Interconnected Power Grid Research Articles

Identification of Mode Shapes Based on Ambient Signals and the IA-VMD Method

The paper presents a multiaspect analysis of multivalues and the broadband nature of system oscillation. By analyzing the ambient signal caused by random small disturbances during the normal operation of interconnected power grids, many system operation characteristics can be obtained. The traditional signal processing method cannot extract the information from ambient signals effectively. Aiming at the problem of broadband oscillation mode superposition and the difficulty of extracting information from ambient signals, an iterative adaptive variational mode decomposition (IA-VMD) method is proposed based on frequency domain analysis and signal energy. Additionally, the IA-VMD method, combined with a bandpass filter and the Prony algorithm, is used to realize the modal identification of broadband oscillation and ambient signals. Simulation experiments show that the IA-VMD method has good adaptability, antinoise characteristics, and a certain significant engineering application value as well.

A Multi-Step Unified Reinforcement Learning Method for Automatic Generation Control in Multi-Area Interconnected Power Grid

As the penetration rate of new energies, energy storage devices and electric vehicles increases continuously in power grid, power grid faces strong random disturbances, as well as the issues of downfall in frequency control ability induced by the factors such as system inertia reduction and frequency control under-capacity in traditional power units. Therefore, an algorithm of automatic generation control with DQ(σ, λ) is proposed for the multi-area interconnected power grid. By integrating the eligibility trace, DQ(σ, λ) adopts the principle of double Q-learning to unify double Q(λ) and double Expected-Sarsa(λ), thereby the over-estimation of Q in the algorithm and the phenomenon of over-fitting can be avoided. The simulations are provided to demonstrate the effectiveness of the proposed algorithm, where the improved IEEE standard two-area load-frequency control model and the model of the multi-area interconnected power grid based on Central China Power Grid are adopted. The results show that the phenomena of random disturbances and frequency instability can be eliminated in multi-area interconnected power grid. The convergence is faster and the dynamic performance is better in the proposed algorithm compared with the traditional algorithms.

On-line Update Method for the Sensitivity Consistency Model of Interconnected Power Grid Based on Electric Power Big Data

Real-time fast calculation of the power flow of the interconnected power grid is an important guarantee for the reliable operation of the interconnected power grid. The topology of the interconnected power grid is complex, and the calculation of the power flow of the whole network is large and timeconsuming. The sensitivity equivalent model can effectively simplify the interconnected power grid and shorten the time of the power flow calculation of the whole network. The operating state of the power grid is constantly changing. In order to ensure the accuracy of the power flow calculation results, it is necessary to update the uniform sensitivity equivalent model in real time. Due to factors such as the vertical management system between the interconnected power grids and the principle of commercial confidentiality, it is difficult to share information between interconnected power grids in real time, and the sensitivity equivalent model cannot be updated in real time, resulting in too much error in the calculation results and no reference value. To solve this problem, this paper proposes an online update method for the sensitivity equivalent model of the interconnected power grid based on power big data to solve the problem of excessive power flow calculation errors caused by the untimely update of the equivalent model parameters, and to ensure the operational reliability of the interconnected power grid.

A Distributed Dynamic Power Flow Algorithm for an Interconnected System Containing Two-Terminal LCC-HVDC Tie-Line

In China, a growing number of regional power grids are interconnected by the line-commutated converter based high voltage direct current (LCC-HVDC) tie-line, forming a large-scale interconnected power grid. As the operation and control of the interconnected power grid are undertaken by multiple control centers, there is a demand for a distributed alternating current (AC)/direct current (DC) power flow algorithm. In this paper, a distributed power flow algorithm considering the LCC-HVDC tie-line is implemented based on the existing work of the author. The paper proposed some technologies to implement the algorithm. In the fixed-point iteration scheme of this paper, the combined boundary bus states are used to calculate the power flow of the DC system, thus the coordination of discrete state variables of the DC system is avoided. Also, the idea that converting the DC tie-line to an AC line is proposed to calculate the extended WARD equivalent of the external network of subsystems. Moreover, the unbalanced power distribution method is improved to make it more in line with the practical situation. Tests were carried out on the IEEE 118-bus system and an interconnected power grid constructed by six IEEE 118-bus systems, the correctness and effectiveness of the algorithm were proved.

Economic Analysis of Power Grid Interconnections Among Europe, North-East Asia, and North America With 100% Renewable Energy Generation

In this paper, we investigate whether the interconnection of power grids with 100% renewable energy generation can bring greater economic benefits now that the technology exists for high power, long distance Ultra High Voltage Direct Current transmission. Based on multi-year historical weather data and demand series, this study compares eight interconnection schemes for three regional grids in Europe, North-East Asia, and North America where there is around 8-hour time difference between any of the two regions. Sensitivity analyses are presented with respect to infrastructure capital cost and different weather year which show that interconnection yields a reduction of approximately 18% in the total annual system cost. The results in this paper also indicate that the regional levelized cost of electricity (LCOE) drops by 31%, 10%, and 10% for Europe, North-East Asia and North America, respectively. It is concluded that there is a strong incentive through both annual cost saving and regional LCOE drop in favour of full long-distance interconnections between the three regions in the context of the international drive towards a net-zero strategy.

Optimized allocation method of the VSC-MTDC system for frequency regulation reserves considering the cost

In recent years, the interconnection of asynchronous power grids through the VSC-MTDC system has been proposed and extensively studied in light of the potential benefits of economical bulk power exchanges and frequency regulation reserves sharing. This paper proposed an optimized allocation method for sharing frequency regulation reserves among the interconnected power systems and the corresponding frequency regulation control of the VSC-MTDC system under emergency frequency deviation events. Firstly, the frequency regulation reserve classification is proposed. In the classification, the available frequency response capacity reserves of each interconnection are divided into commercial reserves and regular reserves. While the commercial reserves are procured through long-term contracts, the regular reserves are purchased based on market prices of frequency regulation services. Secondly, based on the proposed frequency regulation reserve classification, a novel frequency regulation control is then introduced for the VSC-MTDC system. This control method could minimize the costs of the disturbed power grid for the needed frequency response supports from the other power grids. Simulation verifications are performed on a modified IEEE 39 bus system and a highly reduced power system model representing the North American grids. The simulation verification indicates that the developed frequency regulation control significantly reduced ancillary service costs of the disturbed power grid.

Improved Damping Control Method for Grid-Forming Converters Using LQR and Optimally Weighted Feedback Control Loops

Power grid pattern is expected to evolve from generator-based power systems towards converter-based systems in the forthcoming decades. Therefore, grid-forming converters will be pertinent to interconnected power grids in pursuance of enhancement their resilience against disturbances. This paper introduces a new efficient damping control method for grid-forming converters that provides a smooth power modulation and an efficient damping response against frequency and voltage deviations. First, an averaged state-space representation for a grid forming application in dq synchronization frame is derived. Based on this model, a new hybrid damping controller, including the concept of state feedback control and PI control, is proposed to address the main issues in existing controllers. The state feedback controller is optimally designed using a linear-quadratic regulator (LQR) approach to optimize the system performance. Moreover, the PI controller is optimally designed using the pattern search algorithm. The proposed damping control method integrates optimally between the control loops through a mapping matrix to rapidly synchronize with the grid and efficiently damp the oscillations. Simulations are carried out to prove the proposed method robustness. Finally, a comparative study using controller hardware-in-the-loop (CHiL) is employed against conventional system to validate the proposed damping method.

Influence of Hydro Turbine Supervision and Control System on Frequency Characteristics of High Proportion Hydropower System

With the construction of interconnected power grid and the rapid development of clean energy, the frequency problem of power system is becoming increasingly prominent. The problem of ultra-low frequency oscillation affects the stability of system frequency. In order to analyze the frequency regulation characteristics of the system, it is necessary to study the local active power control link and stability calculation model of the hydropower plant computer monitoring system. In this paper, the influence of the local active power control link of the monitoring system on the system frequency small signal stability is studied, and the model is built in the simulation program. Through the simulation of 4-machine-2 regional power grid, the influence characteristics of local active power control on frequency dynamic damping level are verified. In the example of large power grid, the coordination between the local active power control of the monitoring system and the speed regulation system of hydropower units is comprehensively considered, the suggestion of coordination of multi-level frequency modulation resources to system frequency regulation is put forward.

A Comprehensive Method to Mitigate Forced Oscillations in Large Interconnected Power Grids

Multiple severe forced oscillation events have recently been observed across the North American interconnections and around the world. These forced oscillations have caused power swings, limited power transfer capability, damaged equipment, and persisted indefinitely until the driving source was located and removed. This paper proposes a comprehensive method to mitigate forced oscillations. Once a forced oscillation is detected, a new source location algorithm can be used to locate the source based on the oscillation mode angle without requiring system topology information. If the source cannot be quickly located and removed, a control strategy can be activated to modulate the active power of utility-scale inverter-based battery energy storage systems (BESSs) to reduce the energy of forced oscillations to a safe level and allow sufficient time for locating the exact source. The proposed source location algorithm is validated using measurements collected during the January 11, 2019 forced oscillation event in North America and other actual grid events, while the proposed control strategy is verified using the Eastern Interconnection dynamic model under the replicated January 11, 2019 forced oscillation event. The simulation results demonstrated that the proposed source location algorithm can accurately identify the forced oscillation source, and the proposed control strategy can significantly reduce forced oscillation energy.

Multi-Area Load Frequency Control of Hydro-Thermal-Wind Power Based on Improved Grey Wolf Optimization Algorithm

The mathematical model of load frequency control is established in the interconnected power system of hydro, thermal, and wind for solving the problem of frequency instability in this paper. Besides, the improved grey wolf optimization algorithm (GWO) is presented based on the offspring grey wolf optimizer (OGWO) search strategy to handle local convergence for the GWO algorithm in the later stage. The experimental results show that the improved grey wolf algorithm has a superior optimization ability for the standard test function. The traditional proportional integral derivative (PID) controller cannot track the random disturbance of wind power in the hydro, thermal, and wind interconnected power grid. However, the proposed OGWO dynamically adjusts the PID controller control parameters to follow the wind power random disturbance, regional frequency deviation, and tie-line power deviation.

Emergency power balance control based on proactive motor operation of DFIG‐based wind turbines for sending grid stability

The transmission lines between the sending and receiving ends of an interconnected power grid may be tripped under severe disturbance or equipment failure. The tripping will result in a large power imbalance in the sending grid, thereby causing frequency instability and even collapse. The effect of existing emergency control methods based on synchronous generators, such as generator tripping control, is limited due to the lack of available tripped generators, high cost and long recovery time. The high penetration and flexible controllability provide wind farms with the potential to participate in system emergency control. To evacuate excess power from the tripping of transmission lines and improve frequency stability, an emergency power balance control method based on the doubly-fed induction generator (DFIG)-based wind turbine (DFWT) is proposed in this study. A novel idea of the motor operation of DFWT is presented and applied to the proposed method. To realise steady and adjustable power consumption of DFWT under motor operation, a rotor virtual resistor control and supplementary pitch control are introduced under safety constraints. The validity of the proposed method is verified by case studies on single DFWT and DFWT-based wind farms.

Index system and methods for comprehensive assessment of cross-border power grid interconnection projects

With the global economy integration and progress in energy transformation, it has become a general trend to surpass national boundaries to achieve wider and optimal energy resource allocations. Consequently, there is a critical need to adopt scientific approaches in assessing cross-border power grid interconnection projects. First, considering the promotion of large-scale renewable energy resources and improvements in system adequacy, a comprehensive assessment index system, including costs, socio-economic benefits, environmental benefits, and technical benefits, is established in this study. Second, a synthetic assessment framework is proposed for cross-border power grid interconnection projects based on the index system comprising cost–benefit analysis, with market and network simulations, iterative methods for indicator weight evaluation, and technique for order preference by similarity to an ideal solution (TOPSIS) method for the project rankings. Finally, by assessing and comparing three cross-border projects between Europe and Asia, the proposed index system and assessment framework have been proved to be effective and feasible; the results of this system can thus support investment decision-making related to such projects in the future.

Online Equivalent Method of External Network Based on Measurement Information

How to acquire the accurate equivalent network of external system in the interconnected power grid has always been a challenging issue in the fields of both academic and engineering. This paper proposes a new method for online equivalence of the external network based on the measurement information of the internal network. Firstly, it builds an equivalent network of the external system, including the coupled branches between each of the boundary node, the equivalent generators and the equivalent lines from corresponding boundary nodes to them. Then, based on the SCADA (Supervisory Control and Data Acquisition) measurement information, an optimization model to estimate the parameters of the equivalent network is constructed, with the minimization of the mismatch between the boundary’s measurement and the calculation value of the equivalent network being the objective and the parameters of each line of the equivalent network within the reasonable range being the constraints. In order to reduce the calculation scale, measure is adopted to remove the coupled lines whose electrical distances (or impedances) are larger than a relative big threshold. The impedance range of each line in the equivalent network is determined by ward equivalent method under the condition of maximum and minimum operation mode. The model is solved by interior point method, which owns the satisfactory convergency performance. The solution of the model makes each of the calculated value of the equivalent network at the boundary node closest to the measured value, while all the parameters of the equivalent network within a practical range. The results of an example demonstrate the validity and effectiveness of the model and method proposed in the paper.

The Topology of a New Energy Router and Its Coordinated Control Strategy

With the rapid growth of the permeability of distributed new energy and the development of Energy Routers based on power electronics technology, the construction of AC/DC hybrid distribution network based on Energy Routers is expected to become a new development direction of urban power grid. This paper proposes a hybrid AC/DC main urban power Grid and Microgrid interconnection architecture based on a new Energy Router topology and its coordinated control strategy as the basic module of future urban power Grid. In this paper, considering the current situation of land resource shortage in the central area of the city, the new energy generation and energy storage technologies represented by photovoltaic building integration and electric vehicles are considered and connected to the urban distribution network in the form of integrated Microgrid. Considering that the electricity production and consumption patterns of adjacent Microgrids may be greatly different, the interconnection architecture between the main power grid and the Microgrid can be constructed. So in this paper, the Energy Router integrated with AC and DC double busbar and four voltage source inverter, coordinated control strategy is a blend of PQ control strategy and V/f control strategy, based on the disturbance observation method of MPPT control strategy of photovoltaic power generation and the control strategy of energy storage system, it not only make full use of new energy, but also effectively ensure the quality of electricity supply. Simulation and analysis of each model and control strategy were carried out on MATLAB 2016a/Simulink simulation platform, and the results verified the effectiveness and reliability of the proposed Energy Router topology and coordination control strategy.

Study of WAMS Big Data Elastic Store Model in Low-Frequency Oscillation Analysis

Low-frequency oscillation (LFO) is among the key factors that threaten interconnected power grids’ security and stability and restrict transfer capability. In particular, power systems incur now and then weak damping and forced oscillations. To monitor and control LFO, the principles of online calculation and analysis of two types of LFO are studied in this paper. The big data of wide area measurements is an important information source of LFO analysis. Hence, we should make sure it has access to online system continuously, accurately, and reliably. Nevertheless, the conventional linear data store model has difficulty to meet the processing requirements of high rate, multiple concurrency, and high reliability. To deal with it, a new model of double-set elastic store is proposed in this paper. It transforms the storage space linear model to plane model, realizes the management of power system substation group sets in vertical direction and the management of multiple Phase Measurement Units (PMU) uploading data sets in horizontal direction, and hence solves the problems in continuous and reliable access of the wide area measurements data, which is dense and of large scale and has quick update rate, providing technical support of accuracy and robustness of LFO analysis. The performance test and practical application of the proposed new model of double-set elastic store validate its accuracy.

Research on Development Technology of AC / DC Hybrid Distribution Network Construction in Smart Grid

At present, the flexible interconnection of flexible power grids based on flexible DC and the combination of AC and DC distribution networks in smart grids will bring great changes and challenges to the operation of traditional power distribution systems. The AC / DC hybrid distribution network can better accept distributed power and DC loads, alleviate the contradiction between limited corridors and high load density in urban power grid stations, and provide dynamic reactive power support at the load centre, which can effectively improve the urban distribution system. Power quality, reliability and operating efficiency. This article summarizes and analyses key technical issues such as the topology, optimization planning, dispatch control, and economic evaluation of AC-DC hybrid distribution networks. Finally, the application prospects of AC-DC hybrid distribution networks are prospected.

Impact of climate change on water availability and its propagation through the Western U.S. power grid

Climate change is expected to affect the availability of water for electricity generation, yet the propagation of climate impacts across a large and diverse power grid remains unexplored. In this study, we evaluate how projected changes in water availability affect electricity generation at hydroelectric and thermal power plants and how the coincident impacts propagate locally and throughout the interconnected power grid of western United States. We also evaluate whether the prospect of climate-driven change could affect regional power dependencies. Hydrologic simulations derived from three Global Circulation Models (CCSM4, INMCM4, and GFDL-CM3), two radiative scenarios (RCP4.5 and RCP8.5) and the VIC hydrology model are used to force a large-scale, distributed water management model (MOSART-WM), which translates water availability into power generation constraints at hydropower plants and water-dependent thermoelectric plants. Power system dynamics are evaluated using the production cost model PLEXOS. We find that the interregional connections across the contemporary Western U.S. electricity infrastructure play an essential role in managing variations in regional generation due to hydrological variability. Projected WECC-scale changes in mean annual precipitation ranging from −3.8% to +17% are moderated to −6% to +4% in mean annual production cost changes. Climate change impacts on water availability in the Northwest drive future changes in other regions’ generation and in regional power flows. Northwest total generation influences interannual variability in other regions’ net generation, explaining about 40%, 50%, and 35% of the variability in Southwest, Rockies, and Southern California regions respectively. The propagation of Northwest climate change impact throughout the grid is exacerbated by the occurrence of dry years in Northern California. Generation from the Desert Southwest emerges as a critical resource to compensate for variations in water availability, and generation, in these regions. Though the regional power flow directions seem insensitive to long-term variations in water availability, our analysis highlights the need to consider other compounding regional factors, such as changes in Southern California’s net load and changes in regional fuel prices.

Fuzzy control strategy of interconnected power grid AGC system based on particle swarm optimization

Frequency is one of the key indicators of power quality. The power load is constantly changing and has uncontrollability. The change of load will affect the frequency of the system. The power system always hopes to keep the frequency as constant as possible, which leads to the problem of frequency control. The mechanism modeling of the multi-region interconnected power grid system is carried out, and the frequency response of the networked system is analyzed by building a simulation platform. Aiming at the shortcomings of “AGC controller” using fuzzy PID control, according to the particle swarm optimization algorithm, a fuzzy adaptive PID controller based on particle swarm algorithm is designed. The simulation results show that the fuzzy adaptive PID controller based on particle swarm algorithm can better improve the dynamic performance of the system.

Neural optimal self-constrained computing in smart grid considering fine-tuning island constraints with visual information

With the expansion of the power grid and the acceleration of power information construction, the information communication network covers all aspects and collects accurate information in time to provide continuous and reliable operation for users. The modern power system will gradually enter the era of interconnected power grids. It is more environmentally friendly and efficient than traditional power systems, management is more information and lean, and its operation is safer and more stable. As the infrastructure for carrying smart grid and future energy information interaction, the power communication network has higher and higher requirements for reliability. The coupling between the communication network and the power grid is more and more closely related. The real-time acquisition and the reliable transmission of control information such as the power system require the support of the power communication network. This paper uses machine learning algorithms to learn effective features or patterns from these data and apply them to new data. In this paper, we present a neural optimal self-constrained computing model based on fine-tuning island constraints with visual information. The experimental results show that the proposed algorithm has higher processing efficiency and accuracy.

Synchronized Ambient Output-Only Based Online Inter-Area Transfer Capability Assessment Considering Small Signal Stability

Inter-area transfer power is a key factor affecting the damping of electromechanical oscillation. This paper presents an output-only based inter-area transfer capability (ITC) assessment method considering small signal stability constraint. Based on the construction of an equivalent two-machine system (ETmS) of an interconnected power grid, the measurements-based approach for estimating the parameters of the ETmS was studied. Then, we developed an optimization model with a maximum ITC target and damping as constraint. Under the premise of using recursive adaptive stochastic subspace identification (RASSI) to extract the oscillation modes (frequency and damping) from the ambient data, the optimization model was solved by employing the particle swarm optimization (PSO) algorithm. The effectiveness of the proposed approach was demonstrated using numerical simulations on the IEEE 16-machine 68-bus test system and measured data from a real system.