查看更多>>摘要：The equivalent impedance parameters of loads have been widely used to identify and locate the harmonic sources.However,the existing calculation methods suffer from outliers caused by the zero-crossing of the denominator.These outliers can result in inaccuracy and unreliability of harmonic source location.To address this issue,this paper proposes an in-novative method of equivalent impedance parameter calculation of three-phase symmetrical loads that avoid outliers.The cor-rectness and effectiveness of the proposed method are verified by simulations on Simulink using actual monitoring data.The results show that the proposed method is not only simple and easy to implement but also highly accurate.
查看更多>>摘要：As the proportion of renewable energy(RE)in-creases,the inertia and the primary frequency regulation(FR)capability of the power system decrease.Thus,ensuring fre-quency security in the scheduling model has become a new tech-nical requirement in power systems with a high share of RE.Due to a shortage of conventional synchronous generators,the frequency support of multi-source converters has become an in-dispensable part of the system frequency resources,especially variable-speed wind turbine generation(WTG)and battery en-ergy storage(BES).Quantitative expression of the FR capabili-ty of multi-source converters is necessary to construct frequen-cy-constrained scheduling model.However,the frequency sup-port performance of these converter-interfaced devices is relat-ed to their working states,operation modes,and parameters,and the complex coupling of these factors has not been fully ex-ploited in existing models.In this study,we propose an integrat-ed frequency-constrained scheduling model considering the co-ordination of FR capabilities from multi-source converters.Switchable FR control strategies and variable FR parameters for WTG with or without reserved power are modeled,and multi-target allocation of BES capacity between tracking dis-patch instruction and emergency FR is analyzed.Then,the vari-able FR capabilities of WTG and BES are embedded into the integrated frequency-constrained scheduling model.The nonlin-ear constraints for frequency security are precisely linearized through an improved iteration-based strategy.The effectiveness of the proposed model is verified in a modified IEEE 24-bus standard system.The results suggest that the coordinated par-ticipation of BES and WTG in FR can effectively reduce the cost of the scheduling model while meeting frequency security constraints.
查看更多>>摘要：Frequency regulation of voltage source converter-based multi-terminal high-voltage direct current(VSC-MTDC)system with offshore wind farms enhances the frequency stabili-ty by compensating the power for a disturbed AC system.How-ever,it is difficult to reasonably allocate frequency-regulation resources due to a lack of coordination mechanisms between wind farms and the MTDC system.Moreover,it is difficult for the frequency control of the wind farms to manage changes in wind speed;and the risk of wind-turbine stalls is high.Thus,based on the kinetic energy of wind turbines and the power margin of the converters,the frequency-regulation capability of wind turbines is evaluated,and a dynamic frequency-support scheme considering the real-time frequency-support capability of the wind turbines and system frequency evolution is pro-posed to improve the frequency-support performance.A power adaptation technique at variable wind speeds is developed;the active power in the frequency-support stage and restoration stage is switched according to the wind speed.A hierarchical zoning frequency-regulation scheme is designed to use the fre-quency-regulation resources of different links in the MTDC sys-tem with wind farms.The simulation results show that the nov-el frequency-regulation strategy maintains frequency stability with wind-speed changes and avoids multiple frequency dips.
查看更多>>摘要：Line commutated converter based high-voltage di-rect-current(LCC-HVDC)transmissions are prone to harmonic oscillation under weak grids.Impedance modeling is an effec-tive method for assessing interaction stability.Firstly,this paper proposes an improved calculation method for the DC voltage and AC currents of commutation stations to address the com-plex linearization of the commutation process and constructs an overall harmonic state-space(HSS)model of an LCC-HVDC.Based on the HSS model,the closed-loop AC impedances on the LCC-HVDC sending and receiving ends are then derived and verified.The impedance characteristics of the LCC-HVDC are then analyzed to provide a physical explanation for the harmon-ic oscillation of the system.The effects of the grid strength and control parameters on system stability are also analyzed.To im-prove the impedance characteristics and operating stability of the LCC-HVDC system,a virtual impedance based stability en-hancement control is proposed,and a parameter design method is considered to ensure satisfactory phase margins at both the sending and receiving ends.Finally,simulation results are pre-sented to verify the validity of the impedance model and virtual impedance based stability enhancement control.
查看更多>>摘要：With the rapid development of renewable energy,wind-thermal-bundled power transmission by line-commutated converter based high-voltage direct current(LCC-HVDC)sys-tems has been widely developed.The dynamic interaction mech-anisms among permanent magnet synchronous generators(PMSGs),synchronous generators(SGs),and LCC-HVDC sys-tem become complex.To deal with this issue,a path analysis method(PAM)is proposed to study the dynamic interaction mechanism,and the damping reconstruction is used to analyze the damping characteristic of the system.First,based on the modular modeling,linearized models for the PMSG subsystem,the LCC-HVDC subsystem,and the SG subsystem are estab-lished.Second,based on the closed-loop transfer function dia-gram of the system,the disturbance transfer path and coupling relationship among subsystems are analyzed by the PAM,and the damping characteristic analysis of the SG-dominated oscilla-tion mode is studied based on the damping reconstruction.Compared with the PAM,the small-signal model of the system is obtained and eigenvalue analysis results are presented.Then,the effect of the control parameters on the damping characteris-tic is analyzed and the conclusions are verified by time-domain simulations.Finally,the penalty functions of the oscillation modes and decay modes are taken as the objective function,and an optimization strategy based on the Monte Carlo method is proposed to solve the parameter optimization problem.Nu-merical simulation results are presented to validate the effective-ness of the proposed strategy.
查看更多>>摘要：Given large-scale modern power systems with pow-er electronic converters,the numerical simulation with subsyn-chronous oscillation(SSO)faces great challenges in engineering practice due to sharply enlarged modeling scale and high com-putational burden.To reduce the modeling scale,network parti-tion and equivalent becomes a vital technique in numerical sim-ulations.Although several methods have been developed for net-work equivalent,a generally accepted rule for network parti-tion is still required.This paper proposes that the system can be partitioned into three parts,i.e.,the internal,the middle,and the external subsystems,in which the internal subsystem consists of all power electronic components,the middle subsys-tem includes those selected AC dynamic components with de-tailed models,and the remaining components and buses consti-tute the external subsystem.The external subsystem is further represented by an equivalent RLC network determined by the frequency dependent network equivalent(FDNE)method.In the proposed method,the observability index and the electrical distance index are used to identify the interface between the middle and the external subsystems.Case studies based on a modified Hydro-Quebec system are used to verify the efTective-ness of the proposed method.
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