Power System Dynamic Behavior Research Articles

GPU-based transient analysis of modern grids deploying a hybrid DDM algorithm

Solving a significant number of differential-algebraic equations is essential for conducting transient stability simulations on a complex and interconnected electrical power system. Because of the increasing size and intricacy of modern grids, traditional sequential simulation methods are becoming more computationally challenging and time-consuming to use for dynamic simulations. This research aims to examine parallelism techniques from an innovative algorithm viewpoint to the hardware level by utilizing multiple graphics processing units as the main computational tool designed to simulate the dynamic behaviour of power systems on a large scale. Our approach features a novel hybrid algorithm to improve the dynamic simulations of grids with significant renewable energy integration. The algorithm employs a Schwarz-based approach in its initial decomposition phase to isolate synchronous machines and renewable sources from the grid. This separation enhances the algorithm's ability to manage these components effectively. Subsequently, each subsystem undergoes further division into subdomains in the second stage, with separate computations carried out using the Schur-complement technique. The simulations were conducted on various test systems, with a maximum of 25,000 buses, 8,000 synchronous generators, and 256 PV farms all modelled in detail. We introduce a GPU-oriented preprocessing and vectorization parallelization method for the implementation of our two-stage algorithm. This approach provides the flexibility to tailor parallelization techniques, including nested for loops and kernel pragmas, to craft a hardware solution that enhances the performance of our dynamic domain decomposition algorithm. Simulation outcomes have verified that this approach can yield a notable 7.8x acceleration in speed when executed on an NVIDIA GeForce RTX 2070 SUPER GPU.

Review on measurement-based frequency dynamics monitoring and analyzing in renewable energy dominated power systems

The massive integration of clean energy and renewable energy source (RES) is one of the most important trends in the low carbon energy transition toward carbon neutrality. Such an important goal significantly alters the power system dynamic behavior. Consequently, monitoring and analyzing the complex frequency dynamic of RES-dominated power systems play an essential role in ensuring power system security and stability. The measurements, especially those supported by wide area measurement systems (WAMSs), can enable full state awareness and deep informatization of the power system and therefore provide effective solutions for monitoring and analyzing system frequency dynamic behaviors with complex features. This paper focus on the application of measurements in monitoring and modeling analysis technologies for the features of frequency dynamics of RES-dominated power systems. We summarize related research on online monitoring of frequency dynamic behavior features based on the information from measurements. Further, for system frequency security assessment, measurements can improve the traditional methods and promote new data-driven methods for more accuracy and effective frequency dynamics analysis. Finally, future directions and possible solutions for measurement-based frequency dynamics monitoring and analyzing are prospected.

Stability Analysis of Bipolar LVDC Grid

The study and regulation of bipolar DC structures covered by asymmetrical action, the DC symmetric part approach is implemented. This approach is an expansion of the standard principle of symmetrical components in three phase AC-controlled networks. In typical and differential modes, the asymmetrical voltage and current in the positive and negative poles are separated into symmetric segments. For each mode, an analogous circuit is imitative, which produces decoupled case circuits. As a consequence, it provides autonomous recommendations of each situation and offers an informative mode of a bipolar DC power system's static and dynamic behavior. A common methodology which is relevant to numerous cases of device scheme is the DC symmetrical portion process. An improved common-mode voltage control scheme is defined as an example. By incorporating active damping regulation, it suppresses common mode LC resonance and decreases common-mode impedance to enhance power efficiency and stability of voltage. Matlab/Simulink effects validate the main theoretical assumptions.

An Improved Power System State Estimation Using A Dynamically Adapted JAYA Algorithm

State estimation is a central issue for power systems monitoring and control. Applying state estimation schemes ensures the accuracy of system real-time monitoring process. Due to the high nonlinearities and non-smoothness of the dynamic behavior of power systems, state estimation is getting more importance to lessen the error margins. In order to find the best estimate of the various variables of a power system, optimization-based and statistical techniques are applied. Classically, common metering devices are used to measure power system variables. Nevertheless, these devices are associated with errors, especially with the ongoing expansion of the power networks. These errors are linked to many issues related to operation and communication processes besides the errors caused by the metering device itself. The commonly applied technique to solve the power system state estimation problem is the Weighted Least-Squares (WLS) method. In this paper a dynamically adapted algorithm is introduced employing a WLS-based dynamic JAYA optimization technique. The algorithm was validated and applied on the well-known IEEE 14-bus network. The results proved the efficiency and advantages of the proposed algorithm when compared to other methods used for the state estimation problem.

Power Oscillation Analysis of PMSG Wind Power Generation System Considering Power Control Nonlinearity

High proportion of renewable energy generation, especially wind power generation, has changed the dynamic behavior of power systems and leads to emerging stability issues such as oscillation accidents. The commonly used stability analysis methods based on linear system theory cannot tackle the influence of nonlinear elements in the control loop. To fill this gap, the describing function method is used to analyze the stability and power oscillations of a grid-connected permanent magnet synchronous generator (PMSG) wind power generation system in this paper. A complete PMSG system model is taken into consideration, including a wind turbine, a generator, a machine-side converter, a grid-side converter, and a weak grid. Particularly, the nonlinear element introduced by maximum power point tracking control in the power control loop is modeled and analyzed, and the influences of critical system parameters are studied. With the high accuracy of the describing function method, it is revealed that the machine-side converter mainly influences the oscillation amplitude, while the grid-side converter mainly influences the oscillation frequency. Furthermore, the following results can be obtained: 1) High bandwidth of maximum power point tracking control and rotation speed control may enlarge the oscillation amplitude, while a fast current loop of the machine-side converter is beneficial to the stability; 2) Grid-side voltage loop can significantly affect the frequency of the oscillation, and improper high bandwidth of a phase-locked loop (PLL) is harmful to system stability; 3) A stronger grid is not always beneficial to the system stability, and the influence of grid strength should be carefully analyzed and examined when nonlinear elements are considered. All analyses are verified by simulations based on MATLAB/Simulink.

Phasor Modeling Approaches and Simulation Guidelines of Voltage-Source Converters in Grid-Integration Studies

With the large integration of converter-interfaced generation (CIG) and widespread of power electronic interfaced technologies, power system dynamic behaviour is becoming progressively faster. As a consequence, is often unclear when to use EMT or Phasor models in grid integration studies. Therefore, this paper presents useful simulation guidelines of Voltage-Source Converters (VSCs) used in AC grid integration studies. It also presents several EMT and Phasor models suited to simulate converter-interfaced generation (CIG) and renewable energy resources connected to power systems. Several modelling approaches and suitability analyses were provided based on a comprehensive comparative study among the models. Various studies were performed in a small system, composed of two generators, and a CIGRE benchmark system, both modelled in Simulink. We address a gap related to the suitability of CIGs phasor models in studies where the boundary between electromagnetic and electromechanical transients overlap. An insightful analysis of the adequate simulation time step for each model and study is also provided.

Deep multi‐agent Reinforcement Learning for cost‐efficient distributed load frequency control

The rise of microgrid-based architectures is modifying significantly the energy control landscape in distribution systems, making distributed control mechanisms necessary to ensure reliable power system operations. In this article, the use of Reinforcement Learning techniques is proposed to implement load frequency control (LFC) without requiring a central authority. To this end, a detailed model of power system dynamic behaviour is formulated by representing individual generator dynamics, generator rate and network constraints, renewable-based generation, and realistic load realisations. The LFC problem is recast as a Markov Decision Process, and the Multi-Agent Deep Deterministic Policy Gradient algorithm is used to approximate the optimal solution of all LFC layers, that is, primary, secondary and tertiary. The proposed LFC framework operates through centralised learning and distributed implementation. In particular, there is no information interchange between generating units during operation. Thus, no communication infrastructure is necessary and information privacy between them is respected. The proposed framework is validated through numerical results and it is shown that it can be used to implement LFC in a distributed and cost-efficient manner.

Electric Vehicle Charger Static and Dynamic Modelling for Power System Studies

Electric Vehicles (EVs) are becoming increasingly available and are expected to be a large part of the load in future power systems. EV chargers are a relatively new type of load and are mainly interfaced with the grid through power electronics. It is therefore important to investigate the impact they have on power system dynamic behaviour. In this paper, two detailed EV charger models (representing a typical slow and fast charger) were investigated. The aim was to test the capability of standard static—and more importantly, dynamic—load models, commonly used in power system studies, to represent the static and dynamic behaviour of EV chargers. Different control parameter settings for two types of EV chargers were investigated, as were the limits of standard power system dynamic load model structures’ accurate representation. Typical parameter sets have also been provided for cases where proper representation was possible.

Definition and Classification of Power System Stability – Revisited & Extended

Since the publication of the original paper on power system stability definitions in 2004, the dynamic behavior of power systems has gradually changed due to the increasing penetration of converter interfaced generation technologies, loads, and transmission devices. In recognition of this change, a Task Force was established in 2016 to re-examine and extend, where appropriate, the classic definitions and classifications of the basic stability terms to incorporate the effects of fast-response power electronic devices. This paper based on an IEEE PES report summarizes the major results of the work of the Task Force and presents extended definitions and classification of power system stability.

Sensitivity Analysis of the Impact of the Sub- Hourly Stochastic Unit Commitment on Power System Dynamics

Subhourly modeling of power systems and the use of the stochastic optimization are two relevant solutions proposed in the literature to address the integration of stochastic renewable energy sources. With this aim, this paper deals with the effect of different formulations of the subhourly stochastic unit commitment (SUC) problem on power system dynamics. Different SUC models are presented and embedded into time domain simulations (TDS) through a cosimulation platform. The objective of the paper is to study the combined impact of different frequency control/machine parameters and different SUC formulations on the long-term dynamic behaviour of power systems. The analysis is based on extensive Monte Carlo TDS (MC-TDS) and a variety of scenarios based on the New England 39-bus system.

Nonlinear Modeling and Analysis of Grid-Connected Voltage-Source Converters Under Voltage Dips

In power systems, voltage-source converters (VSCs) are gradually replacing traditional devices and dramatically changing power system dynamic behavior, as the VSC's intrinsic high-order nonlinearity and multiple time-scale characteristics. As a simple case of transient stability for power-electronic-based power systems, in this article, we study a VSC system with a fifth-order nonlinear model, with the aid of nonlinear dynamics analysis. For the transient behavior, we find that both the amplitude and the phase of the terminal voltage of VSC show discontinuity when the fault occurs or is cleared. The behavior of time-scale separation is also generally observable, namely, the fast time-scale dynamics damps and disappears quickly, and the system bulk behavior is dominated by the slow time-scale dynamics. In addition, we find that the system transient stability is uniquely determined by whether the fault-clearing state is within or out of the basin of attraction of the post-fault equilibrium point. Finally, simulations and hardware-in-the-loop experiments verify the analytical results. We expect that all these interesting findings could provide an improved physical insight on our understanding of transient stability of power-electronic-based power systems.

A Generic EMT-Type Model for Wind Parks With Permanent Magnet Synchronous Generator Full Size Converter Wind Turbines

Utilities are under considerable pressure to increase the share of wind energy resources in their generation fleet. With the increasing share of wind energy resources, the dynamic behavior of power systems will change considerably due to fundamental differences in technologies used for wind and conventional generators. There is a very little standardization in the ways to model wind turbines (WTs) and wind parks (WPs) in sharp contrast to conventional power plants. Hence, there is an international interest to deliver generic models (i.e. standardized and publicly available) for WTs and WPs that are able to capture all performance aspects as good as manufacturer-specific models. This paper presents an electromagnetic transient (EMT) simulation model for full-size converter (FSC) WT-based WPs that can be used for stability analysis and interconnection studies. The considered topology uses a permanent magnet synchronous generator. Although the collector grid and the FSC WTs are represented with their aggregated models, the overall control structure of the WP is preserved. FSC WT and WP control systems include the non-linearities, and necessary transient and protection functions to simulate the accurate transient behavior of WPs.

Using adaptive control in DFIG‐based wind turbine systems to inhibit power system low‐frequency oscillations

Considering the growing wind power penetration in power systems, using the flexible control ability of these turbines to enhance power system dynamic behaviour has been investigated. One of the major challenges regarding the stability problem of power systems is the low-frequency oscillations (LFOs) of synchronous generators in a power system. Usually, power system stability units are used to damp these oscillations, but using wind turbine systems for this purpose has been suggested in recent studies. In this regard, mostly a linear supplementary control loop has been employed in the control system of wind turbines. Applying a linear structure for the supplementary control loop does not result in optimum performance since the power system operating conditions and the wind turbine power generation change continuously. In this study, adaptive control is used to design the supplementary loop. Doubly-fed induction generator (DFIG)-based wind turbine systems are used for this study. Since adaptive control parameters tend to optimum values, applying this controller will provide better damping for power system (LFOs at different wind speeds, as shown in this study.

Methodology for online identification of dynamic behavior of power systems with an increased amount of power electronics interface units

A methodology for online and offline dynamic stability assessment, suitable for power systems with high penetration of power electronics interface units is presented in this paper. The increasing penetration of renewable energy resources as well as changing market operations, new types of loads and storage technologies, are causing significant changes to power systems dynamic behavior. Unstable generator groups and generators exhibiting poorly damped oscillatory behavior are identified online, opening the possibility to corrective control actions in order to stabilize the system. Moreover, statistical analysis of the abundant data from simulations provides information on the overall impact of power electronics interface units on system stability.

A new approach for df/dt and active power imbalance in power system estimation using Huang’s Empirical Mode decomposition

In this paper, Huang’s Empirical Mode Decomposition approach is proposed for df/dt and active power imbalance in power system estimation. Applied approach implies availability of synchronized phasor measurement units. In addition to the successful applications in the analysis of nonstationary dynamic behavior of power system, identifications and analyses of low-frequency electromechanical oscillations and signals denoising, this approach also enables direct estimation of rate of change of a weighted average frequency (frequency of the center of inertia), as well as assessment of the overall imbalance in the power system. This demonstration is performed using computer simulation testing on the 39 Bus New England System and Western System Coordinating Council 118 bus test systems in the DigSILENT PowerFactory power system analysis software package. To validate the proposed approach the actual frequency information are used. Empirical Mode Decomposition approach is compared with Discrete Wavelet Transform, Method of Least Squares and the results from the DigSILENT PowerFactory. Also, performance of the empirical mode decomposition are compared with performances of the multivariate empirical mode decomposition and noise assisted multivariate empirical mode decomposition on both, simulated signals and field measurements. Applied approach is implemented in the MATLAB environment and results show very high accuracy.

Power System Critical Cutset Identification based on Rolling Double Level Hierarchical Clustering

When a power system is subjected to a large disturbance, effective identification of critical cutset and generator groupings in the electric network contribute to the effective analysis of power system dynamic behavior, which also can be used for determination of optimal locations of FACTS devices, initiation of preventive control actions, decision of emergency control actions and adaptive choice of out-of-step relaying. In this paper, a new power system critical cutset identification named rolling double level hierarchical clustering method is proposed. Case studies using the New England 10-generator test systems are given to illustrate the validity of the proposed method.

Stability Analysis of Power Systems With Inclusion of Realistic-Modeling WAMS Delays

This paper studies the impact of realistic wide-area measurement system (WAMS) time-varying delays on the dynamic behavior of power systems. A detailed model of WAMS delays including quasi-periodic, stochastic, and constant components is presented. Then, this paper discusses numerical methods to evaluate the small-signal stability as well as the time-domain simulation of power systems with inclusion of such delays. The small-signal stability analysis is shown to be able to capture the dominant modes through the combination of a characteristic matrix approximation and a Newton correction technique. A case study based on the IEEE 14-bus system compares the accuracy of the small-signal stability analysis with Monte Carlo time-domain simulations. Finally, the numerical efficiency of the proposed technique is tested through a real-world dynamic model of the all-island Irish system.

Large Time Step Electromagnetic Transient Simulation of Large Scale Power System Based on Time Domain Transformation Method

Electromagnetic Transients (EMT) simulation is an effective approach to study the dynamic behavior of complex AC/DC power grids. However, with increasing applications of the electronic equipment and the expansion of power grid, conventional EMT simulation tools are facing significant challenges with regard to simulation speed and scale. In order to improve the performance of EMT simulation, some approaches have been proposed. A time domain transformation methodology [1] has recently been proposed. In this paper, based on the large time step EMT algorithm, an electromagnetic transient simulation program has been developed and is used to study large scale power system dynamic behaviors. The result shows that the new EMT algorithm can not only guarantee the simulation accuracy, but also effectively improve the speed of full electromagnetic transient simulation of large scale complex power grids.

The Dynamic Behavior of POWER Systems with Two Distinct EMS Control Techniques

The Dynamic Behavior of POWER Systems with Two Distinct EMS Control Techniques

Application of weather forecasting model WRF for operational electric power network management—a case study for Phailin cyclone

Extreme weather events like tropical cyclone result in colossal catastrophe during landfall causing widespread inland flooding due to storm surge and also the post-landfall event result in extensive damage to infrastructural facilities and property hinterland. The state of Odisha located in east coast of India experienced a Very Severe Cyclonic Storm (VSCS) named Phailin during the post-monsoon season of October 2013. Timely warnings and alertness on storm surge coordinated with a massive evacuation effort by National Disaster Management Authorities (NDMA) were quite effective in minimizing the loss of human life. However, there was a trial of destruction due to extremely high winds and rainfall that followed during post-landfall causing extensive damage to property and major infrastructure facilities in the Odisha State. This study critically investigated the Phailin post-landfall phase focusing on the impact of high winds and rainfall on the power distribution network using the Weather Research and Forecasting (WRF) model. The study evaluated the spatial and temporal variability of wind speed and rainfall distribution from the WRF model configured for three different spatial domains and selecting the best available microphysics and land surface parameterization schemes. The proposed outer, intermediate, and inner domains had spatial resolutions of 27, 9, and 3 km respectively and that provided the best estimate for onshore wind speed, track forecast, and rainfall distribution highly relevant for the management of power distribution and transmission network. In context to weather model application for the Indian region, this effort is novel and probably for the first time that linked a suitable customized weather model output to evaluate its impact on observed tripping in transmission network of electric power grids. The dynamic model outputs from WRF were compared with data from synchrophasors used in electrical technology that monitored the transient and dynamic behavior of power systems in real-time operations. A close examination of the results signifies that the atmospheric model performed exceptionally well in capturing the tripping time of power lines, and the overall knowledge obtained from this study has a broader scope to develop a framework for efficient planning operations of the power network, resource allocation, and emergency preparedness.