In this paper,a grid interface current control strategy is presented for a DC microgrid,which aims to reduce the disturbance from PV generation and the load variation to the main grid without a grid interface converte...In this paper,a grid interface current control strategy is presented for a DC microgrid,which aims to reduce the disturbance from PV generation and the load variation to the main grid without a grid interface converter.The grid interface current is directly controlled by a battery DC-DC converter within the DC microgrid.Based on a comprehensive analysis of the battery DC-DC converter and interface current control,the control system has been mathematically modelled.This enabled two transfer functions to be derived that reflect the dynamic response of the inductor current to the duty cycle variation(inner loop),and the dynamic response of the grid interface current to the inductor current variation(outer loop).Experimental study has been done to assess the effectiveness of the proposed control strategy.The experimental results indicate that the proposed control strategy has a good performance to control the grid interface current without an interface converter,regardless the variations of both PV and the load conditions.展开更多
This paper deeply introduces a brand-new research method for the synchronous characteristics of DC microgrid bus voltage and an improved synchronous control strategy.This method mainly targets the problem of bus volta...This paper deeply introduces a brand-new research method for the synchronous characteristics of DC microgrid bus voltage and an improved synchronous control strategy.This method mainly targets the problem of bus voltage oscillation caused by the bifurcation behavior of DC microgrid converters.Firstly,the article elaborately establishes a mathematical model of a single distributed power source with hierarchical control.On this basis,a smallworld network model that can better adapt to the topology structure of DC microgrids is further constructed.Then,a voltage synchronization analysis method based on the main stability function is proposed,and the synchronous characteristics of DC bus voltage are deeply studied by analyzing the size of the minimum non-zero eigenvalue.In view of the situation that the line coupling strength between distributed power sources is insufficient to achieve bus voltage synchronization,this paper innovatively proposes a new improved adaptive controller to effectively control voltage synchronization.And the convergence of the designed controller is strictly proved by using Lyapunov’s stability theorem.Finally,the effectiveness and feasibility of the designed controller in this paper are fully verified through detailed simulation experiments.After comparative analysis with the traditional adaptive controller,it is found that the newly designed controller can make the bus voltages of each distributed power source achieve synchronization more quickly,and is significantly superior to the traditional adaptive controller in terms of anti-interference performance.展开更多
Conventional coordinated control strategies for DC bus voltage signal(DBS)in islanded DC microgrids(IDCMGs)struggle with coordinating multiple distributed generators(DGs)and cannot effectively incorporate state of cha...Conventional coordinated control strategies for DC bus voltage signal(DBS)in islanded DC microgrids(IDCMGs)struggle with coordinating multiple distributed generators(DGs)and cannot effectively incorporate state of charge(SOC)information of the energy storage system,thereby reducing the system flexibility.In this study,we propose an adaptive coordinated control strategy that employs a two-layer fuzzy neural network controller(FNNC)to adapt to varying operating conditions in an IDCMG with multiple PV and battery energy storage system(BESS)units.The first-layer FNNC generates optimal operating mode commands for each DG,thereby avoiding the requirement for complex operating modes based on SOC segmentation.An optimal switching sequence logic prioritizes the most appropriate units during mode transitions.The second-layer FNNC dynamically adjusts the droop power to overcome power distribution challenges among DG groups.This helps in preventing the PV power from exceeding the limits and mitigating the risk of BESS overcharging or over-discharging.The simulation results indicate that the proposed strategy enhances the coordinated operation of multi-DG IDCMGs,thereby ensuring the efficient and safe utilization of PV and BESS.展开更多
The dynamic average consensus(DAC)algorithm is to enable a group of networked agents to track the average of their time-varying reference signals.For most existing DAC algorithms,a necessary assumption is that the upp...The dynamic average consensus(DAC)algorithm is to enable a group of networked agents to track the average of their time-varying reference signals.For most existing DAC algorithms,a necessary assumption is that the upper bounds of the reference signals and their derivatives are known in advance,thereby posing significant challenges in practical scenarios.Introducing adaptive gains in DAC algorithms provides a remedy by relaxing this assumption.However,the current adaptive gains used in this type of DAC algorithms are non-decreasing and may increase to infinity if persist disturbance exists.In order to overcome this defect,this paper presents a novel DAC algorithm with modified adaptive gains.This approach obviates the necessity for prior knowledge concerning the upper bounds of the reference signals and their derivatives.Moreover,the adaptive gains are able to remain bounded even in the presence of external disturbances.Furthermore,the proposed adaptive DAC algorithm is employed to address the distributed secondary control problem of DC microgrids.Comparative case studies are provided to verify the superiority of the proposed DAC algorithm.展开更多
Low-voltage direct current(DC)microgrids have recently emerged as a promising and viable alternative to traditional alternating cur-rent(AC)microgrids,offering numerous advantages.Consequently,researchers are explorin...Low-voltage direct current(DC)microgrids have recently emerged as a promising and viable alternative to traditional alternating cur-rent(AC)microgrids,offering numerous advantages.Consequently,researchers are exploring the potential of DC microgrids across var-ious configurations.However,despite the sustainability and accuracy offered by DC microgrids,they pose various challenges when integrated into modern power distribution systems.Among these challenges,fault diagnosis holds significant importance.Rapid fault detection in DC microgrids is essential to maintain stability and ensure an uninterrupted power supply to critical loads.A primary chal-lenge is the lack of standards and guidelines for the protection and safety of DC microgrids,including fault detection,location,and clear-ing procedures for both grid-connected and islanded modes.In response,this study presents a brief overview of various approaches for protecting DC microgrids.展开更多
Fluxgate current sensors(FGCSs)are increasingly employed in power systems due to their high-precision characteristics,yet their measurement flexibility remains constrained by conventional closed-core designs.To addres...Fluxgate current sensors(FGCSs)are increasingly employed in power systems due to their high-precision characteristics,yet their measurement flexibility remains constrained by conventional closed-core designs.To address this limitation,we proposed a split-core sensor structure comprising four magnetic core strips,which achieved non-intrusive current measurement while maintaining detection accuracy.An analytical model of the induced electromotive force was established based on the probe’s geometric configuration,followed by finite element simulations to optimize key parameters including core radius,core width,excitation coil turns,and sensing coil configuration.A complete prototype integrating the measurement probe,excitation circuit,and signal processing circuitry was developed and experimentally validated.The experimental results show a sensitivity of 0.1099 V/A,a hysteresis error of 0.559%,and a repeatability error of 1.574%over a measurement range of±10 A.After polynomial fitting-based error compensation,the nonlinearity error was reduced to 0.208%,achieving performance comparable to closed-core sensors.This work provided a practical solution for applications demanding both high measurement accuracy and installation flexibility.展开更多
In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results i...In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results in increased leakage current,decreased breakdown voltage,and lower nonlinearity,ultimately compromising their protective performance.To investigate the evolution in electrical properties during DC aging,this work developed a finite element model based on Voronoi networks and conducted accelerated aging tests on commercial varistors.Throughout the aging process,current-voltage characteristics and Schottky barrier parameters were measured and analyzed.The results indicate that when subjected to constant voltage,current flows through regions with larger grain sizes,forming discharge channels.As aging progresses,the current focus increases on these channels,leading to a decline in the varistor’s overall performance.Furthermore,analysis of the Schottky barrier parameters shows that the changes in electrical performance during aging are non-monotonic.These findings offer theoretical support for understanding the aging mechanisms and condition assessment of modern stable ZnO varistors.展开更多
柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,...柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,提出一种利用限流电感两端电压比值实现线路故障识别的方法。在PSCAD/EMTDC仿真平台建立四端模块化多电平换流器型柔性直流输电(modular multilevel converter high voltage direct current,MMC-HVDC)电网模型,对所提出的方法进行故障启动、类型识别和极线选择验证。在故障被正确识别后,相应的直流断路器(DC circuit breaker,DCCB)能够正确动作并隔离故障。此外,还对系统的性能指标以及故障过渡电阻值、故障后系统的噪声、故障距离和通信误差方面因素进行可行性分析。研究结果表明,所提出的故障保护方案能够准确识别并且快速隔离故障,从而保障电网安全稳定运行。展开更多
This article presents a distributed periodic eventtriggered(PET)optimal control scheme to achieve generation cost minimization and average bus voltage regulation in DC microgrids.In order to accommodate the generation...This article presents a distributed periodic eventtriggered(PET)optimal control scheme to achieve generation cost minimization and average bus voltage regulation in DC microgrids.In order to accommodate the generation constraints of the distributed generators(DGs),a virtual incremental cost is firstly designed,based on which an optimality condition is derived to facilitate the control design.To meet the discrete-time(DT)nature of modern control systems,the optimal controller is directly developed in the DT domain.Afterward,to reduce the communication requirement among the controllers,a distributed event-triggered mechanism is introduced for the DT optimal controller.The event-triggered condition is detected periodically and therefore naturally avoids the Zeno phenomenon.The closed-loop system stability is proved by the Lyapunov synthesis for switched systems.The generation cost minimization and average bus voltage regulation are obtained at the equilibrium point.Finally,switch-level microgrid simulations validate the performance of the proposed optimal controller.展开更多
基金funding from the U.K.EPSRC UKRI Innovation Fellowship scheme(EP/S001662/2)the European Union’s Horizon 2020 research and innovation programme under grant agreement No.734796.
文摘In this paper,a grid interface current control strategy is presented for a DC microgrid,which aims to reduce the disturbance from PV generation and the load variation to the main grid without a grid interface converter.The grid interface current is directly controlled by a battery DC-DC converter within the DC microgrid.Based on a comprehensive analysis of the battery DC-DC converter and interface current control,the control system has been mathematically modelled.This enabled two transfer functions to be derived that reflect the dynamic response of the inductor current to the duty cycle variation(inner loop),and the dynamic response of the grid interface current to the inductor current variation(outer loop).Experimental study has been done to assess the effectiveness of the proposed control strategy.The experimental results indicate that the proposed control strategy has a good performance to control the grid interface current without an interface converter,regardless the variations of both PV and the load conditions.
基金supported by the National Natural Science Foundation of China(Nos.51767017 and 51867015)the Basic Research and Innovation Group Project of Gansu(No.18JR3RA13)the Major Science and Technology Project of Gansu(No.19ZD2GA003).
文摘This paper deeply introduces a brand-new research method for the synchronous characteristics of DC microgrid bus voltage and an improved synchronous control strategy.This method mainly targets the problem of bus voltage oscillation caused by the bifurcation behavior of DC microgrid converters.Firstly,the article elaborately establishes a mathematical model of a single distributed power source with hierarchical control.On this basis,a smallworld network model that can better adapt to the topology structure of DC microgrids is further constructed.Then,a voltage synchronization analysis method based on the main stability function is proposed,and the synchronous characteristics of DC bus voltage are deeply studied by analyzing the size of the minimum non-zero eigenvalue.In view of the situation that the line coupling strength between distributed power sources is insufficient to achieve bus voltage synchronization,this paper innovatively proposes a new improved adaptive controller to effectively control voltage synchronization.And the convergence of the designed controller is strictly proved by using Lyapunov’s stability theorem.Finally,the effectiveness and feasibility of the designed controller in this paper are fully verified through detailed simulation experiments.After comparative analysis with the traditional adaptive controller,it is found that the newly designed controller can make the bus voltages of each distributed power source achieve synchronization more quickly,and is significantly superior to the traditional adaptive controller in terms of anti-interference performance.
基金supported by National Key R&D Program of ChinaunderGrant,(2021YFB2601403).
文摘Conventional coordinated control strategies for DC bus voltage signal(DBS)in islanded DC microgrids(IDCMGs)struggle with coordinating multiple distributed generators(DGs)and cannot effectively incorporate state of charge(SOC)information of the energy storage system,thereby reducing the system flexibility.In this study,we propose an adaptive coordinated control strategy that employs a two-layer fuzzy neural network controller(FNNC)to adapt to varying operating conditions in an IDCMG with multiple PV and battery energy storage system(BESS)units.The first-layer FNNC generates optimal operating mode commands for each DG,thereby avoiding the requirement for complex operating modes based on SOC segmentation.An optimal switching sequence logic prioritizes the most appropriate units during mode transitions.The second-layer FNNC dynamically adjusts the droop power to overcome power distribution challenges among DG groups.This helps in preventing the PV power from exceeding the limits and mitigating the risk of BESS overcharging or over-discharging.The simulation results indicate that the proposed strategy enhances the coordinated operation of multi-DG IDCMGs,thereby ensuring the efficient and safe utilization of PV and BESS.
基金supported in part by the National Natural Science Foundation of China(20221017-10,62573258,62188101)the National Natural Science Foundation of Shandong Province(ZR2024 JQ018,ZR2022MF227).
文摘The dynamic average consensus(DAC)algorithm is to enable a group of networked agents to track the average of their time-varying reference signals.For most existing DAC algorithms,a necessary assumption is that the upper bounds of the reference signals and their derivatives are known in advance,thereby posing significant challenges in practical scenarios.Introducing adaptive gains in DAC algorithms provides a remedy by relaxing this assumption.However,the current adaptive gains used in this type of DAC algorithms are non-decreasing and may increase to infinity if persist disturbance exists.In order to overcome this defect,this paper presents a novel DAC algorithm with modified adaptive gains.This approach obviates the necessity for prior knowledge concerning the upper bounds of the reference signals and their derivatives.Moreover,the adaptive gains are able to remain bounded even in the presence of external disturbances.Furthermore,the proposed adaptive DAC algorithm is employed to address the distributed secondary control problem of DC microgrids.Comparative case studies are provided to verify the superiority of the proposed DAC algorithm.
文摘Low-voltage direct current(DC)microgrids have recently emerged as a promising and viable alternative to traditional alternating cur-rent(AC)microgrids,offering numerous advantages.Consequently,researchers are exploring the potential of DC microgrids across var-ious configurations.However,despite the sustainability and accuracy offered by DC microgrids,they pose various challenges when integrated into modern power distribution systems.Among these challenges,fault diagnosis holds significant importance.Rapid fault detection in DC microgrids is essential to maintain stability and ensure an uninterrupted power supply to critical loads.A primary chal-lenge is the lack of standards and guidelines for the protection and safety of DC microgrids,including fault detection,location,and clear-ing procedures for both grid-connected and islanded modes.In response,this study presents a brief overview of various approaches for protecting DC microgrids.
基金supported by Yunnan Fundamental Research Projects(No.202301AT070181)Yunnan Fundamental Research Projects(No.202401CF070126)+1 种基金Xingdian Talent Support Program of Yunnan Province(No.KKRD202203070)Yunnan High level Science and Technology Talents and Innovation Team Selection Special Project(No.202405AS350001).
文摘Fluxgate current sensors(FGCSs)are increasingly employed in power systems due to their high-precision characteristics,yet their measurement flexibility remains constrained by conventional closed-core designs.To address this limitation,we proposed a split-core sensor structure comprising four magnetic core strips,which achieved non-intrusive current measurement while maintaining detection accuracy.An analytical model of the induced electromotive force was established based on the probe’s geometric configuration,followed by finite element simulations to optimize key parameters including core radius,core width,excitation coil turns,and sensing coil configuration.A complete prototype integrating the measurement probe,excitation circuit,and signal processing circuitry was developed and experimentally validated.The experimental results show a sensitivity of 0.1099 V/A,a hysteresis error of 0.559%,and a repeatability error of 1.574%over a measurement range of±10 A.After polynomial fitting-based error compensation,the nonlinearity error was reduced to 0.208%,achieving performance comparable to closed-core sensors.This work provided a practical solution for applications demanding both high measurement accuracy and installation flexibility.
文摘In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results in increased leakage current,decreased breakdown voltage,and lower nonlinearity,ultimately compromising their protective performance.To investigate the evolution in electrical properties during DC aging,this work developed a finite element model based on Voronoi networks and conducted accelerated aging tests on commercial varistors.Throughout the aging process,current-voltage characteristics and Schottky barrier parameters were measured and analyzed.The results indicate that when subjected to constant voltage,current flows through regions with larger grain sizes,forming discharge channels.As aging progresses,the current focus increases on these channels,leading to a decline in the varistor’s overall performance.Furthermore,analysis of the Schottky barrier parameters shows that the changes in electrical performance during aging are non-monotonic.These findings offer theoretical support for understanding the aging mechanisms and condition assessment of modern stable ZnO varistors.
文摘柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,提出一种利用限流电感两端电压比值实现线路故障识别的方法。在PSCAD/EMTDC仿真平台建立四端模块化多电平换流器型柔性直流输电(modular multilevel converter high voltage direct current,MMC-HVDC)电网模型,对所提出的方法进行故障启动、类型识别和极线选择验证。在故障被正确识别后,相应的直流断路器(DC circuit breaker,DCCB)能够正确动作并隔离故障。此外,还对系统的性能指标以及故障过渡电阻值、故障后系统的噪声、故障距离和通信误差方面因素进行可行性分析。研究结果表明,所提出的故障保护方案能够准确识别并且快速隔离故障,从而保障电网安全稳定运行。
基金supported by the U.S.Office of Naval Research(N00014-21-1-2175)。
文摘This article presents a distributed periodic eventtriggered(PET)optimal control scheme to achieve generation cost minimization and average bus voltage regulation in DC microgrids.In order to accommodate the generation constraints of the distributed generators(DGs),a virtual incremental cost is firstly designed,based on which an optimality condition is derived to facilitate the control design.To meet the discrete-time(DT)nature of modern control systems,the optimal controller is directly developed in the DT domain.Afterward,to reduce the communication requirement among the controllers,a distributed event-triggered mechanism is introduced for the DT optimal controller.The event-triggered condition is detected periodically and therefore naturally avoids the Zeno phenomenon.The closed-loop system stability is proved by the Lyapunov synthesis for switched systems.The generation cost minimization and average bus voltage regulation are obtained at the equilibrium point.Finally,switch-level microgrid simulations validate the performance of the proposed optimal controller.
