Energies

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8 pages, 187 KiB

Open AccessEditorial

Modern Power System Dynamics, Stability and Control

by Antonio T. Alexandridis

Energies 2020, 13(15), 3814; https://doi.org/10.3390/en13153814 - 24 Jul 2020

Cited by 3 | Viewed by 2496

Abstract

This Special Issue of Energies, “Modern Power System Dynamics, Stability and Control”, addresses the core problem of deploying novel aspects in the analysis of modern power systems as these are composed after the high penetration of distributed generation (DG) with different renewable energy [...] Read more.

This Special Issue of Energies, “Modern Power System Dynamics, Stability and Control”, addresses the core problem of deploying novel aspects in the analysis of modern power systems as these are composed after the high penetration of distributed generation (DG) with different renewable energy sources (RES). The focus is given either on the new whole power and control system configuration or on individual cases of DG sources, power converters and other general or specific plants and devices. The problem can be tackled with different methodologies and may have several, more or less valuable and complicated solutions. The twenty-three accepted papers certainly offer a good contribution in a wide range of applications; they are extended from basic system theory perspectives, fundamental nonlinear analysis tools and novel modeling deployments to some interesting particular system and control issues. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

Research

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27 pages, 4673 KiB

Open AccessArticle

Controlled Impedance-Admittance-Torque Nonlinear Modeling and Analysis of Modern Power Systems

by Panos C. Papageorgiou and Antonio T. Alexandridis

Energies 2020, 13(10), 2461; https://doi.org/10.3390/en13102461 - 13 May 2020

Cited by 7 | Viewed by 2510

Abstract

Modern power systems are continuously transformed into decentralized ones where distributed generation (DG) plays a key role. Almost all the different distributed energy resources (DERs) are connected in geographically dispersed places through controlled power electronic interfaces in a manner that essentially affects the [...] Read more.

Modern power systems are continuously transformed into decentralized ones where distributed generation (DG) plays a key role. Almost all the different distributed energy resources (DERs) are connected in geographically dispersed places through controlled power electronic interfaces in a manner that essentially affects the dynamic performance and control of the whole power system. Simultaneously, rotating machines in power production or absorption, dominate the system response and stability. In this new frame, this paper proposes a novel generalized dynamic representation and full scale modeling of a modern power system based on the well-known impedance-admittance (IA) network model for the electricity grid, substantially extended to include in detail both the power converter devices by considering the controlled power electronic dynamics and the electrical machines by inserting their full electromechanical dynamics. This formulation results in a holistic nonlinear dynamic description, defined here as controlled impedance-admittance-torque (CIAT) model of the whole system which features common structural characteristics. The model is deployed in state space, involves all the controlled inputs in DG, namely the duty-ratio signals of each power converter interface, all the other external inputs affecting the system, namely all the known or unknown voltage, current, and torque inputs. As shown in the paper, the proposed CIAT model retains its fundamental properties for any DG and network topology, standard or varying. This enables the compression of the accurate analytic power system dynamic description into a matrix-based generic nonlinear model that can be easily used for analysis studies of such large-scale systems. Taking into account the nonlinear nature of the CIAT matrix-based model and the persistent action of the external inputs, Lyapunov methods deployed on recently established input to state stability (ISS) notions are systematically applied for the system analysis. Hence, the traditionally used small-signal model-based analysis that suffers from the intermittent and continuously changing operation of DERs is completely substituted by the proposed formulation. A modern power system example with different DERs involved is analyzed by this way and is extensively simulated to verify the validity of the proposed method. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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18 pages, 2545 KiB

Open AccessArticle

Coordinated Excitation and Static Var Compensator Control with Delayed Feedback Measurements in SGIB Power Systems

by Haris E. Psillakis and Antonio T. Alexandridis

Energies 2020, 13(9), 2181; https://doi.org/10.3390/en13092181 - 1 May 2020

Cited by 8 | Viewed by 2476

Abstract

In this paper, we present a nonlinear coordinated excitation and static var compensator (SVC) control for regulating the output voltage and improving the transient stability of a synchronous generator infinite bus (SGIB) power system. In the first stage, advanced nonlinear methods are applied [...] Read more.

In this paper, we present a nonlinear coordinated excitation and static var compensator (SVC) control for regulating the output voltage and improving the transient stability of a synchronous generator infinite bus (SGIB) power system. In the first stage, advanced nonlinear methods are applied to regulate the SVC susceptance in a manner that can potentially improve the overall transient performance and stability. However, as distant from the generator measurements are needed, time delays are expected in the control loop. This fact substantially complicates the whole design. Therefore, a novel design is proposed that uses backstepping methodologies and feedback linearization techniques suitably modified to take into account the delayed measurement feedback laws in order to implement both the excitation voltage and the SVC compensator input. A detailed and rigorous Lyapunov stability analysis reveals that if the time delays do not exceed some specific limits, then all closed-loop signals remain bounded and the frequency deviations are effectively regulated to approach zero. Applying this control scheme, output voltage changes occur after the large power angle deviations have been eliminated. The scheme is thus completed, in a second stage, by a soft-switching mechanism employed on a classical proportional integral (PI) PI voltage controller acting on the excitation loop when the frequency deviations tend to zero in order to smoothly recover the output voltage level at its nominal value. Detailed simulation studies verify the effectiveness of the proposed design approach. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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20 pages, 3708 KiB

Open AccessArticle

Towards the Integration of Modern Power Systems into a Cyber–Physical Framework

by George C. Konstantopoulos, Antonio T. Alexandridis and Panos C. Papageorgiou

Energies 2020, 13(9), 2169; https://doi.org/10.3390/en13092169 - 1 May 2020

Cited by 23 | Viewed by 2953

Abstract

The cyber–physical system (CPS) architecture provides a novel framework for analyzing and expanding research and innovation results that are essential in managing, controlling and operating complex, large scale, industrial systems under a holistic insight. Power systems constitute such characteristically large industrial structures. The [...] Read more.

The cyber–physical system (CPS) architecture provides a novel framework for analyzing and expanding research and innovation results that are essential in managing, controlling and operating complex, large scale, industrial systems under a holistic insight. Power systems constitute such characteristically large industrial structures. The main challenge in deploying a power system as a CPS lies on how to combine and incorporate multi-disciplinary, core, and advanced technologies into the specific for this case, social, environmental, economic and engineering aspects. In order to substantially contribute towards this target, in this paper, a specific CPS scheme that clearly describes how a dedicated cyber layer is deployed to manage and interact with comprehensive multiple physical layers, like those found in a large-scale modern power system architecture, is proposed. In particular, the measurement, communication, computation, control mechanisms, and tools installed at different hierarchical frames that are required to consider and modulate the social/environmental necessities, as well as the electricity market management, the regulation of the electric grid, and the power injection/absorption of the controlled main devices and distributed energy resources, are all incorporated in a common CPS framework. Furthermore, a methodology for investigating and analyzing the dynamics of different levels of the CPS architecture (including physical devices, electricity and communication networks to market, and environmental and social mechanisms) is provided together with the necessary modelling tools and assumptions made in order to close the loop between the physical and the cyber layers. An example of a real-world industrial micro-grid that describes the main aspects of the proposed CPS-based design for modern electricity grids is also presented at the end of the paper to further explain and visualize the proposed framework. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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11 pages, 2549 KiB

Open AccessArticle

The Influence of VSC–HVDC Reactive Power Control Mode on AC Power System Stability

by Ying Wang, Youbin Zhou, Dahu Li, Dejun Shao, Kan Cao, Kunpeng Zhou and Defu Cai

Energies 2020, 13(7), 1677; https://doi.org/10.3390/en13071677 - 3 Apr 2020

Cited by 7 | Viewed by 3026

Abstract

Voltage source converter-based high-voltage direct current (VSC-HVDC) has the advantage of fast and independent controllability on active and reactive power. This paper focuses on effects of commonly proposed reactive power control modes, constant reactive power control and AC voltage margin control. Based on [...] Read more.

Voltage source converter-based high-voltage direct current (VSC-HVDC) has the advantage of fast and independent controllability on active and reactive power. This paper focuses on effects of commonly proposed reactive power control modes, constant reactive power control and AC voltage margin control. Based on the mathematical model of single machine infinity equivalent system with embedded VSC-HVDC, the influence of VSC-HVDC with different reactive power control strategies on transient stability and dynamic stability of the AC system is studied. Then case studies were conducted with a realistic model of grid. The dynamic responses of AC/DC systems for different VSC-HVDC reactive power control modes were compared in detail. It is shown that compared to constant reactive power control, AC voltage margin control can provide voltage support to enhance the transient angle stability of an AC system. However, the fluctuant reactive power injected into a weak AC system may adversely affect power system oscillation damping for VSC-HVDC with AC voltage margin control, if the parameters of the controller have not been optimized to suppress the low-frequency oscillation. The results of this paper can provide certain reference for the decision of an appropriate VSC-HVDC reactive power control mode in practice. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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15 pages, 1599 KiB

Open AccessArticle

Latin Hypercube Sampling Method for Location Selection of Multi-Infeed HVDC System Terminal

by Xiangqi Li, Yunfeng Li, Li Liu, Weiyu Wang, Yong Li and Yijia Cao

Energies 2020, 13(7), 1646; https://doi.org/10.3390/en13071646 - 2 Apr 2020

Cited by 11 | Viewed by 2977

Abstract

Owing to the stochastic states of power systems with large-scale renewable generation, the impact of high-voltage direct current (HVDC) systems on the stability of the power system should be examined in a probabilistic manner. A probabilistic small signal stability assessment methodology to select [...] Read more.

Owing to the stochastic states of power systems with large-scale renewable generation, the impact of high-voltage direct current (HVDC) systems on the stability of the power system should be examined in a probabilistic manner. A probabilistic small signal stability assessment methodology to select the best locations for multi-infeed high-voltage direct current systems in alternating current (AC) grids is proposed in this paper. The Latin hypercube sampling-based Monte Carlo simulation approach is taken to generate the stochastic operation scenarios of power systems with the consideration of several stochastic factors, i.e., load demand and power generation. The damping ratio of the critical oscillation modes and the controllability of power injection to oscillation modes are analyzed by the probabilistic small signal stability. A probabilistic index is proposed to select the best locations of high-voltage direct current systems for improving the damping of the oscillation modes. The proposed methodology is applied to an IEEE 39 bus system considering the stochastic load demand and power generation. The results of probabilistic small signal stability assessment and a time-domain simulation show that the installation of a high-voltage direct current system on the selected locations can effectively improve the system damping. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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21 pages, 4250 KiB

Open AccessArticle

Multiple Spatiotemporal Characteristics-Based Zonal Voltage Control for High Penetrated PVs in Active Distribution Networks

by Chuanliang Xiao, Lei Sun and Ming Ding

Energies 2020, 13(1), 249; https://doi.org/10.3390/en13010249 - 3 Jan 2020

Cited by 5 | Viewed by 2302

Abstract

The penetration of photovoltaic (PV) outputs brings great challenges to optimal operation of active distribution networks (ADNs), especially leading to more serious overvoltage problems. This study proposes a zonal voltage control scheme based on multiple spatiotemporal characteristics for highly penetrated PVs in ADNs. [...] Read more.

The penetration of photovoltaic (PV) outputs brings great challenges to optimal operation of active distribution networks (ADNs), especially leading to more serious overvoltage problems. This study proposes a zonal voltage control scheme based on multiple spatiotemporal characteristics for highly penetrated PVs in ADNs. In the spatial domain, a community detection algorithm using a reactive/ active power quality function was introduced to partition an ADN into sub-networks. In the time domain, short-term zonal scheduling (SZS) with 1 h granularity was drawn up based on a cluster. The objective was to minimize the supported reactive power and the curtailed active power in reactive and active power sub-networks. Additionally, a real-time zonal voltage control scheme (RZVC) with 1 min granularity was proposed to correct the SZS rapidly by choosing and controlling the key PV inverter to regulate the supported reactive power and the curtailed active power of the inverters to prevent the overvoltage in each sub-network. With the time domain cooperation, the proposed method could achieve economic control and avoid overvoltage caused by errors in the forecast data of the PVs. For the spatial domain, zonal scheduling and zonal voltage control were carried out in each cluster, and the short-term scheduling and voltage controlling problem of the ADN could then be decomposed into several sub-problems. This could simplify the optimization and control which can reduce the computing time. Finally, an actual 10kV, 103-node network in Zhejiang Province of China is employed to verify the effectiveness and feasibility of the proposed approach. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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14 pages, 564 KiB

Open AccessArticle

Phasor-Based Control for Scalable Integration of Variable Energy Resources

by Alexandra von Meier, Elizabeth L. Ratnam, Kyle Brady, Keith Moffat and Jaimie Swartz

Energies 2020, 13(1), 190; https://doi.org/10.3390/en13010190 - 1 Jan 2020

Cited by 14 | Viewed by 4412

Abstract

We propose an innovative framework termed phasor-based control (PBC) to facilitate the integration of heterogeneous and intermittent distributed energy resources (DER) on the electric grid. PBC presents a unified approach that is agnostic to optimization criteria and to the particular characteristics of participating [...] Read more.

We propose an innovative framework termed phasor-based control (PBC) to facilitate the integration of heterogeneous and intermittent distributed energy resources (DER) on the electric grid. PBC presents a unified approach that is agnostic to optimization criteria and to the particular characteristics of participating resources. It is enabled by synchronized, high-precision voltage phasor measurements that allow stating control objectives in grid-specific, rather than resource-specific, terms. We present qualitative justification and examine the general feasibility of this control approach, including the behavior of candidate control algorithms in simulation. Initial results suggest that PBC has significant potential to support stable and resilient grid operations in the presence of arbitrarily high penetrations of DER. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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16 pages, 10686 KiB

Open AccessArticle

Investigation on Dynamic Response of Grid-Tied VSC During Electromechanical Oscillations of Power Systems

by Bo Wang, Guowei Cai, Deyou Yang, Lixin Wang and Zhiye Yu

Energies 2020, 13(1), 94; https://doi.org/10.3390/en13010094 - 23 Dec 2019

Cited by 3 | Viewed by 2204

Abstract

This study focuses on the dynamics of a grid-tied voltage source converter (GVSC) during electromechanical oscillations. A small-signal model with GVSC port variables (DC voltage and AC power) as the outputs and a terminal voltage vector as the input is derived to reveal [...] Read more.

This study focuses on the dynamics of a grid-tied voltage source converter (GVSC) during electromechanical oscillations. A small-signal model with GVSC port variables (DC voltage and AC power) as the outputs and a terminal voltage vector as the input is derived to reveal the passive response of the GVSC on the basis of the power equation in the d–q coordinate system. An input–output transfer function matrix is constructed according to the proposed model. The frequency response of this matrix in the electromechanical bandwidth is described to reflect the dynamic behavior of the GVSC. The effects of the operation parameters, i.e., the grid strength, reference value of the control system, and grid voltage, on the dynamic behavior of the GVSC in the electromechanical bandwidth, are investigated using frequency domain sensitivity. Analysis results show that the GVSC generates responses with respect to the electromechanical mode. These responses have different sensitivities to the operation parameters. The IEEE 10-machine power system simulation is performed, and the power hardware-in-the-loop platform with the GVSC was applied to validate the analysis. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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24 pages, 3839 KiB

Open AccessArticle

Studying State Convergence of Input-to-State Stable Systems with Applications to Power System Analysis

by Antonio T. Alexandridis

Energies 2020, 13(1), 92; https://doi.org/10.3390/en13010092 - 23 Dec 2019

Cited by 17 | Viewed by 2704

Abstract

In stability studies, the response of a system enforced by external, known or unknown, inputs is of great importance. Although such an analysis is quite easy for linear systems, it becomes a cumbersome task when nonlinearities exist in the system model. Nevertheless, most [...] Read more.

In stability studies, the response of a system enforced by external, known or unknown, inputs is of great importance. Although such an analysis is quite easy for linear systems, it becomes a cumbersome task when nonlinearities exist in the system model. Nevertheless, most of the real-world systems are externally enforced nonlinear systems with nonzero equilibriums. Representative examples in this category include power systems, where studies on stability and convergence to equilibrium constitute crucial objectives. Driven by this need, the aim of the present work is twofold: First, to substantially complete the theoretical infrastructure by establishing globally valid sufficient conditions for externally enforced nonlinear systems that converge to nonzero equilibriums and, second, to deploy an efficient method easily applicable on practical problems as it is analyzed in detail on a typical power system example. To that end, in the theoretical first part of the paper, a rigorous nonlinear analysis is developed. Particularly, starting from the well-established nonlinear systems theory based on Lyapunov techniques and on the input-to-state stability (ISS) notion, it is proven after a systematic and lengthy analysis that ISS can also guarantee convergence to nonzero equilibrium. Two theorems and two corollaries are established to provide the sufficient conditions. As shown in the paper, the main stability and convergence objectives for externally enforced systems are fulfilled if simple exponential or asymptotic converging conditions can be proven for the unforced system. Then, global or local convergence is established, respectively, while for the latter case, a novel method based on a distance-like measure for determining the region of attraction (RoA) is proposed. The theoretical results are examined on classic power system generation nonlinear models. The power system examples are suitably selected in order to effectively demonstrate the proposed method as a stability analysis tool and to validate all the particular steps, especially that of evaluating the RoA. The examined system results clearly verify the theoretical part, indicating a rather wide range of applications in power systems. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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29 pages, 1497 KiB

Open AccessArticle

Hybrid Detection of Intermittent Cyber-Attacks in Networked Power Systems

by Efstathios Kontouras, Anthony Tzes and Leonidas Dritsas

Energies 2019, 12(24), 4625; https://doi.org/10.3390/en12244625 - 5 Dec 2019

Cited by 7 | Viewed by 2429

Abstract

This article addresses the concept of a compound attack detection mechanism, that links estimation-based and set-theoretic methods, and is mainly focused on the disclosure of intermittent data corruption cyber-attacks. The detection mechanism is developed as a security enhancing tool for the load-frequency control [...] Read more.

This article addresses the concept of a compound attack detection mechanism, that links estimation-based and set-theoretic methods, and is mainly focused on the disclosure of intermittent data corruption cyber-attacks. The detection mechanism is developed as a security enhancing tool for the load-frequency control loop of a networked power system that consists of several interconnected control areas. The dynamics of the power network are derived in observable form in the discrete-time domain, considering that an adversary corrupts the frequency measurements of certain control areas by means of a bias injection cyber-attack. Simulations indicate that an estimation-based detector is unable to discern an intermittent attack, especially when the latter one occurs at the same time as changes in the power load. The detector can be improved by exploiting the safe operation constraints imposed on the state variables of the system. It is shown that the disclosure of intermittent data corruption cyber-attacks in the presence of unknown power load changes is guaranteed only when the estimation-based detector is combined with its set-theoretic counterpart. To this end, a robust invariant set for the networked power system is computed and an alarm is triggered whenever the state vector exits this set. Simulations indicate that the above detectors can operate jointly in terms of a hybrid scheme, which enhances their detection capabilities. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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26 pages, 6024 KiB

Open AccessArticle

Validating Performance Models for Hybrid Power Plant Control Assessment

by Lennart Petersen, Florin Iov, German Claudio Tarnowski, Vahan Gevorgian, Przemyslaw Koralewicz and Daniel-Ioan Stroe

Energies 2019, 12(22), 4330; https://doi.org/10.3390/en12224330 - 13 Nov 2019

Cited by 15 | Viewed by 4940

Abstract

The need for simple, but accurate performance models of wind turbine generators (WTGs), photovoltaic (PV) plants, and battery energy storage systems (BESS) for various hybrid power plant (HPP) studies motivates the present work. Particularly, the development and verification stage of HPP controls requires [...] Read more.

The need for simple, but accurate performance models of wind turbine generators (WTGs), photovoltaic (PV) plants, and battery energy storage systems (BESS) for various hybrid power plant (HPP) studies motivates the present work. Particularly, the development and verification stage of HPP controls requires reduced-order models to minimize the complexity and computation effort of simulation platforms. In this paper, such models are proposed, and the most essential parts of the models are validated through field measurements. The models target power system integration studies involving active and reactive power, as well as frequency and voltage regulation where detailed models, as proposed in the standards, can be cumbersome. Field measurements of two Vestas WTGs, one 1-MW PV plant, and one 1-MW/1-MWh BESS are used for model validation. The results show that the WTG and PV performance models correctly estimate the power generation variability according to fluctuations in wind speed and solar irradiance. The BESS performance model provides satisfactory results related to grid-forming control performance and estimation of state-of-charge. The presented validation work enables using the proposed performance models for power system studies and HPP control design in all model-based design stages, that is, preliminary analysis, design, verification, and validation with a high level of confidence. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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20 pages, 601 KiB

Open AccessArticle

An Integrated Planning Strategy for a Power Network and the Charging Infrastructure of Electric Vehicles for Power System Resilience Enhancement

by Fang Yao, Jiawei Wang, Fushuan Wen, Chung-Li Tseng, Xingyong Zhao and Qiang Wang

Energies 2019, 12(20), 3918; https://doi.org/10.3390/en12203918 - 16 Oct 2019

Cited by 10 | Viewed by 2897

Abstract

This paper addresses the integrated planning problem of a power network and the charging infrastructure of electric vehicles (EVs) for enhancing power system resilience under various extreme weather scenarios. The planning methodology determines the optimal joint expansion decisions while modeling the benchmark system [...] Read more.

This paper addresses the integrated planning problem of a power network and the charging infrastructure of electric vehicles (EVs) for enhancing power system resilience under various extreme weather scenarios. The planning methodology determines the optimal joint expansion decisions while modeling the benchmark system operation under the n − k resilience criterion. The proposed coordinated planning framework is a robust two-stage/tri-level mixed-integer optimization model. The proposed robust joint planning model includes the construction plan in the first level, identifying the worst-case scenario in the second level, and optimizing the operation cost and load shedding in the final level. To solve this model, a duality-based column and constraint generation (D-CCG) algorithm is developed. Using case studies, both the robust sole transmission planning and joint planning models are demonstrated on the IEEE 30-bus and IEEE 118-bus power systems. Numerical simulations of the benchmark systems validate the effectiveness of the developed framework and the efficiency of the proposed solution approach. Simulation results show the superiority of the proposed robust integrated planning over the sole transmission planning model. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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23 pages, 2700 KiB

Open AccessArticle

Risk-Limiting Real-Time Economic Dispatch in a Power System with Flexibility Resources

by Hongji Lin, Chongyu Wang, Fushuan Wen, Chung-Li Tseng, Jiahua Hu, Li Ma and Menghua Fan

Energies 2019, 12(16), 3133; https://doi.org/10.3390/en12163133 - 15 Aug 2019

Cited by 4 | Viewed by 2808

Abstract

The integration of numerous intermittent renewable energy sources (IRESs) poses challenges to the power supply-demand balance due to the inherent intermittent and uncertain power outputs of IRESs, which requires higher operational flexibility of the power system. The deployment of flexible ramping products (FRPs) [...] Read more.

The integration of numerous intermittent renewable energy sources (IRESs) poses challenges to the power supply-demand balance due to the inherent intermittent and uncertain power outputs of IRESs, which requires higher operational flexibility of the power system. The deployment of flexible ramping products (FRPs) provides a new alternative to accommodate the high penetration of IRESs. Given this background, a bi-level risk-limiting real-time unit commitment/real-time economic dispatch model considering FRPs provided by different flexibility resources is proposed. In the proposed model, the objective is to maximize the social surplus while minimizing the operational risk, quantified using the concept of conditional value-at-risk (CVaR). Energy and ramping capabilities of conventional generating units during the start-up or shut-down processes are considered, while meeting the constraints including unit start-up/shut-down trajectories and ramping up/down rates in consecutive time periods. The Karush–Kuhn–Tucker (KKT) optimality conditions are then used to convert the bi-level programming problem into a single-level one, which can be directly solved after linearization. The modified IEEE 14-bus power system is employed to demonstrate the proposed method, and the role of FRPs in enhancing the system flexibility and improving the accommodation capability for IRESs is illustrated in some operation scenarios of the sample system. The impact of the confidence level in CVaR on the system operational flexibility is also investigated through case studies. Finally, a case study is conducted on a regional power system in Guangdong Province, China to demonstrate the potential of the proposed method for practical applications. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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21 pages, 2925 KiB

Open AccessArticle

Probabilistic Power Flow for Hybrid AC/DC Grids with Ninth-Order Polynomial Normal Transformation and Inherited Latin Hypercube Sampling

by Sui Peng, Huixiang Chen, Yong Lin, Tong Shu, Xingyu Lin, Junjie Tang, Wenyuan Li and Weijie Wu

Energies 2019, 12(16), 3088; https://doi.org/10.3390/en12163088 - 10 Aug 2019

Cited by 7 | Viewed by 3138

Abstract

This paper proposes a new probabilistic power flow method for the hybrid AC/VSC-MTDC (Voltage Source Control-Multiple Terminal Direct Current) grids, which is based on the combination of ninth-order polynomial normal transformation (NPNT) and inherited Latin hypercube sampling (ILHS) techniques. NPNT is utilized to [...] Read more.

This paper proposes a new probabilistic power flow method for the hybrid AC/VSC-MTDC (Voltage Source Control-Multiple Terminal Direct Current) grids, which is based on the combination of ninth-order polynomial normal transformation (NPNT) and inherited Latin hypercube sampling (ILHS) techniques. NPNT is utilized to directly handle historical records of uncertain sources to build the accurate probability model of random inputs, and ILHS is adopted to propagate the randomness from inputs to target outputs. Regardless of whether the underlying probability distribution is known or unknown, the proposed method has the ability to adaptively evaluate the sample size according to a specific operational scenario of the power systems, thus achieving a good balance between computational accuracy and speed. Meanwhile, the frequency histograms, probability distributions, and some more statistics of the results can be accurately and efficiently estimated as well. The modified IEEE 118-bus system, together with the realistic data of wind speeds and diverse consumer behaviors following irregular distributions, is used to demonstrate the effectiveness and superiority of the proposed method. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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21 pages, 8310 KiB

Open AccessArticle

Simultaneous Inertia Contribution and Optimal Grid Utilization with Wind Turbines

by Clemens Jauch and Arne Gloe

Energies 2019, 12(15), 3013; https://doi.org/10.3390/en12153013 - 5 Aug 2019

Cited by 7 | Viewed by 3848

Abstract

This paper presents findings of a study on continuous feed-in management and continuous synthetic inertia contribution with wind turbines. A realistic case study, based on real measurements, is outlined. A wind turbine feeds into a weak feeder, such that its power has to [...] Read more.

This paper presents findings of a study on continuous feed-in management and continuous synthetic inertia contribution with wind turbines. A realistic case study, based on real measurements, is outlined. A wind turbine feeds into a weak feeder, such that its power has to be adapted to the permissible loading of this feeder. At the same time the wind turbine is to provide inertia to the grid by applying the previously published variable inertia constant controller. It is discussed that optimal grid utilization and simultaneous inertia contribution are mandatory for the frequency control in power systems that are heavily penetrated with renewable energies. The study shows that continuous feed-in management can be combined well with continuous inertia provision. There are hardly any negative consequences for the wind turbine. The benefits for the grid are convincing, both in terms of increased system utilization and in terms of provided inertia. It is concluded that wind turbines can enhance angular stability in a power system to a larger extent than conventional power plants. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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15 pages, 3898 KiB

Open AccessArticle

Identification of Three-Phase Grid Impedance in the Presence of Parallel Converters

by Roni Luhtala, Tuomas Messo, Tomi Roinila, Henrik Alenius, Erik de Jong, Andrew Burstein and Alejandra Fabian

Energies 2019, 12(14), 2674; https://doi.org/10.3390/en12142674 - 12 Jul 2019

Cited by 18 | Viewed by 3522

Abstract

Grid impedance is an important parameter which affects the control performance of grid-connected power converters. Several methods already exist for optimizing the converter control system based on knowledge of grid impedance value. Grid impedance may change rapidly due to fault or disconnection of [...] Read more.

Grid impedance is an important parameter which affects the control performance of grid-connected power converters. Several methods already exist for optimizing the converter control system based on knowledge of grid impedance value. Grid impedance may change rapidly due to fault or disconnection of a transmission line. Therefore, online grid identification methods have been recently proposed to have up-to-date information about the grid impedance value. This is usually done by perturbing the converter output current and measuring the response in output voltage. However, any parallel converters connected to the same interface point will cause errors, since the measured current differs from the current that is flowing through the grid interface point. This paper points out challenges and errors in grid impedance identification, caused by parallel converters and their internal control functions, such as grid-voltage support. Experimental grid-impedance measurements are shown from the power hardware-in-the-loop setup developed at DNV-GL Flexible Power Grid Lab. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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28 pages, 2410 KiB

Open AccessArticle

Distributed LQR Design for a Class of Large-Scale Multi-Area Power Systems

by Eleftherios Vlahakis, Leonidas Dritsas and George Halikias

Energies 2019, 12(14), 2664; https://doi.org/10.3390/en12142664 - 11 Jul 2019

Cited by 21 | Viewed by 4041

Abstract

Load frequency control (LFC) is one of the most challenging problems in multi-area power systems. In this paper, we consider power system formed of distinct control areas with identical dynamics which are interconnected via weak tie-lines. We then formulate a disturbance rejection problem [...] Read more.

Load frequency control (LFC) is one of the most challenging problems in multi-area power systems. In this paper, we consider power system formed of distinct control areas with identical dynamics which are interconnected via weak tie-lines. We then formulate a disturbance rejection problem of power-load step variations for the interconnected network system. We follow a top-down method to approximate a centralized linear quadratic regulator (LQR) optimal controller by a distributed scheme. Overall network stability is guaranteed via a stability test applied to a convex combination of Hurwitz matrices, the validity of which leads to stable network operation for a class of network topologies. The efficiency of the proposed distributed load frequency controller is illustrated via simulation studies involving a six-area power system and three interconnection schemes. In the study, apart from the nominal parameters, significant parametric variations have been considered in each area. The obtained results suggest that the proposed approach can be extended to the non-identical case. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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19 pages, 6199 KiB

Open AccessArticle

A Toolbox for Analyzing and Testing Mode Identification Techniques and Network Equivalent Models

by Eleftherios O. Kontis, Georgios A. Barzegkar-Ntovom, Konstantinos A. Staios, Theofilos A. Papadopoulos and Grigoris K. Papagiannis

Energies 2019, 12(13), 2606; https://doi.org/10.3390/en12132606 - 6 Jul 2019

Cited by 4 | Viewed by 2962

Abstract

During the last decade the dynamic properties of power systems have been altered drastically, due to the emerge of new non-conventional types of loads as well as to the increasing penetration of distributed generation. To analyze the power system dynamics and develop accurate [...] Read more.

During the last decade the dynamic properties of power systems have been altered drastically, due to the emerge of new non-conventional types of loads as well as to the increasing penetration of distributed generation. To analyze the power system dynamics and develop accurate models, measurement-based techniques are usually employed by academia and power system operators. In this regard, in this paper an identification toolbox is developed for the derivation of measurement-based equivalent models and the analysis of dynamic responses. The toolbox incorporates eight of the most widely used mode identification techniques as well as several static and dynamic network equivalencing models. First, the theoretical background of the mode identification techniques as well as the mathematical formulation of the examined equivalent models is presented and analyzed. Additionally, multi-signal analysis methods are incorporated in the toolbox to facilitate the development of robust equivalent models. Additionally, an iterative procedure is adopted to automatically determine the optimal order of the derived models. The capabilities of the toolbox are demonstrated using simulation responses, acquired from large-scale benchmark power systems, as well as using measurements recorded at a laboratory-scale active distribution network. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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23 pages, 5996 KiB

Open AccessArticle

Impedance Modeling and Stability Analysis of the Converters in a Double-Fed Induction Generator (DFIG)-Based System

by Xunjun Chen and Zhigang Liu

Energies 2019, 12(13), 2500; https://doi.org/10.3390/en12132500 - 28 Jun 2019

Cited by 10 | Viewed by 3042

Abstract

Harmonic stability of double-fed induction generators (DFIGs) now has become a significant topic because of its harmful impact on power quality issues of the system. Since the double pulse width modulation (PWM) converter is one of the main harmonic sources in DFIGs, it [...] Read more.

Harmonic stability of double-fed induction generators (DFIGs) now has become a significant topic because of its harmful impact on power quality issues of the system. Since the double pulse width modulation (PWM) converter is one of the main harmonic sources in DFIGs, it may cause harmonic instability with increasing harmonic contents. Thus, the modeling and stability analyses of PWM converters in DFIGs are essential steps to assess the harmonic stability of DFIGs. Aiming at dual PWM converters, which include the grid side converter (GSC) and the rotor side converter (RSC), this paper divides converters into two parts: circuit modules and control modules. Closed-loop input impedance models of each module are then derived by means of transfer functions. Hence, the stability of the system can be readily predicted through Nyquist diagrams. The contributions of parameters to the system’s harmonic stability are also identified. Finally, time-domain simulations are conducted in a real-time digital simulation (RTDS) system. Simulation results confirm that the established impedance model can effectively reveal the stability of the DFIG-based system and can give critical conditions for the occurrence of harmonic instability. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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19 pages, 1969 KiB

Open AccessArticle

Feedback Linearization and Reaching Law Based Sliding Mode Control Design for Nonlinear Hydraulic Turbine Governing System

by Bicheng Guo and Jiang Guo

Energies 2019, 12(12), 2273; https://doi.org/10.3390/en12122273 - 13 Jun 2019

Cited by 10 | Viewed by 3351

Abstract

Hydropower as renewable energy has continually expanded at a relatively high rate in the last decade. This expansion calls for more accurate scheme design in hydraulic turbine governing system (HTGS) to ensure its high efficiency. Sliding mode control (SMC) as a robust control [...] Read more.

Hydropower as renewable energy has continually expanded at a relatively high rate in the last decade. This expansion calls for more accurate scheme design in hydraulic turbine governing system (HTGS) to ensure its high efficiency. Sliding mode control (SMC) as a robust control method which is insensitive to system uncertainties and disturbances raises interest in the application in HTGS. However, the feature of highly coupled state variables reflects the nonlinear essence of HTGS and SMC studies on the related mathematical model under certain fluctuations are not satisfied. In this regard, a novel SMC design with proportional-integral-derivative manifold is firstly applied to a nonlinear HTGS with a complex conduit system. In dealing with certain fluctuations in speed and load around the rated working condition, the proposed SMC is capable of driving the system to the desired state with smooth and light responses in aspects of the key state variables. The exponential reaching law and introduced boundary layer fasten the speed of converging time and suppress chattering. A necessary integral of sliding parameter added to manifold successfully reduces the latency caused by the anti-regulation feature of HTGS. Three operating scenarios are simulated compared with the PSO-PID method, and results imply that the proposed SMC method equips with accurate trajectory tracking ability and smooth responses. Finally, the strong robustness against system uncertainties is tested. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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17 pages, 1524 KiB

Open AccessArticle

Impedance Aggregation Method of Multiple Wind Turbines and Accuracy Analysis

by Liang Chen, Heng Nian and Yunyang Xu

Energies 2019, 12(11), 2035; https://doi.org/10.3390/en12112035 - 28 May 2019

Cited by 5 | Viewed by 3368

Abstract

The sequence domain impedance modeling of wind turbines (WTs) has been widely used in the stability analysis between WTs and weak grids with high line impedance. An aggregated impedance model of the wind farm is required in the system-level analysis. However, directly aggregating [...] Read more.

The sequence domain impedance modeling of wind turbines (WTs) has been widely used in the stability analysis between WTs and weak grids with high line impedance. An aggregated impedance model of the wind farm is required in the system-level analysis. However, directly aggregating WT small-signal impedance models will lead to an inaccurate aggregated impedance model due to the mismatch of reference frame definitions among different WT subsystems, which may lead to inaccuracy in the stability analysis. In this paper, we analyze the impacts of the reference frame mismatch between a local small-signal impedance model and a global one on the accuracy of aggregated impedance and the accuracy of impedance-based stability analysis. The results revealed that the impact is related to the power distribution of the studied network. It was found that that the influence of mismatch on stability analysis became subtle when subsystems were balanced loaded. Considering that balanced loading is a common configuration of the practical application, direct impedance aggregation by local small-signal models can be applied due to its acceptable accuracy. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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20 pages, 3393 KiB

Open AccessArticle

Voltage Support under Grid Faults with Inherent Current Limitation for Three-Phase Droop-Controlled Inverters

by Alexandros G. Paspatis and George C. Konstantopoulos

Energies 2019, 12(6), 997; https://doi.org/10.3390/en12060997 - 14 Mar 2019

Cited by 11 | Viewed by 4043

Abstract

A novel nonlinear current-limiting controller for three-phase grid-tied droop-controlled inverters that is capable of offering voltage support during balanced and unbalanced grid voltage drops is proposed in this paper. The proposed controller introduces a unified structure under both normal and abnormal grid conditions [...] Read more.

A novel nonlinear current-limiting controller for three-phase grid-tied droop-controlled inverters that is capable of offering voltage support during balanced and unbalanced grid voltage drops is proposed in this paper. The proposed controller introduces a unified structure under both normal and abnormal grid conditions operating as a droop controller or following the recent fault-ride-through requirement to provide voltage support. In the case of unbalanced faults, the inverter can further inject or absorb the required negative sequence real and reactive power to eliminate the negative sequence voltage at the point of common coupling (PCC) whilst ensuring at all times boundedness for the grid current. To accomplish this task, a novel and easily implementable method for dividing the available current into the two sequences (positive and negative) is proposed, suitably adapting the proposed controller parameters. Furthermore, nonlinear input-to-state stability theory is used to guarantee that the total grid current remains limited below its given maximum value under both normal and abnormal grid conditions. Asymptotic stability for any equilibrium point of the closed-loop system in the bounded operating range is also analytically proven for first time using interconnected-systems stability analysis irrespective of the system parameters. The proposed control concept is verified using an OPAL-RT real-time digital simulation system for a three-phase inverter connected to the grid. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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21 pages, 14913 KiB

Open AccessConcept Paper

Overview on Grid-Forming Inverter Control Methods

by Peter Unruh, Maria Nuschke, Philipp Strauß and Friedrich Welck

Energies 2020, 13(10), 2589; https://doi.org/10.3390/en13102589 - 20 May 2020

Cited by 205 | Viewed by 22882

Abstract

In this paper, different control approaches for grid-forming inverters are discussed and compared with the grid-forming properties of synchronous machines. Grid-forming inverters are able to operate AC grids with or without rotating machines. In the past, they have been successfully deployed in inverter [...] Read more.

In this paper, different control approaches for grid-forming inverters are discussed and compared with the grid-forming properties of synchronous machines. Grid-forming inverters are able to operate AC grids with or without rotating machines. In the past, they have been successfully deployed in inverter dominated island grids or in uninterruptable power supply (UPS) systems. It is expected that with increasing shares of inverter-based electrical power generation, grid-forming inverters will also become relevant for interconnected power systems. In contrast to conventional current-controlled inverters, grid-forming inverters do not immediately follow the grid voltage. They form voltage phasors that have an inertial behavior. In consequence, they can inherently deliver momentary reserve and increase power grid resilience. Full article

(This article belongs to the Special Issue Modern Power System Dynamics, Stability and Control)

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