Publications
254 results found
Jabr RA, Džafic I, Pal BC, 2018, Compensation in complex variables for microgrid power flow, IEEE Transactions on Power Systems, Vol: 33, Pages: 3207-3209, ISSN: 0885-8950
The solution of the distribution network power flow in practical applications is based either on the forward-backward sweep method for radial networks, or the current injection method for meshed networks. While the power flow in microgrids that operate in grid-connected mode could be resolved using the above approaches, their operation in island mode would require simulating local generation droop controllers for sharing the complex power load and network loss amongst the generators. This letter proposes a complex power compensation approach, which is based on Wirtinger calculus, for extending the applicability of practical distribution power flow methods to microgrids operating in island mode. Supporting numerical results are reported on microgrids with up to 3139 nodes.
Majumdar A, Pal BC, 2018, Bad data detection in the context of leverage point attacks in modern power networks, IEEE Transactions on Smart Grid, Vol: 9, Pages: 2042-2054, ISSN: 1949-3061
This paper demonstrates a concept to detect bad data in state estimation when the leverage measurements are tampered with gross error. The concept is based on separating leverage measurements from non-leverage measurements by a technique called diagnostic robust generalized potential (DRGP), which also takes care of the masking or swamping effect, if any. The methodology then detects the erroneous measurements from the generalized studentized residuals (GSR). The effectiveness of the method is validated with a small illustrative example, standard IEEE 14-bus and 123-bus unbalanced network models and compared with the existing methods. The method is demonstrated to be potentially very useful to detect attacks in smart power grid targeting leverage points in the system.
Singh AK, Pal BC, 2018, Decentralized robust dynamic state estimation in power systems using instrument transformers, IEEE Transactions on Signal Processing, Vol: 66, Pages: 1541-1550, ISSN: 1053-587X
This paper proposes a decentralized method for estimation of dynamic states of a power system. The method remains robust to time-synchronization errors and high noise levels in measurements. Robustness of the method has been achieved by incorporating internal angle in the dynamic model used for estimation and by decoupling the estimation process into two stages with continuous updation of measurement-noise variances. Additionally, the proposed estimation method does not need measurements obtained from phasor measurement units; instead, it just requires analog measurements of voltages and currents directly acquired from instrument transformers. This is achieved through statistical signal processing of analog voltages and currents to obtain their magnitudes and frequencies, followed by application of unscented Kalman filtering for nonlinear estimation. The robustness and feasibility of the method have been demonstrated on a benchmark power system model.
Singh AK, Pal BC, 2017, Decentralized nonlinear control for power systems using normal forms and detailed models, IEEE Transactions on Power Systems, Vol: 33, Pages: 1160-1172, ISSN: 1558-0679
This paper proposes a decentralized method fornonlinear control of oscillatory dynamics in power systems. Themethod is applicable for ensuring both transient stability as wellas small-signal stability. The method uses an optimal control lawwhich has been derived in the general framework of nonlinearcontrol using normal forms. The model used to derive the controllaw is the detailed subtransient model of synchronous machinesas recommended by IEEE. Minimal approximations have beenmade in either the derivation or the application of the controllaw. The developed method also requires the application ofdynamic state estimation technique. As the employed control andestimation schemes only need local measurements, the methodremains completely decentralized. The method has been demon-strated as an effective tool to prevent blackouts by simulating amajor disturbance in a benchmark power system model and itssubsequent control using the proposed method.
Majumdar A, Agalgoankar YP, Pal BC, et al., 2017, Centralized volt-var optimization strategy considering malicious attack on distributed energy resources control, IEEE Transactions on Sustainable Energy, Vol: 9, Pages: 148-156, ISSN: 1949-3037
The adoption of information and communication technology (ICT) based centralized volt-var control (VVC) leads to an optimal operation of a distribution feeder. However, it also poses a challenge that an adversary can tamper with the metered data and thus can render the VVC action ineffective. Distribution system state estimation (DSSE) acts as a backbone of centralized VVC. Distributed energy resources (DER) injection measurements constitute leverage measurements from a DSSE point of view. This paper proposes two solutions as a volt var optimization-distribution system state estimation (VVO-DSSE) malicious attack mitigating strategy when the DER injection measurements are compromised. The first solution is based on local voltage regulation controller set-points. The other solution effectively employs historical data or forecast information. The concept is based on a cumulant based probabilistic optimal power flow with the objective of minimizing the expectation of total power losses. The effectiveness of the approach is performed on the 95-bus UK generic distribution system (UKGDS) and validated against Monte Carlo simulations.
Puthenpurayil Kunjumuhammed L, Pal BC, Gupta R, et al., 2017, Stability analysis of a PMSG based large offshore wind farm connected to a VSC-HVDC, IEEE Transactions on Energy Conversion, Vol: 32, Pages: 1166-1176, ISSN: 1558-0059
This paper presents modal analysis of a large offshore wind farm using PMSG type wind turbines connected to a VSC-HVDC. Multiple resonant frequencies are observed in the ac grid of offshore wind farms. Their control is crucial for the uninterrupted operation of the wind farm system. The characteristics of oscillatory modes are presented using modal analysis and participation factor analysis. Sensitivity of critical modes to wind turbine design parameters and their impact on closed loop stability of the system are discussed. A comparison between a full wind farm model and an aggregated model is presented to show differences in the characteristics of critical modes observed in the models, and implication of using the models for stability studies. It is concluded that robust control design is important for reliable operation of the system.
Ma S, Geng H, Lu L, et al., 2017, Grid-synchronization stability improvement of large scale wind farm during severe grid fault, IEEE Transactions on Power Systems, Vol: 33, Pages: 216-226, ISSN: 1558-0679
Loss of synchronization between wind farm and power grid during severe grid faults would cause wind farm tripping. In this paper, the mechanism of grid-synchronization is uncovered, described as motion of an autonomous nonlinear differential equation with specific initial states. The revealed mechanism indicates that even though steady state working point exists, improper initial states and poor system dynamic properties could lead to synchronization instability. In order to keep wind farm synchronous with the power grid during severe grid faults, special requirements on system dynamic properties are stated. Moreover, to satisfy all the requirements, a current injecting method is proposed. By adjusting active and reactive output currents of the wind farm, the proposed method could ensure system synchronization stability during severe grid faults. Implementation of the proposed method on PMSG and DFIG based wind farm is illustrated. Simulation results validate the analysis and the control method.
Anagnostou G, Pal BC, 2017, Derivative-free Kalman filtering based approaches to dynamic state estimation for power systems with unknown inputs, IEEE Transactions on Power Systems, Vol: 33, Pages: 116-130, ISSN: 1558-0679
This paper proposes a decentralized derivative-freedynamic state estimation method in the context of a power systemwith unknown inputs, to address cases when system linearisationis cumbersome or impossible. The suggested algorithm tacklessituations when several inputs, such as the excitation voltage,are characterized by uncertainty in terms of their status. Thetechnique engages one generation unit only and its associatedmeasurements, and it remains totally independent of other systemwide measurements and parameters, facilitating in this way theapplicability of this process on a decentralized basis. The robust-ness of the method is validated against different contingencies.The impact of parameter errors, process and measurement noiseon the unknown input estimation performance is discussed. Thisunderstanding is further supported through detailed studies in arealistic power system model.
Nanchian S, Majumdar A, Pal BC, 2017, Ordinal optimization technique for three phase distribution network state estimation including discrete variables, IEEE Transactions on Sustainable Energy, Vol: 8, Pages: 1528-1535, ISSN: 1949-3037
This paper has discussed transformer tap position estimation with continuous and discrete variables in the context of three phase distribution state estimation (SE). Ordinal optimization (OO) technique has been applied to estimate the transformer tap position for the first time in unbalanced three phase distribution network model. The results on 129 bus system model have demonstrated that OO method can generate a reliable estimate for transformer exact tap position with discrete variables in distribution system state estimation (DSSE) and also in short period of time. In this paper the node voltages and power losses are calculated for 129 bus network. It is also demonstrated that OO is much faster than other accurate methods such HPSO. The losses obtained with OO are much accurate. In view of this OO performs better than WLS as it provides higher accuracy of the loss calculation. In a distribution network where about 5-6% of electricity generated is lost, accurate estimation of this loss has significant technical and commercial value. The authors believe the technique proposed will help realize those benefits.
Cai L, Thornhill NF, Kuenzel S, et al., 2017, Real-time detection of power system disturbances based on k-nearest neighbor analysis, IEEE Access, Vol: 5, Pages: 5631-5639, ISSN: 2169-3536
Efficient disturbance detection is important for power system security and stability. In this paper, a new detection method is proposed based on a time series analysis technique known as k nearest neighbor (kNN) analysis. Advantages of this method are that it can deal with the electrical measurements with oscillatory trends and can be implemented in real time. The method consists of two stages which are the off-line modelling and the on-line detection. The off-line stage calculates a sequence of anomaly index values using kNN on the historical ambient data and then determines the detection threshold. Afterwards, the on-line stage calculates the anomaly index value of presently measured data by readopting kNN and compares it with the established threshold for detecting disturbances. To meet the real-time requirement, strategies for recursively calculating the distance metrics of kNN and for rapidly picking out the kth smallest metric are built. Case studies conducted on simulation data from the reduced equivalent model of Great Britain power system and measurements from an actual power system in Europe demonstrate the effectiveness of the proposed method.
Cai L, Thornhill NF, Pal BC, 2017, Multivariate detection of power system disturbances based on fourth order moment and singular value decomposition, IEEE Transactions on Power Systems, Vol: 32, Pages: 4289-4297, ISSN: 1558-0679
This paper presents a new method to detect power system disturbances in a multivariate context, which is based on Fourth Order Moment (FOM) and multivariate analysisimplemented as Singular Value Decomposition (SVD). The motivation for this development is that power systems are increasingly affected by various disturbances and there is a requirement for the analysis of measurements to detect these disturbances. The application results on the measurements of an actual power system in Europe illustrate that the proposed multivariate detection method achieves enhanced detection reliability and sensitivity.
Nduka O, Pal BC, 2017, Harmonic domain modelling of PV system for the assessment of grid integration impact, IEEE Transactions on Sustainable Energy, Vol: 8, Pages: 1154-1165, ISSN: 1949-3037
In this paper, a comprehensive harmonic domainreference frame (HDRF) model of a voltage source converter(VSC) grid interactive photovoltaic (PV) system is presented.The model is useful for assessing the harmonic coupling betweenthe PV system and the network. Different components of the PVsystem such as inverter, LCL filter and interconnecting trans-former have been incorporated in the model. Using this model,harmonic currents from PV system connected to both distortedand undistorted networks have been quantified. Also, the modelhas been deployed in investigating resonance occurrence in amedium-voltage distribution network (MVDN) where the resultsprovide interesting technical insight and understanding.
Singh A, Pal B, 2016, An extended linear quadratic regulator for LTI systems with exogenous inputs, Automatica, Vol: 76, Pages: 10-16, ISSN: 0005-1098
This paper proposes a cost effective control law for a linear time invariant (LTI) system having an extra set of exogenousinputs (or external disturbances) besides the traditional set of control inputs. No assumption is made with regard to a-prioriknowledge of the modeling equations for the exogenous inputs. The problem of optimal control for such a system is definedin the standard framework of linear quadratic control and an extended linear quadratic regulator (ELQR) is proposed as thesolution to the problem. The ELQR approach is demonstrated through an example and is shown to be significantly more costeffective than currently available approaches for linear quadratic control.
Nduka OS, Pal BC, 2016, Harmonic characterisation model of grid interactive photovoltaic systems, 2016 IEEE International Conference on Power System Technology (POWERCON), Publisher: IEEE
This paper presents an alternative model of a grid interactive photovoltaic (PV) system which can be used for characterising the harmonics from a PV system when connected to a distorted and undistorted network respectively. The approach uses an orthogonal series function in modelling the different sections of a practical PV system thus yielding a complete harmonic domain model. The proposed model accurately handles the harmonic cross-coupling between the PV system and the network. Both single and three phase grid interactive single-stage transformerless PV systems are presented. Simulation results show the effectiveness of the proposed model.
Kuenzel STK, Assis TML, Pal BC, 2016, Impact of Multi-Terminal HVDC Grids onEnhancing Dynamic Power Transfer Capability, IEEE Transactions on Power Systems, Vol: 32, Pages: 2652-2662, ISSN: 1558-0679
This paper proposes the exploitation of MultiTerminalHVDC grids to improve transfer capability in powersystems. Multi-Terminal HVDC systems based on voltagesource converters (VSC-MTDC) have been recognized as apromising alternative for the wind power integration. Under lowwind scenarios, these grids originally dedicated for wind powertransmission can be exploited as an additional interarea transmissionpath, providing extra dynamic security. The paper focuseson small-signal stability assessment, especially in poordamped oscillations associated with interarea modes. Simulationsperformed through a generic computational frameworkhave shown that the high level of flexibility and controllabilityprovided by voltage source converters can considerably improvethe transfer capacity, while preserving adequate dynamic performance.
Pal BC, Kunjumuhammed LP, 2016, POWER TRANSMISSION NETWORK, WO/2016/146795
A power transmission network comprises a single-phase or multi-phase AC electrical system, a converter including at least one AC terminal, a point of common coupling, a phase reactance connecting the point of common coupling to the or each AC terminal of the converter, and at least one power transmission medium to interconnect the point of common coupling and the AC electrical system. The power transmission network further includes a converter controller programmed to: • process the voltage and current at the point of common coupling to compute a state vector corresponding to the power transmission network; • derive a converter demand by combining the computed state vector with a plurality of control parameters, wherein the plurality of control parameters includes the capacitance of the power transmission medium or media presented at the point of common coupling and the impedance of the phase reactance; and • operate the converter in accordance with the converter demand to control the converter voltage at the or each AC terminal and/or the voltage at the point of common coupling so as to inhibit any perturbation in the converter voltage from a target converter voltage or range resulting from the interaction between the capacitance of the power transmission medium or media and the impedance of the phase reactance
Battistelli C, Agalgoankar YP, Pal BC, 2016, Probabilistic dispatch of remote hybrid microgrids including battery storage and load management, IEEE Transactions on Smart Grid, Vol: 8, Pages: 1305-1317, ISSN: 1949-3061
This work presents a probabilistic economic dispatch tool for en-ergy management (EM) studies in the context of remote hybrid AC/DC microgrids (MGs). An EM approach is proposed to en-sure a reliable power supply at the minimum cost of the hybrid MG operation. A comprehensive operational framework is pre-sented, which considers topological features of the hybrid MG and the interlinking converter between AC and DC subsections. Approach and models are tested using several operating scenari-os referred to a test hybrid MG system. In the analyses, the opportunity of integrating battery energy storage and energy demand management in the EM scheme is investigated. The results of the analyses demonstrate the effectiveness and practicality of the optimization tool in different operation contexts.
Dzafic I, Jabr RA, Huseinagic I, et al., 2016, Multi-phase state estimation featuring industrial-grade distribution network models, IEEE Transactions on Smart Grid, Vol: 8, Pages: 609-618, ISSN: 1949-3053
This paper proposes a novel implementation of a multi-phase distribution network state estimator which employs industrial-grade modeling of power components and measurements. Unlike the classical voltage-based and current-based state estimators, this paper presents the implementation details of a constrained weighted least squares state calculation method that includes standard three-phase state estimation capabilities in addition to practical modeling requirements from the industry; these requirements comprise multi-phase line configurations, unsymmetrical and incomplete transformer connections, power measurements on 4-connected loads, cumulative-type power measurements, line-to-line voltage magnitude measurements, and reversible line drop compensators. The enhanced modeling equips the estimator with capabilities that make it superior to a recently presented state-of-the-art distribution network load estimator that is currently used in real-life distribution management systems; comparative performance results demonstrate the advantage of the proposed estimator under practical measurement schemes.
Mokryani G, Majumdar ANKUR, Pal BC, 2016, A Probabilistic Method for the Operation of Three-Phase Unbalanced Active Distribution Networks, IET Renewable Power Generation, Vol: 10, Pages: 944-954, ISSN: 1752-1416
This paper proposes a probabilistic multi-objective optimization method for the operation of three-phase distribution networks incorporating active network management (ANM) schemes including coordinated voltage control and adaptive power factor control. The proposed probabilistic method incorporates detailed modelling of three-phase distribution network components and considers different operational objectives. The method simultaneously minimizes the total energy losses of the lines from the point of view of distribution network operators (DNOs) and maximizes the energy generated by photovoltaic (PV) cells considering ANM schemes and network constraints. Uncertainties related to intermittent generation of PVs and load demands are modelled by probability density functions (PDFs). Monte Carlo simulation method is employed to use the generated PDFs. The problem is solved using ɛ-constraint approach and fuzzy satisfying method is used to select the best solution from the Pareto optimal set. The effectiveness of the proposed probabilistic method is demonstrated with IEEE 13- and 34- bus test feeders.
Kunjumuhammed LP, Pal BC, Oates C, et al., 2016, The adequacy of the present practice in dynamic aggregated modelling of wind farm systems, IEEE Transactions on Sustainable Energy, Vol: 8, Pages: 23-32, ISSN: 1949-3037
Large offshore wind farms are usually composed ofseveral hundred individual wind turbines, each turbine havingits own complex set of dynamics. The analysis of the dynamicinteraction between wind turbine generators (WTG), interconnectingac cables, and voltage source converter (VSC) based HighVoltage DC (HVDC) system is difficult because of the complexityand the scale of the entire system. The detailed modelling andmodal analysis of a representative wind farm system reveal thepresence of several critical resonant modes within the system.Several of these modes have frequencies close to harmonicsof the power system frequency with poor damping. From acomputational perspective the aggregation of the physical modelis necessary in order to reduce the degree of complexity to apractical level. This paper focuses on the present practices ofthe aggregation of the WTGs and the collection system, andtheir influence on the damping and frequency characteristics ofthe critical oscillatory modes. The effect of aggregation on thecritical modes are discussed using modal analysis and dynamicsimulation. The adequacy of aggregation method is discussed.
Canizares C, Farnandes T, Gerladi E, et al., 2016, Benchmark models for the analysis and control of small-signal oscillatory dynamics in power systems, IEEE Transactions on Power Systems, Vol: 32, Pages: 715-722, ISSN: 1558-0679
This paper summarizes a set of six benchmark systemsfor the analysis and control of electromechanical oscillationsin power systems recommended by the IEEE Task Force onBenchmark Systems for Stability Controls of the Power SystemDynamic Performance Committee. The benchmark systems werechosen for their tutorial value and particular characteristicsleading to control system design problems relevant to the researchcommunity. For each benchmark, the modelling guidelinesare provided, along with eigenvalues and time-domain resultsproduced with at least two simulation software, and onepossible control approach is provided for each system as well.Researchers and practicing engineers are encouraged to use thesebenchmark systems when assessing new oscillation dampingcontrol strategies.
Ariff MAM, Pal BC, 2016, Adaptive Protection and Control in Power Systemfor Wide-Area Blackout Prevention, IEEE Transactions on Power Delivery, Vol: 31, Pages: 1815-1825, ISSN: 0885-8977
This paper presents a new approach in adaptive outof-step(OOS) protection settings in power system in real-time.The proposed method uses extended equal area criterion (EEAC)to determine the critical clearing time (CCT) and critical clearingangle (CCA) of the system, which are vital information for OOSprotection setting calculation. The dynamic model parametersand the coherency groups of the system for EEAC analysis aredetermined in real time to ensure that the newly calculatedsettings suit with the prevalent system operating condition. Theeffectiveness of the method is demonstrated in a simulated datafrom 16-machine 68-bus system model.
Majumdar A, Pal BC, 2016, A three-phase state estimation in unbalanced distribution networks with switch modelling, 1st IEEE International Conference on Control, Measurement and Instrumentation (CMI), Publisher: IEEE, Pages: 474-478
State estimation has become an important task in modern energy/distribution management systems. However, the state estimation is not very popular in modern unbalanced three-phase distribution systems. This paper proposes a method for three-phase state estimation with detailed three-phase modelling of system components including switches and star and delta connected loads. This method is then tested on a standard IEEE 13-bus system and the results are compared with load flow results.
Singh A, Pal B, 2016, An extended linear quadratic regulator and its application for control of power system dynamics, IEEE First International Conference on Control, Measurement and Instrumentation (CMI), Publisher: IEEE, Pages: 110-114
This paper presents a generalized solution to the problem of optimal control of systems having an extra set of exogenous inputs besides control inputs. The solution is derived in the framework of linear quadratic control and it is termed `extended linear quadratic regulator (ELQR)'. The ELQR is applied for control of unstable or poorly damped oscillatory dynamics occurring in a power system and is shown to be significantly more cost effective than the classical power system stabilizer (PSS) based approach.
Kunjumuhammed LP, Pal BC, Oates C, et al., 2016, Electrical Oscillations in Wind Farm Systems: Analysis and Insight Based on Detailed Modeling, IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, Vol: 7, Pages: 51-62, ISSN: 1949-3029
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Singh R, Pal BC, Jabr RA, 2016, Choice of solver for distribution system state estimation, POWER DISTRIBUTION AUTOMATION, Editors: Das, Publisher: INST ENGINEERING TECH-IET, Pages: 101-126, ISBN: 978-1-84919-828-8
Singh A, Pal B, 2016, Decentralized Control of Oscillatory Dynamics in Power Systems Using an Extended LQR, IEEE-Power-and-Energy-Society General Meeting (PESGM), Publisher: IEEE, ISSN: 1944-9925
Barocio E, Pal BC, Thornhill NF, et al., 2015, A dynamic mode decomposition framework for global power system oscillation analysis, IEEE Transactions on Power Systems, Vol: 30, Pages: 2902-2912, ISSN: 0885-8950
A global multiscale method based on a dynamic mode decomposition (DMD) algorithm to characterize the global behavior of transient processes recorded using wide-area sensors is proposed. The method interprets global dynamic behavior in terms of both, spatial patterns or shapes and temporal patterns associated with dynamic modes containing essentially single-frequency components, from which the mode shapes, frequencies and growth and decay rates of the modes can be extracted simultaneously. These modes are then used to detect the coherent and dominant structures within the data. The technique is well suited for fast wide-area monitoring and assessment of global instability in the context of modern data fusion-based estimation techniques. Results of the application of the proposed method to large, high-dimensional data sets are encouraging.
Canizares C, Fernandes T, Geraldi Jr E, et al., 2015, Benchmark Systems for Small-Signal Stability Analysis and Control, Publisher: IEEE Power and Energy Society
This report documents the work of the IEEE PES Task Force (TF) on Benchmark Systems for Stability Controls. The following sections present the objectives of the TF, the guidelines used to select the benchmarks, a brief description of each benchmark system so the reader can select the most suitable system for the intended application, the input data and results for each benchmark system, and a set of conclusions.Detailed descriptions of each system are also presented in the Appendices to this report and in the website created by this Task Force to share the data and simulation results related to the benchmark systems.
Singh AK, Pal BC, 2015, Decentralized Control of Oscillatory Dynamics in Power Systems using an Extended LQR, IEEE Transactions on Power Systems, Vol: 31, Pages: 1715-1728, ISSN: 1558-0679
This paper proposes a decentralized algorithm for real-time control of oscillatory dynamics in power systems. The algorithm integrates dynamic state estimation (DSE) with an extended linear quadratic regulator (ELQR) for optimal control. The control for one generation unit only requires measurements and parameters for that unit, and hence the control at a unit remains completely independent of other units. The control gains are updated in real-time, therefore the control scheme remains valid for any operating condition. The applicability of the proposed algorithm has been demonstrated on a representative power system model.
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