For the hybrid multi-infeed HVDC system in which the receiving-end grid is a strong AC grid including LCC-HVDC subsystems and multiple VSC-HVDC subsystems,it has higher voltage support capability.However,for weak AC g...For the hybrid multi-infeed HVDC system in which the receiving-end grid is a strong AC grid including LCC-HVDC subsystems and multiple VSC-HVDC subsystems,it has higher voltage support capability.However,for weak AC grid,the voltage support capability of the multi-VSC-HVDC subsystems to the LCC-HVDC subsystem(voltage support capability-mVSCs-LCC)can resist the risk of commutation failure.Based on this consideration,this paper proposes an evaluation index called Dynamic Voltage Support Strength Factor(DVSF)for the hybrid multi-infeed system,and uses this index to qualitatively judge the voltage support capability-mVSCs-LCC in weak AC grid.In addition,the proposed evaluation index can also indirectly judge the ability of the LCC-HVDC subsystem to suppress commutation failure.Firstly,the mathematical model of the power flow of the LCC and VSC networks in the steady-state is analyzed,and the concept of DVSF applied to hybrid multi-infeed system is proposed.Furthermore,the DVSF index is also used to qualitatively judge the voltage support capability-mVSCs-LCC.Secondly,the influence of multiple VSC-HVDC subsystems with different operation strategies on the DVSF is analyzed with reference to the concept of DVSF.Finally,the indicators proposed in this paper are compared with other evaluation indicators through MATLAB simulation software to verify its effectiveness.More importantly,the effects of multi-VSC-HVDC subsystems using different coordinated control strategies on the voltage support capability of the receiving-end LCC-HVDC subsystem are also verified.展开更多
This paper proposes a fast coordinated power control method based on two augmented channels(AC)in battery energy storage system(BESS)to improve inertial and voltage support capability,i.e.,a frequency-reactive power c...This paper proposes a fast coordinated power control method based on two augmented channels(AC)in battery energy storage system(BESS)to improve inertial and voltage support capability,i.e.,a frequency-reactive power channel(FRPC)and a voltage-real power channel(VRPC).For frequency control in the power distribution system with high resistance/inductance ratio,the coupling mechanism between rate of change of frequency(RoCoF)and required reactive power(RRP)of grids is analyzed,indicating RoCoF is proportional to RRP.Thus,RoCoF is utilized in FRPC to generate reactive power for complementary inertial emulating control.Meanwhile,for voltage control,coupling characteristics between rate of change of voltage(RoCoV)and demanding real power(DRP)of grids is also studied,revealing RoCoV is proportional to DRP.Therefore,it can be adopted in VRPC to generate real power for complementary voltage control.Then,grid-voltage-modulated direct power control is selected as the inner power control loop to track power references with faster dynamic performance compared with traditional vector-oriented control.Finally,simulations and hardware-in-loop experiments validate improvement in performance of grid frequency and voltage control based on the proposed method.展开更多
High-power trains are dynamic moving loads in the traction power supply system.When trains move to the end of the traction power supply arm,voltage drop and current phase lag along the catenary are caused by the combi...High-power trains are dynamic moving loads in the traction power supply system.When trains move to the end of the traction power supply arm,voltage drop and current phase lag along the catenary are caused by the combined effects of increased line impedance and high-power traction load.The voltage drop along the catenary line may cause overcurrent in the traction drive system,trigger power limitation protection and threaten operation safety.In this paper,a control method for the traction line-side converter with the ability of active catenary voltage support is proposed.First,a coupled dynamic impedance model of the traction power supply system and the traction drive system is established,revealing the causes of voltage drops and the mechanism of catenary voltage support.Then,the active catenary voltage support control is introduced,including the limitations on voltage support capability for safety consideration,the dynamic reactive power regulation method based on the depth of voltage drop and the requirement for strength of system.Finally,both the simulation in MATLAB/Simulink and the experiment on a full-scale test platform verify that the proposed method can quickly respond to catenary voltage drops,and dynamically support catenary voltage,without using extra compensation equipment.展开更多
Generally,voltage support at the point of common coupling(PCC)of a wind farm is achieved through centralized static var generators(SVGs).Since the reactive power requirements occupy their capacity in a steady state,th...Generally,voltage support at the point of common coupling(PCC)of a wind farm is achieved through centralized static var generators(SVGs).Since the reactive power requirements occupy their capacity in a steady state,the reactive power support capacity of the SVG is limited during high voltage ride through(HVRT)or low voltage ride through(LVRT).While wind turbines can provide voltage support in accordance with the grid code,their responses are usually delayed due to communication and transmission lags.To enhance the dynamic performance of wind farms during fault ride-through,a reactive power substitution(RPS)control strategy is proposed in this paper.In a steady state,this RPS control method preferentially utilizes the remaining capacity of wind turbines to substitute for the output of the SVG.Considering differences in terminal voltage characteristics and operating conditions,this RPS control method employs a particle swarm optimization(PSO)algorithm to ensure that wind turbines can provide their optimal reactive power support capacity.When the grid voltage swells or drops,the SVG has a sufficient reactive power reserve to support the grid quickly.This paper utilizes a regional power grid incorporating two wind farms connected to different buses as a case study to validate this RPS control strategy.展开更多
In the last decades the voltage regulation has been challenged by the increase of power variability in the electric grid,due to the spread of non-dispatchable generation sources.This paper introduces a Smart Transform...In the last decades the voltage regulation has been challenged by the increase of power variability in the electric grid,due to the spread of non-dispatchable generation sources.This paper introduces a Smart Transformer(ST)-based Medium Voltage(MV)grid support by means of active power control in the ST-fed Low Voltage(LV)grid.The aim of the proposed strategy is to improve the voltage profile in MV grids before the operation of On-Load Tap Changer in the primary substation transformer,which needs tens of seconds.This is realized through reactive power injection by the AC/DC MV converter and simultaneous decrease of the active power consumption of voltage-dependent loads in ST-fed LV grid,controlling the ST output voltage.The last feature has two main effects:the first is to reduce the active power withdrawn from MV grid,and consequently the MV voltage drop caused by the active current component.At the same time,higher reactive power injection capability in the MV converter is unlocked,due to the lower active power demand.As result,the ST increases the voltage support in MV grid.The analysis and simulation results carried out in this paper show improvements compared to similar solutions,i.e.the only reactive power compensation.The impact of the proposed solution has been finally evaluated under different voltage-dependence of the loads in the LV grid.展开更多
A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient volt...A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter（GSC） is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter（RSC） has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive（priority） and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.展开更多
This paper presents a controller for fast and ultrafast electric vehicle(EV)charging stations.Without affecting the charging efficiency,the proposed controller enables the charger to provide support to the interconnec...This paper presents a controller for fast and ultrafast electric vehicle(EV)charging stations.Without affecting the charging efficiency,the proposed controller enables the charger to provide support to the interconnection voltage to counter and damp its transients.Existing solutions are either hardware-based such as using supercapacitors and flywheels which increase the cost and bulkiness of the charging station,or software-based such as P/V droop methods which are still unable to provide a robust and strong voltage support.This paper proposes an emulated supercapacitor concept in the control system of the ultra-fast EV charger in an islanded DC microgrid.Thus,it converts the EV from a static load to a bus voltage supportive load,leading to reduced bus voltage oscillations during single and multiple ultra-fast EV charging operations,and rides through and provides supports during extreme external disturbances.Detailed analysis and design guidelines of the proposed controller are presented,and its effectiveness and improved performance compared with conventional techniques are shown for different case studies.展开更多
This paper proposes a grid synchronization control strategy for the grid-connected voltage source converters(VSCs)based on the voltage dynamics of the DC-link capacitor in the VSC.The voltage dynamics of the DC-link c...This paper proposes a grid synchronization control strategy for the grid-connected voltage source converters(VSCs)based on the voltage dynamics of the DC-link capacitor in the VSC.The voltage dynamics of the DC-link capacitor are used to regulate the frequency and phase angle of the inner potential of the VSC,synchronizing the VSC with grid.Firstly,in the proposed strategy,the active power regulation and grid synchronization of the VSC are combined,which are separated in the traditional control strategy.This can avoid the instability of the VSC in a weak grid with a low short circuit ratio(SCR),aroused by the dynamic interaction between the separated control loops in traditional control strategies.Secondly,the energy stored in the DC-link capacitor is directly coupled with the grid via the inner potential of the VSC,and the inertia characteristic is naturally featured in the inner potential by the proposed strategy.With the increase of the capacitance,the natural inertial response of the VSC is helpful to improve the grid frequency dynamic.Finally,simulation results are presented to validate the correctness and effectiveness of the proposed strategy in the enhancement of the grid frequency and voltage dynamic support capability.展开更多
基金supported by the National Natural Science Foundation of China-State Grid Joint Fund for Smart Grid(No.U2066210).
文摘For the hybrid multi-infeed HVDC system in which the receiving-end grid is a strong AC grid including LCC-HVDC subsystems and multiple VSC-HVDC subsystems,it has higher voltage support capability.However,for weak AC grid,the voltage support capability of the multi-VSC-HVDC subsystems to the LCC-HVDC subsystem(voltage support capability-mVSCs-LCC)can resist the risk of commutation failure.Based on this consideration,this paper proposes an evaluation index called Dynamic Voltage Support Strength Factor(DVSF)for the hybrid multi-infeed system,and uses this index to qualitatively judge the voltage support capability-mVSCs-LCC in weak AC grid.In addition,the proposed evaluation index can also indirectly judge the ability of the LCC-HVDC subsystem to suppress commutation failure.Firstly,the mathematical model of the power flow of the LCC and VSC networks in the steady-state is analyzed,and the concept of DVSF applied to hybrid multi-infeed system is proposed.Furthermore,the DVSF index is also used to qualitatively judge the voltage support capability-mVSCs-LCC.Secondly,the influence of multiple VSC-HVDC subsystems with different operation strategies on the DVSF is analyzed with reference to the concept of DVSF.Finally,the indicators proposed in this paper are compared with other evaluation indicators through MATLAB simulation software to verify its effectiveness.More importantly,the effects of multi-VSC-HVDC subsystems using different coordinated control strategies on the voltage support capability of the receiving-end LCC-HVDC subsystem are also verified.
基金supported by the National Natural Science Foundation of China under Project U22B20100in part by State Key Laboratory of Power System Operation and Control(SKLD24 KM14)State-funded Postdoctoral Researcher Program(GZC20231212)。
文摘This paper proposes a fast coordinated power control method based on two augmented channels(AC)in battery energy storage system(BESS)to improve inertial and voltage support capability,i.e.,a frequency-reactive power channel(FRPC)and a voltage-real power channel(VRPC).For frequency control in the power distribution system with high resistance/inductance ratio,the coupling mechanism between rate of change of frequency(RoCoF)and required reactive power(RRP)of grids is analyzed,indicating RoCoF is proportional to RRP.Thus,RoCoF is utilized in FRPC to generate reactive power for complementary inertial emulating control.Meanwhile,for voltage control,coupling characteristics between rate of change of voltage(RoCoV)and demanding real power(DRP)of grids is also studied,revealing RoCoV is proportional to DRP.Therefore,it can be adopted in VRPC to generate real power for complementary voltage control.Then,grid-voltage-modulated direct power control is selected as the inner power control loop to track power references with faster dynamic performance compared with traditional vector-oriented control.Finally,simulations and hardware-in-loop experiments validate improvement in performance of grid frequency and voltage control based on the proposed method.
文摘High-power trains are dynamic moving loads in the traction power supply system.When trains move to the end of the traction power supply arm,voltage drop and current phase lag along the catenary are caused by the combined effects of increased line impedance and high-power traction load.The voltage drop along the catenary line may cause overcurrent in the traction drive system,trigger power limitation protection and threaten operation safety.In this paper,a control method for the traction line-side converter with the ability of active catenary voltage support is proposed.First,a coupled dynamic impedance model of the traction power supply system and the traction drive system is established,revealing the causes of voltage drops and the mechanism of catenary voltage support.Then,the active catenary voltage support control is introduced,including the limitations on voltage support capability for safety consideration,the dynamic reactive power regulation method based on the depth of voltage drop and the requirement for strength of system.Finally,both the simulation in MATLAB/Simulink and the experiment on a full-scale test platform verify that the proposed method can quickly respond to catenary voltage drops,and dynamically support catenary voltage,without using extra compensation equipment.
基金supported in part by the National Natural Science Foundation of China under Grant U2166601 and 51977163.
文摘Generally,voltage support at the point of common coupling(PCC)of a wind farm is achieved through centralized static var generators(SVGs).Since the reactive power requirements occupy their capacity in a steady state,the reactive power support capacity of the SVG is limited during high voltage ride through(HVRT)or low voltage ride through(LVRT).While wind turbines can provide voltage support in accordance with the grid code,their responses are usually delayed due to communication and transmission lags.To enhance the dynamic performance of wind farms during fault ride-through,a reactive power substitution(RPS)control strategy is proposed in this paper.In a steady state,this RPS control method preferentially utilizes the remaining capacity of wind turbines to substitute for the output of the SVG.Considering differences in terminal voltage characteristics and operating conditions,this RPS control method employs a particle swarm optimization(PSO)algorithm to ensure that wind turbines can provide their optimal reactive power support capacity.When the grid voltage swells or drops,the SVG has a sufficient reactive power reserve to support the grid quickly.This paper utilizes a regional power grid incorporating two wind farms connected to different buses as a case study to validate this RPS control strategy.
基金the German Federal Ministry of Education and Research(BMBF)within the Kopernikus Project ENSURE“New ENergy grid StructURes for the German Energiewende”(03SFK1I0 and 03SFK1I0-2)the Ministry of Science,Research and the Arts of the State of Baden-Württemberg Nr.33−7533−30−10/67/1.
文摘In the last decades the voltage regulation has been challenged by the increase of power variability in the electric grid,due to the spread of non-dispatchable generation sources.This paper introduces a Smart Transformer(ST)-based Medium Voltage(MV)grid support by means of active power control in the ST-fed Low Voltage(LV)grid.The aim of the proposed strategy is to improve the voltage profile in MV grids before the operation of On-Load Tap Changer in the primary substation transformer,which needs tens of seconds.This is realized through reactive power injection by the AC/DC MV converter and simultaneous decrease of the active power consumption of voltage-dependent loads in ST-fed LV grid,controlling the ST output voltage.The last feature has two main effects:the first is to reduce the active power withdrawn from MV grid,and consequently the MV voltage drop caused by the active current component.At the same time,higher reactive power injection capability in the MV converter is unlocked,due to the lower active power demand.As result,the ST increases the voltage support in MV grid.The analysis and simulation results carried out in this paper show improvements compared to similar solutions,i.e.the only reactive power compensation.The impact of the proposed solution has been finally evaluated under different voltage-dependence of the loads in the LV grid.
基金supported by the National Natural Science Foundation of China(Grant No.51307124)the Major Program of the National Natural Science Foundation of China(Grant No.51190105)
文摘A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter（GSC） is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter（RSC） has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive（priority） and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.
文摘This paper presents a controller for fast and ultrafast electric vehicle(EV)charging stations.Without affecting the charging efficiency,the proposed controller enables the charger to provide support to the interconnection voltage to counter and damp its transients.Existing solutions are either hardware-based such as using supercapacitors and flywheels which increase the cost and bulkiness of the charging station,or software-based such as P/V droop methods which are still unable to provide a robust and strong voltage support.This paper proposes an emulated supercapacitor concept in the control system of the ultra-fast EV charger in an islanded DC microgrid.Thus,it converts the EV from a static load to a bus voltage supportive load,leading to reduced bus voltage oscillations during single and multiple ultra-fast EV charging operations,and rides through and provides supports during extreme external disturbances.Detailed analysis and design guidelines of the proposed controller are presented,and its effectiveness and improved performance compared with conventional techniques are shown for different case studies.
基金supported by Science and Technology Project of Yunnan Power Grid Co.,Ltd.(No.YNKJXM20222105)。
文摘This paper proposes a grid synchronization control strategy for the grid-connected voltage source converters(VSCs)based on the voltage dynamics of the DC-link capacitor in the VSC.The voltage dynamics of the DC-link capacitor are used to regulate the frequency and phase angle of the inner potential of the VSC,synchronizing the VSC with grid.Firstly,in the proposed strategy,the active power regulation and grid synchronization of the VSC are combined,which are separated in the traditional control strategy.This can avoid the instability of the VSC in a weak grid with a low short circuit ratio(SCR),aroused by the dynamic interaction between the separated control loops in traditional control strategies.Secondly,the energy stored in the DC-link capacitor is directly coupled with the grid via the inner potential of the VSC,and the inertia characteristic is naturally featured in the inner potential by the proposed strategy.With the increase of the capacitance,the natural inertial response of the VSC is helpful to improve the grid frequency dynamic.Finally,simulation results are presented to validate the correctness and effectiveness of the proposed strategy in the enhancement of the grid frequency and voltage dynamic support capability.
