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Summary: This paper presents a low‐voltage ride‐through capability (LVRT) solution for the photovoltaic (PV) grid‐connected inverters compliant with the Indian grid code. The LVRT strategy ensures the uninterrupted connection of solar energy to the grid, safeguarding against system shutdown in the event of various grid faults. During this time, the inverter supplies reactive power to the utility grid, effectively utilizing converter capacity and aiding the restoration of the voltage profile at the point of common coupling (PCC). The system used in this study involves a two‐stage grid‐interfaced solar PV setup with a boost converter that tracks the maximum power point (MPP) and an inverter that maintains the DC‐link voltage. A modified dynamic braking chopper control (MDBCC) has also been implemented to minimize the DC‐link voltage oscillations during asymmetrical faults while simultaneously injecting the sinusoidal current into the grid. To improve grid synchronization in the presence of unbalanced abnormalities, a modified dual second‐order generalized integrator phase‐locked loop (DSOGI‐PLL) has been employed to track the grid voltage angle precisely. Furthermore, a new control system has been developed in conjunction with the LVRT approach. The suggested system is simulated in MATLAB/Simulink to validate the efficacy of the LVRT control method during symmetrical and asymmetrical faults using a 100‐kW two‐stage grid‐interfaced solar PV facility. Finally, for experimental validation, a real‐time test bench (RTS) OPAL‐RT 4510 is used to implement the setup with its control, and the practical results are compared with the simulation outcomes. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a low‐voltage ride‐through capability (LVRT) solution for the photovoltaic (PV) grid‐connected inverters compliant with the Indian grid code. The LVRT strategy ensures the uninterrupted connection of solar energy to the grid, safeguarding against system shutdown in the event of various grid faults. During this time, the inverter supplies reactive power to the utility grid, effectively utilizing converter capacity and aiding the restoration of the voltage profile at the point of common coupling (PCC). The system used in this study involves a two‐stage grid‐interfaced solar PV setup with a boost converter that tracks the maximum power point (MPP) and an inverter that maintains the DC‐link voltage. A modified dynamic braking chopper control (MDBCC) has also been implemented to minimize the DC‐link voltage oscillations during asymmetrical faults while simultaneously injecting the sinusoidal current into the grid. To improve grid synchronization in the presence of unbalanced abnormalities, a modified dual second‐order generalized integrator phase‐locked loop (DSOGI‐PLL) has been employed to track the grid voltage angle precisely. Furthermore, a new control system has been developed in conjunction with the LVRT approach. The suggested system is simulated in MATLAB/Simulink to validate the efficacy of the LVRT control method during symmetrical and asymmetrical faults using a 100‐kW two‐stage grid‐interfaced solar PV facility. Finally, for experimental validation, a real‐time test bench (RTS) OPAL‐RT 4510 is used to implement the setup with its control, and the practical results are compared with the simulation outcomes. [ABSTRACT FROM AUTHOR]

The Timor system is one of the large systems in the East Nusa Tenggara region. Based on the general plan for electricity supply for 2021-2030, there is a plan to interconnect a 2x11 MW wind power plant. The addition of wind power plants will pose a considerable threat to the system due to the intermittency nature of renewable energy plants. Therefore, a comprehensive grid impact study is needed to convince network managers that adding wind farms will not cause disruptions to the system either locally or in general and is expected to strengthen the electricity system. The power flow simulation results, installing a 2x11 MW wind farm on the Timor system can improve voltage quality and reduce losses on both 70 and 150 kV systems. For transient stability, the frequency value on the Timor system still meets the grid code requirements. In addition, the simulation results of the intermittency impact of the wind power plant output show that the Timor system is still in a stable condition. The stability of the rotor angle of the existing power plant when the transient stability simulation is carried out shows that it is still in a balanced condition. [ABSTRACT FROM AUTHOR]

This paper investigates the challenges in the grid caused by high penetration of photovoltaic (PV) systems and measures to achieve efficient islanding detection during grid abnormalities. To achieve this an islanding classification approach is developed by using a multi-layer perceptron neural network (MLPNN) to train with the possible islanding scenarios that can occur in a grid. The proposed approach aids the grid-connected system to isolate the healthy portion from the faulty portion of the system and ensure uninterrupted operations of the system even in the case of fault and grid maintenance. The performance of the proposed method was tested on the data obtained for different grid abnormalities simulated on a grid-connected photovoltaic system using a Typhoon-HIL environment. The obtained results depicted 95.6% training efficiency and 98.3% testing efficiency, and the trained approach can effectively detect an islanding scenario in 0.02 s with 1.7% misclassification error. [ABSTRACT FROM AUTHOR]

Compared with the traditional grid-following photovoltaic grid-connected converter (GFL-PGC), the grid-forming photovoltaic grid-connected converter (GFM-PGC) can provide voltage and frequency support for power systems, which can effectively enhance the stability of power electronic power systems. Consequently, GFM-PGCs have attracted great attention in recent years. When an asymmetrical short-circuit fault occurs in the power grid, GFM-PGC systems may experience transient instability, which has been less studied so far. In this paper, a GFM-PGC system is investigated under asymmetrical short-circuit fault conditions. A novel Q-V droop control structure is proposed by improving the traditional droop control. The proposed control structure enables the system to accurately control the positive- and negative-sequence reactive current without switching the control strategy during the low-voltage ride-through (LVRT) period so that it can meet the requirements of the renewable energy grid code. In addition, a dual-loop control structure model of positive- and negative-sequence voltage and current is established for the GFM-PGC system under asymmetrical short-circuit fault conditions. Based on the symmetrical component method, the composite sequence network of the system is obtained under asymmetrical short-circuit fault conditions, and positive- and negative-sequence power-angle characteristic curves are analyzed. The influence law of system parameters on the transient synchronous stability of positive- and negative-sequence systems is quantitatively analyzed through the equal area criterion. Finally, the correctness of the theoretical analysis is verified by simulation and hardware-in-the-loop experiments. [ABSTRACT FROM AUTHOR]

Deep neural networks have made tremendous gains in emulating human-like intelligence, and have been used increasingly as ways of understanding how the brain may solve the complex computational problems on which this relies. However, these still fall short of, and therefore fail to provide insight into how the brain supports strong forms of generalization of which humans are capable. One such case is out-of-distribution (OOD) generalization – successful performance on test examples that lie outside the distribution of the training set. Here, we identify properties of processing in the brain that may contribute to this ability. We describe a two-part algorithm that draws on specific features of neural computation to achieve OOD generalization, and provide a proof of concept by evaluating performance on two challenging cognitive tasks. First we draw on the fact that the mammalian brain represents metric spaces using grid cell code (e.g., in the entorhinal cortex): abstract representations of relational structure, organized in recurring motifs that cover the representational space. Second, we propose an attentional mechanism that operates over the grid cell code using determinantal point process (DPP), that we call DPP attention (DPP-A) – a transformation that ensures maximum sparseness in the coverage of that space. We show that a loss function that combines standard task-optimized error with DPP-A can exploit the recurring motifs in the grid cell code, and can be integrated with common architectures to achieve strong OOD generalization performance on analogy and arithmetic tasks. This provides both an interpretation of how the grid cell code in the mammalian brain may contribute to generalization performance, and at the same time a potential means for improving such capabilities in artificial neural networks.

Low-voltage ride-through (LVRT) is one of the most important criteria for integrating wind energy into the power grid. Based on grid connection codes, wind generators must remain connected during fault conditions. However, this requires a careful protection scheme design for addressing the successful ride through of the brushless doubly fed induction generator (BDFIG) during severe voltage dips. This paper proposes a comprehensive solution for enhancing the BDFIG ride through during asymmetrical faults. Furthermore, since the proposed solution is dependent on the type and severity of voltage dips, an updated harmonic resilient scheme is developed to detect the dip level and type of faults. Performance of the proposed protection scheme is investigated for further improvement of the brushless DFIG LVRT capability based on series dynamic resistor (SDR) circuit design in order to limit post-fault oscillations. With the proposed solution, the BDFIG can satisfy ride through requirements for severe voltage dip scenarios. The proposed framework which includes a voltage detection method, appropriate SDR value determination procedure, and SDR control circuit was implemented and validated with a coupled circuit model in MATLAB/Simulink for a BDFIG prototype.

This paper proposes a robust protection technology to enhance the grid-connected capability of the doubly fed induction generator (DFIG) based on wind turbines (WTs) under low voltage ride through (LVRT) conditions. The proposed method to control the rotor side converter (RSC) and grid side converter (GSC) uses proportional–integral (PI) controllers. The protection devices are the static compensator (STATCOM), crowbar, series dynamic resistor (SDR), and DC-chopper, with the proposed method to control STATCOM using proportional–integral (PI) controllers and the proposed method to control the rest of the protection devices based on the allowable threshold values of rotor current and DC-link voltage. The protection coordination strategy between them is proposed to avoid the disconnection between the rotor circuit and grid, maintain the DC-link at constant voltage, enhance the dynamic response of WT, and improve the voltage response at the point of common coupling (PCC) of WT. The DFIG-WT of 2 MW-575 V connecting to the 34-bus IEEE network is carried out to verify the effectiveness of the proposed method under the conditions of symmetrical and asymmetrical faults, and the LVRT requirements of the Spanish grid code are considered. The obtained simulation results using the PSCAD/EMTDC software show that the rotor current, DC-link voltage, voltage PCC, and power oscillation damping are significantly improved compared to not using it or applying the conventional method based on passivity theory. Therefore, the LVRT capability of the proposed DFIG-WT system is significantly enhanced, and it has enough ability to continue to provide electrical energy to the power network. [ABSTRACT FROM AUTHOR]

Summary: This paper presents sliding mode pulse‐width modulation (SMPWM) for current‐controlled five‐leg converter (FLC) in wind energy system. The proposed topology substitutes at once two three‐phase converters, classified as back‐to‐back (BTB), by sharing one leg between the permanent magnet synchronous generator (PMSG) and power grid. To overcome the coupling of the two sides, the control of common leg is introduced. SMPWM methodology is designed using system dynamic model and surface decoupling approach to make system tracking desired references. The reference currents are selected to perform control requirements of PMSG wind turbine. The phase currents are controlled simultaneously during normal operation and in the event of unbalanced grid voltages. Different operating conditions are tested under wind variations including a turbulence component. The main objectives are to achieve balanced and sinusoidal currents, as well as smooth active and reactive powers injected into the grid. Simulation results show that FLC can act as BTB converters and demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Compared with the traditional grid-following photovoltaic grid-connected converter (GFL-PGC), the grid-forming photovoltaic grid-connected converter (GFM-PGC) can provide voltage and frequency support for power systems, which can effectively enhance the stability of power electronic power systems. Consequently, GFM-PGCs have attracted great attention in recent years. When an asymmetrical short-circuit fault occurs in the power grid, GFM-PGC systems may experience transient instability, which has been less studied so far. In this paper, a GFM-PGC system is investigated under asymmetrical short-circuit fault conditions. A novel Q-V droop control structure is proposed by improving the traditional droop control. The proposed control structure enables the system to accurately control the positive- and negative-sequence reactive current without switching the control strategy during the low-voltage ride-through (LVRT) period so that it can meet the requirements of the renewable energy grid code. In addition, a dual-loop control structure model of positive- and negative-sequence voltage and current is established for the GFM-PGC system under asymmetrical short-circuit fault conditions. Based on the symmetrical component method, the composite sequence network of the system is obtained under asymmetrical short-circuit fault conditions, and positive- and negative-sequence power-angle characteristic curves are analyzed. The influence law of system parameters on the transient synchronous stability of positive- and negative-sequence systems is quantitatively analyzed through the equal area criterion. Finally, the correctness of the theoretical analysis is verified by simulation and hardware-in-the-loop experiments.

The integration of new renewable power capacity into the grid constitutes an important challenge. Control issues become more complex, and the behavior of the new installations must be carefully assessed. In this sense, countries are establishing strict technical requirements when integrating new generation facilities into networks. Within this framework, given the great importance of photovoltaic solar energy as a clean electricity generation technology that is experiencing an unstoppable increase, the present paper evaluates the compliance of a real solar photovoltaic power plant with a number of technical requirements established in the new Spanish grid code. The analyses are performed by means of a photovoltaic power plant simulation model representing the actual facility. Thus, the main contribution of the present work consists of mitigating the lack of information about the performance of real experiences on the commissioning process of new renewable power plants, as well as demonstrating the usefulness of simulation models towards the modernization of grid codes. The results reveal the compliance of the renewable facility with the requirements analyzed, showing a maximum deviation of 0.47% in the case of the power–frequency requirements, and very accurate responses of the power plant under the reactive power control requisites. The results also reveal the facility fully covers the reactive power capability requirements. This paper has served not only to deepen the process of compliance with grid codes, but also to obtain approval from the Spanish transmission system operator, Red Eléctrica de España, to commission the power plant under consideration, this being a contribution of special interest to industry.

• Analytical formulas for inrush currents and voltage dips of three-phase transformer • The formulas make it easy for anyone to calculate inrush currents and voltage dips • The formulas are composed of only simple trigonometric and exponential functions • Calculation results using the formulas agree well with the results of EMT analysis A method has been developed to calculate the inrush currents and voltage dips during transformer energization with the same accuracy as electromagnetic transient (EMT) analysis. The developed method is based on analytical formulas obtained by directly solving the circuit equations formulated by simplifying the power system and transformer circuit. The calculation results of inrush currents and voltage dips under severe conditions are compared with EMT analysis results and confirmed to be in good agreement. [ABSTRACT FROM AUTHOR]

Conventional grid-code specifications for dynamic ancillary services provision such as fast frequency and voltage regulation are typically defined by means of piece-wise linear step-response capability curves in the time domain. However, although the specification of such time-domain curves is straightforward, their practical implementation in a converter-based generation system is not immediate, and no customary methods have been developed yet. In this paper, we thus propose a systematic approach for the practical implementation of piece-wise linear time-domain curves to provide dynamic ancillary services by converter-based generation systems, while ensuring grid-code and device-level requirements to be reliably satisfied. Namely, we translate the piece-wise linear time-domain curves for active and reactive power provision in response to a frequency and voltage step change into a desired rational parametric transfer function in the frequency domain, which defines a dynamic response behavior to be realized by the converter. The obtained transfer function can be easily implemented e.g. via a proportional-integral (PI)-based matching control in the power loop of standard converter control architectures. We demonstrate the performance of our method in numerical grid-code compliance tests, and reveal its superiority over classical droop and virtual inertia schemes which may not satisfy the grid codes due to their structural limitations. • Implementing piece-wise linear grid-code curves in converters lacks standard methods. • Our approach implements piece-wise linear grid-code curves for converter systems. • We convert time-domain grid-code curves to frequency-domain transfer functions. • The transfer functions can be implemented in standard converter control setups. [ABSTRACT FROM AUTHOR]

The goal of achieving decarbonized operation of power systems in response to climate change has led to an increase in the number of sources connected to electrical grids through inverters, of which photovoltaic systems are an example. The operating characteristics of these systems in steady-state or transient operation are different from those of synchronous machines, giving rise to issues related to power system stability. The vast majority of grid codes stipulate that fault ride-through operating requirements should be enabled during severe contingencies in the transmission network, prioritizing delivery of reactive power to the power system to support voltage stability. However, this control action may contribute to rapid collapse of the system voltage under adverse operating conditions, such as when the critical voltage in the power vs. voltage curve is near the reliable voltage operating bound. Supporting power system stability under these circumstances represents a new challenge for inverter control schemes. This paper adapts a recently published fault ride-through control scheme for PV inverters for use in a multimachine power system and shows that the scheme can successfully maintain transient and voltage stability even under adverse voltage operating conditions.

In this paper, the impacts of large-scale OWPPs penetration on the Turkish power system are addressed. The grid compliance analyses for the large-scale OWPP integration are carried out by using the grid connection criteria defined in the Turkish grid code. PV and QV curves are obtained to assess the effect of OWPP on the static voltage stability limit. Eight scenarios are conducted to analyze the effect of the OWPP on the static and dynamic characteristics of the power grid. To observe the large-scale OWPP impact on the voltage and frequency stability, transient events such as the outage of conventional power plants and three-phase to ground faults are applied. The results of the voltage and frequency stability analysis reveal that the Turkish grid remains stable after the integration of an 1800 MW OWPP. Furthermore, the Turkish system remains stable even in the event of an outage of the international transmission lines to Bulgaria and Greece.

World leaders and scientists have been putting immense efforts into strengthening energy security and reducing greenhouse gas (GHG) emissions by meeting growing energy demand for the last couple of decades. Their efforts accelerate the need for large-scale renewable energy resources (RER) integration into existing electricity grids. The intermittent nature of the dominant RER, e.g., solar photovoltaic (PV) and wind systems, poses operational and technical challenges in their effective integration by hampering network reliability and stability. This article reviews and discusses the challenges reported due to the grid integration of solar PV systems and relevant proposed solutions. Among various technical challenges, it reviews the non-dispatch-ability, power quality, angular and voltage stability, reactive power support, and fault ride-through capability related to solar PV systems grid integration. Also, it addresses relevant socio-economic, environmental, and electricity market challenges. Finally, it highlights the proposed solution methodologies, including grid codes, advanced control strategies, energy storage systems, and renewable energy policies to combat the discussed challenges. The findings of this article assist the power system scholars and researchers in conducting further research in this field. Furthermore, it helps the decision-makers to choose the appropriate technologies to deal with the anticipated challenges associated with the grid integration of PV systems.

With increasing penetration of wind power, wind turbines are usually required to stay connected and provide reactive current support according to LVRT (low voltage ride through) grid code during grid faults. However, for WTC (wind turbine converter) connected to high impedance AC grid, the voltage dependent current injection required by LVRT grid code may conflict with the injection current dependent voltage response of WTC, resulting in LVRT failure. In this letter, the matching of them is studied in detail. First, the voltage dependent current injection defined by LVRT grid code and injection current dependent voltage response of WTC are developed, respectively. Then the matching of them is revealed from the source-load matching analysis of equivalent circuit. It is identified that there exists constraints on the selection of K-factor to ensure the matching during low voltage grid faults. Simulated results are also presented to verify the analysis. [ABSTRACT FROM AUTHOR]

Rapid integration of renewable energy into the electric grid has ramifications for grid management and planning. Therefore, system operators have formulated grid code requirements to ensure that the grid continues to operate in a secure, safe, and cost-effective manner. The current state of grid code in Ethiopia, as well as the need for it, is discussed in this article. It lays out the technological grid integration requirements, with a focus on small and microgrids, which are especially important for the integration of renewable. The barriers to grid code normalization and renewable energy grid compatibility testing are identified, and suggestions for continued grid code development in Ethiopia based on Danish observations are provided. Further, a detailed comparative analysis of the Ethiopian grid code with the IEEE 1547-2003 and IEEE 1547-2018 standards is presented. [ABSTRACT FROM AUTHOR]

• Pioneer Spain: first country to include in grid code the synthetic inertia capability. • Synthetic inertial response of a PV inverter studied based on the Spanish grid code. • Analyzed the role of power plant controller in the dynamic response of the facility. • PV system able to contribute to frequency control providing an inertial response. As the large-scale integration of renewable energy grows, inertia in power systems is reduced, which causes the rate of change of frequency to increase and worsens the frequency nadir during disturbances. There is, therefore, an urgent need to accelerate the development of international standards and regulations that require solar PV systems and other renewable installations to also contribute to stability in the network by emulating inertia. Spain is a pioneer in this field: it is currently the only country that includes the synthetic inertia technical requirement in its grid code. In this context, the present paper analyzes the synthetic inertial response of a PV system model that forms part of an actual PV power plant in Spain under two scenarios, according to its grid code: i) when measurements are conducted at the power conversion PV system level and hence only its control algorithms are executed; and ii) when measurements are conducted at the power plant level and the power plant controller also influences the response of the entire installation. Among its aims, this paper seeks to thoroughly assess the response of an actual PV power conversion system that has the capability of actively contributing to frequency regulation in a network and to critically analyze the suitability of having a power plant controller when the PV facility contributes to power-frequency control by means of an inertial response. The results reveal, at the power conversion PV system level, that the inertia emulation module significantly reduces the response times of the installation to changes in frequency -by more than 68% in the worst case under frequency increases, and by 73% under frequency decreases, thus contributing to more rapid power-frequency regulation in the network. However, at the power plant level, the power plant controller disturbs the PV power conversion system's behavior and causes the opposite effect: response times increase -up to more than 7% in the most unfavorable case when the inertia module is enabled. [ABSTRACT FROM AUTHOR]

The transient stability of traditional power systems is concerned with the ability of generators to stay synchronized with the positive-sequence voltage of the network, whether for symmetrical or asymmetrical faults. In contrast, both positive- and negative-sequence synchronizations should be of concern for inverter-based generation (IBG) under asymmetrical faults. This is because the latest grid codes stipulate that IBG should inject dual-sequence current when riding through asymmetrical faults. Currently, much less is known about the synchronization stability during asymmetrical faults. This significantly differs from the positive-sequence synchronization alone because the coupled dual-sequence synchronization is involved. This paper aims to fill this gap. Considering the sequence coupling under asymmetrical faults, the dual-sequence synchronization model of IBG is developed. Based on the model, the conditions that steady-state equilibrium points should follow are identified. The conditions throw light on the possible types of synchronization instability, including the positive-sequence dominated instability and the negative-sequence dominated one. For different types of instability, the dominant factors are analyzed quantitatively, which are reflected by the limit on the current injection amplitude. Exceeding the limit will lead to the loss of both positive- and negative-sequence synchronizations. The model and the analysis are verified by simulations and hardware-in-the-loop experiments. [ABSTRACT FROM AUTHOR]

The operation of offshore wind power plants with respect to power quality and grid code compliance must be verified for different conditions in the design phase using harmonic analysis methods. This paper addresses this verification by first considering a scenario in which wind turbines operate with a typically used modulation strategy, carrier-based pulse width modulation. The studies are performed at several operating points, not only at the rated condition, and at two points of the electrical infrastructure, at the point of connection of the wind turbine and at the point of common coupling of the offshore wind farm. For this type of modulation technique and according to the resonance conditions of the studied offshore system, the harmonic distortion of current signals is relatively high and the compliance of the German – grid code is not achieved. To tackle this, wind turbine manufacturer oriented solutions are proposed with the aim of improving the harmonic emission of the offshore wind farm. The implementation of a particular solution of selective harmonic elimination is presented together with complementary solutions to further improve the harmonic emission of the wind power facility. Furthermore, this paper discloses the modeling approach to account for an adequate harmonic assessment of the wind power plant under study.

The aim of this paper is to analyze the situations in which distributed power generation systems (DPGSs) based on renewable energy sources (RESs) can be controlled when operating under voltage sags. Analytical models for both solar photovoltaic (PV) system and doubly-fed induction generator (DFIG)-based wind turbine (WT) written in the complex form of the Park variables are given. Three kinds of control for the grid-side converter (GSC) of a PV system are compared: constant forward voltage control (CFVC), balanced positive-sequence control (BPSC) and the proposed BPSC with grid code requirements (BPSC-GCR). Regarding the rotor-side converter (RSC) of a DFIG-based WT, its controllability is studied considering three different-sized DFIG-based WT units: 6 MW (offshore), 2 MW (onshore) and 7.5 kW (setup). The converter limits are also considered. Simulations carried out in MATLAB reveal that a RES-based DPGS can achieve fault ride-through (FRT) when subject to a certain fault (i.e., with a specific duration and depth), but it may be uncontrollable for different-sized units operating under different faults without considering the grid code requirements. Finally, experimental results prove the robustness of the BPSC-GCR method to let GSCs of PV systems achieve FRT under sags. [ABSTRACT FROM AUTHOR]

The Republic of Serbia must make significant efforts to promote and exploit renewable energy sources and increase energy efficiency in all energy sectors to ensure energy security and economic competitiveness, reduce the negative impact on the environment from energy production and use, and contribute to global efforts to reduce greenhouse gases. Within the paper several issues of integration of recently realized CHP plant are introduced and discussed. Firstly, the legal and energy policy issues in the Republic of Serbia regarding connecting CHP to the grid are presented. The challenges and technical solutions for CHP connection to the grid, as well as power quality issues and the role of the CHP plant during the restoration of power supply during the maintenance of the substation and unplanned loss of high voltage supply, are presented and discussed. Finally, the impact of prospective massive integration of CHP on the energy balance and CO2 emission reduction in the province of Vojvodina in Serbia is investigated and discussed. Since it is the first CHP plant realized in Serbia, it is crucial that experience be shared to all potential stakeholders in the future energy efficiency projects. [ABSTRACT FROM AUTHOR]

Deep neural networks have made tremendous gains in emulating human-like intelligence, and have been used increasingly as ways of understanding how the brain may solve the complex computational problems on which this relies. However, these still fall short of, and therefore fail to provide insight into how the brain supports strong forms of generalization of which humans are capable. One such case is out-of-distribution (OOD) generalization - successful performance on test examples that lie outside the distribution of the training set. Here, we identify properties of processing in the brain that may contribute to this ability. We describe a two-part algorithm that draws on specific features of neural computation to achieve OOD generalization, and provide a proof of concept by evaluating performance on two challenging cognitive tasks. First we draw on the fact that the mammalian brain represents metric spaces using grid cell code (e.g., in the entorhinal cortex): abstract representations of relational structure, organized in recurring motifs that cover the representational space. Second, we propose an attentional mechanism that operates over the grid cell code using determinantal point process (DPP), that we call DPP attention (DPP-A) - a transformation that ensures maximum sparseness in the coverage of that space. We show that a loss function that combines standard task-optimized error with DPP-A can exploit the recurring motifs in the grid cell code, and can be integrated with common architectures to achieve strong OOD generalization performance on analogy and arithmetic tasks. This provides both an interpretation of how the grid cell code in the mammalian brain may contribute to generalization performance, and at the same time a potential means for improving such capabilities in artificial neural networks., Competing Interests: SM, SF, TW, JC No competing interests declared, (© 2023, Mondal et al.)

Summary: Low voltage ride‐through is considered as one of the key technologies for the operation of grid‐connected photovoltaic power generation systems. At present, the most used control methods are based mainly on PI controllers, and their robustness results are still unsatisfactory. In contrast, this article introduces a new robust control strategy that uses the compensation effect of "total disturbance" before affecting the system; this control strategy is called Active Disturbance Rejection Control (ADRC) method. In addition, most of the controllers use the standard SRF PLL to achieve the phase lock and grid synchronization. However, when the grid voltage is distorted or other unbalanced, it is necessary to use the positive sequence voltage component of the fundamental wave as a reference, but the component of the negative sequence cannot be effectively filtered because of its narrow bandwidth, and then, accurate phase lock cannot be achieved, which may cause a failure. In this purpose, a Double Second Order Generalized Integrator based Frequency Locked Loop (DSOGI‐FLL) is proposed and used to improve the system operating performance and non‐off‐line capability. In order to confirm the robustness of the proposed control strategies, a multiple simulations tests were done by utilizing the Matlab/Simulink software. The results have demonstrated the superiority of the proposed methods and their robustness to symmetrical and unsymmetrical faults. [ABSTRACT FROM AUTHOR]

• In order to learn adaptively from surprising observations, it is important to identify the underlying state. • The norepinephrine system signals state transitions after a prediction error. • The hippocampus and medial prefrontal cortex represent the relevant context and segregate information between states to prevent interference. • The entorhinal cortex grid code transfers relevant structure from one context to another, to enable fast generalization and expedite learning. People use information flexibly. They often combine multiple sources of relevant information over time in order to inform decisions with little or no interference from intervening irrelevant sources. They adjust the degree to which they use new information over time rationally in accordance with environmental statistics and their own uncertainty. They can even use information gained in one situation to solve a problem in a very different one. Learning flexibly rests on the ability to infer the context at a given time, and therefore knowing which pieces of information to combine and which to separate. We review the psychological and neural mechanisms behind adaptive learning and structure learning to outline how people pool together relevant information, demarcate contexts, prevent interference between information collected in different contexts, and transfer information from one context to another. By examining all of these processes through the lens of optimal inference we bridge concepts from multiple fields to provide a unified multi-system view of how the brain exploits structure in time to optimize learning. [ABSTRACT FROM AUTHOR]

This work presents a novel method to identify the source of current unbalance during the interaction between industrial consumers and the utility. Since such unbalance yields detrimental effects over the network operation and efficiency; it must be mitigated to avoid their propagation towards the whole grid. To prevent this situation, regulations about the maximum permissible limits of unbalance are recently incorporated in grid codes. Unfortunately, in the absence of an accurate method to identify the agent inducing the unbalance; the problem, responsibility, as well as the solution, is vulnerable to misinterpretation. This situation is quite relevant, for both the consumer and the utility since imputations are subject to penalties. Prompted by this issue, we devised a method based on the computation of sequence impedance matrices. Then the underlying elements of the sequence impedance matrix will expose the occurrence of an unbalance as well as its source, which leads to a theoretically derived metric. This method is tested using real measurements of actual industrial loads connected to different voltage levels (i.e. 230 kV, 161 kV and 115 kV). The results demonstrate accuracy in the detection and identification of the cause of unbalance, considering a wide range of power consumption. [ABSTRACT FROM AUTHOR]

Rapid integration of renewable energy into the electric grid has ramifications for grid management and planning. Therefore, system operators have formulated grid code requirements to ensure that the grid continues to operate in a secure, safe, and cost-effective manner. The current state of grid code in Ethiopia, as well as the need for it, is discussed in this article. It lays out the technological grid integration requirements, with a focus on small and microgrids, which are especially important for the integration of renewable. The barriers to grid code normalization and renewable energy grid compatibility testing are identified, and suggestions for continued grid code development in Ethiopia based on Danish observations are provided. Further, a detailed comparative analysis of the Ethiopian grid code with the IEEE 1547-2003 and IEEE 1547-2018 standards is presented.

As the wind power penetration level has started increasing in the grid, it has become essential to employ wind turbine with frequency regulation capabilities. This has become a challenging issue for researchers working in the area of wind power integration and to seek solution to this problem. To date, a piecemeal approach has been adopted in various review papers in this area, hence lagging completeness. This article presents a comprehensive review of frequency control techniques, various grid codes, load frequency control involving wind power plant with and without frequency control technique and modification in design of wind turbines for frequency regulation. Particularly, load frequency control including wind power plant with and without frequency control techniques at wind turbine manufacturer's level has not been considered for review so far. More than 100 research publications in the form of research papers, reports, guidelines, and standards on the state of the art in this area have been rigorously examined, critically reviewed with research gaps identified and presented in a systematic manner. [ABSTRACT FROM AUTHOR]

With the increase of grid‐connected renewable power generation units, the three‐level converter (TLC) is widely utilized. However, when unbalanced grid voltage occurs, the converter should provide a certain of reactive power to satisfy the grid code, which decreases the power factor and degrades neutral‐point (NP) voltage balance. The existing model predictive control methods for NP voltage balance in TLC mainly focus on high power factor operation, which are not applicable to low power factor operation. To solve this problem, this study proposes a generalized model predictive control (GMPC) scheme for the TLC. By analyzing the influence of P‐type and N‐type small vectors on NP voltage, it is indicated that the charging and discharging operation of the dc‐link capacitors are determined by the grid currents directions with the defined small vectors. Since the directions of grid currents are changed with different power factors, the effect of one small vector on NP voltage is change. In the proposed GMPC scheme, the direction of grid currents and the capacitor voltage difference are simultaneously used to select the appropriate small vector to mitigate the NP voltage unbalance effectively in the full power factor range. The validity is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This research presents a secondary control for a grid-supporting microgrid with photovoltaics sources to guarantee grid code compliance and ancillary services. The secondary control accomplishes the fault ride-through, which implements a delayed signal cancellation (DSC) algorithm for negative sequence detection. Without mode switching, the proposed control strategy meets grid code requirements and ensures voltage regulation at the secondary level, which is active and more salient throughout the transient period of host grid disturbances. This control also ensures a constant supply of the microgrid’s sensitive local load while adhering to grid code requirements. Similarly, active power injection into the main grid is limited by progressively altering the MPPT operating point dependent on the depth of voltage sag to optimize reactive power injection to sustain grid voltage sag. The recommended secondary control is triggered by utilizing the DSC process’s detection algorithm to identify the occurrence of a fault in a tiny fraction of a half-cycle in a grid fault. Consequently, while satisfying microgrid load needs, the devised technique guaranteed that increases in DC-link voltage and AC grid current were controlled. MATLAB Simscape ElectricalTM and OPAL-RT Lab are used to do time-domain simulations of the model using the recommended secondary control systems.

Health-related limitations prohibit a human from working in hazardous environments, due to which cognitive robots are needed to work there. A robot cannot learn the spatial semantics of the environment or object, which hinders the robot from interacting with the working environment. To overcome this problem, in this work, an agent is computationally devised that mimics the grid and place neuron functionality to learn cognitive maps from the input spatial data of an environment or an object. A novel quadrant-based approach is proposed to model the behavior of the grid neuron, which, like the real grid neuron, is capable of generating periodic hexagonal grid-like output patterns from the input body movement. Furthermore, a cognitive map formation and their learning mechanism are proposed using the place–grid neuron interaction system, which is meant for making predictions of environmental sensations from the body movement. A place sequence learning system is also introduced, which is like an episodic memory of a trip that is forgettable based on their usage frequency and helps in reducing the accumulation of error during a visit to distant places. The model has been deployed and validated in two different spatial data learning applications, one being the 2D object detection by touch, and another is the navigation in an environment. The result analysis shows that the proposed model is significantly associated with the expected outcomes. [ABSTRACT FROM AUTHOR]

Electric power systems foresee challenges in stability due to the high penetration of power electronics interfaced renewable energy sources. The value of energy storage systems (ESS) to provide fast frequency response has been more and more recognized. Although the development of energy storage technologies has made ESSs technically feasible to be integrated in larger scale with required performance, the policies, grid codes and economic issues are still presenting barriers for wider application and investment. Recent years, a few regions and countries have designed new services to meet the upcoming grid challenges. A number of grid-scale ESS projects are also implemented aiming to trial performance, demonstrate values, and gain experience. This paper makes a review on the above mentioned aspects, including the emerging frequency regulation services, updated grid codes and grid-scale ESS projects. Some key technical issues are also discussed and prospects are outlined. [ABSTRACT FROM AUTHOR]

With the increase of electrical energy consumption and associated power grid expansion the complexity in the grid network increases which tends to increase the fault occurrence possibilities. Low voltage ride‐through capability helps the system to achieve the standard of grid code by remaining connected with the grid during fault occurrence. Direct current‐based saturated core fault current limiter (DC‐SCFCL) is a type of fault current limiter with superior influence in fault ride‐through (FRT) capability. It has an arrangement of embedded alternating current coil and direct current (DC) coil across the side and centre of the core limb. However, being more effective in FRT, the ideal DC‐SCFCL has some of its drawback such as development of high voltage across the DC coil and more current difference during fault occurrence. To limit these drawbacks a modified DC‐SCFCL with shorted ring and also working with the coil below its critical temperature has been proposed in this study. The voltage profile, as well as the current profile, has been analysed which comprises its behaviour in all conditions. The proposed technique is applied to DFIG‐based wind energy system to restrict the fault current and enhance the FRT capability. [ABSTRACT FROM AUTHOR]

This research reviews the technical requirements of grid-connected photovoltaic power plants to increase their competitiveness and efficiently integrate into the grid to satisfy future demand requirements and grid management challenges, focusing on Spain as a case study. The integration of distributed resources into the electric network, in particular photovoltaic energy, requires an accurate control of the system. The integration of photovoltaic energy has resulted in significant changes to the regulatory framework to ensure proper integration of distributed generation units in the grid. In this study, the requirements of the system operator for the management and smart control are first analysed and then the technical specifications established by the network operator in reference to the components of the facility are evaluated. This analysis identifies the shortcomings of the current legislation and concludes with a summary of the main technical recommendations and future regulatory challenges that need to be undertaken in the future. It is presented as a reference case that can be adapted worldwide. Image 1078 • Technical requirements of grid-connected photovoltaic power plants are reviewed. • Analysis of the main technical requirements is particularized for the case of Spain. • Challenges in communications, control and monitoring and metering are analysed. • Technical and safety requirements for grid connection are studied. • Future trends focused in smart grid PV integration are highlighted. [ABSTRACT FROM AUTHOR]

Abstract—To reduce the negative effects of wind farms connection on power system stability, many countries have elaborated grid code requirements. Low-voltage ride through (LVRT) capability is the core of these requirements. This paper presents a framework to design and apply the series resonance fault current limiter (SRFCL) with a metal oxide varistor (MOV) for LVRT performance enhancement of doubly fed induction Machine (DFIG)-based wind farms. The main advantages of the SRFCL are simplicity, high reliability and automatically operation during fault condition for enhancing the LVRT performance. To demonstrate the capability of the SRFCL, a comparative study of the SRFCL and the bridge-type fault current limiter (BFCL) is performed. The study wind farm has been modeled with equivalent aggregated DFIG. Simulations were carried out in PSCAD/EMTDC environment. Simulation results demonstrate that the SRFCL provides a simple and effective solution to enhance the LVRT and reduce the fault current contribution of wind farms. [ABSTRACT FROM AUTHOR]

The proliferation of solar power plants has begun to have an impact on utility grid operation, stability, and security. As a result, several governments have developed additional regulations for solar photovoltaic grid integration in order to solve power system stability and security concerns. With the development of modern and innovative inverter topologies, efficiency, size, weight, and reliability have all increased dramatically. This paper provides a thorough examination of all most aspects concerning photovoltaic power plant grid connection, from grid codes to inverter topologies and control. The reader is guided through a survey of recent research in order to create high-performance grid-connected equipments. Efficiency, cost, size, power quality, control robustness and accuracy, and grid coding requirements are among the features highlighted. Nine international regulations are examined and compared in depth, exposing the lack of a worldwide harmonization and a consistent communication protocol. The latest and most innovative inverter topologies that help to enhance power quality are compared. Modern control approaches are evaluated in terms of robustness, flexibility, accuracy, and disturbance rejection on both the DC and grid sides. The purpose of this review paper is to provide the reader with a comprehensive overview of alternatives and performance, highlighting lacks and deficiencies of recent technologies and critically discussing and proposing new solutions paving the way for future investigations and developments. • The proliferation of solar plants have an impact on grid operation and stability. • Nine international regulations are examined and compared in depth. • PV power system architecture, topologies, and control are examined. • Cutting-edge solutions that handle all facets of PV system design are examined. • The reader obtain a comprehensive grasp of most relevant challenges and concerns. [ABSTRACT FROM AUTHOR]

Each country must determine the Grid Code conditions and apply these criteria to integrate distributed generation (DG) systems into the existing electricity grid and to ensure a stable power system. Thus, experimental studies are required to provide an effective, national, and specific Grid Code. In this study, the Turkish Grid Code’s electrical criteria were examined, and the application of these criteria was carried out on a developed PV-based DG. A real-time energy management system (RTEMS) was proposed in the study. Electrical parameters on the developed DG were monitored in real-time by considering IEEE 1547, IEEE 929–2000, and Turkey’s electrical criteria. A practical grid code study was firstly investigated in detail about the Turkish Grid Code by a developed real-time monitoring-control and protection system. The proposed RTEMS method in the study is implemented as an inverter-resident system; thus, it provides advantages over many energy management systems embedded in the inverter. The degradation in power quality and non-detection zone (NDZ) problems encountered in active and passive island mode detection methods developed embedded in the inverter are eliminated in the proposed method. With the RTEMS method, where under and over-voltage, under and over voltage frequency, and unintentional island mode events can be detected in real-time, both the existing grid-code requirements are met, and the existing power quality and NDZ problem is eliminated with the recommended inverter-independent RTEMS method.

As the amount of collected spatial information (2D/3D) increases, the real-time processing of these massive data is among the urgent issues that need to be dealt with. Discretizing the physical earth into a digital gridded earth and assigning an integral computable code to each grid has become an effective way to accelerate real-time processing. Researchers have proposed optimization algorithms for spatial calculations in specific scenarios. However, a complete set of algorithms for real-time processing using grid coding is still lacking. To address this issue, a carefully designed, integral grid-coding algebraic operation framework for GeoSOT-3D (a multilayer latitude and longitude grid model) is proposed. By converting traditional floating-point calculations based on latitude and longitude into binary operations, the complexity of the algorithm is greatly reduced. We then present the detailed algorithms that were designed, including basic operations, vector operations, code conversion operations, spatial operations, metric operations, topological relation operations, and set operations. To verify the feasibility and efficiency of the above algorithms, we developed an experimental platform using C++ language (including major algorithms, and more algorithms may be expanded in the future). Then, we generated random data and conducted experiments. The experimental results show that the computing framework is feasible and can significantly improve the efficiency of spatial processing. The algebraic operation framework is expected to support large geospatial data retrieval and analysis, and experience a revival, on top of parallel and distributed computing, in an era of large geospatial data.