This study analyzes the stability and reactive characteristics of the hybrid offshore wind farm that includes gridforming(GFM)and grid-following(GFL)wind turbines(WTs)integrated with a diode rectifier unit(DRU)based h...This study analyzes the stability and reactive characteristics of the hybrid offshore wind farm that includes gridforming(GFM)and grid-following(GFL)wind turbines(WTs)integrated with a diode rectifier unit(DRU)based high-voltage direct current(HVDC)system.The determination method for the proportion of GFM WTs is proposed while considering system stability and optimal offshore reactive power constraints.First,the small-signal stability is studied based on the developed linear model,and crucial factors that affect the stability are captured by eigenvalue analysis.The reactive power-frequency compensation control of GFM WTs is then proposed to improve the reactive power and frequency dynamics.Second,the relationship between offshore reactive power imbalance and the effectiveness of GFM capability is analyzed.Offshore reactive power optimization methods are next proposed to diminish offshore reactive load.These methods include the optimal design for the reactive capacity of the AC filter and the reactive power compensation control of GFL WTs.Third,in terms of stability and optimal offshore reactive power constraints,the principle and calculation method for determining the proportion of GFM WTs are proposed,and the critical proportion of GFM WTs is determined over the full active power range.Finally,case studies using a detailed model are conducted by timedomain simulations in PSCAD/EMTDC.The simulations verify the theoretical analysis results and the effectiveness of the proposed determination method for the proportion of GFM WTs and reactive power optimization methods.展开更多
With the rapid development of large-scale offshore wind farms,efficient and reliable power transmission systems are urgently needed.Hybrid high-voltage direct current(HVDC)configurations combining a diode rectifier un...With the rapid development of large-scale offshore wind farms,efficient and reliable power transmission systems are urgently needed.Hybrid high-voltage direct current(HVDC)configurations combining a diode rectifier unit(DRU)and a modular multilevel converter(MMC)have emerged as a promising solution,offering advantages in cost-effectiveness and control capability.However,the uncontrollable nature of the DRU poses significant challenges for systemstability under offshore AC fault conditions,particularly due to its inability to provide fault current or voltage support.This paper investigates the offshore AC fault characteristics and fault ride-through(FRT)strategy of a hybrid offshore wind power transmission system based on a diode rectifier unit DRU and MMC.First,the dynamic response of the hybrid system under offshore symmetrical three-phase faults is analyzed.It is demonstrated that due to the unidirectional conduction nature of the DRU,its AC current rapidly drops to zero during faults,and the fault current is solely contributed by the wind turbine generators(WTGs)and wind farm MMC(WFMMC).Based on this analysis,a coordinated FRT strategy is proposed,which combines a segmented current limiting control for the wind-turbine(WT)grid-side converters(GSCs)and a constant AC current control for the WFMMC.The strategy ensures effective voltage support during the fault and prevents MMC current saturation during fault recovery,enabling fast and stable system restoration.Electromagnetic transient simulations in PSCAD/EMTDC verify the feasibility of the proposed fault ride-through strategy.展开更多
Diode rectifier unit(DRU)-based high-voltage direct current(HVDC)transmissionsystems areeffectivein achieving the stableandeconomical operation of offshore wind-powergeneration.Considering theuncontrollable characteri...Diode rectifier unit(DRU)-based high-voltage direct current(HVDC)transmissionsystems areeffectivein achieving the stableandeconomical operation of offshore wind-powergeneration.Considering theuncontrollable characteristicsof DRUs,a grid-forming(GFM)strategy forwind-turbine converters isnecessary to support offshore AC voltageand frequency.However,the active power-synchronization control in traditional GFM converters is unsuitable for DRU-based GFM converters.Thus,the stability issue for DRU-based HVDC systems involving DRU-based GFM and grid-following(GFL)converters has not yet been addressed.To solve these issues,this study begins with the characteristics of a DRU-based HVDC system and presents a control scheme for DRU-based GFM converters for power synchronization.Subsequently,the dq-frame impedance model of the DRU-based GFM converteris proposed for the stability analysis of the entire HVDC system.Finally,a simulation platform is built to verify the model accuracy and system stability.展开更多
基金supported by the Research Project of China Southern Power Grid Co.,Ltd.(No.030400KK52220008(GDKJXM20220327))。
文摘This study analyzes the stability and reactive characteristics of the hybrid offshore wind farm that includes gridforming(GFM)and grid-following(GFL)wind turbines(WTs)integrated with a diode rectifier unit(DRU)based high-voltage direct current(HVDC)system.The determination method for the proportion of GFM WTs is proposed while considering system stability and optimal offshore reactive power constraints.First,the small-signal stability is studied based on the developed linear model,and crucial factors that affect the stability are captured by eigenvalue analysis.The reactive power-frequency compensation control of GFM WTs is then proposed to improve the reactive power and frequency dynamics.Second,the relationship between offshore reactive power imbalance and the effectiveness of GFM capability is analyzed.Offshore reactive power optimization methods are next proposed to diminish offshore reactive load.These methods include the optimal design for the reactive capacity of the AC filter and the reactive power compensation control of GFL WTs.Third,in terms of stability and optimal offshore reactive power constraints,the principle and calculation method for determining the proportion of GFM WTs are proposed,and the critical proportion of GFM WTs is determined over the full active power range.Finally,case studies using a detailed model are conducted by timedomain simulations in PSCAD/EMTDC.The simulations verify the theoretical analysis results and the effectiveness of the proposed determination method for the proportion of GFM WTs and reactive power optimization methods.
基金funded by the Science and Technology Projects of State Grid Zhejiang Electric Power Co.,Ltd.(5211DS24000G).
文摘With the rapid development of large-scale offshore wind farms,efficient and reliable power transmission systems are urgently needed.Hybrid high-voltage direct current(HVDC)configurations combining a diode rectifier unit(DRU)and a modular multilevel converter(MMC)have emerged as a promising solution,offering advantages in cost-effectiveness and control capability.However,the uncontrollable nature of the DRU poses significant challenges for systemstability under offshore AC fault conditions,particularly due to its inability to provide fault current or voltage support.This paper investigates the offshore AC fault characteristics and fault ride-through(FRT)strategy of a hybrid offshore wind power transmission system based on a diode rectifier unit DRU and MMC.First,the dynamic response of the hybrid system under offshore symmetrical three-phase faults is analyzed.It is demonstrated that due to the unidirectional conduction nature of the DRU,its AC current rapidly drops to zero during faults,and the fault current is solely contributed by the wind turbine generators(WTGs)and wind farm MMC(WFMMC).Based on this analysis,a coordinated FRT strategy is proposed,which combines a segmented current limiting control for the wind-turbine(WT)grid-side converters(GSCs)and a constant AC current control for the WFMMC.The strategy ensures effective voltage support during the fault and prevents MMC current saturation during fault recovery,enabling fast and stable system restoration.Electromagnetic transient simulations in PSCAD/EMTDC verify the feasibility of the proposed fault ride-through strategy.
基金Supported by State Key Laboratory of HVDC(SKLHVDC-2023-KF-09).
文摘Diode rectifier unit(DRU)-based high-voltage direct current(HVDC)transmissionsystems areeffectivein achieving the stableandeconomical operation of offshore wind-powergeneration.Considering theuncontrollable characteristicsof DRUs,a grid-forming(GFM)strategy forwind-turbine converters isnecessary to support offshore AC voltageand frequency.However,the active power-synchronization control in traditional GFM converters is unsuitable for DRU-based GFM converters.Thus,the stability issue for DRU-based HVDC systems involving DRU-based GFM and grid-following(GFL)converters has not yet been addressed.To solve these issues,this study begins with the characteristics of a DRU-based HVDC system and presents a control scheme for DRU-based GFM converters for power synchronization.Subsequently,the dq-frame impedance model of the DRU-based GFM converteris proposed for the stability analysis of the entire HVDC system.Finally,a simulation platform is built to verify the model accuracy and system stability.
