Thermal performance of a loop heat pipe with two evaporators and two condensers was examined using a lumped network model analysis. Thermosyphon-type vertical loop heat pipe and capillary-pump-type horizontal loop hea...Thermal performance of a loop heat pipe with two evaporators and two condensers was examined using a lumped network model analysis. Thermosyphon-type vertical loop heat pipe and capillary-pump-type horizontal loop heat pipe were calculated by examining the change of heating rate of two evaporators. Calculation results showed that the vapor and liquid flow rates in the loop heat pipe and the thermal conductance of the heat pipe changed significantly depending on the distribution ratio of the heating rate of the multiple evaporators. The thermal performance of the vertical loop heat pipe with two evaporators was also examined and experimental results of flow direction and thermal conductance of the heat pipe agreed with the analytical results. The lumped network model analysis is therefore considered accurate and preferable for the practical design of a loop heat pipe with multiple evaporators.展开更多
Lossy power flow naturally extends lossless linear power flow to lossy distribution networks,further improving the accuracy of approximate computation and analysis.However,these enhanced versions are only applicable a...Lossy power flow naturally extends lossless linear power flow to lossy distribution networks,further improving the accuracy of approximate computation and analysis.However,these enhanced versions are only applicable at the alternating current(AC)transmission level,and the accuracy is limited in distribution networks,especially in hybrid AC-direct current(DC)distribution networks.In this paper,we revisit the lossy power flow model and extend it to hybrid AC-DC distribution networks with multi-terminal voltage source converters.The proposed lossy power flow model can be reformulated as an iteration problem with node power injection as the fixed point.For this purpose,a node power injection modification model based on direct derivation is proposed by exploiting the negligibility of the phase angle differences,and iteratively solving lossy power flows for both AC and DC sub-networks.For coupling devices,to guarantee that the power flow is matched on both AC and DC sides,we formulate a rigorous fixed-point problem to solve the lossy power flow of voltage source converters.Finally,the high accuracy and computational efficiency of the proposed model are verified on multiple test cases.展开更多
合环转供电是提高供电可靠性的关键手段,但直接合环可能产生较大冲击电流影响电网运行安全性。采用旋转潮流控制器(rotary power flow controller,RPFC)的方式能够实现台区的零感知合环,但电压调节轨迹不当将会带来RPFC接入点的电压越...合环转供电是提高供电可靠性的关键手段,但直接合环可能产生较大冲击电流影响电网运行安全性。采用旋转潮流控制器(rotary power flow controller,RPFC)的方式能够实现台区的零感知合环,但电压调节轨迹不当将会带来RPFC接入点的电压越限问题。对此,提出一种基于两阶段最优路径的RPFC配电网柔性合环方法。首先,对输出电压运行轨迹进行合理规划,将其分为两阶段:第1阶段要求合环点两端电压相位一致并约束电压幅值相等,实现端电压的平稳过渡;第2阶段在相位一致的基础上,控制RPFC输出电压至目标值,使合环点两端电压幅值一致。然后,采用分相量夹角计算和旋转角协调控制,选择就近的旋转角设定值作为目标值,从而实现合环点两端电压无差调节;最后,仿真和实验对比分析所提方法将电压越限至少降低至30%,展示RPFC在实现配电网柔性合环中的重要应用价值。展开更多
High penetration of distributed renewable energy promotes the development of an active distribution network(ADN).The power flow calculation is the basis of ADN analysis.This paper proposes an approximate linear three-...High penetration of distributed renewable energy promotes the development of an active distribution network(ADN).The power flow calculation is the basis of ADN analysis.This paper proposes an approximate linear three-phase power flow model for an ADN with the consideration of the ZIP model of the loads and PV nodes.The proposed method is not limited to radial topology and can handle high R/X ratio branches.Case studies on the IEEE 37-node distribution network show a high accuracy and the proposed method is applicable to practical uses such as linear or convex optimal power flow of the ADN.展开更多
Routing loops can cause packet loss and long delay problems in the traditional network. Even in future networks – Software-Defined Networks, with loop-free implementation mechanism, it still suffers loop problems. In...Routing loops can cause packet loss and long delay problems in the traditional network. Even in future networks – Software-Defined Networks, with loop-free implementation mechanism, it still suffers loop problems. In this paper, we propose an architecture to solve the loop problem in SDN. Unlike the existing passive routing loop detection algorithm, this algorithm processes based on the SDN loop-free characteristic, by auditing third-party network forwarding rules’ modification requests to avoids loop generation, thus avoid the network loop problems. Testbed is built to simulate our proposed algorithm. The evaluation shows that the loop audit algorithm proposed in this paper has better performance in extra spatial utilization and smaller number of extra interactions between SDN controller and switches.展开更多
文摘Thermal performance of a loop heat pipe with two evaporators and two condensers was examined using a lumped network model analysis. Thermosyphon-type vertical loop heat pipe and capillary-pump-type horizontal loop heat pipe were calculated by examining the change of heating rate of two evaporators. Calculation results showed that the vapor and liquid flow rates in the loop heat pipe and the thermal conductance of the heat pipe changed significantly depending on the distribution ratio of the heating rate of the multiple evaporators. The thermal performance of the vertical loop heat pipe with two evaporators was also examined and experimental results of flow direction and thermal conductance of the heat pipe agreed with the analytical results. The lumped network model analysis is therefore considered accurate and preferable for the practical design of a loop heat pipe with multiple evaporators.
基金supported by the National Natural Science Foundation of China(No.52022016).
文摘Lossy power flow naturally extends lossless linear power flow to lossy distribution networks,further improving the accuracy of approximate computation and analysis.However,these enhanced versions are only applicable at the alternating current(AC)transmission level,and the accuracy is limited in distribution networks,especially in hybrid AC-direct current(DC)distribution networks.In this paper,we revisit the lossy power flow model and extend it to hybrid AC-DC distribution networks with multi-terminal voltage source converters.The proposed lossy power flow model can be reformulated as an iteration problem with node power injection as the fixed point.For this purpose,a node power injection modification model based on direct derivation is proposed by exploiting the negligibility of the phase angle differences,and iteratively solving lossy power flows for both AC and DC sub-networks.For coupling devices,to guarantee that the power flow is matched on both AC and DC sides,we formulate a rigorous fixed-point problem to solve the lossy power flow of voltage source converters.Finally,the high accuracy and computational efficiency of the proposed model are verified on multiple test cases.
文摘合环转供电是提高供电可靠性的关键手段,但直接合环可能产生较大冲击电流影响电网运行安全性。采用旋转潮流控制器(rotary power flow controller,RPFC)的方式能够实现台区的零感知合环,但电压调节轨迹不当将会带来RPFC接入点的电压越限问题。对此,提出一种基于两阶段最优路径的RPFC配电网柔性合环方法。首先,对输出电压运行轨迹进行合理规划,将其分为两阶段:第1阶段要求合环点两端电压相位一致并约束电压幅值相等,实现端电压的平稳过渡;第2阶段在相位一致的基础上,控制RPFC输出电压至目标值,使合环点两端电压幅值一致。然后,采用分相量夹角计算和旋转角协调控制,选择就近的旋转角设定值作为目标值,从而实现合环点两端电压无差调节;最后,仿真和实验对比分析所提方法将电压越限至少降低至30%,展示RPFC在实现配电网柔性合环中的重要应用价值。
基金supported in part by the National Key R&D Program of China(No.2016YFB0900100)the National Science Foundation of China(No.51325702,51677096).
文摘High penetration of distributed renewable energy promotes the development of an active distribution network(ADN).The power flow calculation is the basis of ADN analysis.This paper proposes an approximate linear three-phase power flow model for an ADN with the consideration of the ZIP model of the loads and PV nodes.The proposed method is not limited to radial topology and can handle high R/X ratio branches.Case studies on the IEEE 37-node distribution network show a high accuracy and the proposed method is applicable to practical uses such as linear or convex optimal power flow of the ADN.
基金supported by the project of Ministry of science and technology special emphasis Research and Development Surveying and Mapping Cyberspace Resources (NO. 112044017001)Cernet Next Generation Internet Technology Innovation(No. NGII20170417)China Ministry of Education-CMCC Research Fund (No. MCM20170306)
文摘Routing loops can cause packet loss and long delay problems in the traditional network. Even in future networks – Software-Defined Networks, with loop-free implementation mechanism, it still suffers loop problems. In this paper, we propose an architecture to solve the loop problem in SDN. Unlike the existing passive routing loop detection algorithm, this algorithm processes based on the SDN loop-free characteristic, by auditing third-party network forwarding rules’ modification requests to avoids loop generation, thus avoid the network loop problems. Testbed is built to simulate our proposed algorithm. The evaluation shows that the loop audit algorithm proposed in this paper has better performance in extra spatial utilization and smaller number of extra interactions between SDN controller and switches.
