With the high penetration of renewable energy and the rapid development of AC/DC(Alternating Current/Direct Current)hybrid power grid,the power grid is confronted with challenges such as frequent voltage fluctuations ...With the high penetration of renewable energy and the rapid development of AC/DC(Alternating Current/Direct Current)hybrid power grid,the power grid is confronted with challenges such as frequent voltage fluctuations and insufficient dynamic reactive power reserves.Full utilization of unified power flow controller(UPFC)in dynamic voltage regulation is of great significance for mitigating voltage excursions of the power grid.This paper proposes a double-time-scale dynamic reactive power optimization method for the AC/DC hybrid power grid with UPFC.A control framework for reactive power optimization of slow-time-scale and fast-time-scale is constructed incorporating the LCC-HVDC and UPFC.In this method,the slow-time-scale aims to improve the voltage profiles and reduce the system cost by setting the voltage regulation weight coefficients based on trajectory sensitivity to preserve reactive power regulation capability.The fast-time-scale adopts an adaptive feedback control mechanism.When slowtime-scale optimization is insufficient to keep the voltage within a safe range,it adjusts the real-time reactive power output of the UPFC,and damps rapid voltage swings accordingly.By implementing the additional fast-time-scale control method,the frequent variations of both the Photovoltaic(PV)and load are managed for the reactive power compensation.Case studies on a modified IEEE-30 bus system demonstrate that compared with the conventional control method,the proposed method reduces the maximum voltage deviation by 3.17%compared to the baseline,while ensuring the economic efficiency.展开更多
The increasing integration of distributed renewable energy sources in the distribution network leads to unbalanced load rates in the distribution network.The traditional load balancing methods are mainly based on netw...The increasing integration of distributed renewable energy sources in the distribution network leads to unbalanced load rates in the distribution network.The traditional load balancing methods are mainly based on network reconfiguration,which have problems such as a long time scale and poor adaptability.In response to these issues,this paper proposes a distributed iterative learning control(ILC)strategy for load balancing in flexible AC/DC hybrid distribution systems.This method combines the consensus algorithm with the ILC mechanism to construct a multi-terminal AC/DC flexible interconnection system model.It is only necessary to measure the load rate of adjacent units without observing the overall system status,which greatly reduces complexity and enhances robustness.In this paper,a new energy photovoltaic and energy storage integrated system was built through MATLAB/Simulink simulation,and the effectiveness of the proposed strategy under normal working conditions and port faults was verified through this system.Through comparative studies with event-triggered control and traditional consensus algorithms,as well as real-time simulations on the RT-LAB simulation platform,it has been confirmed that this method has superior performance in terms of convergence speed,steady-state accuracy,and dynamic response,and has the potential to be applied in practical models.It is suitable for application in medium and low voltage distribution systems with new energy access.展开更多
This paper presents an optimal operation method for embedded DC interconnections based on low-voltage AC/DC distribution areas(EDC-LVDA)under three-phase unbalanced compensation conditions.It can optimally determine t...This paper presents an optimal operation method for embedded DC interconnections based on low-voltage AC/DC distribution areas(EDC-LVDA)under three-phase unbalanced compensation conditions.It can optimally determine the transmission power of the DC and AC paths to simultaneously improve voltage quality and reduce losses.First,considering the embedded interconnected,unbalanced power structure of the distribution area,a power flow calculation method for EDC-LVDA that accounts for three-phase unbalanced compensation is introduced.This method accurately describes the power flow distribution characteristics under both AC and DC power allocation scenarios.Second,an optimization scheduling model for EDC-LVDA under three-phase unbalanced conditions is developed,incorporating network losses,voltage quality,DC link losses,and unbalance levels.The proposed model employs an improved particle swarm optimization(IPSO)two-layer algorithm to autonomously select different power allocation coefficients for the DC link and AC section under various operating conditions.This enables embedded economic optimization scheduling while maintaining compensation for unbalanced conditions.Finally,a case study based on the IEEE 13-node system for EDC-LVDA is conducted and tested.The results show that the proposed optimal operation method achieves a 100%voltage compliance rate and reduces network losses by 13.8%,while ensuring three-phase power balance compensation.This provides a practical solution for the modernization and upgrading of low-voltage power grids.展开更多
混合交流(alternating current,AC)/直流(direct current,DC)/分布式储能(distributed energy storage,DS)微电网通过整合交流、直流及分布式储能子网,可有效提升偏远地区的能源可及性与供电稳定性。然而,传统微电网结构单一,多聚焦于...混合交流(alternating current,AC)/直流(direct current,DC)/分布式储能(distributed energy storage,DS)微电网通过整合交流、直流及分布式储能子网,可有效提升偏远地区的能源可及性与供电稳定性。然而,传统微电网结构单一,多聚焦于交流频率或直流母线电压的单一调节。相比之下,混合微电网中频率和电压相互耦合,必须同时调节频率和电压,防止其出现暂态深度跌落和稳态大幅偏移。针对上述问题,该文提出面向混合微电网的暂态全局惯量互济与稳态频率/电压自主恢复控制策略,实现子网间惯量多边传导和频率/电压稳态自主恢复;此外,该文构建混合微电网的全局等效电路模型,从电路视角刻画系统的全时间尺度响应特性,阐明交直流混联系统的暂态惯量传导和频率/电压自主恢复机制;最后,基于硬件在环实验平台,验证所提控制策略与等效电路模型的有效性。展开更多
三相双有源桥双向AC/DC变换器具备高效双向变换和升降压运行的优势,适合应用于储能系统,但是该变换器在宽电压范围下运行时的参数设计与性能优化面临挑战。针对适用于该变换器在宽电压范围下实现零电压开关(zero voltage switching,ZVS...三相双有源桥双向AC/DC变换器具备高效双向变换和升降压运行的优势,适合应用于储能系统,但是该变换器在宽电压范围下运行时的参数设计与性能优化面临挑战。针对适用于该变换器在宽电压范围下实现零电压开关(zero voltage switching,ZVS)的混合调制策略,提出基于遗传算法的多目标参数优化方法;以开关管损耗和电感电流有效值作为优化目标,建立多目标优化模型,对电感值和变压器匝比进行求解;在实验室搭建一台1.5 kW的原理样机,实验结果表明,采用混合调制策略的变换器可在宽电压和宽功率范围下实现ZVS。此外,多目标优化参数设计方法能降低变换器的损耗,从而提升效率,为其性能提升提供了有效方案。展开更多
In wind and solar renewable-dominant hybrid alternating current/direct current(AC/DC)power systems,the active power of high-voltage direct current(HVDC)system is significantly limited by the security and stability eve...In wind and solar renewable-dominant hybrid alternating current/direct current(AC/DC)power systems,the active power of high-voltage direct current(HVDC)system is significantly limited by the security and stability events caused by cascading failures.To identify critical lines in cascading failures,a rapid risk assessment method is proposed based on the gradient boosting decision tree(GBDT)and frequent pat-tern growth(FP-Growth)algorithms.First,security and stability events triggered by cascading failures are analyzed to explain the impact of cascading failures on the maximum DC power.Then,a cascading failure risk index is defined,focusing on the DC power being limited.To handle the strong nonlinear relationship between the maximum DC power and cascading failures,a GBDT with an update strategy is utilized to rapidly predict the maximum DC power under uncertain operating conditions.Finally,the FP-Growth algorithm is improved to mine frequent patterns in cascading failures.The importance index for each fault in a frequent pattern is defined by evaluating its impact on cascading failures,enabling the identification of critical lines.Simulation results of a modified Ningxia–Shandong hybrid AC/DC system in China demonstrate that the proposed method can rapidly assess the risk of cascading failures and effectively identify critical lines.展开更多
The AC/DC hybrid distribution network is one of the trends in distribution network development, which poses great challenges to the traditional distribution transformer. In this paper, a new topology suitable for AC/D...The AC/DC hybrid distribution network is one of the trends in distribution network development, which poses great challenges to the traditional distribution transformer. In this paper, a new topology suitable for AC/DC hybrid distribution network is put forward according to the demands of power grid, with advantages of accepting DG and DC loads, while clearing DC fault by blocking the clamping double sub-module(CDSM) of input stage. Then, this paper shows the typical structure of AC/DC distribution network that is hand in hand. Based on the new topology, this paper designs the control and modulation strategies of each stage, where the outer loop controller of input stage is emphasized for its twocontrol mode. At last, the rationality of new topology and the validity of control strategies are verified by the steady and dynamic state simulation. At the same time, the simulation results highlight the role of PET in energy regulation.展开更多
基金Project Supported by Science and Technology Project of State Grid Jiangsu Electric Power Company:Research on Weak Node Identification and UPFC Response Strategy for AC/DC Hybrid Receiving Urban Power Grid(J2024013).
摘要With the high penetration of renewable energy and the rapid development of AC/DC(Alternating Current/Direct Current)hybrid power grid,the power grid is confronted with challenges such as frequent voltage fluctuations and insufficient dynamic reactive power reserves.Full utilization of unified power flow controller(UPFC)in dynamic voltage regulation is of great significance for mitigating voltage excursions of the power grid.This paper proposes a double-time-scale dynamic reactive power optimization method for the AC/DC hybrid power grid with UPFC.A control framework for reactive power optimization of slow-time-scale and fast-time-scale is constructed incorporating the LCC-HVDC and UPFC.In this method,the slow-time-scale aims to improve the voltage profiles and reduce the system cost by setting the voltage regulation weight coefficients based on trajectory sensitivity to preserve reactive power regulation capability.The fast-time-scale adopts an adaptive feedback control mechanism.When slowtime-scale optimization is insufficient to keep the voltage within a safe range,it adjusts the real-time reactive power output of the UPFC,and damps rapid voltage swings accordingly.By implementing the additional fast-time-scale control method,the frequent variations of both the Photovoltaic(PV)and load are managed for the reactive power compensation.Case studies on a modified IEEE-30 bus system demonstrate that compared with the conventional control method,the proposed method reduces the maximum voltage deviation by 3.17%compared to the baseline,while ensuring the economic efficiency.
基金funded by State Grid Anhui Electric Power Co. (No. B3120524003J).
摘要The increasing integration of distributed renewable energy sources in the distribution network leads to unbalanced load rates in the distribution network.The traditional load balancing methods are mainly based on network reconfiguration,which have problems such as a long time scale and poor adaptability.In response to these issues,this paper proposes a distributed iterative learning control(ILC)strategy for load balancing in flexible AC/DC hybrid distribution systems.This method combines the consensus algorithm with the ILC mechanism to construct a multi-terminal AC/DC flexible interconnection system model.It is only necessary to measure the load rate of adjacent units without observing the overall system status,which greatly reduces complexity and enhances robustness.In this paper,a new energy photovoltaic and energy storage integrated system was built through MATLAB/Simulink simulation,and the effectiveness of the proposed strategy under normal working conditions and port faults was verified through this system.Through comparative studies with event-triggered control and traditional consensus algorithms,as well as real-time simulations on the RT-LAB simulation platform,it has been confirmed that this method has superior performance in terms of convergence speed,steady-state accuracy,and dynamic response,and has the potential to be applied in practical models.It is suitable for application in medium and low voltage distribution systems with new energy access.
基金supported by the key technology project of China Southern Power Grid Corporation(GZKJXM20220041)partly by the National Key Research and Development Plan(2022YFE0205300).
摘要This paper presents an optimal operation method for embedded DC interconnections based on low-voltage AC/DC distribution areas(EDC-LVDA)under three-phase unbalanced compensation conditions.It can optimally determine the transmission power of the DC and AC paths to simultaneously improve voltage quality and reduce losses.First,considering the embedded interconnected,unbalanced power structure of the distribution area,a power flow calculation method for EDC-LVDA that accounts for three-phase unbalanced compensation is introduced.This method accurately describes the power flow distribution characteristics under both AC and DC power allocation scenarios.Second,an optimization scheduling model for EDC-LVDA under three-phase unbalanced conditions is developed,incorporating network losses,voltage quality,DC link losses,and unbalance levels.The proposed model employs an improved particle swarm optimization(IPSO)two-layer algorithm to autonomously select different power allocation coefficients for the DC link and AC section under various operating conditions.This enables embedded economic optimization scheduling while maintaining compensation for unbalanced conditions.Finally,a case study based on the IEEE 13-node system for EDC-LVDA is conducted and tested.The results show that the proposed optimal operation method achieves a 100%voltage compliance rate and reduces network losses by 13.8%,while ensuring three-phase power balance compensation.This provides a practical solution for the modernization and upgrading of low-voltage power grids.
摘要混合交流(alternating current,AC)/直流(direct current,DC)/分布式储能(distributed energy storage,DS)微电网通过整合交流、直流及分布式储能子网,可有效提升偏远地区的能源可及性与供电稳定性。然而,传统微电网结构单一,多聚焦于交流频率或直流母线电压的单一调节。相比之下,混合微电网中频率和电压相互耦合,必须同时调节频率和电压,防止其出现暂态深度跌落和稳态大幅偏移。针对上述问题,该文提出面向混合微电网的暂态全局惯量互济与稳态频率/电压自主恢复控制策略,实现子网间惯量多边传导和频率/电压稳态自主恢复;此外,该文构建混合微电网的全局等效电路模型,从电路视角刻画系统的全时间尺度响应特性,阐明交直流混联系统的暂态惯量传导和频率/电压自主恢复机制;最后,基于硬件在环实验平台,验证所提控制策略与等效电路模型的有效性。
摘要三相双有源桥双向AC/DC变换器具备高效双向变换和升降压运行的优势,适合应用于储能系统,但是该变换器在宽电压范围下运行时的参数设计与性能优化面临挑战。针对适用于该变换器在宽电压范围下实现零电压开关(zero voltage switching,ZVS)的混合调制策略,提出基于遗传算法的多目标参数优化方法;以开关管损耗和电感电流有效值作为优化目标,建立多目标优化模型,对电感值和变压器匝比进行求解;在实验室搭建一台1.5 kW的原理样机,实验结果表明,采用混合调制策略的变换器可在宽电压和宽功率范围下实现ZVS。此外,多目标优化参数设计方法能降低变换器的损耗,从而提升效率,为其性能提升提供了有效方案。
基金supported by the National Key Research and Development Program of China"Key technologies for system stability and HVDC transmission of large-scale renewable energy generation base without conventional power support(2022YFB2402700)"the project of the State Grid Corporation of China(52272222001J).
摘要In wind and solar renewable-dominant hybrid alternating current/direct current(AC/DC)power systems,the active power of high-voltage direct current(HVDC)system is significantly limited by the security and stability events caused by cascading failures.To identify critical lines in cascading failures,a rapid risk assessment method is proposed based on the gradient boosting decision tree(GBDT)and frequent pat-tern growth(FP-Growth)algorithms.First,security and stability events triggered by cascading failures are analyzed to explain the impact of cascading failures on the maximum DC power.Then,a cascading failure risk index is defined,focusing on the DC power being limited.To handle the strong nonlinear relationship between the maximum DC power and cascading failures,a GBDT with an update strategy is utilized to rapidly predict the maximum DC power under uncertain operating conditions.Finally,the FP-Growth algorithm is improved to mine frequent patterns in cascading failures.The importance index for each fault in a frequent pattern is defined by evaluating its impact on cascading failures,enabling the identification of critical lines.Simulation results of a modified Ningxia–Shandong hybrid AC/DC system in China demonstrate that the proposed method can rapidly assess the risk of cascading failures and effectively identify critical lines.
基金supported by National Key Research and Development Program of China (2016YFB0900500,2017YFB0903100)the State Grid Science and Technology Project (SGRI-DL-F1-51-011)
摘要The AC/DC hybrid distribution network is one of the trends in distribution network development, which poses great challenges to the traditional distribution transformer. In this paper, a new topology suitable for AC/DC hybrid distribution network is put forward according to the demands of power grid, with advantages of accepting DG and DC loads, while clearing DC fault by blocking the clamping double sub-module(CDSM) of input stage. Then, this paper shows the typical structure of AC/DC distribution network that is hand in hand. Based on the new topology, this paper designs the control and modulation strategies of each stage, where the outer loop controller of input stage is emphasized for its twocontrol mode. At last, the rationality of new topology and the validity of control strategies are verified by the steady and dynamic state simulation. At the same time, the simulation results highlight the role of PET in energy regulation.