Hasil untuk "Distribution or transmission of electric power"

M. Rabie, C. Franck

Jinli Zhu, Yuan Li, Fang Z. Peng et al.

More-electric and pure-electric ship and aircraft, and electric-grid power systems include three subsystems: generation (generators and inverter-based renewable energy sources), delivery (transmission and distribution lines and cables, transformers, capacitor banks, and inductors), and energy storage. Therefore, power systems are dominantly inductive and capacitive. Resistors are rarely used, and circuits are designed and built with minimal resistance to minimize power loss and maximize efficiency. Due to this nature, however, there have been problematic resonances, instability, and prolonged transients. To solve these problems, power converters/inverters were first presented in the 1980s as active, lossless, and virtual resistors to suppress/damp resonances, instability, and transients. In this article, we provide a comprehensive review of this innovative power converter-/inverter-based technology from the active resistor to lossless and virtual resistors. We present theoretical analysis and insights about their interrelationship and physical meanings; discuss their implementation constraints; and examine broader applications and renewed potentials to revolutionize today’s power/energy grids.

Fawad Nawaz, Ehsan Pashajavid, Yuanyuan Fan et al.

In the islanded DC Microgrid (MG) with the significant presence of renewable energy sources (RES), the integration of energy storage units (ESU) becomes crucial in mitigating the stochastic and intermittent nature of these RES. This research article introduces an intelligent distributed collaborative control scheme for managing multiple hybrid energy storage systems (HESS) within the islanded DC MG. The hierarchical control assembly is built to ensure coordinated and secure operation among the HESS units, and accurate power sharing and voltage regulation. The primary control layer utilizes a virtual-resistance droop control approach, employing a low-pass filter (LPF) to distribute the power between a battery and a supercapacitor. The state of charge (SoC) based Control schemes are presented to achieve safe and coordinated operation among the HESSs. Operating on a sparse communication network, the secondary control layer focuses on regulating the average voltage and proportional current of each hybrid energy storage system. This approach addresses issues arising from significant bus voltage deviations and inaccurate power-sharing due to virtual and line resistances. To enhance the performance of the islanded DC microgrid, an intelligent control scheme is implemented, utilizing the attributes of an Artificial Neural Network (ANN) controller alongside a traditional PI controller. To validate the proposed control method’s effectiveness and robustness in an islanded DC microgrid, extensive simulations and analyses are conducted using MATLAB/Simulink software. The results are compared with those obtained using a PI-based distributed collaborative control strategy. The Performance of ANN demonstrates that the presented controller has the capability to maintain the voltage stability of the islanded DC MG and achieve accurate power-sharing.

Fahad S. Alshammari, Ayman El-Refaie, Saleh Alyahya et al.

Micro-grids function to connect to power system power produced by the renewable energy resources. In islanded micro-grids, grid-forming units collaborate to maintain the micro-grids voltage and frequency by utilizing droop control technique that includes primary, secondary and tertiary levels. Secondary control intervenes to improve power sharing and restore voltage and frequency to their nominal levels. However, the conventional droop control applied to a grid with mismatched line parameters experiences a trade-off between reactive power sharing and voltage regulations. This paper applies real-time trajectory tracking convex optimization to ensure by communicating power sharing between units in a consensus topology. The optimization function is designed with local frequency and voltage constraints to maintain the frequency at its nominal value and ensure the voltage remains within a 5% tolerance range.. The proposed controller maintains power sharing among all units at the global consensus average value with constraints to within the limits. When the voltage limit is reached, the reactive power automatically deviates from the agreed global average in an optimal manner. The performance of the controller is shown using MATLAB/SIMULINK for different control parameters. The performance is compared to centralized-based topology. Finally, the controller is tested for grids with different line-parameters mismatches. The results show the reactive power sharing in an optimized manner.

Mojtaba Fereydani, Mohammad Amin Latify

Abstract Integrating renewable energy, particularly wind generation, into power systems brings significant uncertainty and intermittency, challenging generation companies (GenCos) to maintain economic operations. This paper proposes a strategy for a wind‐based GenCo equipped with a gas turbine and a power‐to‐gas (PtG) system to balance wind variability. The gas turbine offsets power shortfalls by consuming natural gas, while the PtG system absorbs excess wind energy, converting it to natural gas and injecting it into the natural gas network as a form of storage. The GenCo operates in day‐ahead electricity and natural gas markets and the real‐time electricity market, addressing uncertainties from wind output, energy prices, and natural gas access. A tri‐level adaptive robust optimization model is introduced for the GenCo’s short‐term operational scheduling. At the first level, decisions related to the GenCo's participation in the day‐ahead electricity and natural gas markets are made. The second level deals with determining the worst‐case realization of the uncertainties, constrained by the budget of uncertainty and the limited range of variations of uncertain variables. The third level sets the operational strategy on the actual day, considering power and gas balance, as well as constraints for the wind farm, gas turbine, and PtG unit. A column & constraint generation (C&CG) algorithm is used to solve the model. Numerical results demonstrate the model’s effectiveness in various case studies, showing that the GenCo can manage wind uncertainties, benefit from arbitrage opportunities in electricity and gas markets, and improve economic outcomes. This approach supports the broader integration of renewable energy into power systems.

Yuyang Zhao, Lincong Li, Yingjun Guo et al.

Abstract Wind power is an exceptionally clean source of energy; its rational utilization can fundamentally alleviate the energy, environment, and development problems, especially under the goals of ‘carbon peak’ and ‘carbon neutrality’. A combined short‐term wind power prediction based on long short‐term memory  (LSTM) artificial neural network has been studied aiming at the non‐linearity and volatility of wind energy. Due to the large amount of historical data required to predict the wind power precisely, the ambient temperature and wind speed, direction, and power are selected as model input. The Complete Ensemble Empirical Mode Decomposition with Adaptive Noise has been introduced as data preprocessing to decompose wind power data and reduce the noise. And the Particle Swarm Optimization is conducted to optimize the LSTM network parameters. The combined prediction model with high accuracy for different sampling intervals has been verified by the wind farm data of Chongli Demonstration Project in Hebei Province. The results illustrate that the algorithm can effectively overcome the abnormal data influence and wind power volatility, thereby providing a theoretical reference for precise short‐term wind power prediction.

Patrick Düllmann, Christopher Klein, Pascal Winter et al.

Abstract To create synergies between offshore wind integration and operational flexibility, interconnecting HVDC links to multi‐terminal networks is highly desired. However, its technical realisation remains a major challenge: In particular, it is crucial to prevent DC faults from leading to an intolerable loss of power infeed to the connected AC grids. To restrict this loss of power infeed, this paper proposes a concept for linear HVDC networks that is based on state‐of‐the‐art equipment only—that is, without dependence on DC circuit breakers. In this concept, the DC interconnection is preventively decoupled via DC high‐speed switches whenever the cumulative wind infeed exceeds the frequency containment reserve of the AC grid, but remains coupled at all other times. The decoupling is realised via controlling the coupling line current to zero through coordinated setpoint changes for the converters’ (VDC/P)‐droop controls. Both the decoupling sequence and the DC fault behaviour in decoupled state are validated via EMT simulations. In addition, limitations with regard to expandability are discussed. The proposed concept may not only limit the loss of infeed, but mitigates risks as a fall‐back level for more complex offshore (multi‐vendor) multi‐terminal HVDC topologies—and may thus accelerate their development at reasonable costs.

Weilun Gao, Zhigang Wu

Abstract The power characteristics of offshore wind power will change the regional power flow distribution and affect the regional voltage. Here, the direct‐drive wind turbine generator controlled by unity power factor is selected as the research object, and the influence of change of wind power on voltage at the grid connection point is analyzed from the simple integration model. Based on the two critical states of the external equivalent power of the grid connection point, an analytical expression of the output of wind power in the corresponding state is obtained, and the relationship among the critical state outputs, the output of wind power and the parameters at the grid connection point is drawn, hence the related influence laws is analyzed. The influence of change of wind power on voltage and regional reactive power and the reactance distribution of transmission lines near the grid connection point is considered to analyze the influence of offshore wind power on the vicinity region of grid connection point. The rationality of the conclusion is verified by study the cases of the integration of offshore wind power into Guangdong power grid, and some suggestions are put forward for the planning of offshore wind power integration.

Boyu Qin, Xin Gao, Tao Ding et al.

Abstract Optimizing short‐term load forecasting performance is a challenge due to the randomness of nonlinear power load and variability of system operation mode. The existing methods generally ignore how to reasonably and effectively combine the complementary advantages among them and fail to capture enough internal information from load data, resulting in accuracy reduction. To achieve accurate and efficient short‐term load forecasting, an integral implementation framework is proposed based on convolutional neural network (CNN), gated recurrent unit (GRU) and channel attention mechanism. CNN and GRU are first combined to fully extract the highly complicated dynamic characteristics and learn time compliance relationships of load sequence. Based on CNN‐GRU network, the channel attention mechanism is introduced to further reduce the loss of historical information and enhance the impact of important characteristics. Then, the overall framework of short‐term load forecasting based on CNN‐GRU‐Attention network is proposed, and the coupling relationship between each stage is revealed. Finally, the developed framework is implemented on realistic load dataset of distribution networks, and the experimental results verify the effectiveness of the proposed method. Compared with the state‐of‐the‐art models, the CNN‐GRU‐Attention model outperforms in different evaluation metrics.

Haiyang Wan, Wenxia Liu, Shuai Zhang et al.

Abstract Focusing solely on enhancing the resilience of power systems at a systemic level would lead to a significant underestimation of the actual impact of extreme disasters. Equally vital is the assurance of livelihood security amidst such extreme conditions, which is crucial for the development of a truly resilient power system. Hence, this paper attempts to incorporate quantifiable metrics assessing public safety impacts into resilience enhancement works, thereby guiding the precise allocation of funds. Considering that the residents' intuitive feelings are the most direct reflection of the severity of the disaster, this paper employs the modified prospect theory to formulate functions representing residents' psychological risk perception and risk‐taking willingness to tolerate risks during disruptions in power, gas, and water supplies. Meanwhile, in order to accurately calculate the energy loss duration for each residential customer, a resilience enhancement method for post‐disaster collaborative dispatch of electricity‐gas‐water systems is proposed. With the objective of minimizing the public safety and economic impact of disasters, the optimal multi‐source collaborative emergency restoration strategy is developed. The significant necessity and efficiency of the proposed strategy are verified with exhaustive case studies. Numerical results evince the resilience enhancement by considering the livelihood security in the post‐disaster restoration stage.

Z. Darabi, M. Ferdowsi

Ren Zhang, Haoming Liu, Meng Yang et al.

Abstract The fluctuation of photovoltaics (PVs) output may cause the voltage out‐of‐limit, while the PV inverters and hybrid distribution transformers (HDTs) bring flexible controllability to distribution networks (DNs). However, there are differences in response speeds between power electronic equipment and traditional discrete regulating equipment. Therefore, a network partitioning and hierarchical voltage regulation method using holomorphic embedding method (HEM) ‐based sensitivity is proposed. Firstly, the HEM‐based voltage sensitivity is derived, and the network partitioning method is proposed using the HEM‐based sensitivity matrix. Then, the hierarchical voltage regulation framework is constructed. The objects of the upper layer are the minimum network loss and voltage deviation, which centrally optimizes the operation status of discrete regulation equipment. The lower layer exploits the fast control ability of PV inverters and HDTs, so as to autonomously regulate the voltage of each partition. Finally, a practical 10 kV DN in China is used for case studies. The results demonstrate that the HEM‐based voltage sensitivity calculation method has advantages in computational efficiency and accuracy compared with the conventional method. Moreover, the proposed voltage regulation method can suppress the voltage fluctuation.

Mohamed A. Abdelrahman, Sheng Wang, Wenlong Ming et al.

Abstract A transformer‐less unified power flow controller (UPFC) is a power electronic device consisting of series and shunt voltage source converters (VSCs) that are not connected to a common DC bus. It can control power flow in medium voltage (MV) distribution networks without the need for interfacing transformers. Hence there is a significant reduction in size and cost compared to a conventional UPFC. This paper investigates the operating range of a transformer‐less UPFC in an MV distribution network and the required power ratings of the series and shunt converters. The results showed that a transformer‐less UPFC is able to provide active power control using partially rated converters. However, its ability to control reactive power is limited by the current ratings of the converters. The analysis was verified using software simulation and hardware experiment.

Roshan L. Kini, David Raker, Roan Martin-Hayden et al.

Variability and uncertainty of renewable distributed generation increase power grid complexity, necessitating the development of advanced control strategies. demonstrates a real-world testbed and the implementation of control strategies on it to mitigate the challenges associated with variability and uncertainty of renewable distributed generation. This control-centric testbed includes 4.6 MW of controllable building loads, a 1 MW solar array, and a 125 kW / 130 kWh battery energy storage system (BESS). The capabilities of the testbed are illustrated by highlighting the implementation of three specific scenarios relevant to future smart grid infrastructures. In the first scenario, photovoltaic output variability is mitigated with the BESS using adaptive moving average and adaptive state of charge control methods. The second and third scenarios demonstrate peak load management and load following control to manage uncertainty using the Intelligent Load Control (ILC) algorithm. The ILC modifies controllable loads using a prioritization matrix and an analytical hierarchy process. The three scenarios all operate at a different time-constant, and are each effectively addressed, demonstrating the versatility and flexibility of the presented testbed. This demonstrated ability to rapidly test the efficacy of alternate control algorithms on a real system is crucial to the maturation of future smart-grid.

Patrick Düllmann, Christina Brantl, Christopher Klein et al.

Abstract For future multi‐terminal HVDC networks, protection systems based on DC circuit breakers (DCCBs) are envisioned to limit the loss of power transmission towards AC grid(s). Yet, HVDC protection system design is considered a major challenge—especially in a multi‐vendor setup. In particular, protection systems shall enable HVDC converters to ride through DC faults without protective blocking. Several studies have performed sensitivity analyses to determine the DCCB properties and current‐limiting inductor properties that are required to enable converter fault‐ride‐through (FRT), but the HVDC converters themselves have been simplified and kept identical. However, in a multi‐vendor setup, the exact converter design is not known at the time of DC protection planning. Therefore, this paper investigates the impact of different converter properties on the DC‐FRT behaviour, and reveals implications on HVDC protection design. Firstly, analytical approaches are proposed to mathematically derive potential impact factors on the converters’ FRT characteristics, also considering different converter control architectures. Secondly, a comprehensive EMT study demonstrates a significant impact of the converter parameters on the FRT behaviour. Analytical approaches and EMT results are compared with regard to limitations and applicability, such that the paper's findings can support the development of functional requirements for multi‐vendor multi‐terminal HVDC networks.

Xiuyan Wei, Guibin Zou, Shuo Zhang et al.

Abstract The total electric field around the DC line is composed of both the ion flow field produced by coronae and the electrostatic field produced by the conductor charge. Under the effect of the total electric field, the disconnected pole will generate a coupling voltage. Therefore, based on the coupling voltage, this paper proposes an adaptive reclosing scheme for flexible DC grid to prevent power supply interruption caused by temporary fault. First, the disconnected pole coupling voltage (DPCV) under the total electric field is analysed when single pole to ground fault (SPGF) and pole to pole fault (PPF) occur respectively. Then, according to the DPCV difference between permanent fault and temporary fault, a fault property identification (FPI) criterion is constructed. The scheme is very simple and not affected by the transition resistance, fault position and wiring mode which has high reliability. Compared with the non‐selective reclosing strategy, the adaptive reclosing scheme can avoid the secondary impact on the system from the permanent fault. Extensive simulations and experiments verify the effectiveness of the proposed adaptive reclosing strategy.

Yuan Kong, Yidan Lu, Feng Tu

Arturo Conde Enríquez, Yendry González Cardoso

Digvijay Deswal, Francisco De Leon

This paper presents a novel model for transformer windings to accurately represent the duality between electrical and magnetic circuits. The model can be used for the calculation of high-frequency transients in power systems and the design of high-frequency transformers, for example, those to be used in solid-state (utility-grade) transformers and power electronic converters. Existing circuit models do not consider the flux linkage in the winding thickness in a physical (dual) way. Duality is achieved by discretizing the winding thickness into thin sub-sections and distributing the proposed model building block across the winding. Analytical calculations are carried out to compare the accuracy of the proposed circuit for the computation of the terminal impedance, flux duality, and current distribution in the physical geometry of the winding. Further discretization is performed to extend the circuit to represent high-frequency phenomena: eddy currents and capacitive effects. The model can be easily implemented in any circuit simulation program using available circuit elements. The circuit parameters are computed with very simple expressions. The model is validated with finite element simulations. Differences of around 1% are obtained for relatively low model orders for high frequencies.

Yifan Li, Peng Sun, Hui Li et al.

Abstract Concerning the distance protection steady‐state over‐reach or under‐reach caused by the transition resistance, a novel distance protection scheme based on transient information is proposed. First, multiple fault features are extracted using the Generalized Stockwell Transform (GST), and a criterion for identifying low‐resistance and high‐resistance ground faults is constructed. Then, a GST coefficient matrix is established for the single‐ended transient voltage of the line, the attenuation coefficient and delay coefficient are derived by the least‐squares method and the beat phenomenon, and the transition resistance is calculated. On this basis, adjust the operation boundary in the +R axis direction of the operation zone according to the transition resistance value. Finally, test results on real‐time digital simulation system (RTDS) demonstrate that the protection scheme operates reliably in different fault cases and is highly immune to fault resistance. Compared with the traditional distance protection scheme, this scheme performs better when the transition resistance is large.