scale properties, and problem size. In a realistic system, electric power system consist of the interconnection of large numbers of synchronous generators operating in parallel. These generators are connected together by transmission lines. In the operation process, the rotor angles of generators swing relatively to another one during transients. Under disturbances the synchronism of machines in system is achieved when maintaining equilibrium between electromagnetic and mechanical torques. In other words, a system is unstable if the angle difference between two interconnected generators is not sufficiently damped in the evaluation time. The instability typically occurs as increasingly swings angle generators leading to some loss of synchronism with other generators. One of the constraints for long distance AC transmission is the large phase angular difference which is required to transmit a given amount of power. Therefore, in order to gain dynamic behavior characteristics of system when subject to disturbances, this work will focus on modeling two synchronous generators linked by long AC transmission line. Within the content of this work, for the analysis of system modes, the system is computed based on a detailed model of synchronous machines, transformers, loads and the long transmission line including voltage dynamics and frequency response. The system power equilibrium equations are derived and linearized for the small disturbance stability analysis and some transient disturbances. These results can serve to define stability margin of a power system. This stability limit would play important role in improving designs of the different system connection conditions.V posledních dynamických letech významně vzrostly nároky na pružnost výměny elektrické energie, což klade zvýšené nároky na dynamickou analýzu energetických systémů. Zatím co dynamika a stabilita sítí je dlouhodobě studována při dlouhodobém plánování, je nyní zapotřebí k zamezení nežádoucích výpadků přenosu energie tuto analýze provádět daleko rychleji on-line s okamžitými on-line naměřenými daty. Dynamicky stabilní výkon přenášený v energetických systémech je důležitý jak z organizačních důvodů, tak z ekonomického hlediska spolu s hlediskem spolehlivosti. Analýzou dynamiky a stability energetických systémů se v současnosti zabývá velké množství aktuální odborné literatury. Literární studie se liší podle detailnosti popisu systému a jeho velikosti. Dynamické jevy byly diskutovány podle základní funkce, podle vlastností, podle časového měřítka atd. V reálném systému se elektrická energetická soustava skládá z propojení velkého počtu synchronních generátorů pracujících paralelně. Tyto generátory jsou propojeny přenosovými linkami. Při provozním procesu se úhly rotorů generátorů v průběhu přechodových otáček relativně otáčejí jiným. Při poruchách dochází k synchronizaci strojů v systému při zachování rovnováhy mezi elektromagnetickými a mechanickými momenty. Jinými slovy, systém je nestabilní, pokud úhlový rozdíl mezi dvěma propojenými generátory není dostatečně tlumen. Nestabilita se zpravidla vede ke ztrátě synchronizace s ostatními generátory a k rozpadu okrsku sítě vypnutím proudových, napěťových a výkonových ochran. Jedním z omezení stability přináší pro dálkový přenos dlouhým vedením. Dlouhé metalické vedení zvyšuje fázový úhlový rozdíl, který je nutný k přenosu daného výkonu střídavým proudem. Proto se za účelem získání popisu dynamického chování systému při poruchách soustředí tato práce na modelování dvou synchronních generátorů propojených dlouhým AC přenosovým vedením. V rámci této práce je pro analýzu systémových režimů systém vypočítán na základě podrobného modelu synchronních strojů, transformátorů, zátěží a dlouhé přenosové linky včetně dynamiky napětí a frekvenční odezvy

    Pattern Recognition of Power System Voltage Stability using Statistical and Algorithmic Methods

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    In recent years, power demands around the world and particularly in North America increased rapidly due to increase in customer’s demand, while the development in transmission system is rather slow. This stresses the present transmission system and voltage stability becomes an important issue in this regard. Pattern recognition in conjunction with voltage stability analysis could be an effective tool to solve this problem In this thesis, a methodology to detect the voltage stability ahead of time is presented. Dynamic simulation software PSS/E is used to simulate voltage stable and unstable cases, these cases are used to train and test the pattern recognition algorithms. Statistical and algorithmic pattern recognition methods are used. The proposed method is tested on IEEE 39 bus system. Finally, the pattern recognition models to predict the voltage stability of the system are developed

    Pattern Recognition of Power System Voltage Stability using Statistical and Algorithmic Methods

    Get PDF
    In recent years, power demands around the world and particularly in North America increased rapidly due to increase in customer’s demand, while the development in transmission system is rather slow. This stresses the present transmission system and voltage stability becomes an important issue in this regard. Pattern recognition in conjunction with voltage stability analysis could be an effective tool to solve this problem In this thesis, a methodology to detect the voltage stability ahead of time is presented. Dynamic simulation software PSS/E is used to simulate voltage stable and unstable cases, these cases are used to train and test the pattern recognition algorithms. Statistical and algorithmic pattern recognition methods are used. The proposed method is tested on IEEE 39 bus system. Finally, the pattern recognition models to predict the voltage stability of the system are developed
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