A microgrid is defined as a local electric power distribution system with diverse DG （distributed generation） units, energy storage systems, and loads, which can operate as a part of the distribution system or when ...A microgrid is defined as a local electric power distribution system with diverse DG （distributed generation） units, energy storage systems, and loads, which can operate as a part of the distribution system or when needed can operate in an islanded mode. Energy storage systems play a key role in improving security, stability, and power quality of the microgrid. During grid-connected mode, these storage units are charged from various DG sources as well as the main grid. During islanded mode, DG sources along with the storage units need to supply the load. Power electronic interfaces between the microgrid buses and the storage units should be able to detect the mode of operation, allow seamless transition between the modes, and allow power flow in both directions, while maintaining stability and power quality. An overview of bidirectional converter topologies relevant to microgrid energy storage application and their control strategies will be presented in this paper.展开更多
Hybrid AC/DC distribution networks are promising candidates for future applications due to their rapid advancement in power electronics technology.They use interface converters(IFCs)to link DC and AC distribution netw...Hybrid AC/DC distribution networks are promising candidates for future applications due to their rapid advancement in power electronics technology.They use interface converters(IFCs)to link DC and AC distribution networks.However,the networks possess drawbacks with AC voltage and frequency offsets when transferring from grid-tied to islanding modes.To address these problems,this paper proposes a simple but effective strategy based on the reverse droop method.Initially,the power balance equation of the distribution system is derived,which reveals that the cause of voltage and frequency offsets is the mismatch between the IFC output power and the rated load power.Then,the reverse droop control is introduced into the IFC controller.By using a voltage-active power/frequency-reactive power(U-P/f-Q)reverse droop loop,the IFC output power enables adaptive tracking of the rated load power.Therefore,the AC voltage offset and frequency offset are suppressed during the transfer process of operational modes.In addition,the universal parameter design method is discussed based on the stability limitations of the control system and the voltage quality requirements of AC critical loads.Finally,simulation and experimental results clearly validate the proposed control strategy and parameter design method.展开更多
随着“双碳”目标的提出,大量新能源接入电网,以模块化多电平换流器(modular multilevel converters high voltage dc,MMC)为代表的柔性直流输电系统获得广泛的工程应用。而电磁暂态仿真在MMC系统规划与运行过程中均发挥重要作用,但是...随着“双碳”目标的提出,大量新能源接入电网,以模块化多电平换流器(modular multilevel converters high voltage dc,MMC)为代表的柔性直流输电系统获得广泛的工程应用。而电磁暂态仿真在MMC系统规划与运行过程中均发挥重要作用,但是大步长机电暂态仿真精度不足,小步长电磁暂态仿真耗时过长,无法适应MMC的发展需求。因此基于混合仿真的基本思想,将MMC详细等效模型拆分为交流和直流两部分,建立了接口等值模型,提出数据交互算法,从而实现交流系统使用大步长仿真、直流系统采用小步长仿真。基于PSCAD/EMTDC的MMC系统仿真验证表明,混合仿真方法相较于大步长机电暂态仿真的仿真精度明显提高,相较于小步长电磁暂态仿真的仿真时间大幅缩短。展开更多
文摘A microgrid is defined as a local electric power distribution system with diverse DG （distributed generation） units, energy storage systems, and loads, which can operate as a part of the distribution system or when needed can operate in an islanded mode. Energy storage systems play a key role in improving security, stability, and power quality of the microgrid. During grid-connected mode, these storage units are charged from various DG sources as well as the main grid. During islanded mode, DG sources along with the storage units need to supply the load. Power electronic interfaces between the microgrid buses and the storage units should be able to detect the mode of operation, allow seamless transition between the modes, and allow power flow in both directions, while maintaining stability and power quality. An overview of bidirectional converter topologies relevant to microgrid energy storage application and their control strategies will be presented in this paper.
基金This work was supported by the National Key R&D Program of China(2018YFB0904700).
文摘Hybrid AC/DC distribution networks are promising candidates for future applications due to their rapid advancement in power electronics technology.They use interface converters(IFCs)to link DC and AC distribution networks.However,the networks possess drawbacks with AC voltage and frequency offsets when transferring from grid-tied to islanding modes.To address these problems,this paper proposes a simple but effective strategy based on the reverse droop method.Initially,the power balance equation of the distribution system is derived,which reveals that the cause of voltage and frequency offsets is the mismatch between the IFC output power and the rated load power.Then,the reverse droop control is introduced into the IFC controller.By using a voltage-active power/frequency-reactive power(U-P/f-Q)reverse droop loop,the IFC output power enables adaptive tracking of the rated load power.Therefore,the AC voltage offset and frequency offset are suppressed during the transfer process of operational modes.In addition,the universal parameter design method is discussed based on the stability limitations of the control system and the voltage quality requirements of AC critical loads.Finally,simulation and experimental results clearly validate the proposed control strategy and parameter design method.
文摘随着“双碳”目标的提出,大量新能源接入电网,以模块化多电平换流器(modular multilevel converters high voltage dc,MMC)为代表的柔性直流输电系统获得广泛的工程应用。而电磁暂态仿真在MMC系统规划与运行过程中均发挥重要作用,但是大步长机电暂态仿真精度不足,小步长电磁暂态仿真耗时过长,无法适应MMC的发展需求。因此基于混合仿真的基本思想,将MMC详细等效模型拆分为交流和直流两部分,建立了接口等值模型,提出数据交互算法,从而实现交流系统使用大步长仿真、直流系统采用小步长仿真。基于PSCAD/EMTDC的MMC系统仿真验证表明,混合仿真方法相较于大步长机电暂态仿真的仿真精度明显提高,相较于小步长电磁暂态仿真的仿真时间大幅缩短。
