This two-part paper presents a generic methodology for measuring the short-term voltage stability(STVS)of power systems dominated by inverter-based resources(IBRs),which introduces the concept of generalized voltage d...This two-part paper presents a generic methodology for measuring the short-term voltage stability(STVS)of power systems dominated by inverter-based resources(IBRs),which introduces the concept of generalized voltage damping(GVD)for quantifying STVS from both global and local perspectives.It leads to a model-independent approach to assessing the voltage stability,the system strength,and the capability of dynamic devices to support voltage during transient process.Part I of this paper focuses on deriving the system-wise generalized voltage damping(sGVD)index and its applications.The sGVD index is defined as the decay rate of voltage-related transient energy(VTE)dissipated on the(aggregated)buses of the power system,which can be obtained using the maximum Lyapunov exponent(MLE)technique.The proposed sGVD index is theoretically demonstrated to capture the actual voltage damping of devices and to be strongly linked with STVS.These unique properties enable a model-independent approach to measuring STVS and system strength,even in the presence of heterogeneous and strongly nonlinear dynamics of IBRs.We verify the theoretical results by conducting simulations on the modified IEEE 39-bus system and two large-scale practical power systems with integration of massive renewable resources,demonstrating the effectiveness and practicality of the methodology.展开更多
This paper proposes a resilient restoration method for low-inertia networked microgrids(NMGs)dominated with inverter-based energy resources(IBERs).First,a frequency dynamics-aware NMG restoration model is developed,in...This paper proposes a resilient restoration method for low-inertia networked microgrids(NMGs)dominated with inverter-based energy resources(IBERs).First,a frequency dynamics-aware NMG restoration model is developed,integrating a unified frequency control response framework that accommodates various control strategies while ensuring the system stability during restoration.Case studies for a low-inertia NMG demonstrate the effectiveness of the proposed method.Numerical results show that different IBER control methods could have a significant impact on restoration efficiency and economic losses.Additionally,strict frequency security requirements can predominantly increase the restoration time,calling for a critical trade-off between maintaining network security margins and restoration time for enhancing the resilience of low-inertia NMGs dominated with IBERs.展开更多
This paper proposes a novel control scheme for inverter-based resources(IBRs)based on the complex frequency(CF)concept.The control objective is to maintain a constant CF of voltage at the terminals of IBR by adjusting...This paper proposes a novel control scheme for inverter-based resources(IBRs)based on the complex frequency(CF)concept.The control objective is to maintain a constant CF of voltage at the terminals of IBR by adjusting its current reference.This current is imposed based on the well-known power flow equation,the dynamics of which are calculated through estimating the CFs for the voltages of adjacent buses.The performance is evaluated by analyzing the local variations in frequency and voltage magnitude,as well as the frequency of center of inertia(CoI),and then compared with conventional frequency droop,proportional-integral(PI)voltage controllers,and virtual inertia.The case study utilizes a modified version of WSCC 9-bus system and a 1479-bus model of the Irish transmission grid and considers various contingencies and sensitivities such as the impact of current limiters,delays,noise,R/X ratio,and electromagnetic transient(EMT)dynamics.Results show that the proposed control scheme consistently outperforms the conventional controllers,leading to significant improvements in the overall dynamic response of the system.展开更多
Inverter-based resources(IBRs),such as wind and photovoltaic generation,are characterized by low capacity and extensive distribution,which can exacerbate the weak properties of power systems.Precise identification of ...Inverter-based resources(IBRs),such as wind and photovoltaic generation,are characterized by low capacity and extensive distribution,which can exacerbate the weak properties of power systems.Precise identification of weak system status is essential for ensuring the security and economic efficiency of IBR integration.This paper proposes the index of the multiple renewable short-circuit ratio(MRSCR)and its critical value calculated by the voltage(CMRSCR)to provide a comprehensive assessment of power system strength in the presence of high IBR penetration,enhancing the accuracy and reliability of system strength evaluation.First,we introduce a single-infeed equivalent model of the power system integrating multiple IBRs.We examine the factors associated with system properties that are crucial in the strength assessment process.Subsequently,the MRSCR is derived from this analysis.The MRSCR describes the connection between system strength and voltage variation caused by power fluctuations.This implies that voltage variation caused by IBR power fluctuations is more pronounced under weak grid conditions.Following this,the CMRSCR is proposed to precisely evaluate the stability boundary.The disparity between MRSCR and CMRSCR is utilized to evaluate the stability margin of the power system.Unlike a fixed value,the CMRSCR exhibits higher sensitivity as the system approaches a critical state.These indexes have been implemented in the PSD power tools and power system analysis software package,facilitating engineering calculation and analysis of bulk power systems in China.Finally,simulation results validate the effectiveness of the proposed indexes and the research findings.展开更多
This work considers the problem of decentralized control of inverter-based ac micro-grid in different operation modes.The main objectives are to(i)design decentralized frequency and voltage controllers,to gather with ...This work considers the problem of decentralized control of inverter-based ac micro-grid in different operation modes.The main objectives are to(i)design decentralized frequency and voltage controllers,to gather with power sharing,without information exchange between microsources(ii)design passive dynamic controllers which ensure stability of the entire microgrid system(iii)capture nonlinear,interconnected and large-scale dynamic of the micro-grid system with meshed topology as a port-Hamiltonian formulation(iv)expand the property of shifted-energy function in the context of decentralized control of ac micro-grid(v)analysis of system stability in large signal point of view.More precisely,to deal with nonlinear,interconnected and large-scale structure of micro-grid systems,the port-Hamiltonian formulation is used to capture the dynamic of micro-grid components including microsource,distribution line and load dynamics as well as interconnection controllers.Furthermore,to deal with large signal stability problem of the microgrid system in the grid-connected and islanded conditions,the shifted-Hamiltonian energy function is served as a storage function to ensure incremental passivity and stability of the microgrid system.Moreover,it is shown that the aggregating of the microgrid dynamic and the decentralized controller dynamics satisfies the incremental passivity.Finally,the effectiveness of the proposed controllers is evaluated through simulation studies.The different scenarios including grid-connected and islanded modes as well as transition between both modes are simulated.The simulation conforms that the decentralized control dynamics are suited to achieve the desired objective of frequency synchronization,voltage control and power sharing in the grid-connected and islanded modes.The simulation results demonstrate the effectiveness of the proposed control strategy.展开更多
The increasing penetration of inverter-based distributed generations(DGs)significantly affects the fault characteristics of distribution networks.Fault analysis is a keystone for suitable protection scheme design.This...The increasing penetration of inverter-based distributed generations(DGs)significantly affects the fault characteristics of distribution networks.Fault analysis is a keystone for suitable protection scheme design.This paper presents the modelling methodology for distribution networks with inverter-based DGs and performs fault simulation based on the model.Firstly,a single inverter-based DG model based on the cascaded control structure is developed.Secondly,a simulation model of distribution network with two inverter-based DGs is established.Then,different fault simulations are performed based on the Real Time Digital Simulator(RTDS).Theoretical analyses are conducted to justify the simulation results,including the equivalent circuit of distribution networks with inverter-based DGs and the solution method for loop currents.展开更多
High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,wh...High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,while the RES dynamic response,mainly governed by inverters,is not considered.Consequently,some relevant algorithms of transmission line protection are experiencing challenges because of the fact that magnitude and phase angle com-parison,amount of negative-sequence,and short-circuit current level are affected by the RES.Therefore,an in-depth study of this issue is necessary,one which considers the main causes and new methodological criteria solutions.This work presents an extensive literature review of the evaluation of electrical protection performance and the effects of RES connected to a power grid through inverters.Bibliographic data on many representative publications related to this topic are obtained to show the current research lines and their proposed solutions.In addition,this work identi-fies the main protection functions affected and describes the new protection schemes that consider RES.Finally,an analysis and discussion of the selected bibliography are presented.展开更多
Along with the growing integration of renewable energy resources,the new power systems,which are dominated by inverter-based resources(IBRs),are facing critical challenges in both planning and operation stages.The con...Along with the growing integration of renewable energy resources,the new power systems,which are dominated by inverter-based resources(IBRs),are facing critical challenges in both planning and operation stages.The conventionally used system strength metric,short-circuit ratio(SCR),exhibits limitations in assessing connections of new IBRs due to their unique dynamic behaviour and control interactions.In this paper,the definition of system strength is reviewed.The underlying principles of conventional SCR and its variants are then discussed,with their constraints explained.To describe the system strength in a more comprehensive way,this paper further classifies system strength into three categories:quasi-static,small-signal,and large-signal.For each category,relevant metrics are introduced and their relative merits are discussed.Electromagnetic transient simulations are presented to illustrate key insights.展开更多
In this paper,a strength-constrained unit commitment(UC)model incorporating system strength constraints based on the weighted short-circuit ratio(WSCR)is proposed.This model facilitates the comprehensive assessment of...In this paper,a strength-constrained unit commitment(UC)model incorporating system strength constraints based on the weighted short-circuit ratio(WSCR)is proposed.This model facilitates the comprehensive assessment of area-wide system strength in power systems with high inverter-based resource(IBR)penetration,thereby contributing to the mitigation of weak grid issues.Unlike traditional models,this approach considers the interactions among multiple IBRs.The UC problem is initially formulated as a mixed-integer nonlinear programming(MINLP)model,reflecting WSCR and bus impedance matrix modification constraints.To enhance computational tractability,the model is transformed into a mixed-integer linear programming(MILP)form.The effectiveness of the proposed approach is validated through simulations on the IEEE 5-bus,IEEE 39-bus,and a modified Korean power system,demonstrating the ability of the proposed UC model enhancing system strength compared to the conventional methodologies.展开更多
Cross-regional high voltage direct current(HVDC)systems bring remarkable renewable power injections to the receiver side of power grids.However,HVDC failures result in large disturbances to receivers and cause critica...Cross-regional high voltage direct current(HVDC)systems bring remarkable renewable power injections to the receiver side of power grids.However,HVDC failures result in large disturbances to receivers and cause critical frequency security problems.High renewable energy penetration also reduces the system inertia and damping coefficients.Thus,some nodal frequency nadirs may be much lower than those calculated by the center-of-inertia(COI)and may trigger low-frequency protection.Energy storage is a promising solution for frequency-related problems.In this study,we build an energy storage planning model considering both COI and nodal frequency security constraints.The energy storage capacities and locations are determined in the planning scheme based on year-round operations.First,we carry out a year-round COI-frequency-constrained unit commitment to obtain comprehensive operation modes.Next,we propose a hybrid data-model driven approach to generate nodal frequency security constraints for extensive operation modes effectively.Finally,we achieve optimal energy storage planning with both COI and nodal frequency constraints.Case studies on a modified RTS-79 test system and a 1089-bus power system in practical in Jiangsu,China,verify the effectiveness of the proposed methods.展开更多
In recent years,the increased application of inverter-based resources in power grids,along with the gradual replacement of synchronous generators,has made the grid support capability of inverters essential for maintai...In recent years,the increased application of inverter-based resources in power grids,along with the gradual replacement of synchronous generators,has made the grid support capability of inverters essential for maintaining system stability under large disturbances.Critical clearing time provides a quantitative measure of fault severity and system stability,and its sensitivity can help guide parameter adjustments to enhance the grid support capability of inverters.Building on previous researches,this paper proposes a method for calculating critical clearing time sensitivity in power systems with a high proportion of power electronic devices,accounting for the new dynamic characteristics introduced by these devices.The current limit and switching control of inverterbased resources are considered,and the critical clearing time sensitivity under controlling periodic orbits is derived.The proposed critical clearing time sensitivity calculation method is then validated using a double generator single load system and a modified 39-bus system.展开更多
The move to Inverter-Based Renewable Resources(IBRs)is a challenge for power system protection since IBRs generate much lower fault currents than traditional synchronous generators.This compromises the operation of co...The move to Inverter-Based Renewable Resources(IBRs)is a challenge for power system protection since IBRs generate much lower fault currents than traditional synchronous generators.This compromises the operation of conventional protection relays.In order to solve this problem,the present study employs a detailed Institute of Electrical and Electronics Engineers(IEEE)9-bus model in Real Time Simulation for Computer Aided Design(RSCAD)to examine the fault behaviour at four different levels of renewable energy penetration.The investigation measures the reduction of the fault current as a result of the gradual substitution of synchronous generation by photovoltaics.The findings enable the production of different sets of relay settings for each case,thus assuring the correct functioning of protection coordination in terms of reliability and selectivity.The main point is an extensive adaptive protection concept.This thoughtful plan serves as an essential guide for the dynamic adjustment of relay settings,thus ensuring the resilience and stability of the grid during the energy transition.展开更多
The increasing penetration of inverter-based resources(IBRs)and renewable energy resources poses significant challenges to the stability and controllability of modern power systems.Dynamic virtual power plants(DVPPs)h...The increasing penetration of inverter-based resources(IBRs)and renewable energy resources poses significant challenges to the stability and controllability of modern power systems.Dynamic virtual power plants(DVPPs)have emerged as a transformative solution for aggregating and controlling heterogeneously distributed energy resources(DERs)flexibly and dynamically.This paper presents a comprehensive review of DVPPs,covering their conceptual evolution—from microgrids to virtual power plants(VPPs)and fast-acting VPPs—culminating in the dynamic DVPP paradigm.This review explores key architectural frameworks,including grid-forming and grid-following roles,as well as AC/DC interfacing strategies.Emphasis is placed on secondary frequency and voltage control mechanisms,dynamic-based and market-based disaggregation,and control methodologies tailored to DERs.展开更多
This paper proposes an AI-based approach for islanding detection in active distribution networks.A review of existing AI-based studies reveals several gaps,including model complexity and stability concerns,limited acc...This paper proposes an AI-based approach for islanding detection in active distribution networks.A review of existing AI-based studies reveals several gaps,including model complexity and stability concerns,limited accuracy in noisy conditions,and limited applicability to systems with different types of resources.To address these challenges,this paper proposes a novel approach that adapts the WaveNet generator into a classifier,enhanced with a denoising UNet model,to improve performance in varying signal-to-noise ratio(SNR)conditions.In designing this model,we deviate from state-of-the-art approaches that primarily rely on long short-term memory(LSTM)architectures by employing 1D convolutional layers.This enables the model to focus on spatial analysis of the input signal,making it particularly well-suited for processing long input sequences.Additionally,residual connections are incorporated to mitigate overfitting and significantly enhance the model’s generalizability.To verify the effectiveness of the proposed scheme,over 14000 islanding/non-islanding cases are tested,considering different load active/reactive power values,load switching transients,capacitor bank switching,fault conditions in the main grid,different load quality factors,SNR levels,changes in network topology,and both types of conventional and inverter-based sources.展开更多
Integration of inverter-based resources(IBRs)reshapes conventional power swing patterns,challenging the operation of legacy power swing protec-tion schemes.This paper highlights the significant con-sequences of the di...Integration of inverter-based resources(IBRs)reshapes conventional power swing patterns,challenging the operation of legacy power swing protec-tion schemes.This paper highlights the significant con-sequences of the distinctive power swing patterns exhib-ited by grid-forming IBRs(GFM-IBRs).The swing mechanism involving GFM-IBRs is elucidated using an-alytical modeling of GFM-IBRs with various power syn-chronization loops(PSLs).With varying GFM-IBR pen-etration levels and different generator scenarios,the per-formance of power swing protection functions is examined,including power swing blocking(PSB)and out-of-step tripping(OST).Additionally,the IEEE PSRC D29 test system is employed to present power swing protection results in a large-scale power system integrated with synchronous generators(SGs)and IBRs.The results in-dicate that,GFM-IBRs with sufficient voltage support capability can provide positive impact on power swing dynamics,and power swing protection performance can be enhanced by emulating the inertia and droop mecha-nism of SGs and rapidly adjusting the active power output.However,with high penetration levels of GFM-IBRs,OST maloperation may occur in scenarios with inadequate voltage support capability.展开更多
Variable renewable energy(VRE)integrated via non-synchronous inverters exhibits low inertia and fluctuating output,posing substantial frequency security challenges for future power systems.When frequency security cons...Variable renewable energy(VRE)integrated via non-synchronous inverters exhibits low inertia and fluctuating output,posing substantial frequency security challenges for future power systems.When frequency security constraints are omitted from generation planning,the resulting low-inertia generation portfolios often fail to meet critical frequency requirements.To address this issue,this paper proposes a novel frequency security constrained generation planning(FSCGP)model that leverages the frequency support potential of diverse power sources,including conventional thermal generators(CTGs),VRE units,concentrating solar power(CSP)units,and energy storage systems(ESSs).A physics-data hybrid-driven method is introduced to formulate frequency security constraints,enabling accurate representation of diverse frequency regulation characteristics,particularly the fast frequency support capabilities of inverter-based generators(IBGs).To further enhance the computational efficiency,several acceleration techniques are incorporated into the proposed FSCGP model.Case studies based on a modified IEEE RTS-79 system validate the effectiveness of the proposed FSCGP model.The numerical results identify the primary contributors to frequency security under different renewable energy penetration(REP)levels and demonstrate the cost-effectiveness of coordinating various frequency support sources,especially CSP units and IBGs,in mitigating challenges in low-inertia grids.展开更多
This study investigates a safe reinforcement learning algorithm for grid-forming(GFM)inverter based frequency regulation.To guarantee the stability of the inverter-based resource(IBR)system under the learned control p...This study investigates a safe reinforcement learning algorithm for grid-forming(GFM)inverter based frequency regulation.To guarantee the stability of the inverter-based resource(IBR)system under the learned control policy,a modelbased reinforcement learning(MBRL)algorithm is combined with Lyapunov approach,which determines the safe region of states and actions.To obtain near optimal control policy,the control performance is safely improved by approximate dynamic programming(ADP)using data sampled from the region of attraction(ROA).Moreover,to enhance the control robustness against parameter uncertainty in the inverter,a Gaussian process(GP)model is adopted by the proposed algorithm to effectively learn system dynamics from measurements.Numerical simulations validate the effectiveness of the proposed algorithm.展开更多
Battery energy storage systems(BESSs)need to comply with grid code and fault ride through(FRT)requirements during disturbances whether they are in charging or discharging mode.Previous literature has shown that consta...Battery energy storage systems(BESSs)need to comply with grid code and fault ride through(FRT)requirements during disturbances whether they are in charging or discharging mode.Previous literature has shown that constant charging current control of BESSs in charging mode can prevent BESSs from complying with emerging grid codes such as the German grid code under stringent unbalanced fault conditions.To address this challenge,this paper proposes a new FRTactivated dual control strategy that consists of switching from constant battery current control to constant DC-link voltage control through a positive droop structure.The results show that the strategy ensures proper DC-link voltage and current management as well as adequate control of the positive-and negative-sequence active and reactive currents according to the grid code priority.It is also shown that the proposed FRT control strategy is tolerant to initial operating conditions of BESS plant,grid code requirements,and fault severity.展开更多
This paper presents an ultra-low power incremental ADC for biosensor interface circuits. The ADC consists of a resettable second-order delta-sigma （△ ∑） modulator core and a resettable decimation filter. Several t...This paper presents an ultra-low power incremental ADC for biosensor interface circuits. The ADC consists of a resettable second-order delta-sigma （△ ∑） modulator core and a resettable decimation filter. Several techniques are adopted to minimize its power consumption. A feedforward path is introduced to the modulator core to relax the signal swing and linearity requirement of the integrators. A correlated-double-sampling （CDS） technique is applied to reject the offset and 1/f noise, thereby removing the integrator leakage and relaxing the gain requirement of the OTA. A simple double-tailed inverter-based fully differential OTA using a thick-oxide CMOS is proposed to operate in the subthreshold region to fulfill both an ultra-low power and a large output swing at 1.2 V supply. The signal addition before the comparator in the feedforward architecture is performed in the current domain instead of the voltage domain to minimize the capacitive load to the integrators. The capacitors used in this design are of customized metal-oxide metal （MOM） type to reach the minimum capacitance set by the k T~ C noise limit. Fabricated with a 1P6M 0.18/zm CMOS technology, the presented incremental ADC consumes 600 nW at 2 kS/s from a 1.2 V supply, and achieves 68.3 dB signal to noise and distortion ratio （SNDR） at the Nyquist frequency and an FOM of 0.14 pJ/conversion step. The core area is 100 × 120 μm^2.展开更多
Fault currents emanating from inverter-based resources(IBRs)are controlled to follow specific references to support the power grid during faults.However,these fault currents differ from the typical fault currents fed ...Fault currents emanating from inverter-based resources(IBRs)are controlled to follow specific references to support the power grid during faults.However,these fault currents differ from the typical fault currents fed by synchronous generators,resulting in an improper operation of conventional phase selection methods(PSMs).In this paper,the relative angles between sequence voltages measured at the relay location are determined analytically in two stages:(1)a short-circuit analysis is performed at the fault location to determine the relative angles between sequence voltages;and(2)an analysis of the impact of transmission line on the phase difference between the sequence voltages of relay and fault is conducted for different IBR controllers.Consequently,new PSM zones based on relative angles between sequence voltages are devised to facilitate accurate PSM regardless of the fault currents,resistances,or locations of IBR.Comprehensive time-domain simulations confirm the accuracy of the proposed PSM with different fault locations,resistances,types,and currents.展开更多
基金supported by the Science and Technology Project of State Grid Corporation of China(No.5100-202355765A-3-5-YS).
文摘This two-part paper presents a generic methodology for measuring the short-term voltage stability(STVS)of power systems dominated by inverter-based resources(IBRs),which introduces the concept of generalized voltage damping(GVD)for quantifying STVS from both global and local perspectives.It leads to a model-independent approach to assessing the voltage stability,the system strength,and the capability of dynamic devices to support voltage during transient process.Part I of this paper focuses on deriving the system-wise generalized voltage damping(sGVD)index and its applications.The sGVD index is defined as the decay rate of voltage-related transient energy(VTE)dissipated on the(aggregated)buses of the power system,which can be obtained using the maximum Lyapunov exponent(MLE)technique.The proposed sGVD index is theoretically demonstrated to capture the actual voltage damping of devices and to be strongly linked with STVS.These unique properties enable a model-independent approach to measuring STVS and system strength,even in the presence of heterogeneous and strongly nonlinear dynamics of IBRs.We verify the theoretical results by conducting simulations on the modified IEEE 39-bus system and two large-scale practical power systems with integration of massive renewable resources,demonstrating the effectiveness and practicality of the methodology.
基金supported by the National Key Research and Development Program of China(No.2022YFB2403100).
文摘This paper proposes a resilient restoration method for low-inertia networked microgrids(NMGs)dominated with inverter-based energy resources(IBERs).First,a frequency dynamics-aware NMG restoration model is developed,integrating a unified frequency control response framework that accommodates various control strategies while ensuring the system stability during restoration.Case studies for a low-inertia NMG demonstrate the effectiveness of the proposed method.Numerical results show that different IBER control methods could have a significant impact on restoration efficiency and economic losses.Additionally,strict frequency security requirements can predominantly increase the restoration time,calling for a critical trade-off between maintaining network security margins and restoration time for enhancing the resilience of low-inertia NMGs dominated with IBERs.
基金supported by Sustainable Energy Authority of Ireland(SEAI)by funding R.Bernal and F.Milano under project FRESLIPS(No.RDD/00681)。
文摘This paper proposes a novel control scheme for inverter-based resources(IBRs)based on the complex frequency(CF)concept.The control objective is to maintain a constant CF of voltage at the terminals of IBR by adjusting its current reference.This current is imposed based on the well-known power flow equation,the dynamics of which are calculated through estimating the CFs for the voltages of adjacent buses.The performance is evaluated by analyzing the local variations in frequency and voltage magnitude,as well as the frequency of center of inertia(CoI),and then compared with conventional frequency droop,proportional-integral(PI)voltage controllers,and virtual inertia.The case study utilizes a modified version of WSCC 9-bus system and a 1479-bus model of the Irish transmission grid and considers various contingencies and sensitivities such as the impact of current limiters,delays,noise,R/X ratio,and electromagnetic transient(EMT)dynamics.Results show that the proposed control scheme consistently outperforms the conventional controllers,leading to significant improvements in the overall dynamic response of the system.
基金supported by the National Key R&D Program of China(2021YFB2400800).
文摘Inverter-based resources(IBRs),such as wind and photovoltaic generation,are characterized by low capacity and extensive distribution,which can exacerbate the weak properties of power systems.Precise identification of weak system status is essential for ensuring the security and economic efficiency of IBR integration.This paper proposes the index of the multiple renewable short-circuit ratio(MRSCR)and its critical value calculated by the voltage(CMRSCR)to provide a comprehensive assessment of power system strength in the presence of high IBR penetration,enhancing the accuracy and reliability of system strength evaluation.First,we introduce a single-infeed equivalent model of the power system integrating multiple IBRs.We examine the factors associated with system properties that are crucial in the strength assessment process.Subsequently,the MRSCR is derived from this analysis.The MRSCR describes the connection between system strength and voltage variation caused by power fluctuations.This implies that voltage variation caused by IBR power fluctuations is more pronounced under weak grid conditions.Following this,the CMRSCR is proposed to precisely evaluate the stability boundary.The disparity between MRSCR and CMRSCR is utilized to evaluate the stability margin of the power system.Unlike a fixed value,the CMRSCR exhibits higher sensitivity as the system approaches a critical state.These indexes have been implemented in the PSD power tools and power system analysis software package,facilitating engineering calculation and analysis of bulk power systems in China.Finally,simulation results validate the effectiveness of the proposed indexes and the research findings.
文摘This work considers the problem of decentralized control of inverter-based ac micro-grid in different operation modes.The main objectives are to(i)design decentralized frequency and voltage controllers,to gather with power sharing,without information exchange between microsources(ii)design passive dynamic controllers which ensure stability of the entire microgrid system(iii)capture nonlinear,interconnected and large-scale dynamic of the micro-grid system with meshed topology as a port-Hamiltonian formulation(iv)expand the property of shifted-energy function in the context of decentralized control of ac micro-grid(v)analysis of system stability in large signal point of view.More precisely,to deal with nonlinear,interconnected and large-scale structure of micro-grid systems,the port-Hamiltonian formulation is used to capture the dynamic of micro-grid components including microsource,distribution line and load dynamics as well as interconnection controllers.Furthermore,to deal with large signal stability problem of the microgrid system in the grid-connected and islanded conditions,the shifted-Hamiltonian energy function is served as a storage function to ensure incremental passivity and stability of the microgrid system.Moreover,it is shown that the aggregating of the microgrid dynamic and the decentralized controller dynamics satisfies the incremental passivity.Finally,the effectiveness of the proposed controllers is evaluated through simulation studies.The different scenarios including grid-connected and islanded modes as well as transition between both modes are simulated.The simulation conforms that the decentralized control dynamics are suited to achieve the desired objective of frequency synchronization,voltage control and power sharing in the grid-connected and islanded modes.The simulation results demonstrate the effectiveness of the proposed control strategy.
基金Nation Natural Science Foundation of China(51377100)the Key Scientific and Technological Project of State Grid Shandong Power Company(SGSDWF00YJJS1400563).
文摘The increasing penetration of inverter-based distributed generations(DGs)significantly affects the fault characteristics of distribution networks.Fault analysis is a keystone for suitable protection scheme design.This paper presents the modelling methodology for distribution networks with inverter-based DGs and performs fault simulation based on the model.Firstly,a single inverter-based DG model based on the cascaded control structure is developed.Secondly,a simulation model of distribution network with two inverter-based DGs is established.Then,different fault simulations are performed based on the Real Time Digital Simulator(RTDS).Theoretical analyses are conducted to justify the simulation results,including the equivalent circuit of distribution networks with inverter-based DGs and the solution method for loop currents.
基金supported in part by the German academic exchange service (DAAD)and CONICET.
文摘High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,while the RES dynamic response,mainly governed by inverters,is not considered.Consequently,some relevant algorithms of transmission line protection are experiencing challenges because of the fact that magnitude and phase angle com-parison,amount of negative-sequence,and short-circuit current level are affected by the RES.Therefore,an in-depth study of this issue is necessary,one which considers the main causes and new methodological criteria solutions.This work presents an extensive literature review of the evaluation of electrical protection performance and the effects of RES connected to a power grid through inverters.Bibliographic data on many representative publications related to this topic are obtained to show the current research lines and their proposed solutions.In addition,this work identi-fies the main protection functions affected and describes the new protection schemes that consider RES.Finally,an analysis and discussion of the selected bibliography are presented.
文摘Along with the growing integration of renewable energy resources,the new power systems,which are dominated by inverter-based resources(IBRs),are facing critical challenges in both planning and operation stages.The conventionally used system strength metric,short-circuit ratio(SCR),exhibits limitations in assessing connections of new IBRs due to their unique dynamic behaviour and control interactions.In this paper,the definition of system strength is reviewed.The underlying principles of conventional SCR and its variants are then discussed,with their constraints explained.To describe the system strength in a more comprehensive way,this paper further classifies system strength into three categories:quasi-static,small-signal,and large-signal.For each category,relevant metrics are introduced and their relative merits are discussed.Electromagnetic transient simulations are presented to illustrate key insights.
基金partially supported by Korea Electrotechnology Research Institute(KERI)Primary research program through the National Research Council of Science&Technology(NST)funded by the Ministry of Science and ICT(MSIT)(No.25A01038)partially supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.RS-2024-00218377).
文摘In this paper,a strength-constrained unit commitment(UC)model incorporating system strength constraints based on the weighted short-circuit ratio(WSCR)is proposed.This model facilitates the comprehensive assessment of area-wide system strength in power systems with high inverter-based resource(IBR)penetration,thereby contributing to the mitigation of weak grid issues.Unlike traditional models,this approach considers the interactions among multiple IBRs.The UC problem is initially formulated as a mixed-integer nonlinear programming(MINLP)model,reflecting WSCR and bus impedance matrix modification constraints.To enhance computational tractability,the model is transformed into a mixed-integer linear programming(MILP)form.The effectiveness of the proposed approach is validated through simulations on the IEEE 5-bus,IEEE 39-bus,and a modified Korean power system,demonstrating the ability of the proposed UC model enhancing system strength compared to the conventional methodologies.
基金supported in part by the National Natural Science Foundation of China(No.52177093)in part by the Scientific&technical project of China Electric Power Planning&Engineering Institute(K202317).
文摘Cross-regional high voltage direct current(HVDC)systems bring remarkable renewable power injections to the receiver side of power grids.However,HVDC failures result in large disturbances to receivers and cause critical frequency security problems.High renewable energy penetration also reduces the system inertia and damping coefficients.Thus,some nodal frequency nadirs may be much lower than those calculated by the center-of-inertia(COI)and may trigger low-frequency protection.Energy storage is a promising solution for frequency-related problems.In this study,we build an energy storage planning model considering both COI and nodal frequency security constraints.The energy storage capacities and locations are determined in the planning scheme based on year-round operations.First,we carry out a year-round COI-frequency-constrained unit commitment to obtain comprehensive operation modes.Next,we propose a hybrid data-model driven approach to generate nodal frequency security constraints for extensive operation modes effectively.Finally,we achieve optimal energy storage planning with both COI and nodal frequency constraints.Case studies on a modified RTS-79 test system and a 1089-bus power system in practical in Jiangsu,China,verify the effectiveness of the proposed methods.
文摘In recent years,the increased application of inverter-based resources in power grids,along with the gradual replacement of synchronous generators,has made the grid support capability of inverters essential for maintaining system stability under large disturbances.Critical clearing time provides a quantitative measure of fault severity and system stability,and its sensitivity can help guide parameter adjustments to enhance the grid support capability of inverters.Building on previous researches,this paper proposes a method for calculating critical clearing time sensitivity in power systems with a high proportion of power electronic devices,accounting for the new dynamic characteristics introduced by these devices.The current limit and switching control of inverterbased resources are considered,and the critical clearing time sensitivity under controlling periodic orbits is derived.The proposed critical clearing time sensitivity calculation method is then validated using a double generator single load system and a modified 39-bus system.
文摘The move to Inverter-Based Renewable Resources(IBRs)is a challenge for power system protection since IBRs generate much lower fault currents than traditional synchronous generators.This compromises the operation of conventional protection relays.In order to solve this problem,the present study employs a detailed Institute of Electrical and Electronics Engineers(IEEE)9-bus model in Real Time Simulation for Computer Aided Design(RSCAD)to examine the fault behaviour at four different levels of renewable energy penetration.The investigation measures the reduction of the fault current as a result of the gradual substitution of synchronous generation by photovoltaics.The findings enable the production of different sets of relay settings for each case,thus assuring the correct functioning of protection coordination in terms of reliability and selectivity.The main point is an extensive adaptive protection concept.This thoughtful plan serves as an essential guide for the dynamic adjustment of relay settings,thus ensuring the resilience and stability of the grid during the energy transition.
文摘The increasing penetration of inverter-based resources(IBRs)and renewable energy resources poses significant challenges to the stability and controllability of modern power systems.Dynamic virtual power plants(DVPPs)have emerged as a transformative solution for aggregating and controlling heterogeneously distributed energy resources(DERs)flexibly and dynamically.This paper presents a comprehensive review of DVPPs,covering their conceptual evolution—from microgrids to virtual power plants(VPPs)and fast-acting VPPs—culminating in the dynamic DVPP paradigm.This review explores key architectural frameworks,including grid-forming and grid-following roles,as well as AC/DC interfacing strategies.Emphasis is placed on secondary frequency and voltage control mechanisms,dynamic-based and market-based disaggregation,and control methodologies tailored to DERs.
文摘This paper proposes an AI-based approach for islanding detection in active distribution networks.A review of existing AI-based studies reveals several gaps,including model complexity and stability concerns,limited accuracy in noisy conditions,and limited applicability to systems with different types of resources.To address these challenges,this paper proposes a novel approach that adapts the WaveNet generator into a classifier,enhanced with a denoising UNet model,to improve performance in varying signal-to-noise ratio(SNR)conditions.In designing this model,we deviate from state-of-the-art approaches that primarily rely on long short-term memory(LSTM)architectures by employing 1D convolutional layers.This enables the model to focus on spatial analysis of the input signal,making it particularly well-suited for processing long input sequences.Additionally,residual connections are incorporated to mitigate overfitting and significantly enhance the model’s generalizability.To verify the effectiveness of the proposed scheme,over 14000 islanding/non-islanding cases are tested,considering different load active/reactive power values,load switching transients,capacitor bank switching,fault conditions in the main grid,different load quality factors,SNR levels,changes in network topology,and both types of conventional and inverter-based sources.
基金supported by the Hong Kong Research Grant Council for the Research Project(No.15229421)the PolyU Presidential PhD Fellowship Scheme。
文摘Integration of inverter-based resources(IBRs)reshapes conventional power swing patterns,challenging the operation of legacy power swing protec-tion schemes.This paper highlights the significant con-sequences of the distinctive power swing patterns exhib-ited by grid-forming IBRs(GFM-IBRs).The swing mechanism involving GFM-IBRs is elucidated using an-alytical modeling of GFM-IBRs with various power syn-chronization loops(PSLs).With varying GFM-IBR pen-etration levels and different generator scenarios,the per-formance of power swing protection functions is examined,including power swing blocking(PSB)and out-of-step tripping(OST).Additionally,the IEEE PSRC D29 test system is employed to present power swing protection results in a large-scale power system integrated with synchronous generators(SGs)and IBRs.The results in-dicate that,GFM-IBRs with sufficient voltage support capability can provide positive impact on power swing dynamics,and power swing protection performance can be enhanced by emulating the inertia and droop mecha-nism of SGs and rapidly adjusting the active power output.However,with high penetration levels of GFM-IBRs,OST maloperation may occur in scenarios with inadequate voltage support capability.
基金supported in part by Carbon Neutrality and Energy System Transformation Projectby National Natural Science Foundation of China(No.52177093)by Organized Research Support Program,Department of Electrical Engineering,Tsinghua University.
文摘Variable renewable energy(VRE)integrated via non-synchronous inverters exhibits low inertia and fluctuating output,posing substantial frequency security challenges for future power systems.When frequency security constraints are omitted from generation planning,the resulting low-inertia generation portfolios often fail to meet critical frequency requirements.To address this issue,this paper proposes a novel frequency security constrained generation planning(FSCGP)model that leverages the frequency support potential of diverse power sources,including conventional thermal generators(CTGs),VRE units,concentrating solar power(CSP)units,and energy storage systems(ESSs).A physics-data hybrid-driven method is introduced to formulate frequency security constraints,enabling accurate representation of diverse frequency regulation characteristics,particularly the fast frequency support capabilities of inverter-based generators(IBGs).To further enhance the computational efficiency,several acceleration techniques are incorporated into the proposed FSCGP model.Case studies based on a modified IEEE RTS-79 system validate the effectiveness of the proposed FSCGP model.The numerical results identify the primary contributors to frequency security under different renewable energy penetration(REP)levels and demonstrate the cost-effectiveness of coordinating various frequency support sources,especially CSP units and IBGs,in mitigating challenges in low-inertia grids.
基金funded in part by the CURENT Research Center and in part by the National Science Foundation(NSF)(No.ECCS-2033910)。
文摘This study investigates a safe reinforcement learning algorithm for grid-forming(GFM)inverter based frequency regulation.To guarantee the stability of the inverter-based resource(IBR)system under the learned control policy,a modelbased reinforcement learning(MBRL)algorithm is combined with Lyapunov approach,which determines the safe region of states and actions.To obtain near optimal control policy,the control performance is safely improved by approximate dynamic programming(ADP)using data sampled from the region of attraction(ROA).Moreover,to enhance the control robustness against parameter uncertainty in the inverter,a Gaussian process(GP)model is adopted by the proposed algorithm to effectively learn system dynamics from measurements.Numerical simulations validate the effectiveness of the proposed algorithm.
文摘Battery energy storage systems(BESSs)need to comply with grid code and fault ride through(FRT)requirements during disturbances whether they are in charging or discharging mode.Previous literature has shown that constant charging current control of BESSs in charging mode can prevent BESSs from complying with emerging grid codes such as the German grid code under stringent unbalanced fault conditions.To address this challenge,this paper proposes a new FRTactivated dual control strategy that consists of switching from constant battery current control to constant DC-link voltage control through a positive droop structure.The results show that the strategy ensures proper DC-link voltage and current management as well as adequate control of the positive-and negative-sequence active and reactive currents according to the grid code priority.It is also shown that the proposed FRT control strategy is tolerant to initial operating conditions of BESS plant,grid code requirements,and fault severity.
基金supported by the National Natural Science Foundation of China(No.61204033) the Science and Technology Commission of Shanghai Municipality(No.13511500200)
文摘This paper presents an ultra-low power incremental ADC for biosensor interface circuits. The ADC consists of a resettable second-order delta-sigma （△ ∑） modulator core and a resettable decimation filter. Several techniques are adopted to minimize its power consumption. A feedforward path is introduced to the modulator core to relax the signal swing and linearity requirement of the integrators. A correlated-double-sampling （CDS） technique is applied to reject the offset and 1/f noise, thereby removing the integrator leakage and relaxing the gain requirement of the OTA. A simple double-tailed inverter-based fully differential OTA using a thick-oxide CMOS is proposed to operate in the subthreshold region to fulfill both an ultra-low power and a large output swing at 1.2 V supply. The signal addition before the comparator in the feedforward architecture is performed in the current domain instead of the voltage domain to minimize the capacitive load to the integrators. The capacitors used in this design are of customized metal-oxide metal （MOM） type to reach the minimum capacitance set by the k T~ C noise limit. Fabricated with a 1P6M 0.18/zm CMOS technology, the presented incremental ADC consumes 600 nW at 2 kS/s from a 1.2 V supply, and achieves 68.3 dB signal to noise and distortion ratio （SNDR） at the Nyquist frequency and an FOM of 0.14 pJ/conversion step. The core area is 100 × 120 μm^2.
基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)(No.RGPIN-2023-0368)Qatar University(No.QUCG-CENG-24/25-485)。
文摘Fault currents emanating from inverter-based resources(IBRs)are controlled to follow specific references to support the power grid during faults.However,these fault currents differ from the typical fault currents fed by synchronous generators,resulting in an improper operation of conventional phase selection methods(PSMs).In this paper,the relative angles between sequence voltages measured at the relay location are determined analytically in two stages:(1)a short-circuit analysis is performed at the fault location to determine the relative angles between sequence voltages;and(2)an analysis of the impact of transmission line on the phase difference between the sequence voltages of relay and fault is conducted for different IBR controllers.Consequently,new PSM zones based on relative angles between sequence voltages are devised to facilitate accurate PSM regardless of the fault currents,resistances,or locations of IBR.Comprehensive time-domain simulations confirm the accuracy of the proposed PSM with different fault locations,resistances,types,and currents.
