The voltage source converter based high voltage direct current(VSC-HVDC)system is based on voltage source converter,and its control system is more complex.Also affected by the fast control of power electronics,oscilla...The voltage source converter based high voltage direct current(VSC-HVDC)system is based on voltage source converter,and its control system is more complex.Also affected by the fast control of power electronics,oscillation phenomenon in wide frequency domain may occur.To address the problem of small signal stability of the VSCHVDC system,a converter control strategy is designed to improve its small signal stability,and the risk of system oscillation is reduced by attaching a damping controller and optimizing the control parameters.Based on the modeling of the VSC-HVDC system,the general architecture of the inner and outer loop control of the VSCHVDC converter is established;and the damping controllers for DC control and AC control are designed in the phase-locked loop and the inner and outer loop control parts respectively;the state-space statemodel of the control system is established to analyze its performance.And the electromagnetic transient simulation model is built on the PSCAD/EMTDC simulation platform to verify the accuracy of the small signal model.The influence of the parameters of each control part on the stability of the system is summarized.The main control parts affecting stability are optimized for the phenomenon of oscillation due to changes in operation mode occurring on the AC side due to faults and other reasons,which effectively eliminates system oscillation and improves system small signal stability,providing a certain reference for engineering design.展开更多
Since the voltage source converter based high voltage direct current(VSC-HVDC)systems owns the features of nonlinearity,strong coupling and multivariable,the classical proportional integral(PI)control is hard to obtai...Since the voltage source converter based high voltage direct current(VSC-HVDC)systems owns the features of nonlinearity,strong coupling and multivariable,the classical proportional integral(PI)control is hard to obtain content control effect.Hence,a new perturbation observer based fractional-order PID(PoFoPID)control strategy is designed in this paper for(VSC-HVDC)systems with offshore wind integration,which can efficiently boost the robustness and control performance of entire system.Particularly,it employs a fractional-order PID(FoPID)fra-mework for the sake of compensating the perturbation estimate,which dramatically boost the dynamical responds of the closed-loop system,and the cooperative beetle antennae search(CBAS)algorithm is adopted to quickly and effi-ciently search its best control parameters.Besides,CBAS algorithm is able to efficiently escape a local optimum because of a suitable trade-off between global exploration and local exploitation can be realized.At last,comprehensive case studies are carried out,namely,active and reactive power tracking,5-cycle line-line-line-ground(LLLG)fault,and offshore wind farm integration.Simulation results validate superiorities and effectiveness of PoFoPID control in com-parison of that of PID control and feedback linearization sliding-mode control(FLSMC),respectively.展开更多
With the continuous development of power electronic devices,intelligent control systems,and other technologies,the voltage level and transmission capacity of voltage source converter (VSC)-high-voltage direct current ...With the continuous development of power electronic devices,intelligent control systems,and other technologies,the voltage level and transmission capacity of voltage source converter (VSC)-high-voltage direct current (HVDC) technology will continue to increase,while the system losses and costs will gradually decrease.Therefore,it can be foreseen that VSC-HVDC transmission technology will be more widely applied in future large-scale renewable energy development projects.Adopting VSC-HVDC transmission technology can be used to overcome issues encountered by large-scale renewable energy transmission and integration projects,such as a weak local power grid,lack of support for synchronous power supply,and insufficient accommodation capacity.However,this solution also faces many technical challenges because of the differences between renewable energy and traditional synchronous power generation systems.Based on actual engineering practices that are used worldwide,this article analyzes the technical challenges encountered by integrating large-scale renewable energy systems that adopt the use of VSC-HVDC technology,while aiming to provide support for future research and engineering projects related to VSC-HVDC-based large-scale renewable energy integration projects.展开更多
The fault recovery of VSC-HVDC transmission system is often influenced by many factors, such as the reactive power compensation characteristics of the inverter and the dynamic performance of DC controllers. In this pa...The fault recovery of VSC-HVDC transmission system is often influenced by many factors, such as the reactive power compensation characteristics of the inverter and the dynamic performance of DC controllers. In this paper, the PSCAD/ EMTDC simulation tool is used to study the dynamic recovery performance of VSC-HVDC system for several different var compensating devices in VSC-HVDC inverter-Fixed capacitor (FC), Static Var compensator (SVC), and Static synchronous compensator (STATCOM) when VSC-HVDC is subject to various faults, including three phase groundings, single phase grounding and three phase breakings. The result shows that the recovery process of the whole system will be slowed down due to its negative influence on the strength of AC power system with the application of SVC, while the STATCOM can improve VSC-HVDC recovery performance greatly for its advantages over other compensating devices in areas such as voltage support ability and DC power recovery.展开更多
电压源型直流输电系统(voltage source converter based high voltage direct current,VSC-HVDC)并入弱交流电网可能产生振荡失稳现象,严重威胁电力系统安全稳定运行。VSC-HVDC结构日渐复杂,系统中同时存在多种控制策略,针对多端、多控...电压源型直流输电系统(voltage source converter based high voltage direct current,VSC-HVDC)并入弱交流电网可能产生振荡失稳现象,严重威胁电力系统安全稳定运行。VSC-HVDC结构日渐复杂,系统中同时存在多种控制策略,针对多端、多控制策略下VSC-HVDC的稳定特性还需深入研究。针对上述问题,以定直流电压/定功率混合控制的双受端VSC-HVDC系统为研究对象,探讨了系统在不同电网条件下的稳定特性。首先,分别推导了定直流电压/定功率控制策略VSC-HVDC子系统的数学模型和小信号模型,依据交直流拓扑关系构建混合控制策略下的全系统模型;其次,搭建双受端VSC-HVDC系统电磁暂态模型验证了不同运行工况下小信号模型的准确性;最后,分析了交流系统强度及联络线长度对双受端VSC-HVDC系统稳定性的影响,获得了定直流电压/定功率VSC-HVDC系统所能接受的最小电网强度,形成了系统安全稳定运行空间,并且基于MATLAB/Simulink时域仿真验证了理论分析的正确性。展开更多
When multiple LCC-HVDC transmission lines are densely fed into a receiving AC system,voltage dips can easily propagate in the power system,resulting in multiple LCC commutation failures simultaneously.The VSC-HVDC can...When multiple LCC-HVDC transmission lines are densely fed into a receiving AC system,voltage dips can easily propagate in the power system,resulting in multiple LCC commutation failures simultaneously.The VSC-HVDC can be used to divide the receiving sys-tem into several interconnected sub-partitions and improve the voltage support capability of the receiving system.Compared with asyn-chronous interconnection,which completely separates the receiving systems with VSC-HVDC,incomplete segmentation with an AC connection is a more pertinent segmenting method for multilayer complex regional power grids.To analyze the voltage support capability of the VSC in incomplete segmentation,a micro-incremental model of the VSC was established,the operating impedance of the VSC was calculated,and the voltage support function of the VSC was quantified.The effect of the fault on the system short-circuit capacity was analyzed,and a calculation method for the multi-infeed short-circuit ratio in an incompletely segmented scenario was obtained.A VSC-segmented model of a two-infeed DC system was built on the EMTDC/PSCAD simulation platform,and the validity of the micro-increment model and accuracy of the proposed conclusions were verified.展开更多
Traditional protection methods are not suitable for hybrid(cable and overhead)transmission lines in voltage source converter based high-voltage direct current(VSC-HVDC)systems.Accordingly,this paper presents the robus...Traditional protection methods are not suitable for hybrid(cable and overhead)transmission lines in voltage source converter based high-voltage direct current(VSC-HVDC)systems.Accordingly,this paper presents the robust fault detection,classification,and location based on the empirical wavelet transform-Teager energy operator(EWT-TEO)and artificial neural network(ANN)for hybrid transmission lines in VSC-HVDC systems.The operational scheme of the proposed protection method consists of two loops①an EWT-TEO based feature extraction loop,②and an ANN-based fault detection,classification,and location loop.Under the proposed protection method,the voltage and current signals are decomposed into several sub-passbands with low and high frequencies using the empirical wavelet transform(EWT)method.The energy content extracted by the EWT is fed into the ANN for fault detection,classification,and location.Various fault cases,including the high-impedance fault(HIF)as well as noises,are performed to train the ANN with two hidden layers.The test system and signal decomposition are conducted by PSCAD/EMTDC and MATLAB,respectively.The performance of the proposed protection method is compared with that of the traditional non-pilot traveling wave(TW)based protection method.The results confirm the high accuracy of the proposed protection method for hybrid transmission lines in VSC-HVDC systems,where a mean percentage error of approximately 0.1%is achieved.展开更多
Under weak grid conditions,grid impedance is coupled with a control system for voltage source converter based high-voltage direct current(VSC-HVDC)systems,resulting in decreased synchronization stability.Unfortunately...Under weak grid conditions,grid impedance is coupled with a control system for voltage source converter based high-voltage direct current(VSC-HVDC)systems,resulting in decreased synchronization stability.Unfortunately,most studies are based on the assumption that impedance ratio(R/X)is sufficiently small to ignore the effects of grid impedance.In this study,we establish a dynamic coupling model that includes grid impedance and control loops,revealing the influence mechanism of R/X on synchronization stability from a physical perspective.We also quantify the stability range of R/X in the static analysis model and introduce a sensitivity factor to measure its effect on voltage stability.Additionally,we utilize a dynamic analysis model to evaluate power angle convergence,proposing a corresponding stability criterion.We then present a method of synchronous voltage reconstruction aimed at enhancing the grid strength.Theoretical analysis shows that this method can effectively mitigate the effects of coupling between grid impedance and the controller under weak grid conditions,ensuring stable operation even under extremely weak grid conditions.Experiments validate the accuracy and effectiveness of the analysis and method.展开更多
针对光伏发电与电压源换流器高压直流输电(voltagesource converter-high voltage direct current,VSC-HVDC)系统直流电压等级不匹配问题,提出了一种新的光伏电站经VSC-HVDC并网拓扑和控制策略,研究了该并网方案中光伏电站的运行特性,...针对光伏发电与电压源换流器高压直流输电(voltagesource converter-high voltage direct current,VSC-HVDC)系统直流电压等级不匹配问题,提出了一种新的光伏电站经VSC-HVDC并网拓扑和控制策略,研究了该并网方案中光伏电站的运行特性,分析了单个光伏发电单元的控制策略和串联光伏发电单元支路故障控制策略;针对该拓扑结构中串联光伏发电单元效率易受不均匀辐照度影响的问题,提出了改进的电压源换流器(voltage source converter,VSC)直流侧电压斜率控制策略。在几种典型辐射情况下进行仿真,结果验证了所提控制策略的有效性,表明该方案可解决VSC-HVDC技术应用于光伏发电并网所面临的电压等级匹配问题。展开更多
基金supported by Research on the Oscillation Mechanism and Suppression Strategy of Yu-E MMC-HVDC Equipment and System(2021Yudian Technology 33#).
文摘The voltage source converter based high voltage direct current(VSC-HVDC)system is based on voltage source converter,and its control system is more complex.Also affected by the fast control of power electronics,oscillation phenomenon in wide frequency domain may occur.To address the problem of small signal stability of the VSCHVDC system,a converter control strategy is designed to improve its small signal stability,and the risk of system oscillation is reduced by attaching a damping controller and optimizing the control parameters.Based on the modeling of the VSC-HVDC system,the general architecture of the inner and outer loop control of the VSCHVDC converter is established;and the damping controllers for DC control and AC control are designed in the phase-locked loop and the inner and outer loop control parts respectively;the state-space statemodel of the control system is established to analyze its performance.And the electromagnetic transient simulation model is built on the PSCAD/EMTDC simulation platform to verify the accuracy of the small signal model.The influence of the parameters of each control part on the stability of the system is summarized.The main control parts affecting stability are optimized for the phenomenon of oscillation due to changes in operation mode occurring on the AC side due to faults and other reasons,which effectively eliminates system oscillation and improves system small signal stability,providing a certain reference for engineering design.
基金the National Natural Science Foundation of China(51807085).
文摘Since the voltage source converter based high voltage direct current(VSC-HVDC)systems owns the features of nonlinearity,strong coupling and multivariable,the classical proportional integral(PI)control is hard to obtain content control effect.Hence,a new perturbation observer based fractional-order PID(PoFoPID)control strategy is designed in this paper for(VSC-HVDC)systems with offshore wind integration,which can efficiently boost the robustness and control performance of entire system.Particularly,it employs a fractional-order PID(FoPID)fra-mework for the sake of compensating the perturbation estimate,which dramatically boost the dynamical responds of the closed-loop system,and the cooperative beetle antennae search(CBAS)algorithm is adopted to quickly and effi-ciently search its best control parameters.Besides,CBAS algorithm is able to efficiently escape a local optimum because of a suitable trade-off between global exploration and local exploitation can be realized.At last,comprehensive case studies are carried out,namely,active and reactive power tracking,5-cycle line-line-line-ground(LLLG)fault,and offshore wind farm integration.Simulation results validate superiorities and effectiveness of PoFoPID control in com-parison of that of PID control and feedback linearization sliding-mode control(FLSMC),respectively.
基金State Grid Corporation of China Science and Technology Project: Research on Power Transmission of Largescale Renewable Energy Base by VSC-LCC hybrid HVDC(No. NY71-19-037)
文摘With the continuous development of power electronic devices,intelligent control systems,and other technologies,the voltage level and transmission capacity of voltage source converter (VSC)-high-voltage direct current (HVDC) technology will continue to increase,while the system losses and costs will gradually decrease.Therefore,it can be foreseen that VSC-HVDC transmission technology will be more widely applied in future large-scale renewable energy development projects.Adopting VSC-HVDC transmission technology can be used to overcome issues encountered by large-scale renewable energy transmission and integration projects,such as a weak local power grid,lack of support for synchronous power supply,and insufficient accommodation capacity.However,this solution also faces many technical challenges because of the differences between renewable energy and traditional synchronous power generation systems.Based on actual engineering practices that are used worldwide,this article analyzes the technical challenges encountered by integrating large-scale renewable energy systems that adopt the use of VSC-HVDC technology,while aiming to provide support for future research and engineering projects related to VSC-HVDC-based large-scale renewable energy integration projects.
文摘The fault recovery of VSC-HVDC transmission system is often influenced by many factors, such as the reactive power compensation characteristics of the inverter and the dynamic performance of DC controllers. In this paper, the PSCAD/ EMTDC simulation tool is used to study the dynamic recovery performance of VSC-HVDC system for several different var compensating devices in VSC-HVDC inverter-Fixed capacitor (FC), Static Var compensator (SVC), and Static synchronous compensator (STATCOM) when VSC-HVDC is subject to various faults, including three phase groundings, single phase grounding and three phase breakings. The result shows that the recovery process of the whole system will be slowed down due to its negative influence on the strength of AC power system with the application of SVC, while the STATCOM can improve VSC-HVDC recovery performance greatly for its advantages over other compensating devices in areas such as voltage support ability and DC power recovery.
文摘电压源型直流输电系统(voltage source converter based high voltage direct current,VSC-HVDC)并入弱交流电网可能产生振荡失稳现象,严重威胁电力系统安全稳定运行。VSC-HVDC结构日渐复杂,系统中同时存在多种控制策略,针对多端、多控制策略下VSC-HVDC的稳定特性还需深入研究。针对上述问题,以定直流电压/定功率混合控制的双受端VSC-HVDC系统为研究对象,探讨了系统在不同电网条件下的稳定特性。首先,分别推导了定直流电压/定功率控制策略VSC-HVDC子系统的数学模型和小信号模型,依据交直流拓扑关系构建混合控制策略下的全系统模型;其次,搭建双受端VSC-HVDC系统电磁暂态模型验证了不同运行工况下小信号模型的准确性;最后,分析了交流系统强度及联络线长度对双受端VSC-HVDC系统稳定性的影响,获得了定直流电压/定功率VSC-HVDC系统所能接受的最小电网强度,形成了系统安全稳定运行空间,并且基于MATLAB/Simulink时域仿真验证了理论分析的正确性。
基金supported by the State Grid Science and Technology Project 5108-202218280A-2-87-XG.
文摘When multiple LCC-HVDC transmission lines are densely fed into a receiving AC system,voltage dips can easily propagate in the power system,resulting in multiple LCC commutation failures simultaneously.The VSC-HVDC can be used to divide the receiving sys-tem into several interconnected sub-partitions and improve the voltage support capability of the receiving system.Compared with asyn-chronous interconnection,which completely separates the receiving systems with VSC-HVDC,incomplete segmentation with an AC connection is a more pertinent segmenting method for multilayer complex regional power grids.To analyze the voltage support capability of the VSC in incomplete segmentation,a micro-incremental model of the VSC was established,the operating impedance of the VSC was calculated,and the voltage support function of the VSC was quantified.The effect of the fault on the system short-circuit capacity was analyzed,and a calculation method for the multi-infeed short-circuit ratio in an incompletely segmented scenario was obtained.A VSC-segmented model of a two-infeed DC system was built on the EMTDC/PSCAD simulation platform,and the validity of the micro-increment model and accuracy of the proposed conclusions were verified.
文摘Traditional protection methods are not suitable for hybrid(cable and overhead)transmission lines in voltage source converter based high-voltage direct current(VSC-HVDC)systems.Accordingly,this paper presents the robust fault detection,classification,and location based on the empirical wavelet transform-Teager energy operator(EWT-TEO)and artificial neural network(ANN)for hybrid transmission lines in VSC-HVDC systems.The operational scheme of the proposed protection method consists of two loops①an EWT-TEO based feature extraction loop,②and an ANN-based fault detection,classification,and location loop.Under the proposed protection method,the voltage and current signals are decomposed into several sub-passbands with low and high frequencies using the empirical wavelet transform(EWT)method.The energy content extracted by the EWT is fed into the ANN for fault detection,classification,and location.Various fault cases,including the high-impedance fault(HIF)as well as noises,are performed to train the ANN with two hidden layers.The test system and signal decomposition are conducted by PSCAD/EMTDC and MATLAB,respectively.The performance of the proposed protection method is compared with that of the traditional non-pilot traveling wave(TW)based protection method.The results confirm the high accuracy of the proposed protection method for hybrid transmission lines in VSC-HVDC systems,where a mean percentage error of approximately 0.1%is achieved.
基金supported in part by the National Natural Science Foundation of China(No.52077037)in part by the Science and Technology Projects of Jiangsu Province(No.BE2022016).
文摘Under weak grid conditions,grid impedance is coupled with a control system for voltage source converter based high-voltage direct current(VSC-HVDC)systems,resulting in decreased synchronization stability.Unfortunately,most studies are based on the assumption that impedance ratio(R/X)is sufficiently small to ignore the effects of grid impedance.In this study,we establish a dynamic coupling model that includes grid impedance and control loops,revealing the influence mechanism of R/X on synchronization stability from a physical perspective.We also quantify the stability range of R/X in the static analysis model and introduce a sensitivity factor to measure its effect on voltage stability.Additionally,we utilize a dynamic analysis model to evaluate power angle convergence,proposing a corresponding stability criterion.We then present a method of synchronous voltage reconstruction aimed at enhancing the grid strength.Theoretical analysis shows that this method can effectively mitigate the effects of coupling between grid impedance and the controller under weak grid conditions,ensuring stable operation even under extremely weak grid conditions.Experiments validate the accuracy and effectiveness of the analysis and method.
文摘针对光伏发电与电压源换流器高压直流输电(voltagesource converter-high voltage direct current,VSC-HVDC)系统直流电压等级不匹配问题,提出了一种新的光伏电站经VSC-HVDC并网拓扑和控制策略,研究了该并网方案中光伏电站的运行特性,分析了单个光伏发电单元的控制策略和串联光伏发电单元支路故障控制策略;针对该拓扑结构中串联光伏发电单元效率易受不均匀辐照度影响的问题,提出了改进的电压源换流器(voltage source converter,VSC)直流侧电压斜率控制策略。在几种典型辐射情况下进行仿真,结果验证了所提控制策略的有效性,表明该方案可解决VSC-HVDC技术应用于光伏发电并网所面临的电压等级匹配问题。
