A Graph-Based Collision Resolution Scheme for Asynchronous Unsourced Random Access

This paper investigates the multiple-input-multiple-output (MIMO) massive unsourced random access in an asynchronous orthogonal frequency division multiplexing (OFDM) system, with both timing and frequency offsets (TFO) and non-negligible user collisions. The proposed coding framework splits the data into two parts encoded by sparse regression code (SPARC) and low-density parity check (LDPC) code. Multistage orthogonal pilots are transmitted in the first part to reduce collision density. Unlike existing schemes requiring a quantization codebook with a large size for estimating TFO, we establish a \textit{graph-based channel reconstruction and collision resolution (GB-CR$^2$)} algorithm to iteratively reconstruct channels, resolve collisions, and compensate for TFO rotations on the formulated graph jointly among multiple stages. We further propose to leverage the geometric characteristics of signal constellations to correct TFO estimations. Exhaustive simulations demonstrate remarkable performance superiority in channel estimation and data recovery with substantial complexity reduction compared to state-of-the-art schemes.Comment: 6 pages, 6 figures, submitted to IEEE GLOBECOM 202

A Wasserstein distributionally robust planning model for renewable sources and energy storage systems under multiple uncertainties

Nowadays, electricity markets and carbon trading mechanisms can promote investment in renewable sources but also generate new uncertainties in decision-making. In this paper, a two-stage Wasserstein distributionally robust optimization (WDRO) model is presented to determine the optimal planning strategy for renewable energy generators (REGs) and energy storage systems (ESSs) in the distribution network. This model considers supply-side and demand-side uncertainties in the distribution network and the interaction uncertainty from the main grid which are depicted by the ambiguity sets based on the Wasserstein metric and historical data. Meanwhile, both 1-norm and -norm Wasserstein metric constraints are considered to satisfy the decision-makers different preference. Furthermore, to solve this WDRO model, a systematic solution method with a three-step process is developed. Numerical results from a modified IEEE 33-node system and a 130-node system in the real world demonstrate the advantages of the two-stage WDRO model and the effectiveness of the solution method.</p

Kernel solver design of FPGA-based real-time simulator for active distribution networks

The field-programmable gate array (FPGA)-based real-time simulator takes advantage of many merits of FPGA, such as small time-step, high simulation precision, rich I/O interface resources, and low cost. The sparse linear equations formed by the node conductance matrix need to be solved repeatedly within each time-step, which introduces great challenges to the performance of the real-time simulator. In this paper, a fine-grained solver of the FPGA-based real-time simulator for active distribution networks is designed to meet the computational demand. The framework of the solver, offline process design on PC and online process design on FPGA are proposed in detail. The modified IEEE 33-node system with photovoltaics is simulated on a 4-FPGA-based real-time simulator. Simulation results are compared with PSCAD/EMTDC under the same conditions to validate the solver design

A coordinated control method of voltage and reactive power for active distribution net-works based on soft open point

The increasing penetration of distributed generators (DGs) exacerbates the risk of voltage violations in active distribu-tion networks (ADNs). The conventional voltage regulation de-vices limited by the physical constraints are difficult to meet the requirement of real-time voltage and VAR control (VVC) with high precision when DGs fluctuate frequently. However, soft open point (SOP), a flexible power electronic device, can be used as the continuous reactive power source to realize the fast voltage regu-lation. Considering the cooperation of SOP and multiple regula-tion devices, this paper proposes a coordinated VVC method based on SOP for ADNs. Firstly, a time-series model of coordi-nated VVC is developed to minimize operation costs and eliminate voltage violations of ADNs. Then, by applying the linearization and conic relaxation, the original nonconvex mixed-integer non-linear optimization model is converted into a mixed-integer sec-ond-order cone programming (MISOCP) model which can be efficiently solved to meet the requirement of voltage regulation rapidity. Case studies are carried out on the IEEE 33-node system and IEEE 123-node system to illustrate the effectiveness of the proposed method

Extended MANA formulation for time-domain simulations of combined power and gas networks

ABSTRACT: The promise of improved system efficiency, reliability, and higher renewable energy hosting capability of the Integrated Energy System concept has driven the development of innovative network coupling technologies and energy system integration methods. Co-ordinated design and operation of the traditionally separate energy systems, including electric power, gas, and heat will lead to the optimal use of synergies between energy networks and bring forth numerous benefits to the energy sector. To fully understand the potential and quantitatively assess the operation performance of the combined energy networks, a unified modeling and simulation framework using an extended MANA formulation is proposed in this paper, which is capable of incorporating arbitrary gas network configurations and unbalanced power networks in a systematic manner needed. A case study with combined power and gas networks via EnergyHubs is implemented to demonstrate the application of the proposed method. (C) 2019 The Authors. Published by Elsevier Ltd

Intrashelf basin record of redox and productivity changes along the Arabian margin of Neo-Tethys during Oceanic Anoxic Event 1a

The biotic, environmental, climatic, oceanic, and sea-level perturbations during the Early Aptian Oceanic Anoxic Event (OAE) 1a have been extensively documented from both deep- and shallow-marine deposits worldwide. However, there has been relatively little comparative assessment of the simultaneous interplay among organic carbon burial, redox conditions, terrigenous output, and productivity, leading to a lack of precise constraints on these relationships. Here, we use analyses of stable carbon isotopes (δ13Corg, δ13Ccarb, and Δ13C), total organic carbon (TOC), detrital proxies (Al, Si, Ti, K), redox-sensitive (RSTE: U, V, Mo) and productive-sensitive (PSTE: P, Cu, Ni) trace elements from a continuous, predominantly carbonate succession of the Kazhdumi Intrashelf Basin to evaluate the culprits for the OAE1a-associated changes in bottom-water oxygenation, organic-rich layer formation, and biotic shifts along the Arabian margin of the Neo-Tethys. Concentrations of Al-normalized RSTE and TOC values indicate that the bottom water conditions ranged from oxic prior to and at the onset of the OAE 1a (carbon-isotope segments C2 to basalmost C4 sensu Menegatti et al., 1998), to anoxic-suboxic but not euxinic (Mo 100 m), continental-margin basins during major oceanic perturbations

Voltage control method of distribution networks using PMU based sensitivity estimation

Application of phasor measurement unit (PMU) at distribution networks provide new options for voltage-to-power sensitivity estimation and voltage regulation. A novel voltage control method for distribution networks using PMU based sensitivity estimation is proposed in this paper. The voltage control records are extracted from the historical synchronized phasor measurements. The voltage-to-power sensitivities to reflect the relation of voltage change and power fluctuation are estimated with the obtained voltage control records. In addition to linear parameter, parameters to match the nonlinear relation between voltage and power variation and to track the operation conditions are introduced in the fitting model for sensitivity estimation to improve the accuracy of the voltage control strategy. A voltage control scheme is proposed based on the sensitivities estimated in which the measurements of partial nodes at the distribution network are the only needed data. Case studies on IEEE 33-node test feeder verify the correctness and effectiveness of the proposed method

PMU-based estimation of voltage-to-power sensitivity for distribution networks considering the sparsity of Jacobian matrix

With increasing integration of various distributed energy resources, electric distribution networks are changing to an energy exchange platform. Accurate voltage-to-power sensitivities play a vital role in system operation and control. Relative to the off-line method, measurement-based sensitivity estimation avoids the errors caused by incorrect device parameters and changes in network topology. An online estimation of the voltage-to-power sensitivity based on phasor measurement units is proposed. The sparsity of the Jacobian matrix is fully used by reformulating the original least-squares estimation problem as a sparse-recovery problem via compressive sensing. To accommodate the deficiency of the existing greedy algorithm caused by the correlation of the sensing matrix, a modified sparse-recovery algorithm is proposed based on the mutual coherence of the phase angle and voltage magnitude variation vectors. The proposed method can ensure the accuracy of estimation with fewer measurements and can improve the computational efficiency. Case studies on the IEEE 33-node test feeder verify the correctness and effectiveness of the proposed method

A decentralized voltage control strategy of soft open points in active distribution networks

With the integration of high shares of distributed generators (DGs), it is increasingly difficult to cope with the risk of voltage violations and puts forward a higher requirement for the operational flexibility in active distribution networks (ADNs). Soft open point (SOP) is a novel power electronic device which can realize accurate power flow control and continuous voltage regulation. Currently, the centralized control strategy is mainly used to operate SOPs. However, the heavy burden of communication and complex global optimization processing will hinder its fast response to the frequent voltage fluctuations. This paper proposes a decentralized voltage control strategy of SOPs in ADNs. Based on the results of network partition, the alternating direction method of multipliers (ADMM) algorithm is applied to realize the decentralized optimization of the transmission power of SOPs among connected areas. The near-global optimal solution can be obtained without the huge calculation burden. The potential benefits of SOPs are fully explored to reduce power losses and improve the voltage profile of ADNs. Finally, the effectiveness of the decentralized voltage control strategy of SOPs is validated on the PG&E 69-node distribution system