Optimal UAV Deployment and Resource Management in UAV Relay Networks

UAV equipped three-dimensional (3D) wireless networks can provide a solution for the requirements of 5G communications, such as enhanced Mobile Broadband (eMBB) and massive Machine Type Communications (mMTC). Especially, the introduction of an unmanned aerial vehicle (UAV) as a relay node can improve the connectivity, extend the terrestrial base station (BS) coverage and enhance the throughput by taking advantage of a strong air-to-ground line of sight (LOS) channel. In this paper, we consider the deployment and resource allocation of UAV relay network (URN) to maximize the throughput of user equipment (UE) within a cell, while guaranteeing a reliable transmission to UE outside the coverage of BS. To this end, we formulate joint UAV deployment and resource allocation problems, whose analytical solutions can be hardly obtained, in general. We propose a fast and practical algorithm to provide the optimal solution for the number of transmit time slots and the UAV relay location in a sequential manner. The transmit power at BS and UAV is determined in advance based on the availability of channel state information (CSI). Simulation results demonstrate that the proposed algorithms can significantly reduce the computational effort and complexity to determine the optimal UAV location and transmit time slots over an exhaustive search.

New Infeed Correction Methods for Distance Protection in Distribution Systems

The reliability and security of power systems may be jeopardized by the increase in the amounts of renewable generation and the uncertainties produced by these devices. In particular, the protection schemes of traditional power systems have been challenged by the integration of distributed generation (DG) resources. Distance relays (DRs), which have been mainly employed to protect transmission systems, are increasingly proposed as one of the solutions to protect distribution systems with a heavy penetration of DGs. However, conventional distance protection faces several drawbacks that might lead to maloperation. One of those challenges is the “infeed effect”, which causes the impedance seen by the distance relay to be larger than the actual positive-sequence line impedance between the fault and relay location. This paper proposes three new methods to estimate the distance to the fault in the presence of infeeds, whether in a radial distribution feeder or the transmission line. Unlike other solution methodologies in the literature that require communication links to estimate the distance to the fault, the proposed methods only need the local measurement (i.e., the voltage and current measurements at the location of the distance relay) to do the same. The performance of the method is demonstrated with a radial distribution system model in PSCAD™/EMTDC™.

Three zone detection and distance relay co-ordination of power system protection

To secure the transmission lines against power system faults, the distance relays are mostly used. Distance relay has its own Resistance (R)–Reactance (X) characteristics. Co-ordination of different distance relays is necessary for the fast operation of circuit breaker. Various distance relays which are being tripped with respect to circuit breakers which are attached at individual buses faraway from each other. These relays will be operated with respect to the distance between the occurred fault and relay location. In this paper, detection of three zones using relay characteristics, co-ordination of distance relays and circuit breakers are shown with the faults placed at different locations of an IEEE Nine bus system using MATLAB/Simulink GUI environment. A comparison also made between the relays performance and circuit breaker tripping operation with respect to severe faults at different locations on IEEE Nine bus system.

Sequence component direction element based on power frequency variation

Unlike the relatively stable network structure of the transmission and distribution network, under the new distribution network, resulting in errors in the impedance tuning of the fault directional element, misjudgment of the fault directional element, and a decrease in sensitivity. For this reason, this paper proposes a sequence component adaptive fault directional element based on power frequency variation. The sequence impedance amplitude is calculated through the measured values of the voltage sequence component and the current sequence component of the relay location. Then the phase angle of the setting impedance is determined according to various sequence components in the system. It improves the problem that the setting impedance of power frequency distance directional element is greatly affected by the amplitude and phase angle fluctuation of distribution system impedance and line impedance. The reliability and stability of the sequence component adaptive fault directional element based on the power fresquency variation are verified by Matlab simulation.

Impact of engineering parameters on performance of relay-assisted network

<span>This paper compares the performance of a relay assisted network to the performance given by a classical macrocell network without the presence of relay node schemes. The capacity enhancement provided by a relaying system as a function of the relay antenna height and the propagation environment surrounding the relay nodes is analyzed and discussed in details. The analysis in this work is based on the theoretical Shannon capacity where both measured/experimental path loss and calibrated path loss models are taken into consideration. In this work, we assume a decode and forward scheme, a full-duplex relaying protocol and an optimized relay location is investigated. A 30 % of improvement in the macrocell capacity is achieved with the usage of relaying scenario compared to a classical macrocell network. Furthermore, increasing the relay antenna height from 4 meters to 12 meters can significantly increase the relay capacity to more than 20 % in suburban and moderate urban environments.</span>

Impact of Active Superconducting FCL on Distance Protection in Nine Bus

In this paper, Active Superconducting Fault Current Limiters (ASFCLs) has been introduced in the existing nine bus ring system to validate prompt reduction in fault current magnitude. Instigation of FCL in rapidly expanding transmission and distribution network supports existing installed equipment. ASFCL uses converter in association with superconducting transformer to decrease fault current with its inception instantaneously. In nine bus ring system, with and without ASFCL, various faults are simulated, sampled and processed using MATLAB/Simulink. The mitigation of current during LG fault has been observed to be effective with ASFCL placement near the generating buses in the existing system. This inclusion of ASFCLs in the existing system appends the impedance seen by the distance relays affecting its characteristics operation and the protection scheme. Resistance, reactance, impedance and phase angle as seen by the relay have been computed using fundamental component of the voltages and currents, extracted by applying Discrete Fourier Transform (DFT) on sampled data. The change in the impedance and its component have been tabulated and plotted without and with ASFCL for different types of fault with respect to distance between fault points and relay location. The zone settings of protected transmission line, need to be modified as per appended reactance and impedance seen by distance relay with inclusion of SFCL to prevent maloperation.

Optimal Power Allocation and Relay Location for DF Energy Harvesting Relaying Sensor Networks

This paper considers a simultaneous wireless information and power transfer (SWIPT) based decode-and-forward (DF) relaying sensor network, where the “save-and-forward” strategy is utilized at the relay sensor node. We investigate a joint power splitting (PS) and relay location (RL) optimization scheme for delay-sensitive transmission mode using the instantaneous channel state information (CSI). In particular, two optimization problems are formulated to minimize the outage probability and maximize the average capacity, respectively. For the two optimization problems, the optimal solutions to the PS ratio and RL are obtained based on the instantaneous CSI. On the basis of optimal solutions, the analytical expressions for outage probability and average capacity are derived, and the corresponding achievable throughputs are obtained. Numerical results verify the correctness of theoretical derivations and validate the advantages of our proposed scheme.

Prediction of overcurrent rRelay miscoordination time using artificial neural network

Overcurrent relay plays an important role in the protection of power system. For protection, proper coordination of relays with an appropriate relay settings need to be done. Coordination can be done by selecting an optimal Time Multiplier Setting (TMS) and Plug Setting (PS) considering the fault current at the relay location. Continuous Time Intervals (CTI) must be maintained between primary relay and secondary relay to ensure correct sequential operation of the relays. However, miscoordination can occurs due to secondary relay trips faster than primary relay. This paper presents an approach for predicting overcurrent relay miscoordination time using Artificial Neural Network (ANN) algorithm in MATLAB software. The efficiency of the proposed approach have been tested successfully on 17 bus test system. The simulation results indicated that the ANN Levenber-Maequardt algorithm is capable to predict the miscoordination time occurs between the primary and secondary relay operating time.