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文章采用电力暂态仿真软件PSCAD/EMTDC,对图6所示的典型多电源直流微网进行建模仿真分析,系统参数如表1所示。仿真中采用故障电流自主控制技术 [19-20],使各支路电源在短路故障下所输出的故障电流略小于2 pu。由于光伏发电模块可等效为电流源,在不增加限流的情况下,所输出的故障电流较小,对系统影响较小,不需要对此支路进行限流。仿真中采用机械式断路器,分断时间为20 ms,各支路额定电流如表2所示。
表 1 典型的多电源端直流微网系统参数
Table 1. Typical parameters of DC microgrid systems with multiple power sources
系统 系统参量 数值 母线 额定电压/V 750 交直流接入系统 系统容量/kW 500 光伏发电系统 系统容量/kW 150 风力发电系统 系统容量/kW 300 储能系统 系统容量/kW 200 充电桩 额定功率/kW 200 直流负荷1、2 额定功率/kW 300 表 2 各支路电流额定值
Table 2. Rated current of each branch
断路器 I/kA K1 0.667 K2 0.200 K3 0.400 K4 0.267 K5 0.267 K6、K7 0.400 结合表2,设置各电源支路的故障电流控制目标不大于2 pu。仿真中设置交流电源支路故障电流控制目标为1.1 kA,风力发电支路故障电流控制目标为0.7 kA,储能电池支路故障电流控制目标为0.45 kA。
根据2.2节中的保护配合原则,设置各电源支路的I段保护整定值略小于2 pu,且大于故障电流控制目标值;Ⅱ段保护整定值略小于支路故障电流控制值;Ⅲ段保护整定值略大于正常运行的最大负荷电流;设置各负荷支路I段保护整定值为2倍额定电流,Ⅱ段保护整定值为1.5倍额定电流,Ⅲ段保护整定值为1.1倍额定电流;光伏发电支路等同于负荷支路处理。直流微网各支路的保护整定值如表3所示,其中K1为交直流接入系统支路断路器,K2为光伏发电系统支路断路器,K3为风力发电系统支路断路器,K4为储能系统支路断路器,K5为充电桩支路断路器,K6、K7为直流负荷支路断路器。
表 3 典型的双电源端直流微网各支路保护整定值
Table 3. Typical setting values for protection of each branch of dual power supply DC microgrid
kA 断路器 Ⅲ段(100 ms) Ⅱ段(30 ms) Ⅰ段 K1 0.73 1.00 1.30 K2 0.22 0.30 0.40 K3 0.44 0.60 0.80 K4 0.29 0.40 0.53 K5 0.29 0.40 0.53 K6、K7 0.44 0.60 0.80 文章以典型支路故障为例,对图5中交流接入支路故障f1、储能支路故障f2、充电桩支路故障f3和母线故障f4进行仿真验证,设置故障发生时刻为500 ms。图7为不同故障下各支路电流变化情况。
根据仿真结果可知,f1处故障时,K1在故障发生后0.1 ms达到Ⅰ段保护整定值,随后迅速切断,其他支路断路器不动作;f2处故障时,K4在故障发生后0.1 ms达到Ⅰ段保护整定值,随后迅速切断,K2在故障后0.2 ms触发Ⅰ段保护,随着电流的下降,保护返回,其他支路断路器不动作;f3处故障时,K5在故障发生后0.1 ms达到Ⅰ段保护整定值,随后迅速切断,K2在故障后0.3 ms触发Ⅰ段保护,随着电流的下降,保护返回,其他支路断路器不动作。
母线故障时,K1在故障发生后5.9 ms达到Ⅱ段保护整定值,在故障后35.9 ms断开;由于流过K2电流会短时间内上升,会触发Ⅰ段保护,随着电流迅速下降,保护返回,K2在故障后102.7 ms后由Ⅲ段保护断开;K3在故障发生后3.2 ms达到Ⅱ段保护整定值,在故障后33.2 ms断开;随着故障初始时刻电流短时刻上升,K4触发Ⅰ段保护,随后保护返回,在故障后31 ms断开,K5、K6、K7不动作。
综上,短路故障发生时,采用与限流结合的过流保护方法,在支路故障下能迅速判断故障点并切除,故障切除后系统能迅速恢复并正常运行;在母线故障下,光伏发电支路断路器经长延时断开,其他电源支路断路器经短延时断开。
Research on Protection Scheme of DC Microgrid Integrated with Fault Current Limiting Control Technology
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摘要:
目的 随着分布式电源以及电动汽车等新型负荷的发展,直流微网相较于交流微网有着换流环节少,系统损耗低等优点,成为目前的研究热点。直流微网覆盖范围小,且接入了大量的分布式电源,因此发生极间短路故障时,故障电流上升速度快,幅值大,使得传统交流配电网采用的过流保护难以实现级差配合,给故障定位造成了极大的困难。 方法 对此,针对直流微网故障电流的特点,提出限流与保护相融合,基于故障电流精确控制值设计过流保护整定值的方法,结合各支路合理的容量设计,可轻松实现级差配合,准确定位故障。 结果 文章在PSCAD/EMTDC仿真平台上搭建相应的直流微网模型,对所提保护方案进行了仿真验证,结果表明该方案能正确定位故障点并迅速切除故障。 结论 所提的保护方案保证了过电流的选择性。这验证了所提保护方案的合理性。 Abstract:Introduction With the development of new loads, such as distributed power sources and electric vehicles, DC(Direct Current) microgrids have the advantages of fewer commutation links and lower system losses than AC(Alternating Current) microgrids, and have become the current research hotspot. Due to the small coverage of the DC microgrid and access to a large amount of distributed power sources, the fault current rises quickly with a large amplitude when inter-pole short-circuit fault occurs, making it difficult to achieve differential coordination with traditional overcurrent protection used in AC distribution networks and posing a great challenge to fault localization. Method Therefore, in response to the characteristics of fault current in DC microgrids, the method for designing overcurrent protection setting value based on the precise control value of fault current through the integration of current limiting and protection was proposed. Combined with the reasonable capacity design of each branch, it can easily achieve differential coordination and accurately locate faults. Result A corresponding DC microgrid model is built on the PSCAD/EMTDC simulation platform. The proposed protection scheme is simulated and verified, and the result shows that the scheme can correctly locate the fault point and quickly remove the fault. Conclusion The proposed protection scheme can ensure the selectivity of overcurrent, which verifies the rationality of the scheme. -
表 1 典型的多电源端直流微网系统参数
Tab. 1. Typical parameters of DC microgrid systems with multiple power sources
系统 系统参量 数值 母线 额定电压/V 750 交直流接入系统 系统容量/kW 500 光伏发电系统 系统容量/kW 150 风力发电系统 系统容量/kW 300 储能系统 系统容量/kW 200 充电桩 额定功率/kW 200 直流负荷1、2 额定功率/kW 300 表 2 各支路电流额定值
Tab. 2. Rated current of each branch
断路器 I/kA K1 0.667 K2 0.200 K3 0.400 K4 0.267 K5 0.267 K6、K7 0.400 表 3 典型的双电源端直流微网各支路保护整定值
Tab. 3. Typical setting values for protection of each branch of dual power supply DC microgrid
kA 断路器 Ⅲ段(100 ms) Ⅱ段(30 ms) Ⅰ段 K1 0.73 1.00 1.30 K2 0.22 0.30 0.40 K3 0.44 0.60 0.80 K4 0.29 0.40 0.53 K5 0.29 0.40 0.53 K6、K7 0.44 0.60 0.80 -
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