Virtual Power System Research Articles

Short-Term Photovoltaic Power Forecasting Using PV Data and Sky Images in an Auto Cross Modal Correlation Attention Multimodal Framework

The accurate prediction of photovoltaic (PV) power generation is crucial for improving virtual power plant (VPP) efficiency and power system stability. However, short-term PV power forecasting remains highly challenging due to the significant impact of weather changes, especially the complexity of cloud motion. To this end, this paper proposes an end-to-end innovative deep learning framework for data fusion based on multimodal learning, which utilizes a new auto cross modal correlation attention (ACMCA) mechanism designed in this paper for feature extraction and fusion by combining historical PV power generation time-series data and sky image data, thereby enhancing the model’s prediction performance under complex weather conditions. In this paper, the effectiveness of the proposed model was verified through a large number of experiments, and the experimental results showed that the model’s forecast skill (FS) reached 24.2% under all weather conditions 15 min in advance, and 24.32% under cloudy conditions with the largest fluctuations. This paper also compared the model with a variety of existing unimodal and multimodal models, respectively. The experimental results showed that the model in this paper outperformed other benchmark methods in all indices under different weather conditions, demonstrating stronger adaptability and robustness.

Virtual inertia calculation and virtual power system stabiliser design for stability enhancement of virtual synchronous generator system under transient condition

AbstractEnhancing the stability of the Virtual Synchronous Generator (VSG) under transient conditions has become a new challenge for VSG operation. This paper presents the design of a Virtual Power System Stabiliser (VPSS) with virtual inertia calculations for the stability enhancement of the VSG system under transient conditions. The virtual inertia is calculated by considering the transient conditions resulting from a three‐phase ground fault and the allowable phase margin in the VSG. This aims to prevent the coupling effect, which can cause the active power loop control and reactive power loop control to operate non‐independently. Subsequently, the VPSS is specifically designed based on the determined virtual inertia characteristics. The VPSS design is developed by taking into account the phase angle shift of the VSG. The proposed combination of virtual inertia and VPSS is capable of providing accurate compensation for phase angle changes under transient conditions. To evaluate the performance of the proposed virtual inertia and VPSS, a system‐level VSG model is used to thoroughly analyse the system's performance. Based on the results and analysis, it is shown that the control strategy utilising the combination of virtual inertia and the proposed VPSS design can improve VSG stability under transient conditions.

An Optimized Power-Angle and Excitation Dual Loop Virtual Power System Stabilizer for Enhanced MMC-VSG Control and Low-Frequency Oscillation Suppression

Modular Multilevel Converter Virtual Synchronous Generator (MMC-VSG) technology is gaining widespread attention for its ability to enhance the inertia and frequency stability of the power grid integrated with converter-interfaced renewable energy sources. However, the excitation voltage regulation in the MMC-VSG can generate equivalent negative damping torque and cause low-frequency oscillation problems similar to those in synchronous machines. This article aims to improve the system’s damping torque and minimize low-frequency oscillations by introducing a Virtual Power System Stabilizer (VPSS) into the power control loop. Building on the study of dynamic interactions between various control links of the MMC, this research establishes a reduced-order model (ROM) and a Phillips–Heffron state equation for the MMC-VSG single machine infinite bus system, using a hybrid modeling approach and a zero-pole truncation method. It also analyzes the mechanism of low-frequency oscillations in the MMC-VSG system through the damping torque method. The analysis reveals that the negative damping torque produced during the excitation voltage regulation process causes changes in the virtual power angle, which in turn increases the risk of low-frequency oscillation in the MMC-VSG. To address this issue, the article proposes an optimized control method for the MMC-VSG dual power loop architecture (power-angle/excitation) VPSS. This strategy compensates for the inadequate damping torque of a single loop VPSS and effectively suppresses low-frequency oscillations in the system.

Virtual Power System: Novel approach for Distributed Generation and Consumption Coordination

Worldwide the introduction of dispersed generators (DG) in the distribution network is assuming a significant importance. There is an increasing relevance of the energy process efficiency improvement; as for electric power systems, the most interesting perspective concerns the capability of the system to increase the exploitation of the renewable resources. The integration of DGs in the electric distribution network requires a revision of this infrastructure, so far designed and developed assuming that power flows in one direction: from the high voltage transmission network to the medium voltage distribution, to reach final customers on the low voltage network. The attention to an efficient operation of distribution networks is increasing all over the world; this interest is becoming higher and higher also in Italy, where the high energy prices push in the direction of fostering efficiency as much as possible. This work describes a study developed in the Alpenergy project framework: an International Cooperation Program aimed at introducing an efficient operational model for the distributed production and consumption. In particular it is proposed a new model for the integration and the management of the DG in the distribution network. The new model (defined VPS: Virtual Power System) is based on a communication channel between the active users (generators), the loads and, eventually, the Distribution System Operators (DSOs).

Research on improving low-frequency oscillation characteristics of wind power grid-connected power system with doubly-fed wind generator based on virtual impedance power system stabilizer

Research on improving low-frequency oscillation characteristics of wind power grid-connected power system with doubly-fed wind generator based on virtual impedance power system stabilizer

Influence mechanism and virtual power system stabiliser method of virtual synchronous generator for low‐frequency oscillation of power system

AbstractThe virtual synchronous generator (SG) (VSG) can not only enhance the inertia of the grid, but also introduce the oscillation characteristics of SG, which is easy to interact with the power angle of SG in the grid, and even produce low‐frequency oscillation (LFO). The authors first construct a two‐machine interconnected power system model containing VSG and traditional SG. The model is linearised to construct the state space equations to obtain the Phillips–Heffron model with VSG. The LFO path of action between VSG and SG is analysed. To reduce the negative damping torque provided by VSG to SG through this path, a virtual power system stabiliser (VPSS) is proposed and the controller parameters are adjusted according to the phase compensation method. Finally, the effectiveness of VPSS is verified by modal analysis and simulation comparison.

A robust transient energy function‐based controller for enhancing transient stability of virtual power system

AbstractThis paper offers non‐linear control for enhancing the transient stability in power systems containing a photovoltaic (PV) and doubly fed induction generator (DFIG) by transient energy function (TEF) method and finite‐time observers. At first, the TEF method is utilized to enhance the transient stability in a power system containing a PV, DFIG, and synchronous generator (SG) by constructing a hybrid Lyapunov function. Then, the derivative terms in control are estimated with finite‐time observers. The main contribution of the research is the application of the TEF technique in the transient stability evaluation of a power system consisting of PV, SG, and DFIG. Another innovation of the research is the simultaneous control of DFIG and PV, whose uncertain parameters are estimated with the use of finite‐time observer. The proposed non‐linear control scheme is robust against changes in the configuration of the power system. In order to show the capability of this control scheme, time domain simulations are performed on the IEEE 9‐bus, and the NEW ENGLAND Standard 39‐Bus power system. Using the obtained result, some comparisons are made with the back‐stepping control scheme to clarify the superiority of the proposed method. The comparisons show that the proposed non‐linear control scheme can properly provide extra damping to reduce the first‐swing fluctuations in less time.

Real-time Scheduling of Virtual Power System Based on the Hidden Markov Model

With the large-scale grid connection of renewable energy, the grid operation gradually presents a new feature of high-order uncertainty, which poses a severe challenge to the security and stability of the system operation. At present, the intelligent degree of dispatching instruction operation is low, and the human-computer interaction is still in the stage of manual operation. In this paper, a virtual power system for real-time power grid scheduling is proposed. Firstly, a grid model is established based on graph theory. Secondly, a GES agent is designed for power grid scheduling decisions. The implementation effect of the strategy is verified by simulation, and the scheduling strategy is sent to the new energy station. The analysis results show that compared with the traditional manual scheduling method, the proposed man-machine scheduling scheme can effectively improve the execution time and accuracy of scheduling, effectively reduce the risk of overload in the power grid, and provide a solution for the man-machine interaction system in the environment of power scheduling.

A simplified virtual power system lab for distance learning and ABET accredited education systems

COVID-19 pandemic has had an adverse impact on higher education worldwide. In particular, the situation can be more crucial for electrical power engineering education due to the importance of the direct relationship between the students and their instructor embodied in the campus’ classroom interaction and the requisite face-to-face learning. Apparently, e-learning instructional design has provided a fairly accepted solution through online lectures and exams for power engineering courses. Nevertheless, the difficulty persists in moving the experiment equipment of the laboratories to the homes of the students since most experiments were likely to be carried out on the University campus’ dedicated power system panels. An urgent and reduced cost solution is therefore needed. This paper introduces a shortcut design method as a compensatory solution at no extra cost, which during this challenging period is suitable for teaching power system labs and also suitable for full online education programs. The work presented in the paper goes beyond that to discuss the relevance to ABET student outcomes. Two experiments are presented in the PowerWorld Simulator environment with systematic steps to facilitate the expansion of the rest of the laboratory experiments. The method is based on the simulation of a textbook example and the verification of results from another textbook followed by a discussion of the relevant students' outcomes of ABET. The paper may be used as an educational guide for instructors in the following academic year in institutions that embrace distance learning programs.

Low-frequency Oscillation Damping Control for Large-scale Power System with Simplified Virtual Synchronous Machine

This study focuses on a virtual synchronous machine (VSM) based on voltage source converters to mimic the behavior of synchronous machines (SMs) and improve the damping ratio of the power system. The VSM model is simplified according to some assumptions (neglecting the speed variation and the stator transients) to allow for the possibility of dealing with low-frequency oscillation in large-scale systems with many VSMs. Furthermore, a virtual power system stabilizer (VPSS) structure is proposed and tuned using a method based on a linearized power system dynamic model. The linear and nonlinear analyses examine the stability of two modified versions of a 16-machine power system in which, in the first case, partial classical machines are replaced by VSMs, and in the second case, all SMs are replaced by VSMs. The simulation results of the case studies validate the efficiency of the proposed control strategy.

Coordinated Control of Doubley Fed Induction Generator Virtual Inertia and Power System Oscillation Damping Using Fuzzy Logic

Doubly-fed induction generator (DFIG) based wind turbines with traditional maximum power point tracking (MPPT) control provide no inertia response under system frequency events. Recently, the DFIG wind turbines have been equipped with virtual inertia controller (VIC) for supporting power system frequency stability. However, the conventional VICs with fixed gain have negative effects on inter-area oscillations of regional networks. To cope with this drawback, this paper proposes a novel adaptive VIC to improve both the inter-area oscillations and frequency stability. In the proposed scheme, the gain of VIC is dynamically adjusted using fuzzy logic. The effectiveness and control performance of the adaptive fuzzy VIC is evaluated under different frequency events such as loss of generation, short circuit disturbance with load shedding. The simulation studies are performed on a generic two-area network integrated with a DFIG wind farm and the comparative results are presented between three cases: DFIG without VIC, DFIG with fixed gain VIC, and DFIG with adaptive fuzzy VIC. All the results confirm the proposed fuzzy VIC can improve both the inter-area oscillations and frequency stability.

Low-Order Response Modeling for Wind Farm-MTDC Participating in Primary Frequency Controls

A low-order and system-level response model for wind farms (WFs) and voltage source converter based high-voltage direct current (VSC-HVDC) participating in primary frequency regulation using virtual synchronous machine (VSM) control is developed and validated. The VSM control with virtual power system stabilizer (PSS) function is presented being applicable to all multi-terminal HVDC (MTDC) VSCs. In this context, a general low-order response model (LRM) for presenting the WF-MTDC participating in the frequency control of main AC system is readily established. This modeling method derives transfer function based block diagram offering an illustrative insight into dynamic interaction between AC frequencies and DC voltages. Such a model can also provide a convenient way performing control system designing and parameter tuning. As a paradigm, LRM-based linear quadratic regulation optimization is applied to obtain the droop and damping gains for feasible frequency regulation. The effectiveness of the LRM method is verified through comparisons of the simulation results obtained from different models, controller designs, and parameter tuning approaches, which are all performed on a five-terminal VSC-HVDC connecting WF-side and main AC systems.

Singular value decomposition‐based dynamic response analysis of VSC‐MTDC/AC systems for renewable energy integration

The dynamic performance of voltage source converter-based multi-terminal high-voltage direct current (VSC-MTDC) grid for large-scale renewable energy integration is becoming a concern. This study proposes a system-level dynamic response model of wind farm (WF)-MTDC-main AC systems, and then analyses the dynamic performance based on the singular value decomposition (SVD) technique. In the modelling, an improved virtual synchronous machine control is developed, and the interaction between AC frequency and DC voltage can be readily described. Using the SVD technique, parameters of the controllers are tuned, thereby making the AC frequency and DC voltage deviations within the limitations. Some oscillation modes of the system are observed and virtual power system stabiliser is proposed to suppress the oscillations. Additionally, the oscillation can be mitigated by emulating capacitance-based inertia response. The efficiency of the proposed model and analysis is verified through the frequency-domain and time-domain results.

SMART GRID DEVELOPMENT IN INDIA WITH CHALLENGES AND OPPORTUNITIES: EXECUTION WITH GAME THEORY

Advancement in energy technologies are much needed for social and economical enlargement of our society. The weakest electric grid in the world in India lost 26% of total power generation as transmission and distribution losses. The sustainable energy resources and development of efficient modules are highly required in present power system. Existing power system is designed as a one way supply system from source to utility. The objective of this paper is to study the problems of conventional power grids in India, and optimize the problems through smart grid to enhance the bidirectional flow of power in distribution network. The increasing embodiment of renewable energy sources and variable energy consumption patterns make the smart grid complex. Smart grid (SG) components such as smart meters, virtual power system and microgrid are discussed with challenges in adoption of smart grid. Renewable energy sources provides a solution against the emission of CO2 from conventional power system by the establishment of smart grid. Game theory approach has been proposed in smart grid to conflicting the grid secure in global environment and reduces the dependency of consumers on fossil fuel sources. This paper discusses the overview of game theory, Cooperative and noncooperative game theory.

A power hardware-in-loop based testing bed for auxiliary active power control of wind power plants

Auxiliary active power control (AAPC) of wind power plants (WPP) has been an emerging subject of modern power systems. However, there is currently lack of appropriate platform to test AAPC performances of an actual WPP. Under the background, this paper presents a testing bed for AAPC in both frequency regulation and damping control of WPP. The main novelty is that the platform is designed based on power hardware-in-loop (PHIL) technologies. PHIL technologies enable a physical WPP to integrate to a virtual real-time power system, which is simulated with StarSim software. The technologies combine the advantages of software and hardware simulations. Based on the testing bed, this paper compares the frequency regulation and damping control performances of an aggregated wind farm integrated to an isolated system. The PHIL simulation results demonstrate the strength of the platform, which extends the flexibility of system configurations of software simulation to an actual physical WPP experiment.

AlpStore Project: A Viable Model for Renewables Exploitation in the Alps

Nowadays, the integration of intermittent and unpredictable Renewable Energy Sources (RESs) has led to new issues for the electrical system. The paper proposes a model, named Virtual Power System (VPS), which enables the management of generators and loads as a single (virtual) entity in order to achieve a “global” benefit, i.e. to improve the capability of the grid to host RESs. Moreover Energy Storage Systems (ESSs) could be integrated in the VPS in order to provide ancillary services: voltage regulation, primary frequency regulation and exchange profiles adjustment for a better RESs programmability. This work proposes a quantitative approach for ESSs design and integration in a VPS. Numerical results are reported with respect to an experimental application in the AlpStore project (Alpine Space Program 2007-2013).

A Megawatt-Scale Power Hardware-in-the-Loop Simulation Setup for Motor Drives

We report on the application of a 5-MW variable voltage source (VVS) amplifier converter for utilization in power hardware-in-the-loop (PHIL) experiments with megawatt-scale motor drives. In particular, a commercial 2.5-MW variable speed motor drive (VSD) with active front end was connected to a virtual power system using the VVS for integrating the drive with a simulated power system. An illustrative example is given, whereby a 4-MW gas turbine generator system, including various loads, is simulated and interfaced with the VSD hardware in the lab through the VVS using current feedback to the simulation. Mechanical loading is applied to the motor via an identical 2.5-MW dynamometer connected to the same shaft. This paper first describes the PHIL facility, illustrates the challenges of powering a motor drive from a controlled voltage source converter at the multimegawatt scale, and provides experimental results from dynamic simulations. While certain challenges remain with the accuracy of the interface, it is concluded that PHIL simulations at the megawatt power level are possible and may prove useful for validating models of drive systems in the future.

Virtual power plant and system integration of distributed energy resources

A concept is presented along with the overarching structure of the virtual power plant (VPP), the primary vehicle for delivering cost efficient integration of distributed energy resources (DER) into the existing power systems. The growing pressure, primarily driven by environmental concerns, for generating more electricity from renewables and improving energy efficiency have promoted the application of DER into electricity systems. So far, DER have been used to displace energy from conventional generating plants but not to displace their capacity as they are not visible to system operators. If this continues, this will lead to problematic over-capacity issues and under-utilisation of the assets, reduce overall system efficiency and eventually increase the electricity cost that needs to be paid by society. The concept of VPP was developed to enhance the visibility and control of DER to system operators and other market actors by providing an appropriate interface between these system components. The technical and commercial functionality facilitated through the VPP are described and concludes with case studies demonstrating the benefit of aggregation (VPP concept) and the use of the optimal power flow algorithm to characterise VPP.

A Virtual Environment for Protective Relaying Evaluation and Testing

Protective relaying is a fundamental discipline of power system engineering. At Georgia Tech, we offer three courses that cover protective relaying: an undergraduate course that devotes one-third of the semester on relaying, a graduate course entitled "Power System Protection," and a three-and-a-half-day short course for practicing engineers. To maximize student understanding and training on the concepts, theory, and technology associated with protective relaying, we have developed a number of educational tools, all wrapped in a virtual environment. The virtual environment includes a) a power system simulator, b) a simulator of instrumentation for protective relaying with visualization and animation modules, c) specific protective relay models with visualization and animation modules, and d) interfaces to hardware so that testing of actual relaying equipment can be performed. We refer to this set of software as the "virtual power system." The virtual power system permits the in-depth coverage of the protective relaying concepts in minimum time and maximizes student understanding. The tool is not used in a passive way. Indeed, the students actively participate with well-designed projects such as a) design and implementation of multifunctional relays, b) relay testing for specific disturbances, etc. The paper describes the virtual power system organization and "engines," such as solver, visualization, and animation of protective relays, etc. It also discusses the utilization of this tool in the courses via specific application examples and student assignments.