查看更多>>摘要：With more and more offshore wind power being increasingly connected to power grids,fluctuations in offshore wind speeds result in risks of high operation costs.To mitigate this problem,a risk-averse stochastic economic dispatch(ED)model of power system with multiple offshore wind farms(OWFs)is proposed in this paper.In this model,a novel Glue VaR method is used to measure the tail risk of the probability distribution of operation cost.The weighted sum of the expected operation cost and the GlueVaR is used to reflect the risk of operation cost,which can consider different risk requirements including risk aversion and risk neutrality flexibly by adjusting param-eters.Then,a risk-averse approximate dynamic programming(ADP)algorithm is designed for solving the proposed model,in which multi-period ED problem is decoupled into a series of single-period ED problems.Besides,GlueVaR is introduced into the approximate value function training process for risk aversion.Finally,a distributed and risk-averse ADP algorithm is constructed based on the alternating direction method of multipliers,which can further decouple single-period ED between transmission system and multiple OWFs for ensuring information privacy.Case studies on the modified IEEE 39-bus system with an OWF and an actual provincial power system with four OWFs demonstrate correctness and efficiency of the proposed model and algorithm.
查看更多>>摘要：Distribution systems are facing challenges in serving lifeline loads after extreme events.Network reconfiguration is a traditional and practical method for power supply restoration,which has strong but inflexible power transfer capabilities in-fluenced by network topology.Multiple failures of utility power under extreme events will further limit the efficiency of network reconfiguration.Electric buses(EBs)can be utilized to achieve power supply considering their discharging capabilities as mobile storage devices.However,the mobility of EBs and the influences of transport systems must be carefully considered to enhance the resilience of distribution systems.Reconfiguration and EBs are complementary in terms of recovery capabilities and location flexibility,and more important loads can be recovered by the coordination between EBs and network reconfiguration.This paper proposes a coordinated restoration method for EBs and reconfigurations considering the influences of transport systems.The post-disaster restoration problem is formulated as a bi-level model,in which the network topology is optimized in the upper-level aiming at maximizing restoration loads through the main grid and EBs,while the traffic paths of all EBs are optimized with the goal of maximizing the restoration loads by the EBs in the lower-level considering time consumption and energy consumption during movement.The PSO and a genetic algorithm are used to solve the proposed bi-level optimization problem.Simulation studies are performed to verify the superiority of the proposed method.
查看更多>>摘要：The stability problem of weak grid connected con-verter interfaced generation(CIG)cannot be ignored.For mul-tiple weak grid connected CIGs with different parameters,the system oscillation characteristics and equivalence methods still need to be further studied.This paper first discusses the oscilla-tion characteristics when CIGs are perfectly coupled,perfectly decoupled and their general conditions respectively.Based on the Monte Caro simulation,the number of critical eigenvalues,the participation of each CIG to critical eigenvalues and the correlative parameters to participation are analyzed.Then the single-CIG and multi-CIG equivalence methods are proposed for stations containing nonidentical CIGs.The CIG parameters of a single-CIG equivalent model are identified based on the consistency of the output admittance characteristics.According to the different participations of CIGs with critical eigenvalues,the station is equivalent to a multi-CIG model.Results of large simulation samples show that the two equivalent models can both preserve the critical eigenvalues very well,and can be used for stability analysis.Furthermore,the multi-CIG equivalent model can also very well reflect the participation of CIGs in detailed models,and can be used for damping control study.
查看更多>>摘要：This paper proposes an implicit function based open-loop analysis method to detect the subsynchronous res-onance(SSR),including asymmetric subsynchronous modal at-traction(ASSMA)and asymmetric subsynchronous modal repul-sion(ASSMR),of doubly-fed induction generator based wind farms(DFIG-WFs)penetrated power systems.As some important parameters of DFIG-WF are difficult to obtain,reinforcement learning and least squares method are applied to identify those important parameters.By predicting the location of closed-loop subsynchronous oscillation(SSO)modes based on the calculation of partial differentials of characteristic equation,both ASSMA and ASSMR can be found.The proposed method in this paper can select SSO modes which move to the right half complex planes as control parameters change.Besides,the proposed open-loop analysis method is adaptive to parameter uncertainty.Simulation studies are carried out on the 4-machine 11-bus power system to verify properties of the proposed method.
查看更多>>摘要：With the advancements in voltage source converter(VSC)technology,VSC based high voltage direct current(VSC-HVDC)systems provide system operators with a prospective approach to enhance system operating stability and resilience.In addition to long-distance transmission,the VSC-HVDC system can also provide multiple ancillary services,such as frequency regulation,due to its power controllability.However,if a time delay exists in the control signal,the VSC-HVDC system may bring destabilizing influences to the system,which will decrease the system resilience under the disturbance.In order to reduce control deviation caused by time delay,in this paper,a small signal model is first conducted to analyze the impact of time delay on system stability.Then a time-delay correction control strategy for HVDC frequency regulation control is developed to reduce the influence of the time delay.The control performance of the proposed time-delay correction control is verified both in the established small signal model and the runtime simulation in a modified IEEE 39 bus system.The results indicate that the proposed time-delay correction control strategy shows significant improvement in system stability.
查看更多>>摘要：This paper investigates integration of distributed energy resources(DERs)in microgrids(MGs)through two-stage power conversion structures consisting of DC-DC boost converter and DC-AC voltage source converter(VSC)subsystems.In con-trast to existing investigations that treated DC-link voltage as an ideal constant voltage,this paper considers the non-ideal dynamic coupling between both subsystems for completeness and higher accuracy,which introduces additional DC-side dynamics to the VSC.The analysis shows parameters of the boost converter's power model that impact stability through the DC-link.Carefully selecting these parameters can mitigate this effect on stability and improve dynamic performance across the DC-link.Hence,an optimization framework is developed to facilitate in selecting adequate boost converter parameters in designing a stable voltage source converter-based microgrid(VSC-MG).The developed optimization framework,based on particle swarm optimization,considers dynamic coupling between both subsystems and is also effective in avoiding inadequate boost converter parameters capable of propagating instability through the DC-link to the VSC.Simulations are performed with MATLAB/Simulink to validate theoretical analyses.
查看更多>>摘要：This paper focuses on synchronization stability anal-ysis of the power system,in which power electronics are synchro-nized by the phase-locked loop(PLL).It provides new insight into the synchronization stability of power electronics from the voltage perspective.The synchronization stability analysis based on space vector is carried out by establishing a simplified model of the grid-connected voltage source converter(VSC)system.Without complex mathematical calculation,the existence criterion of equilibrium points and the criterion of transient instability dominated by the unstable equilibrium point(UEP)are derived,respectively.With the proposed method,synchronization stability can be determined by the voltage space vectors,which are more observable in potential engineering applications.At the end of this study,the steps of the synchronization stability determination by voltage space vectors are summarized,and the effectiveness and applicability of the proposed method are demonstrated by numerical simulations performed on the PSCAD/EMTDC platform.
查看更多>>摘要：The coordinated control of parallel three-phase four-wire converters in autonomous AC microgrids is investigated in this paper.First,based on droop control,virtual impedance is inserted in positive-,negative-and zero-sequences to enhance system damping and imbalance power sharing.Then,to fa-cilitate virtual impedance design,small signal models of the three-sequence equivalent circuits are established respectively.Corresponding indexes are proposed to comprehensively evaluate the impact of sequence virtual impedance on current sharing accuracy,voltage quality at the point of common coupling(PCC)and system stability.In addition,constraint of DC-link voltage is also considered to avoid over modulation when subjected to unbalanced loads.Furthermore,to address the PCC voltage degradation resulting from virtual impedance,a voltage imbalance compensation method,based on low-bandwidth com-munication,is proposed.Finally,simulation and experimental results are provided to verify the correctness of the theory model,indicating that the proposed method can achieve PCC voltage restoration while guaranteeing the current sharing accuracy with desirable dynamics.
查看更多>>摘要：For dq control strategies in single-phase pulse width modulation(PWM)converters,the β-axis current must be cre-ated by imaginary axis current estimation(IACE)methods.The estimated error of the β-axis current during the transient process causes d-q axis current loops to be incompletely decoupled,thereby affecting the dynamic performance of the current loop.The second-order generalized integrator(SOGI)method suffers from slow dynamic response.The fictive-axis emulation(FAE)method provides fast dynamic response but it is sensitive to circuit parameters.A reference-input(RI)-based IACE method is proposed to overcome the above shortcomings.According to the characteristic that the β-axis current loop has no transient process,the β-axis current is estimated by the d-q axis reference inputs.This is equivalent to introducing the β-axis reference input as a feedforward term into the d-q axis current loop,so the parameter sensitivity problem is solved,and the parameter tuning is not needed.The proposed method can maintain good steady-state performance and significantly improve the dynamic perfor-mance of the current loop.Furthermore,it is straightforward and can be easily implemented in digital controllers.Comprehensive hardware-in-the-loop(HIL)experimental comparisons with the SOGI and FAE methods have been conducted to verify the correctness and effectiveness of the proposed RI-based IACE method.
查看更多>>摘要：The small-signal stability of multi-terminal high voltage direct current(HVDC)systems has become one of the vital issues in modern power systems.Interactions among voltage source converters(VSCs)have a significant impact on the stability of the system.This paper proposes an interaction quantification method based on the self-/en-stabilizing coefficients of the general N-terminal HVDC system with a weak AC network connection.First,we derive the explicit formulae of self-/en-stabilizing coef-ficients for any N-terminal HVDC system,which can quantify the interactions through different paths analytically.The relation between the self-/en-stabilizing coefficients and the poles of the system can be used to evaluate the impact of the interactions on the system stability effectively.Then,we employ the obtained formulae to analyze the parameter sensitivity and explain how a parameter affects the stability of the system through different paths of interactions.Finally,extensive examples are given to demonstrate the effectiveness of the proposed method.
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