Power Grid Control Research Articles

Optimization and promotion of automatic generation control strategy under large-scale wind power

With the increasing proportion of wind power in power grid system, the frequency control ability of power grid system were weakened. The security and stability control of power grid is facing great challenges. The research of frequency control for thermal power need to be further strengthened. The characteristics of wind power and automatic generation control (AGC) strategy were analyzed and studied, the optimization method and system design of unit’s AGC were pointed out. Under the premise of ensuring safety and economy, the proposed approaches can fully used the load control capacity of thermal power generation and effectively improved the frequency characteristics of the power system.

Primary frequency optimization control method of thermal power unit based on safe and stable operation

With the rapid development of energy-saving and clean new energy, power fluctuations bring great challenges to frequency control of power grid. The main ways of dealing with the instantaneous power gap depends on primary frequency compensation(PFC) of thermal power units. The characteristics and questions of automatic generation control (AGC) and PFC were analyzed, and the optimization of unit control were offered. It can ensure that the frequency modulation and peak shaving capacity of the thermal power unit meets the requirements of power grid standards, and effectively ensure the priority of the PFC action when the grid frequency fluctuates, improve the coordinated operation of the AGC and PFC.

Power management and operational planning of multiport HPCS for residential applications

Renewable energy integration to the power grid has seen a tremendous rise in last few years. A novel hybrid AC and DC bus layout (i.e. medium-voltage DC bus of 380 V and low-voltage DC bus of 48 or 12 V DC) for the residential consumer premises has been proposed in this study. This would enable the consumer to directly connect DC loads to the system, without the need of an individual power conversion device. This study summarises the strategical operational modes of the proposed hybrid power conditioning system (HPCS) for multiple distributed energy resources (DER) integrated residential premises located within urban/rural area. Modified HPCS converter control strategy has been proposed, such that the system operation is efficient and self-adaptive in both, grid forming (or, islanded) and feeding (or, grid connected) modes. System is configured by using a single power conditioning unit, capable of performing wide range of operations, such as, multiple DER interface, battery power management, grid power control and accessibility to AC and DC household loads at the desired voltage levels. Performance of the designed system has been tested via simulation and experimental studies.

A tri-level programming model for attack-resilient control of power grids

The significance of modern power grids is acknowledged every time there is a major threat. This paper proposes the novel approaches to aid power system planner to improve power grid resilience by making appropriate hardening strategies against man-made attack or natural hazards. The vulnerability indices are introduced, which return the most vulnerable component in the system based on a tri-level defender-attacker-operator (DAO) interdiction problem which solves iteratively. The output of DAO is the set of hardening strategies that optimally allocated along the network to mitigate the impact of the worst-case damages. By repeating DAO problem based on the proposed algorithm, the various crafted attack is imposed on the system, and the defender’s behavior demonstrates how an element is vulnerable to threats. The WSCC 9-bus, IEEE 24-bus, and IEEE 118-bus systems are employed to evaluate the model performance. The counter-intuitive results are proven by the proposed robust hardening strategy, which shows how the hardening strategy should be allocated to improve power network resilience against threats.

Curing Braess’ paradox by secondary control in power grids

The robust operation of power transmission grids is essential for most of today’s technical infrastructure and our daily life. Adding renewable generation to power grids requires grid extensions and sophisticated control actions on different time scales to cope with short-term fluctuations and long-term power imbalance. Braess’ paradox constitutes a counterintuitive collective phenomenon that occurs if adding new transmission line capacity to a network increases loads on other lines, effectively reducing the system’s performance and potentially even entirely destabilizing its operating state. Combining simple analytical considerations with numerical investigations on a small sample network, we here study dynamical consequences of secondary control in AC power grid models. We demonstrate that sufficiently strong control not only implies dynamical stability of the system but may also cure Braess’ paradox. Our results highlight the importance of demand control in conjunction with the grid topology to ensure stable operation of the grid and reveal a new functional benefit of secondary control.

Full- and Reduced-Order State-Space Modeling of Wind Turbine Systems with Permanent Magnet Synchronous Generator

Full-order state-space models represent the starting point for the development of advanced control methods for wind turbine systems (WTSs). Regarding existing control-oriented WTS models, two research gaps must be noted: (i) There exists no full-order WTS model in form of one overall ordinary differential equation that considers all dynamical effects which significantly influence the electrical power output; (ii) all existing reduced-order WTS models are subject to rather arbitrary simplifications and are not validated against a full-order model. Therefore, in this paper, two full-order nonlinear state-space models (of 11th and 9th-order in the (a,b,c)- and (d,q)-reference frame, resp.) for variable-speed variable-pitch permanent magnet synchronous generator WTSs are derived. The full-order models cover all relevant dynamical effects with significant impact on the system’s power output, including the switching behavior of the power electronic devices. Based on the full-order models, by a step-by-step model reduction procedure, two reduced-order WTS models are deduced: A non-switching (averaging) 7th-order WTS model and a non-switching 3rd-order WTS model. Comparative simulation results reveal that all models capture the dominant system dynamics properly. The full-order models allow for a detailed analysis covering the high frequency oscillations in the instantaneous power output due to the switching in the power converters. The reduced-order models provide a time-averaged instantaneous power output (which still correctly reflects the energy produced by the WTS) and come with a drastically reduced complexity making those models appropriate for large-scale power grid controller design.

An adaptive zone-division approach for voltage control of power grid with distributed wind farms: A case study of a regional power grid in central south China

With the increasing penetration level of wind power generation, it is essential to coordinate the dispersed wind farms with the automatic voltage control (AVC) system to take part in the voltage regulation of the power grid. In this paper, an adaptive zone-division approach is proposed to identify the optimal controllable zone for each wind farm. The reactive power generation capability of wind farms with inverters is adequately exploited. A multidimensional V-Q sensitivity analysis is implemented to evaluate the ability of reactive power regulations, based on which an online zone-division method is adopted to determine the control clusters for wind farms. The proposed approach can be applied in the AVC system of power grid to alleviate the regulation burden for voltage stability. Moreover, the reactive power generations from wind farms can be effectively utilized to improve the penetration of wind power. A case study on a regional power grid from central south China is carried out, which indicates that, with the proposed approach the capability to maintain the voltage stability for power system operations can be enhanced with more wind power penetration.

Lifelong Learning for Complementary Generation Control of Interconnected Power Grids With High-Penetration Renewables and EVs

This paper proposes a lifelong learning (LL) based complementary generation control (CGC) of interconnected power grids with high-penetration renewable energy sources and electric vehicles (EVs). The wind farms (WFs), photovoltaic stations (PVs), and EVs are aggregated as a wide-area virtual power plant (WVPP) for automatic generation control (AGC), which can significantly accelerate the system response and reduce the regulation costs of balancing unexpected power mismatches between generation side and demand side. Under such framework, CGC is decomposed into a multi-layer generation command dispatch to rapidly compute an optimal solution. LL is first employed for the primary layer CGC between conventional power plants and a WVPP. Then, the secondary layer is implemented according to the ascending order of regulation costs of all reserve sources. Finally, the tertiary layer is accomplished by a coordinated control in each WFs or PVs, whereas an online optimization of EVs is adopted by considering the charging demands. The imitation learning is introduced to improve the learning efficiency of agents with transfer learning, thus an online optimization of CGC can be satisfied. Case studies are carried out to evaluate the performance of LL for multi-layer CGC of AGC on a practical Hainan power grid of southern China.

Wide-Area Damping Control Using Multiple DFIG-Based Wind Farms Under Stochastic Data Packet Dropouts

Data dropouts in communication network can have a significant impact on wide-area oscillation damping control of a smart power grid with large-scale deployment of distributed and networked phasor measurement units and wind energy resources. Remote feedback signals sent through communication channels encounter data dropout, which is represented by the Gilbert-Elliott model. An observer-driven reduced copy (ORC) approach is presented, which uses the knowledge of the nominal system dynamics during data dropouts to improve the damping performance where conventional feedback would suffer. An expression for the expectation of the bound on the error norm between the actual and the estimated states relating uncertainties in the cyber system due to data dropout and physical system due to change in operating conditions is also derived. The key contribution comes from the analytical derivation of the impact of coupling between the cyber and the physical layer on ORC performance. Monte Carlo simulation is performed to calculate the dispersion of the error bound. Nonlinear time-domain simulations demonstrate that the ORC produces significantly better performance compared to conventional feedback under higher data drop situations.

On statistical power grid observability under communication constraints (invited paper)

Phasor Measurement Units (PMUs) have enabled real-time power grid monitoring and control applications realizing an integrated power grid and communication system. The communication network formed by PMUs has strict latency requirements. If PMU measurements cannot reach the control centre within the latency bound, they will be invalid for calculation and may compromise the observability of the whole power grid as well as related applications. To address this issue, this study proposes a model to account for the power grid observability under communication constraints, where effective capacity is adopted to perform a cross-layer statistical analysis in the communication system. Based on this model, three algorithms are proposed for improving power grid observability, which are an observability redundancy algorithm, an observability sensitivity algorithm and an observability probability algorithm. These three algorithms aim at enhancing the power system observability via the optimal communication resource allocation for a given grid infrastructure. Case studies show that the proposed algorithms can improve the power system performance under constrained wireless communication resources.

Detection of Ozone and Nitric Oxide in Decomposition Products of Air-Insulated Switchgear Using Ultraviolet Differential Optical Absorption Spectroscopy (UV-DOAS).

Air-insulated switchgear cabinets play a role in the protection and control of the modern power grid, and partial discharge (PD) switchgear is a long-term process in the non-normal operation of one of the situations; thus, condition monitoring of the switchgear is important. The air-insulated switchgear during PD enables the decomposition of air components, namely, O3 and NO. A set of experimental platforms was designed on the basis of the principle of ultraviolet differential optical absorption spectroscopy (UV-DOAS) to detect O3 and NO concentrations in air-insulated switchgear. Differential absorption algorithm and wavelet transform were used to extract effective absorption spectra; a linear relationship between O3 and NO concentrations and absorption spectrum data were established. O3 detection linearity was up to 0.9992 and the detection limit was at 3.76 ppm. NO detection linearity was up to 0.9990 and the detection limit was at 0.64 ppm. Results indicate that detection platform is suitable for detecting trace O3 and NO gases produced by PD of the air-insulated switchgear.

Message from Editor

Message from Editor
 Dear Readers,
 
 It is a great honor for us to publish Volume 8, Issue 1 of Global Journal of Computer Sciences: Theory and Research. 
 
 Global Journal of Computer Sciences: Theory and Research (GJCS) is an international online journal for scientists and professionals involved in all aspects of computer sciences. This journal serves as an international platform that fosters theoretical and practical issues and new applications for all scientists and professionals from the field of computer sciences including original research and innovative applications from all parts of the world.
 
 Aim of this issue is to give the researchers an opportunity to share the results of their academic studies. There are different research topics discussed in the articles. Articles focusing on performance analysis of software maintenance process using stochastic Petri nets, modelling and power control of grid connected wind energy system, study and identification of short-circuit currents at the complex distribution network SIDER EL Hadjar (ex ArceloMittal-Algerie), Bangladeshi consumers’ e-commerce security and privacy satisfactions in small to mid-sized enterprises (SMEs), STATCOM’s contribution to the improvement of voltage plan and power flow in an electrical transmission network and a technological platform for the creation and evaluation of psycho-technical tests are included in the current issue.
 
 A total number of twelve (12) manuscripts were submitted for this issue and each paper has been subjected to double-blind peer review process by the reviewers specialized in the related field. At the end of the review process, a total number of six (6) high quality research papers were selected and accepted for publication.
 
 We present many thanks to all the contributors who helped us to publish this issue.
 
 Best regards,
 
 Prof. Dr. Dogan Ibrahim
 
 Editor – in Chief

Modelling and power control of grid connected wind energy system


 Wind energy generation has attracted great interests in recent years. Doubly-fed induction generator (DFIG) for wind turbines (WTs) are largely deployed, because variable-speed WTs have many advantages over fixed-speed generation such as increased energy capture, operation at maximum power point, improved efficiency and power quality. This paper presents the operation and vector control of a DFIG system, where the stator is connected directly to a stiff grid and the rotor is connected to the grid through bidirectional back-to-back AC–DC–AC converter. The basic operational characteristics, mathematical model of the aerodynamic system and vector control technique, which is used to obtain decoupled control of powers, are investigated using the software Matlab/Simulink.
 
 Keywords: Wind turbine, doubly-fed induction generator, active and reactive power controller.

Energy Function Inspired Value Priority Based Global Wide-Area Control of Power Grid

Conventional wide-area control strategies that are deployed to damp inter-area oscillations use fixed a priori schemes based on modal analysis of the power system. As these controllers cannot be tuned online, such schemes fail to perform well during severe dynamic system changes. In this paper, a wide-area control architecture designed based on reinforcement learning and optimal adaptive critic network is proposed, that learns and optimizes the system closed-loop performance. Also, a value priority scheme is designed using a derived Lyapunov energy function for prioritization of local and the proposed wide-area global controller which ensures coherent damping of local and inter-area oscillations. The method increases the reliability and allows for automatic tuning of stabilizing controllers especially in the presence of wide-area monitoring constraints. Simulation results on 8-bus 5-machine and 68-bus 16-machine IEEE test systems highlight the efficiency of the proposed method.

Detection of PMU spoofing in power grid based on phasor measurement analysis

In some recent articles, the vulnerability of phasor measurement unit (PMU) to the time synchronisation attack by spoofing its global positioning system (GPS) has been highlighted as a threat to power grid protection, control and monitoring system. Having spoofed PMU GPS signals, one can manipulate the measurements and inject bad data to power grid protection and monitoring system. The existing anti-spoofing methods are all based on GPS signal analysis. The mentioned methods are just able to detect spoofing without any data refinement as the data of power grid has not been practically used in calculations. Furthermore, some of these methods lose their certainty in noisy and harsh environments due to low power of GPS signals. A novel anti-spoofing algorithm has been proposed based on power grid infrastructures which can join to any of the existing anti-spoofing algorithm to empower spoofing detection process. The proposed algorithm adopts phasor measurement analysis and state estimation methods to detect spoofing. The composite of this algorithm with any of the existing algorithms will not only cover the probable malfunctioning in spoofing detection but also be able to refine counterfeit measurements.

Design of Intelligent Operation and Maintenance Architecture for Grid Dispatching and Control System

As the scale of the grid expanding, the operation and maintenance of power grid dispatching and control system becomes more complex, the traditional passive operation mode of grid dispatching and control system is difficult to meet the challenges. In order to improve the quality and efficiency of operation and maintenance, the design of intelligent operation and maintenance architecture for grid dispatching and control system is proposed. In this paper, with the boost of the information technology level in the power grid, disaster-tolerant and load balancing technology of operation and maintenance are studied in detail as well. The new architecture can effectively improve the efficiency of operation and maintenance, and ensure the system operation safety and stability.

AI‐based approach to identify compromised meters in data integrity attacks on smart grid

False data injection attacks can pose serious threats to the operation and control of power grid. The smarter the power grid gets, the more vulnerable it becomes to cyber-attacks. Various detection methods of cyber-attacks have been proposed in the literature in recent past. However, to completely alleviate the possibility of cyber-threats, the compromised meters must be identified and secured. In this study, the authors are presenting an artificial intelligence (AI)-based identification method to correctly single out the malicious meters. The proposed AI-based method successfully identifies the compromised meters by anticipating the correct measurements in the event of the cyber-attack. New York Independent System Operator load data is mapped with the IEEE 14-bus system to validate the proposed method. The efficiency of the proposed method is compared for artificial neural network and extreme learning machine-based AI techniques. It is observed that both the techniques identify the corrupted meters with high accuracy.

Analysis of the impact of electric vehicles on the power grid

The paper presents problems related to the impact of electric vehicles connected to the power grid on energy parameters. Basic methods of control in power grids were discussed and results of the simulation were presented with regards to the power distribution, voltage drops and losses in the transmission lines. The simulation was conducted based on the example of CIGRE 11, to which electric vehicle charging stations were connected in several selected points, with the possibility of energy release into the grid. The obtained results were compared for the simulation conducted in two variants – without the connected electric vehicles and with them. The obtained results were analyzed and commented upon.

Volt/Var Control for Power Grids With Connections of Large-Scale Wind Farms: A Review

Large-scale wind farms (LSWFs) have become a popular form of exploiting abundant wind energy. However, the integration of LSWFs presents challenges to the volt/var control (VVC) of power grids. In this regard, various VVC methods for power grids with connections of LSWFs have been proposed from different viewpoints. This paper provides a comprehensive review on VVC for power grids with connections of LSWFs. First, the challenges presented by LSWFs to VVC are investigated with regard to the uncertainty of power flow and voltage, conflicts of VVCs among interconnected power grids, operation of discrete devices, voltage stability, and reactive power market. Second, an overview on current research regarding VVC methods for LSWFs connected power grids is presented, where the VVC methods are classified into three categories: decentralized VVC, centralized VVC, and hierarchical VVC. The three categories of VVC methods are analyzed and compared in terms of their advantages, disadvantages, and applications. In addition, drawbacks of current research are concluded. Finally, to overcome the drawbacks presented in current research, this paper provides directions for future research, including event-triggered VVC methods, big data techniques, reactive power markets, energy storage systems, and VSC-based HVDC.

Research on Security Framework of Mobile Application in Dispatch and Control Domain of Power Grid

The rapid development of mobile Internet technology and the wide spread of smart terminals have brought opportunities for the transformation of power grid business model. Compared to the non-real-time information, the real-time and running data of dispatch and control domain is easy to be intercepted and cracked. To solve this problem, this paper presents a new approach to mobile application security framework for the power grid control field. It is to realize secondary encryption by using the method of MD5+AES mixed encryption algorithm and combining the time stamp in real-time data transmission process. At the same time it is to prevent cross-border operations and brute force by using Token authentication and Session technology. China EPRI safety test results show that the application of the framework significantly improves the integrity, safety and reliability of real-time data in power grid control.