Grid-Forming(GFM)converters are prone to fault-induced overcurrent and power angle instability during grid fault-induced voltage sags.To address this,this paper develops a multi-loop coordinated fault ridethrough(FRT)...Grid-Forming(GFM)converters are prone to fault-induced overcurrent and power angle instability during grid fault-induced voltage sags.To address this,this paper develops a multi-loop coordinated fault ridethrough(FRT)control strategy based on a power outer loop and voltage-current inner loops,aiming to enhance the stability and current-limiting capability of GFM converters during grid fault conditions.During voltage sags,the GFM converter’s voltage source behavior is maintained by dynamically adjusting the reactive power reference to provide voltage support,thereby effectively suppressing the steady-state component of the fault current.To address the active power imbalance induced by voltage sags,a dynamic active power reference correction method based on apparent power is designed to mitigate power angle oscillations and limit transient current.Moreover,an adaptive virtual impedance loop is implemented to enhance dynamic transient current-limiting performance during the fault initiation phase.This approach improves the responsiveness of the inner loop and ensures safe system operation under various fault severities.Under asymmetric fault conditions,a negative-sequence reactive current compensation strategy is incorporated to further suppress negative-sequence voltage and improve voltage symmetry.The proposed control scheme enables coordinated operation of multiple control objectives,including voltage support,current suppression,and power angle stability,across different fault scenarios.Finally,MATLAB/Simulink simulation results validate the effectiveness of the proposed strategy,showcasing its superior performance in current limiting and power angle stability,thereby significantly enhancing the system’s fault ride-through capability.展开更多
With continuously increasing of photovoltaic (PV) plant’s penetration, it has become a critical issue to improve the fault ride-through capability of PV plant. This paper refers to the German grid code, and the PV sy...With continuously increasing of photovoltaic (PV) plant’s penetration, it has become a critical issue to improve the fault ride-through capability of PV plant. This paper refers to the German grid code, and the PV system is controlled to keep grid connected, as well as inject reactive current to grid when fault occurs. The mathematical model of PV system is established and the fault characteristic is studied with respect to the control strategy. By analyzing the effect of reactive power supplied by the PV system to the point of common coupling (PCC) voltage, this paper proposes an adaptive voltage support control strategy to enhance the fault ride-through capability of PV system. The control strategy fully utilizes the PV system’s capability of voltage support and takes the safety of equipment into account as well. At last, the proposed control strategy is verified by simulation.展开更多
In order to ensure power system stability, modern wind turbines are required to be able to endure deep voltage dips. The specifications that determine the voltage dip versus time are called fault r/de-through （FRT） ...In order to ensure power system stability, modern wind turbines are required to be able to endure deep voltage dips. The specifications that determine the voltage dip versus time are called fault r/de-through （FRT） requirements. The purpose of this paper is not only to examine the FRT behavior of a full-power converter wind turbine but also to combine the power system viewpoint to the studies. It is not enough for the turbine to be FRT capable; the loss of mains （LOM） protection of the turbine must also be set to allow the FRT. Enabling FRT, however, means that the LOM protection settings must be loosen, which may sometimes pose a safety hazard. This article introduces unique real-time simulation environment and proposes an FRT method for a wind turbine that also takes the operation of LOM protection relay into account. Simulations are carried out using the simulation environment and results show that wind turbine is able to ride-through a symmetrical power system fault.展开更多
The installation of wind energy has increased rapidly around the world. The grid codes about the wind energy require wind turbine (WT) has the ability of fault (or low voltage) ride-through (FRT). To study the FRT ope...The installation of wind energy has increased rapidly around the world. The grid codes about the wind energy require wind turbine (WT) has the ability of fault (or low voltage) ride-through (FRT). To study the FRT operation of the wind farms, three methods were discussed. First, the rotor short current of doubly-fed induction generator (DFIG) was limited by introducing a rotor side protection circuit. Second, the voltage of DC bus was limited by a DC energy absorb circuit. Third, STATCOM was used to increase the low level voltages of the wind farm. Simulation under MATLAB was studied and the corresponding results were given and discussed. The methods proposed in this paper can limit the rotor short current and the DC voltage of the DFIG WT to some degree, but the voltage support to the power system during the fault largely depend on the installation place of STATCOM.展开更多
Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive p...Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive power injecting into a grid but also implements other importance duties as well. In this study, negative-sequence current injection has been fulfilled in three-phase power electronic interface for two important duties besides injecting reference power into utility grids. The first one is for islanding detection, and the other one is to enhance unbalance-fault ride-through capability of dispersed generation. This paper introduces a mechanism of negative-sequence injection based on controlling two separate coordinates of dq-control and explains the effect of negative-sequence injection in limiting the unbalanced currents generated from a dispersed generation. Using adaptive notch filter as a signal processing unit for the three-phase system, negative-sequence components are observed. The performance of entire control system is evaluated by time domain simulations, PSCAD/EMTDC （power systems computer aided design/electromagnetic transients including DC）.展开更多
Modeling and validation of full power converter wind turbine models with field measurement data are rarely reported in papers. In this paper an aggregated generic dynamic model of the wind farm consisting of full powe...Modeling and validation of full power converter wind turbine models with field measurement data are rarely reported in papers. In this paper an aggregated generic dynamic model of the wind farm consisting of full power converter wind turbines is composed and the model validation based on actual field measurements is performed. The paper is based on the measurements obtained from the real short circuit test applied to connection point of observed wind farm. The presented approach for validating the composed model and fault ride-through （FRT） capability for the whole wind park is unique in overall practice and its significance and importance is described and analyzed.展开更多
Multiport magnetic network energy routers(MNERs)are a key technology in the energy internet that can improve the consumption level of renewable energy,realize the integration of source-grid-load-storage,and ensure the...Multiport magnetic network energy routers(MNERs)are a key technology in the energy internet that can improve the consumption level of renewable energy,realize the integration of source-grid-load-storage,and ensure the stable operation of power systems.However,the power grid may break down,causing the grid currents to exceed the safe threshold and the DC bus voltages to fluctuate,thereby threatening the stability of the power system.A coordinated low-voltage ride-through(LVRT)control strategy for an MNER-based grid connection system is proposed.The proposed control strategy can provide significant LVRT capability for an MNER-based grid-connection system and maintain the DC bus voltage of each port at the rated value.A simulation is conducted using the PLECS platform,and the results validate the effectiveness of the proposed coordinated LVRT control strategy.展开更多
The virtual synchronous generator(VSG),utilized as a control strategy for grid-forming inverters,is an effective method of providing inertia and voltage support to the grid.However,the VSG exhibits limited capabilitie...The virtual synchronous generator(VSG),utilized as a control strategy for grid-forming inverters,is an effective method of providing inertia and voltage support to the grid.However,the VSG exhibits limited capabilities in low-voltage ride-through(LVRT)mode.Specifically,the slow response of the power loop poses challenges for VSG in grid voltage support and increases the risk of overcurrent,potentially violating present grid codes.This paper reveals the mechanism behind the delayed response speed of VSG control during the grid faults.On this basis,a compound compensation control strategy is proposed for improving the LVRT capability of the VSG,which incorporates adaptive frequency feedforward compensation(AFFC),direct power angle compensation(DPAC),internal potential compensation(IPC),and transient virtual impedance(TVI),effectively expediting the response speed and reducing transient current.Furthermore,the proposed control strategy ensures that the VSG operates smoothly back to its normal control state following the restoration from the grid faults.Subsequently,a large-signal model is developed to facilitate parameter design and stability analysis,which incorporates grid codes and TVI.Finally,the small-signal stability analysis and simulation and experimental results prove the correctness of the theoretical analysis and the effectiveness of the proposed control strategy.展开更多
Energy storage systems support electrical grid stability by enabling strategies to tackle issues,such as power fluctuations,low inertia,and insufficient damping.The present study proposes a battery energy storage syst...Energy storage systems support electrical grid stability by enabling strategies to tackle issues,such as power fluctuations,low inertia,and insufficient damping.The present study proposes a battery energy storage system based on a modular multilevel converter with multiplexed submodule arms(M-MMC-BESS)to reduce the number of switching devices while embedding DC short-circuit fault ride-through capability.Compared to the conventional two-stage half-bridge topology,the M-MMC-BESS retains the same number of switching devices but allows uninterrupted operation under DC short-circuit faults.In addition,compared to the two-stage full-bridge topology,the proposed topology reduces the number of switching devices by one-third.The control of the M-MMC-BESS is thoroughly investigated under both normal and DC short-circuit operating conditions.Simulation and experimental results are used to demonstrate the effectiveness of the proposed system and control approach.展开更多
Full-Bridge Modular Multilevel Converter(FBMMC) has strong ability to ride through serious DC faults,thus it is very suitable for multi-terminal flexible HVDC applications.However,no references have reported the locat...Full-Bridge Modular Multilevel Converter(FBMMC) has strong ability to ride through serious DC faults,thus it is very suitable for multi-terminal flexible HVDC applications.However,no references have reported the locating and isolating of DC faults and corresponding DC faults ride-through capability evaluation index.This paper introduces the topology mechanism of FBMMC and its loss reduction operation mode,theoretically certifies that the universal decoupled control strategy of Voltage Source Converter(VSC) and the similar modulation strategies of Half-Bridge MMC(HBMMC) can be applied to FBMMC for constructing complete closed-loop control system.On the basis of the existing DC faults locating and isolating schemes of 2-level VSC based Multi-Terminal HVDC(VSC-MTDC) system and the particularity of FBMMC,this paper proposes the DC faults wire selection "handshaking" method of the FBMMC-MTDC system,and proposes the DC Fault Ride-Through Capability Index(DFRTI) for evaluating the DC faults suppressing capability of the VSC-MTDC systems,including FBMMC-MTDC.Simulations of FBMMC-MTDC in PSCAD/EMTDC validate the correctness and effectiveness of the proposed control strategy and evaluation index.展开更多
Asymmetrical voltage swells during recovery of a short-circuit fault lead to fluctuations in the dc-link voltage of a renewable energy conversion system(RECS),and may induce reversed power flow and even trip the RECS....Asymmetrical voltage swells during recovery of a short-circuit fault lead to fluctuations in the dc-link voltage of a renewable energy conversion system(RECS),and may induce reversed power flow and even trip the RECS. This paper studies characteristics of both typical causes resulting in the practical asymmetrical voltage swell and the voltage at the point of common coupling(PCC)during the fault recovery. As analyzed, the fault recovery process can be divided into two continuous periods in which different control strategies have to be applied. Also protective measures are necessary in the transient period of the process. Additionally, the asymmetrical high-voltage ride-through capability and the controllability criteria of the RECS are analyzed based on eliminating the fluctuations. Furthermore, an asymmetrical control scheme is proposed to maintain the controllability of the RECS and ride through the entire recovery process. As verified by the simulation, the scheme can promise the RECS to deal with the practical fault recovery period and mitigate the dc-link voltage fluctuations, which improves the reliability of the RECS and the power system.展开更多
Given the“carbon neutralization and carbon peak”policy,enhancing the low voltage ride-through(LVRT)capability of wind farms has become a current demand to ensure the safe and stable operation of power systems in the...Given the“carbon neutralization and carbon peak”policy,enhancing the low voltage ride-through(LVRT)capability of wind farms has become a current demand to ensure the safe and stable operation of power systems in the context of a possible severe threat of large-scale disconnection caused by wind farms.Currently,research on the LVRT of wind farms mainly focuses on suppressing rotor current and providing reactive current support,while the impact of active current output on LVRT performance has not been thoroughly discussed.This paper studies and reveals the relation-ship between the limit of reactive current output and the depth of voltage drop during LVRT for doubly-fed induction generator(DFIG)based wind farms.Specifically,the reactive current output limit of the grid-side converter is inde-pendent of the depth of voltage drop,and its limit is the maximum current allowed by the converter,while the reac-tive current output limit of the DFIG stator is a linear function of the depth of voltage drop.An optimized scheme for allocating reactive current among the STATCOM,DFIG stator,and grid-side converter is proposed.The scheme maximizes the output of active current while satisfying the standard requirements for reactive current output.Com-pared to traditional schemes,the proposed LVRT optimization strategy can output more active power during the LVRT period,effectively suppressing the rate of rotor speed increase,and improving the LVRT performance and fault recov-ery capability of wind farms.Simulation results verify the effectiveness of the proposed scheme.展开更多
Doubly-fed induction generator(DFIG)-based wind farms(WFs)are interfaced with power electronic converters.Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes ...Doubly-fed induction generator(DFIG)-based wind farms(WFs)are interfaced with power electronic converters.Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes prevalent in a fault scenario.Therefore,transient stability enhancement along with frequency stability in DFIG-based WFs is a major concern in the present scenario.In this paper,a cooperative approach consisting of virtual inertia control(VIC)and a modified grid-side converter(GSC)approach for low voltage ride-through(LVRT)is proposed to achieve fault ride-through(FRT)capabilities as per the grid code requirements(GCRs)while providing frequency support to the grid through a synthetic inertia.The proposed approach provides LVRT and reactive power compensation in the system.The participation of the VIC in a rotor-side converter(RSC)provides frequency support to the DFIG-based WFs.The combined approach supports active power compensation and provides sufficient kinetic energy support to the system in a contingency scenario.Simulation studies are carried out in MATLAB/Simulink environment for symmetrical and unsymmetrical faults.The superiority of the proposed scheme is demonstrated through analysis of the performance of the scheme and that of a series resonance bridge-type fault current limiter(SR-BFCL).展开更多
The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which ...The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which is the so-called Baihetan-Jiangsu HVDC(BJ-HVDC)project of China.In one LCC and two MMCs(1+2)operation mode,the sub-module(SM)capacitors suffer the most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC and valve-side single-phase-to-ground fault in internal MMC.In order to suppress such huge overvoltage,this paper demonstrates a novel alternative by employing the MMC-based embedded battery energy storage system(MMC-BESS).Firstly,the inducements of SM overvoltage are analyzed.Then,coordinated with MMC-BESS,new fault ride-through(FRT)strategies are proposed to suppress the overvoltage and improve the FRT capability.Finally,several simulation scenarios are carried out on PSCAD/EMTDC.The overvoltage suppression is verified against auxiliary device used in the BJ-HVDC project in a monopolar BJ-HVDC system.Further,the proposed FRT strategies are validated in the southern Jiangsu power grid of China based on the planning data in the summer of 2025.Simulation results show that the MMC-BESS and proposed FRT strategies could effectively suppress the overvoltage and improve the FRT capability.展开更多
Among all renewable energies,wind power is rapidly growing,whereby it has the most participation to supply power.Doubly fed induction generator(DFIG)is the most popular wind turbine,as it can play a very significant r...Among all renewable energies,wind power is rapidly growing,whereby it has the most participation to supply power.Doubly fed induction generator(DFIG)is the most popular wind turbine,as it can play a very significant role to enhance low voltage ride through(LVRT)capability.Ancillary services such as voltage control and reactive power capability are the main topics in wind power control systems that should be handled profoundly and carefully.The lack of reactive power during fault period can result in instability in generators and/or disconnection of the wind turbine from the power system.The main aims of this study are to illustrate the most effective approaches subject to improve the efficiency,stability,and reliability of wind power plant associated with LVRT capability enhancement.This effectiveness and efficiency are demonstrated by,firstly,comparison between all types of wind turbines,focusing on the ancillary services,after the existing advanced control strategies.According to the literature,there is a consensus that modifying converter-based control topology is the most effective approach to enhance LVRT capability in DFIG-based wind turbine(WT).Therefore,an advanced integrated control strategy is designed by considering the effect of the rotor side converter(RSC)and the grid side converter(GSC).A model of the wind power plant is presented based on the control objectives.MATLAB/Simulink is also used to illustrate the effectiveness of the designed algorithm.展开更多
The installed capacity of renewable energy generation has continued to grow rapidly in recent years along with the global energy transition towards a 100%renewable-based power system.At the same time,the grid-connecte...The installed capacity of renewable energy generation has continued to grow rapidly in recent years along with the global energy transition towards a 100%renewable-based power system.At the same time,the grid-connected large-scale renewable energy brings significant challenges to the safe and stable operation of the power system due to the loss of synchronous machines.Therefore,self-synchronous wind turbines have attracted wide attention from both academia and industry.However,the understanding of the physical operation mechanisms of self-synchronous wind turbines is not clear.In particular,the transient characteristics and dynamic processes of wind turbines are fuzzy in the presence of grid disturbances.Furthermore,it is difficult to design an adaptive fault ride-through(FRT)control strategy.Thus,a dual-mode switching FRT control strategy for self-synchronous wind turbines is developed.Two FRT control strategies are used.In one strategy,the amplitude and phase of the internal potential are directly calculated according to the voltage drop when a minor grid fault occurs.The other dual-mode switching control strategy in the presence of a deep grid fault includes three parts:vector control during the grid fault,fault recovery vector control,and self-synchronous control.The proposed control strategy can significantly mitigate transient overvoltage,overcurrent,and multifrequency oscillation,thereby resulting in enhanced transient stability.Finally,simulation results are provided to validate the proposed control strategy.展开更多
In this paper,an overview of several strategies for fault ride-through(FRT)capability improvement of a doubly-fed induction generator(DFIG)-based wind turbine is presented.Uncertainties and parameter variations have a...In this paper,an overview of several strategies for fault ride-through(FRT)capability improvement of a doubly-fed induction generator(DFIG)-based wind turbine is presented.Uncertainties and parameter variations have adverse effects on the performance of these strategies.It is desirable to use a control method that is robust to such distur-bances.Auto disturbance rejection control(ADRC)is one of the most common methods for eliminating the effects of disturbances.To improve the performance of the conventional ADRC,a modified ADRC is introduced that is more robust to disturbances and offers better responses.The non-derivability of the fal function used in the conventional ADRC degrades its efficiency,so the modified ADRC uses alternative functions that are derivable at all points,i.e.,the odd trigonometric and hyperbolic functions(arcsinh,arctan,and tanh).To improve the effciency of the proposed ADRC,fuzzy logic and fractional-order functions are used simultaneously.In fuzzy fractional-order ADRC(FFOADRC),all disturbances are evaluated using a nonlinear fractional-order extended state observer(NFESO).The performance of the suggested structure is investigated in MATLAB/Simulink.The simulation results show that during disturbances such as network voltage sag/swell,using the modified ADRCs leads to smaller fluctuations in stator flux amplitude and DC-link voltage,lower variations in DFIG velocity,and lower total harmonic distortion(THD)of the stator current.This demonstrates the superiority over conventional ADRC and a proportional-integral(PI)controller.Also,by chang-ing the crowbar resistance and using the modified ADRCs,the peak values of the waveforms(torque and currents)can be controlled at the moment of fault occurrence with no significant distortion.展开更多
Experimental and theoretical studies have confirmed that,relative to a one-shot voltage fault,a doubly-fed induction generator(DFIG)will suffer a greater transient impact during continuous voltage faults.This paper pr...Experimental and theoretical studies have confirmed that,relative to a one-shot voltage fault,a doubly-fed induction generator(DFIG)will suffer a greater transient impact during continuous voltage faults.This paper presents the design and application of an effective scheme for DFIGs when a commutation failure(CF)occurs in a line-commutated converter based high-voltage direct current(LCC-HVDC)transmission system.First,transient demagnetization control without filters is proposed to offset the electromotive force(EMF)induced by the natural flux and other low-frequency flux components.Then,a rotor-side integrated impedance circuit is designed to limit the rotor overcurrent to ensure that the rotor-side converter(RSC)is controllable.Furthermore,coordinated control of the demagnetization and segmented reactive currents is implemented in the RSC.Comparative studies have shown that the proposed scheme can limit rotor fault currents and effectively improve the continuous fault ride-through capability of DFIGs.展开更多
文摘Grid-Forming(GFM)converters are prone to fault-induced overcurrent and power angle instability during grid fault-induced voltage sags.To address this,this paper develops a multi-loop coordinated fault ridethrough(FRT)control strategy based on a power outer loop and voltage-current inner loops,aiming to enhance the stability and current-limiting capability of GFM converters during grid fault conditions.During voltage sags,the GFM converter’s voltage source behavior is maintained by dynamically adjusting the reactive power reference to provide voltage support,thereby effectively suppressing the steady-state component of the fault current.To address the active power imbalance induced by voltage sags,a dynamic active power reference correction method based on apparent power is designed to mitigate power angle oscillations and limit transient current.Moreover,an adaptive virtual impedance loop is implemented to enhance dynamic transient current-limiting performance during the fault initiation phase.This approach improves the responsiveness of the inner loop and ensures safe system operation under various fault severities.Under asymmetric fault conditions,a negative-sequence reactive current compensation strategy is incorporated to further suppress negative-sequence voltage and improve voltage symmetry.The proposed control scheme enables coordinated operation of multiple control objectives,including voltage support,current suppression,and power angle stability,across different fault scenarios.Finally,MATLAB/Simulink simulation results validate the effectiveness of the proposed strategy,showcasing its superior performance in current limiting and power angle stability,thereby significantly enhancing the system’s fault ride-through capability.
文摘With continuously increasing of photovoltaic (PV) plant’s penetration, it has become a critical issue to improve the fault ride-through capability of PV plant. This paper refers to the German grid code, and the PV system is controlled to keep grid connected, as well as inject reactive current to grid when fault occurs. The mathematical model of PV system is established and the fault characteristic is studied with respect to the control strategy. By analyzing the effect of reactive power supplied by the PV system to the point of common coupling (PCC) voltage, this paper proposes an adaptive voltage support control strategy to enhance the fault ride-through capability of PV system. The control strategy fully utilizes the PV system’s capability of voltage support and takes the safety of equipment into account as well. At last, the proposed control strategy is verified by simulation.
文摘In order to ensure power system stability, modern wind turbines are required to be able to endure deep voltage dips. The specifications that determine the voltage dip versus time are called fault r/de-through （FRT） requirements. The purpose of this paper is not only to examine the FRT behavior of a full-power converter wind turbine but also to combine the power system viewpoint to the studies. It is not enough for the turbine to be FRT capable; the loss of mains （LOM） protection of the turbine must also be set to allow the FRT. Enabling FRT, however, means that the LOM protection settings must be loosen, which may sometimes pose a safety hazard. This article introduces unique real-time simulation environment and proposes an FRT method for a wind turbine that also takes the operation of LOM protection relay into account. Simulations are carried out using the simulation environment and results show that wind turbine is able to ride-through a symmetrical power system fault.
文摘The installation of wind energy has increased rapidly around the world. The grid codes about the wind energy require wind turbine (WT) has the ability of fault (or low voltage) ride-through (FRT). To study the FRT operation of the wind farms, three methods were discussed. First, the rotor short current of doubly-fed induction generator (DFIG) was limited by introducing a rotor side protection circuit. Second, the voltage of DC bus was limited by a DC energy absorb circuit. Third, STATCOM was used to increase the low level voltages of the wind farm. Simulation under MATLAB was studied and the corresponding results were given and discussed. The methods proposed in this paper can limit the rotor short current and the DC voltage of the DFIG WT to some degree, but the voltage support to the power system during the fault largely depend on the installation place of STATCOM.
文摘Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive power injecting into a grid but also implements other importance duties as well. In this study, negative-sequence current injection has been fulfilled in three-phase power electronic interface for two important duties besides injecting reference power into utility grids. The first one is for islanding detection, and the other one is to enhance unbalance-fault ride-through capability of dispersed generation. This paper introduces a mechanism of negative-sequence injection based on controlling two separate coordinates of dq-control and explains the effect of negative-sequence injection in limiting the unbalanced currents generated from a dispersed generation. Using adaptive notch filter as a signal processing unit for the three-phase system, negative-sequence components are observed. The performance of entire control system is evaluated by time domain simulations, PSCAD/EMTDC （power systems computer aided design/electromagnetic transients including DC）.
文摘Modeling and validation of full power converter wind turbine models with field measurement data are rarely reported in papers. In this paper an aggregated generic dynamic model of the wind farm consisting of full power converter wind turbines is composed and the model validation based on actual field measurements is performed. The paper is based on the measurements obtained from the real short circuit test applied to connection point of observed wind farm. The presented approach for validating the composed model and fault ride-through （FRT） capability for the whole wind park is unique in overall practice and its significance and importance is described and analyzed.
基金Supported by the National Key Research and Development Program of China(2022YFE0196300)Science,Technology&Innovation Funding Authority(STDF)(46505).
文摘Multiport magnetic network energy routers(MNERs)are a key technology in the energy internet that can improve the consumption level of renewable energy,realize the integration of source-grid-load-storage,and ensure the stable operation of power systems.However,the power grid may break down,causing the grid currents to exceed the safe threshold and the DC bus voltages to fluctuate,thereby threatening the stability of the power system.A coordinated low-voltage ride-through(LVRT)control strategy for an MNER-based grid connection system is proposed.The proposed control strategy can provide significant LVRT capability for an MNER-based grid-connection system and maintain the DC bus voltage of each port at the rated value.A simulation is conducted using the PLECS platform,and the results validate the effectiveness of the proposed coordinated LVRT control strategy.
基金supported by the National Natural Science Foundation of China(No.62222309)the Natural Science Foundation of Shandong Province(No.ZR2022JQ29).
文摘The virtual synchronous generator(VSG),utilized as a control strategy for grid-forming inverters,is an effective method of providing inertia and voltage support to the grid.However,the VSG exhibits limited capabilities in low-voltage ride-through(LVRT)mode.Specifically,the slow response of the power loop poses challenges for VSG in grid voltage support and increases the risk of overcurrent,potentially violating present grid codes.This paper reveals the mechanism behind the delayed response speed of VSG control during the grid faults.On this basis,a compound compensation control strategy is proposed for improving the LVRT capability of the VSG,which incorporates adaptive frequency feedforward compensation(AFFC),direct power angle compensation(DPAC),internal potential compensation(IPC),and transient virtual impedance(TVI),effectively expediting the response speed and reducing transient current.Furthermore,the proposed control strategy ensures that the VSG operates smoothly back to its normal control state following the restoration from the grid faults.Subsequently,a large-signal model is developed to facilitate parameter design and stability analysis,which incorporates grid codes and TVI.Finally,the small-signal stability analysis and simulation and experimental results prove the correctness of the theoretical analysis and the effectiveness of the proposed control strategy.
基金supported by the National Natural Science Foundation of China(No.52277188)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province(No.22KJB470005).
文摘Energy storage systems support electrical grid stability by enabling strategies to tackle issues,such as power fluctuations,low inertia,and insufficient damping.The present study proposes a battery energy storage system based on a modular multilevel converter with multiplexed submodule arms(M-MMC-BESS)to reduce the number of switching devices while embedding DC short-circuit fault ride-through capability.Compared to the conventional two-stage half-bridge topology,the M-MMC-BESS retains the same number of switching devices but allows uninterrupted operation under DC short-circuit faults.In addition,compared to the two-stage full-bridge topology,the proposed topology reduces the number of switching devices by one-third.The control of the M-MMC-BESS is thoroughly investigated under both normal and DC short-circuit operating conditions.Simulation and experimental results are used to demonstrate the effectiveness of the proposed system and control approach.
基金supported by the National Natural Science Foundation of China (Grant No. 51177042)the Key Project of the National Twelfth FiveYear Research Program of China (Grant No. 2010BAA01B01)
文摘Full-Bridge Modular Multilevel Converter(FBMMC) has strong ability to ride through serious DC faults,thus it is very suitable for multi-terminal flexible HVDC applications.However,no references have reported the locating and isolating of DC faults and corresponding DC faults ride-through capability evaluation index.This paper introduces the topology mechanism of FBMMC and its loss reduction operation mode,theoretically certifies that the universal decoupled control strategy of Voltage Source Converter(VSC) and the similar modulation strategies of Half-Bridge MMC(HBMMC) can be applied to FBMMC for constructing complete closed-loop control system.On the basis of the existing DC faults locating and isolating schemes of 2-level VSC based Multi-Terminal HVDC(VSC-MTDC) system and the particularity of FBMMC,this paper proposes the DC faults wire selection "handshaking" method of the FBMMC-MTDC system,and proposes the DC Fault Ride-Through Capability Index(DFRTI) for evaluating the DC faults suppressing capability of the VSC-MTDC systems,including FBMMC-MTDC.Simulations of FBMMC-MTDC in PSCAD/EMTDC validate the correctness and effectiveness of the proposed control strategy and evaluation index.
基金supported by National Natural Science Foundation of China(NSFC)(No.U1510208,No.61273045,No.51361135705)National High Technology Research and Development Program of China(No.2012AA050217)Grants from Beijing Higher Education Young Elite Teacher Project
文摘Asymmetrical voltage swells during recovery of a short-circuit fault lead to fluctuations in the dc-link voltage of a renewable energy conversion system(RECS),and may induce reversed power flow and even trip the RECS. This paper studies characteristics of both typical causes resulting in the practical asymmetrical voltage swell and the voltage at the point of common coupling(PCC)during the fault recovery. As analyzed, the fault recovery process can be divided into two continuous periods in which different control strategies have to be applied. Also protective measures are necessary in the transient period of the process. Additionally, the asymmetrical high-voltage ride-through capability and the controllability criteria of the RECS are analyzed based on eliminating the fluctuations. Furthermore, an asymmetrical control scheme is proposed to maintain the controllability of the RECS and ride through the entire recovery process. As verified by the simulation, the scheme can promise the RECS to deal with the practical fault recovery period and mitigate the dc-link voltage fluctuations, which improves the reliability of the RECS and the power system.
基金supported by the National Natural Science Foundation of China 52177108。
文摘Given the“carbon neutralization and carbon peak”policy,enhancing the low voltage ride-through(LVRT)capability of wind farms has become a current demand to ensure the safe and stable operation of power systems in the context of a possible severe threat of large-scale disconnection caused by wind farms.Currently,research on the LVRT of wind farms mainly focuses on suppressing rotor current and providing reactive current support,while the impact of active current output on LVRT performance has not been thoroughly discussed.This paper studies and reveals the relation-ship between the limit of reactive current output and the depth of voltage drop during LVRT for doubly-fed induction generator(DFIG)based wind farms.Specifically,the reactive current output limit of the grid-side converter is inde-pendent of the depth of voltage drop,and its limit is the maximum current allowed by the converter,while the reac-tive current output limit of the DFIG stator is a linear function of the depth of voltage drop.An optimized scheme for allocating reactive current among the STATCOM,DFIG stator,and grid-side converter is proposed.The scheme maximizes the output of active current while satisfying the standard requirements for reactive current output.Com-pared to traditional schemes,the proposed LVRT optimization strategy can output more active power during the LVRT period,effectively suppressing the rate of rotor speed increase,and improving the LVRT performance and fault recov-ery capability of wind farms.Simulation results verify the effectiveness of the proposed scheme.
文摘Doubly-fed induction generator(DFIG)-based wind farms(WFs)are interfaced with power electronic converters.Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes prevalent in a fault scenario.Therefore,transient stability enhancement along with frequency stability in DFIG-based WFs is a major concern in the present scenario.In this paper,a cooperative approach consisting of virtual inertia control(VIC)and a modified grid-side converter(GSC)approach for low voltage ride-through(LVRT)is proposed to achieve fault ride-through(FRT)capabilities as per the grid code requirements(GCRs)while providing frequency support to the grid through a synthetic inertia.The proposed approach provides LVRT and reactive power compensation in the system.The participation of the VIC in a rotor-side converter(RSC)provides frequency support to the DFIG-based WFs.The combined approach supports active power compensation and provides sufficient kinetic energy support to the system in a contingency scenario.Simulation studies are carried out in MATLAB/Simulink environment for symmetrical and unsymmetrical faults.The superiority of the proposed scheme is demonstrated through analysis of the performance of the scheme and that of a series resonance bridge-type fault current limiter(SR-BFCL).
文摘The series line-commutated converter(LCC)and modular multilevel converter(MMC)hybrid high-voltage direct current(HVDC)system provides a more economical and flexible alternative for ultra-HVDC(UHVDC)transmission,which is the so-called Baihetan-Jiangsu HVDC(BJ-HVDC)project of China.In one LCC and two MMCs(1+2)operation mode,the sub-module(SM)capacitors suffer the most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC and valve-side single-phase-to-ground fault in internal MMC.In order to suppress such huge overvoltage,this paper demonstrates a novel alternative by employing the MMC-based embedded battery energy storage system(MMC-BESS).Firstly,the inducements of SM overvoltage are analyzed.Then,coordinated with MMC-BESS,new fault ride-through(FRT)strategies are proposed to suppress the overvoltage and improve the FRT capability.Finally,several simulation scenarios are carried out on PSCAD/EMTDC.The overvoltage suppression is verified against auxiliary device used in the BJ-HVDC project in a monopolar BJ-HVDC system.Further,the proposed FRT strategies are validated in the southern Jiangsu power grid of China based on the planning data in the summer of 2025.Simulation results show that the MMC-BESS and proposed FRT strategies could effectively suppress the overvoltage and improve the FRT capability.
文摘Among all renewable energies,wind power is rapidly growing,whereby it has the most participation to supply power.Doubly fed induction generator(DFIG)is the most popular wind turbine,as it can play a very significant role to enhance low voltage ride through(LVRT)capability.Ancillary services such as voltage control and reactive power capability are the main topics in wind power control systems that should be handled profoundly and carefully.The lack of reactive power during fault period can result in instability in generators and/or disconnection of the wind turbine from the power system.The main aims of this study are to illustrate the most effective approaches subject to improve the efficiency,stability,and reliability of wind power plant associated with LVRT capability enhancement.This effectiveness and efficiency are demonstrated by,firstly,comparison between all types of wind turbines,focusing on the ancillary services,after the existing advanced control strategies.According to the literature,there is a consensus that modifying converter-based control topology is the most effective approach to enhance LVRT capability in DFIG-based wind turbine(WT).Therefore,an advanced integrated control strategy is designed by considering the effect of the rotor side converter(RSC)and the grid side converter(GSC).A model of the wind power plant is presented based on the control objectives.MATLAB/Simulink is also used to illustrate the effectiveness of the designed algorithm.
基金supported in part by the National Natural Science Foundation of China(No.52007174)。
文摘The installed capacity of renewable energy generation has continued to grow rapidly in recent years along with the global energy transition towards a 100%renewable-based power system.At the same time,the grid-connected large-scale renewable energy brings significant challenges to the safe and stable operation of the power system due to the loss of synchronous machines.Therefore,self-synchronous wind turbines have attracted wide attention from both academia and industry.However,the understanding of the physical operation mechanisms of self-synchronous wind turbines is not clear.In particular,the transient characteristics and dynamic processes of wind turbines are fuzzy in the presence of grid disturbances.Furthermore,it is difficult to design an adaptive fault ride-through(FRT)control strategy.Thus,a dual-mode switching FRT control strategy for self-synchronous wind turbines is developed.Two FRT control strategies are used.In one strategy,the amplitude and phase of the internal potential are directly calculated according to the voltage drop when a minor grid fault occurs.The other dual-mode switching control strategy in the presence of a deep grid fault includes three parts:vector control during the grid fault,fault recovery vector control,and self-synchronous control.The proposed control strategy can significantly mitigate transient overvoltage,overcurrent,and multifrequency oscillation,thereby resulting in enhanced transient stability.Finally,simulation results are provided to validate the proposed control strategy.
文摘In this paper,an overview of several strategies for fault ride-through(FRT)capability improvement of a doubly-fed induction generator(DFIG)-based wind turbine is presented.Uncertainties and parameter variations have adverse effects on the performance of these strategies.It is desirable to use a control method that is robust to such distur-bances.Auto disturbance rejection control(ADRC)is one of the most common methods for eliminating the effects of disturbances.To improve the performance of the conventional ADRC,a modified ADRC is introduced that is more robust to disturbances and offers better responses.The non-derivability of the fal function used in the conventional ADRC degrades its efficiency,so the modified ADRC uses alternative functions that are derivable at all points,i.e.,the odd trigonometric and hyperbolic functions(arcsinh,arctan,and tanh).To improve the effciency of the proposed ADRC,fuzzy logic and fractional-order functions are used simultaneously.In fuzzy fractional-order ADRC(FFOADRC),all disturbances are evaluated using a nonlinear fractional-order extended state observer(NFESO).The performance of the suggested structure is investigated in MATLAB/Simulink.The simulation results show that during disturbances such as network voltage sag/swell,using the modified ADRCs leads to smaller fluctuations in stator flux amplitude and DC-link voltage,lower variations in DFIG velocity,and lower total harmonic distortion(THD)of the stator current.This demonstrates the superiority over conventional ADRC and a proportional-integral(PI)controller.Also,by chang-ing the crowbar resistance and using the modified ADRCs,the peak values of the waveforms(torque and currents)can be controlled at the moment of fault occurrence with no significant distortion.
基金supported by the National Natural Science Foundation of China(No.51907134)。
文摘Experimental and theoretical studies have confirmed that,relative to a one-shot voltage fault,a doubly-fed induction generator(DFIG)will suffer a greater transient impact during continuous voltage faults.This paper presents the design and application of an effective scheme for DFIGs when a commutation failure(CF)occurs in a line-commutated converter based high-voltage direct current(LCC-HVDC)transmission system.First,transient demagnetization control without filters is proposed to offset the electromotive force(EMF)induced by the natural flux and other low-frequency flux components.Then,a rotor-side integrated impedance circuit is designed to limit the rotor overcurrent to ensure that the rotor-side converter(RSC)is controllable.Furthermore,coordinated control of the demagnetization and segmented reactive currents is implemented in the RSC.Comparative studies have shown that the proposed scheme can limit rotor fault currents and effectively improve the continuous fault ride-through capability of DFIGs.
