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In this article, we introduce a new bi-directional dual-relay selection strategy with its bit error rate (BER) performance analysis. During the first step of the proposed strategy, two relays out of a set of N relay-nodes are selected in a way to optimize the system performance in terms of BER, based on the suggested algorithm which checks if the selected relays using the max-min criterion are the best ones. In the second step, the chosen relay-nodes perform an orthogonal space-time coding scheme using the two-phase relaying protocol to establish a bi-directional communication between the communicating terminals, leading to a significant improvement in the achievable coding and diversity gain. To further improve the overall system performance, the selected relay-nodes apply also a digital network coding scheme. Furthermore, this paper discusses the analytical approximation of the BER performance of the proposed strategy, where we prove that the analytical results match almost perfectly the simulated ones. Finally, our simulation results show that the proposed strategy outperforms the current state-of-the-art ones. 相似文献
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配电网中距离Ⅱ段保护与反时限过电流保护作为主/后备保护对时,为了满足选择性要求,通常会增加距离Ⅱ段保护和反时限过电流保护的动作时间。对此,提出了一种改进保护动作特性的保护配合方案,改进后的距离保护将距离Ⅱ段保护分拆为两个阶段,与之相配合的反时限过电流保护动作曲线在T-L坐标系中自适应向下移动,以此可减小主保护和后备保护的动作时间。IEEE8节点系统仿真结果表明,改进后的保护方案在主/后备保护对满足选择性的基础上,能减小系统的平均动作时间,提高保护的速动性,且保护配合无需通信设备。 相似文献
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本文即针对当前智能变电站中的故障诊断问题展开分析,主要以继电保护二次回路故障检测为主,就诊断检测系统进行阐述,总结了能够针对各种故障问题进行检测手段,意在能够借此提升变电站的智能化发展水平。 相似文献
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在传统的三段式继电保护离线整定的定值性能分析过程中,常因定值选择不合理而导致定值计算准确度低。为此,在确定影响分支系数大小的因素的基础上,将分支系数看作为预计算变量,建立故障分析模型,计算三段式继电保护过程后备保护定值;设定三段式继电保护离线整定定值优化约束条件,采用滑膜变结构控制方法设定控制策略,结合惩罚函数的形式将约束条件添加到目标函数中,将定值性能分析问题转化为无约束优化问题,实现基于滑模变结构控制的三段式继电保护离线整定的定值性能分析。实验结果表明,相比于传统方法,该方法的定值准确度更高,定值性能更好。 相似文献
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In cooperative communications, employing the idle relay node for forwarding data can effectively improve the transmission rate and performance of the wireless networks. Therefore, various relay node selection algorithms are proposed. However, most of the existing algorithms just focus on the benefit caused by relay nodes, while ignoring the negative effect of the backoff duration time which does not exist in direct transmission, when more than one flow compete for the same relay node. To this end, considering both advantage and adverse impact caused by the relay node, we adopt the game-theoretic approach and propose a cooperative transmission strategy based on the Nash equilibrium, named the Nash Equilibrium Cooperative Transmission Strategy (NECTS). The NECTS can not only guarantee the gain of each flow, but also maximize the system performance, and improve the system throughput effectively. Simulation results show that the NECTS can take the advantage of cooperative communications. Meanwhile, it can avoid the unnecessary competition, and its performance outperforms that of the existing methods. 相似文献
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Jin'ao Yu Xiaogang Tang Shibing Zhu Haopeng Sun Lunxin Zhong Guangyu Yang 《北京理工大学学报(英文版)》2021,30(1):82-90
This paper investigated a QoS-aware power allocation for relay satellite networks. For the given QoS requirements, we analyzed the signal model of relay transmission and formulated the power minimization problem which is non-convex and difficult to solve. To find the optimal solution to the considered problem, we first analyzed the optimization problem and equivalently turn it into a convex optimization problem. Then, we provided a Lagrangian dual-based method to obtain the closed-form of the power allocation and provided an iterative algorithm to the optimal solution.Moreover, we also extended the results to the cooperative transmission mode. Finally, simulation results were provided to verify the superiority of the proposed algorithm. 相似文献
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This paper presents a fast distance relay for series compensated transmission lines based on the R–L differential-equation algorithm using the theory of equal transfer process of transmission lines. The measuring distances based on the proposed algorithm can fast approach the actual value of fault distance when a fault occurs in front of the series capacitor. When a fault occurs behind of the series capacitor, the fault loop, including the series capacitor, does not match the R–L transmission line model, so the measuring distances fluctuate severely. Based on this, the relative position of the fault with respect to the series capacitor can be judged effectively according to the fluctuation range of the measuring distances, and the accurate fault location can be obtained fast. A variety of PSCAD/EMTDC simulation tests show that the new relay has fast operating speed and high accuracy when applied to the long series compensated transmission lines. 相似文献
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Power transformers are protected by different relays that operate independently. Malfunction of each relay has a major role in reducing the reliability of the protection system. In order to mitigate the main drawbacks of the power transformer relays, an overall protection scheme is presented in this paper. This scheme proposes a novel multi criterion algorithm using decision-making based on fuzzy logic. In this paper the outputs of restricted earth fault relay and a directional check unit, are combined with the output of the differential protection relay. Therefore, problems that are pertaining to independent operation of each relay have been mitigated and the relays cover protection blind spots of each other. The improved power transformer protection (IPTP) scheme enhances the sensitivity and reliability of the power transformer protection. Extensive simulations are used to measure the effectiveness and merit of the proposed IPTP relay. The above efforts result in a multi criteria approach for protection of power transformers. 相似文献