This paper conducts a comprehensive study on high-penetration renewable energy bases and their coupled HVDC transmission systems, addressing critical aspects in planning, operation, control, and efficiency improvement. Due to the complex interaction between large-scale renewable generation and HVDC transmission, enhancing delivery efficiency requires coordinated technological advances across generation, transmission, demand-side management, and energy storage systems. Focusing on Large-scale renewable energy delivery bases, this research systematically analyzes factors influencing HVDC transmission efficiency and proposes actionable measures to increase power transfer capability. The proposed strategies ensure that HVDC projects achieve designed performance rapidly after commissioning. With ongoing development of national energy bases, the findings provide valuable insights for similar systems, facilitating renewable integration, reducing carbon emissions, and improving power system flexibility and sustainability. This work contributes to the theoretical and practical foundations for building a resilient and low-carbon power system.

Under the context where the dual-carbon goals fuel the transformation of energy structure and large-scale hydro-photovoltaic complementary bases in Southwest China are emerging as the core of inter-regional energy transmission,the large-scale integration of renewable energy reduces the synchronous support capability of the sending-end power grid.Traditional thermal power units respond slowly in frequency regulation,and photovoltaic generation can only provide short-term support due to energy constraints,leading to frequency regulation power deficits and instability during cross-regional transmission.To address these issues,this paper develops a new mode that utilizes active power reserves of hydro-photovoltaic complementary bases to ensure frequency security in long-distance transmission.Firstly,an active power-frequency coupled active support control strategy for the hydro-photovoltaic complementary system is proposed,and models of photovoltaic virtual inertia and hydropower frequency response are constructed.Then,taking the cross-regional sequential control signal of the DC system as a disturbance,a frequency response model of the sending-end power grid that takes into account the frequency regulation capability of hydro-photovoltaic complementation is established.The external transmission capacity of frequency regulation active power is quantitatively analyzed,and parameter sensitivity analysis is performed.Finally,simulations are carried out using MATLAB/Simulink.The results show that under the hydro-photovoltaic complementary mode,the nadir frequency of the sending-end power grid is significantly improved,with a steady-state frequency deviation of-0.190 Hz,which is superior to the-0.517 Hz observed with thermal power alone.Increasing grid damping and inertia can mitigate frequency drops;however,due to the dependence of photovoltaics on solar irradiance,their long-term active power modulation capability is limited.The conclusion indicates that large-scale hydro-photovoltaic complementary bases can serve as new regulation resources for long-distance active power support,positively contributing to the frequency stability of the sending-end power grid and providing technical support for secure and stable cross-regional transmission of renewable energy.

High-power DC-DC Converters are crucial for interconnecting HVDC systems with different voltage levels. This paper presents the optimal design and operation of transformer-less hybrid modular multilevel dc-dc converters (MMDCs) that consist of both the half bridge submodules (HBSMs) and the full bridge submodules (FBSMs). Since the arm internal dc component voltage and ac component voltage can be freely selected, the optimal modulation index that minimizes the kVA of switches is derived for different voltage conversion ratios. Overmodulation is also considered to minimize the cost of the converter. For system security and reliability reasons, the dc fault-blocking capability is a preferred feature of dc-dc converters for HVDC applications. Benefitting from using the hybrid SMs, the dc fault-blocking capability of hybrid MMDCs is also investigated. The performance of the hybrid MMDC is validated by real-time simulation and a lab-scale test bench.

Electromagnetic transient (EMT) models of power electronic converters are essential for converter design, control, and fault analysis. This article proposes a switching-function-based detailed equivalent model (SFB-DEM) using combined implicit and explicit (ImEx) multistep Gear's integration methods for numerically efficient and accurate EMT simulation. The proposed SFB-DEM integrates the benefits of ImEx solvers, featuring converter circuit decoupling, node number reduction, and constant nodal-network conductance(G)-matrix in the EMT model. The SFB-DEMs employing the ImEx 2nd and 3rd order Gear's (i.e., ImEx-G2O and ImEx-G3O) methods are implemented for solid-state transformer (SST) simulation. In addition, a switching interpolation technique is proposed and integrated with the ImEx-G2O and ImEx-G3O solvers to account for intra-time-step switching events. The proposed SST SFB-DEMs greatly accelerate the EMT simulation, compared to the conventional detailed model (DM) and variable conductance(G)-matrix DEM (VG-DEM). For the SST with 60 SMs, the proposed SFB-DEM with ImEx-G3O method achieves the EMT simulation speedup by 171 and 7.5 folds, compared to the DM and VG-DEM, respectively.

Modular multilevel converters (MMCs) integrated with battery energy storage systems (BESS) enable efficient utilization of renewable energy resources such as wind and photovoltaic, while enhancing reliability and scalability of high-voltage direct current systems. This paper proposes a decoupled detailed equivalent model (D-DEM) for BESS-integrated MMC for electromagnetic transient (EMT) simulation. The proposed model can accurately represent the dynamics of the converter under deblocking and blocking modes. To efficiently utilize available hardware resources, a multi-rate simulation technique is adopted to simulate the MMC subsystems with different time steps. Additionally, switching interpolation technique is proposed to accurately compensate for the intra-time-step switching events of the MMC multi-valves. To further accelerate the EMT simulation of MMC, a hybrid parallel computing EMT solver is implemented, using both central and graphical processing units (CPU-GPU). The accuracy of the proposed D-DEM is validated against a detailed model (DM) using Simulink/Simscape Electrical toolbox with 1 & micro;s time step. The simulation efficiency of the proposed D-DEM is faster than the conventional DEM model by a factor of 2.81 with CPU-only implementation for the MMC with 400 submodules per arm. Furthermore, the proposed hybrid CPU-GPU solver achieves 79-fold faster than the CPU-only sequential implementation.

Most of studies on the grid-forming (GFM) converter grid-tied systems ignored DC-capacitor voltage dynamics (DVD) and reported that the systems show a perfect weak-grid adaptability. To answer the question whether the GFM converters can lose stability under weak grids by considering or ignoring the DVD, this article systematically investigates five typical GFM converters, including the well-known droop, virtual synchronous generator control, DC capacitor self-synchronization control, etc. and analyses their small-signal weak-grid instability conditions. First, based on the eigenvalue analysis and participation factor calculations on the full-order linearized systems, the system dominant modes including the synchronization loop and/or the DC voltage loop are uncovered and the reduced-order models are obtained. Next, the classical Routh-Hurwitz criterion is employed to obtain the weak-grid critical stability conditions explicitly. They well demonstrate that under an ideal condition of ignoring the DVD, the small-signal stability condition is the same as the equilibrium point existence condition, under the short-circuit ratio (SCR) being 1. In contrast, under a more realistic condition of considering the DVD, the small-signal stability condition becomes stricter, under the SCR being slightly larger than 1. Finally, all these explicit analytical results are verified by wide MATLAB/Simulink simulations and hardware-in-the-loop experiments. These time-domain studies and theoretical analyses provide comprehensive and rigorous results in a unified manner and demonstrate that the small-signal weak-grid instability of GFM systems considering DC-capacitor voltage dynamics is general and it works for all grid-tied converter systems.

Building energy consumption contributes to approximately 34% of global carbon emissions. Direct current (dc) distribution technology, characterized by its significant advantages in efficiently integrating distributed energy resources and flexible loads, alongside high transmission efficiency, presents promising opportunities for the low-carbon transition of the building sector. This review systematically summarizes the key power electronic equipment, coordinated control strategies, and stability analysis methods within building dc distribution systems. First, it introduces the power electronic converters that interconnect system components, and the dc circuit breakers responsible for fault isolation and operational mode switching. Second, this article discusses recent advancements in hierarchical control architectures (including primary, secondary, and tertiary levels), considering the electrical characteristics of buildings, and provides a classification thereof. Concurrently, this review systematically covers small-signal and large-signal stability analysis methods. Comparative analyses highlight the existing gaps in stability criteria for multivoltage-level systems, particularly when considering line impedance. Finally, focusing on the requirements for building decarbonization and efficient, stable operation, this review provides several future research directions.

The energy transition requires not only the deployment of low-carbon technologies, but also the organization of dispersed resources into forms of coordination that are operationally effective, institutionally legitimate, and socially durable. The existing transition frameworks explain institutions, niches, and system formation well, yet they are less explicit about how coordination intensifies across physical, digital, and social domains, why technically capable arrangements may remain socially fragile, and how aggregation redistributes authority and visibility. Building on Xue et al.'s Cyber-Physical-Social Systems in Energy (CPSSE) framework, this Perspective develops an interpretive elaboration of CPSSE to address that gap. Its main contribution is a shared analytical vocabulary that links uncertainty, staged coordination, and aggregation, and that recasts virtual power plants as socio-technical accomplishments rather than merely control architectures. Rather than proposing a measurement model, this article uses concepts drawn from information, coordination, and aggregation to examine what conditions render distributed energy governable, whose participation is stabilized or marginalized, and how legitimacy, accountability, and user acceptance become constitutive conditions of coordination. The Perspective contributes to energy social science by clarifying how cyber-physical capability interacts with governance conditions, participation, and institutional durability, while identifying an empirical agenda for studying how coordination is negotiated, stabilized, contested, and unevenly distributed across distributed energy systems.

Electromagnetic transient (EMT) simulation is an essential analytical tool for the safe and stable operation of new power systems. To address the challenge of initializing and integrating electromagnetic DC models into the grid, this paper proposes an automatic initialization and grid integration method for electromagnetic DC models based on multi-mode power flow results. First, the voltage and power results of the AC-DC connection points are obtained through AC system power flow calculation, and the parameters of the electromagnetic DC model are automatically adjusted by considering the correlation with adjacent operational modes. Then, the clamping voltage source method is used to initialize the DC and AC subsystems separately. Finally, a fully integrated AC-DC electromagnetic transient simulation system is rapidly constructed by disconnecting the clamping voltage sources and closing the grid-connection switches. Simulation tests on an actual power grid demonstrate that the proposed method effectively achieves rapid initialization and grid integration of electromagnetic DC models, verifying its feasibility and engineering practicality.

Electromagnetic transient (EMT) simulation of power electronic converters is critical for analysis, design, and fast control prototyping of power and energy systems. This paper proposes a multi-granular GPU parallel-rate exponential integrator (EI) algorithm for fast offline EMT simulation of power electronic systems. The proposed parallel-rate EI algorithm utilizes the massively parallel GPU architecture to compute multiple discretization steps in parallel. The matrix-vector computations of the EI algorithm within each time step are also parallelized. Additionally, a novel GPU-based framework is proposed for numerically efficient precomputation of matrix exponentials before a simulation loop starts. The high degree of parallelism leads to large simulation speedups compared to single-thread CPU implementations. The discretization technique of high-order EI algorithm is absolutely stable with no numerical ringing and can achieve accurate differential equation discretization with large time-step sizes. The proposed parallel-rate EI solver is further applied to detect passive/diode switching events accurately. Two case studies are used to demonstrate the accuracy and efficiency of the parallel-rate EI algorithm. Two additional case studies showcase the benefit of the proposed parallel precomputation technique for matrix exponentials.

Tie-line faults can induce rapid fluctuations in frequency and voltage in county-level power grids. Grid-forming energy storage has emerged as a crucial solution for enhancing stability under islanded operation. This paper investigates the islanding stability of a long-chain, fully power-electronic-based county-level grid incorporating grid-forming energy storage. A representative electromechanical model is developed, including detailed 35 kV low-voltage-side load configurations. Transient analysis following grid-to-island transition reveals that system stability is highly dependent on the dynamic response of grid-forming storage, whose parameters under grid-connected conditions fall short of islanded operation requirements. Furthermore, insufficient reactive power resources exacerbate regulation challenges. By optimizing storage parameters and implementing reactive power pre-control strategies at the tie-line, the frequency and voltage stability of the islanded system can be significantly improved, thereby enhancing the overall operational robustness of fully power-electronic county grids.

With the access of wind power, the nonlinear characteristics of the power grid system are intensified. The traditional damping control unit is no longer suitable in this case, and there may even be failure risk in extreme cases, which brings hidden dangers to the safety of the power system. We put forward a low frequency oscillation suppression strategy for power systems including wind power access: A multi machine PSS collaborative sparse adaptive optimization, which adaptively updates parameters in the PSS that are strongly related to system stability based on real-time state changes in the system, ensuring full performance of the controller and improving system stability. Finally, the scientificity of this method was verified through numerical simulation.

The rapid growth of wind and solar power has made electricity system simulations increasingly complex, with high-dimensional, tightly interconnected variables that overwhelm traditional solution methods. To address this challenge, this paper proposes a new approach that combines Benders decomposition with data-driven techniques to accelerate large-scale, time-based simulations of integrated generation, grid, and storage operations under high renewable penetration. The method begins with a detailed analysis of the simulation model, which is mathematically structured as a large-scale mixed-integer linear program. Using decomposition, the model is split into a master problem dealing with discrete decisions and subproblems focused on continuous variables. To further streamline computation, the framework incorporates a pre-screening mechanism based on Gaussian process models. This mechanism uses patterns from past solutions to identify and remove inactive parts of the feasible region and redundant safety constraints, effectively narrowing the search space. A case study involving a 90-node provincial power system shows that the proposed method significantly improves computational efficiency without compromising accuracy.

Fatigue damage of wind turbines is a critical factor influencing their operational safety and economic performance. This paper begins by deriving a calculation model for main shaft torque and tower thrust based on the principles of force balance and momentum conservation. By integrating the four-point rainflow counting method and residual wave concatenation method, and applying the Goodman curve along with Palmgren-Miner theory, the cumulative fatigue damage of the main shaft torque and tower thrust is calculated, establishing a quantitative model for turbine fatigue damage. To enhance computational efficiency, the analysis process is executed every 15 seconds, with cycle data recorded and stored, significantly accelerating overall computation speed. Subsequently, this paper develops an optimization objective function and constraints targeting overall turbine fatigue damage, constructs a multi-objective optimization model, and utilizes YALMIP and CPLEX tools for power distribution optimization and solution. The model is validated through data processing and analysis, with results demonstrating that the optimized power dispatch strategy reduces turbine fatigue damage by 19.99%, extends service life, and enhances the safety and economic benefits of the wind farm. This approach offers an innovative technical solution for coordinated scheduling of wind farm clusters and holds significant potential for improving the operational reliability and economic performance of wind farms.

This paper introduces an innovative optimal allocation method for distributed synchronous condensers (DSCs) in the high voltage direct current (HVDC) sending-end AC power system, designed to significantly enhance the system voltage support capability and effectively suppress the overvoltage issues. With the increasing integration of large-scale renewable energy sources (RESs) into the HVDC sending-end AC power system, the system short-circuit ratio and voltage support capability are compromised, which may easily cause the prominent overvoltage problem after the HVDC fault. Our method addresses these challenges by not only enhancing the system voltage support capability but also suppressing the overvoltage problems. The impact of DSCs on multiple renewable energy stations short circuit ratio (MRSCR) of the system is analyzed, and a comprehensive quantitative evaluation index of voltage support capability that can quantitatively represent the system voltage support capability enhancement after installing DSCs is defined. A multi-objective optimization model for DSCs allocation is proposed with the objectives of simultaneously minimizing the investment cost and maximizing the system voltage support capability enhancement. The optimal installation positions and configuration quantities (capacities) of DSCs are then obtained by solving the optimization model. Simulation studies conducted on a practical power system demonstrate the method's effectiveness in maximizing system voltage support capability enhancement, suppressing overvoltage issues, and offering superior economic performance compared to the centralized synchronous condensers (CSCs) configuration method.

In this era of an unprecedented energy transition, the digital representations of dynamic power system models in the time domain for Electro Magnetic Transients including DC (EMTDC) simulations, have become necessary and even mandatory by most grid codes for a range of use cases. This is primarily due to the increased penetration of Inverter Based Resources (IBRs) and other power electronic components like Voltage Source Converters-based High Voltage Direct Current (VSC-HVDC) grids or Multi-Terminal HVDC grids. While accurate, offline EMTDC simulations are limited to some basic, small-scale studies, such as voltage, frequency, fault studies, etc., due to limitations in their performance. In contrast, carefully developed and decoupled models for real-time EMTDC simulations can be both accurate and fast. They can also be leveraged to serve as digital twins/replicas of the existing system to conduct detailed and accurate studies including hardware controllers. In this context, this paper presents a real-time simulation case study of an IBR-dominated, hybrid AC-surrounded Multi-Terminal high voltage DC (AC-MTDC) grid using HYPERSIM on a real-time digital simulator. This paper also includes the integration of Software In-the Loop (SIL) and Hardware In-the Loop (HIL) aspects to show the value of real-time simulations for dynamic and stability studies by considering two different scenarios and by comparing IBR-dominated systems performance with an equivalent synchronous machine (SM)-dominated system.

Using the observation data of Parkes 64 m radio telescope at a central frequency of 1369 MHz, the pulse nulling phenomenon of PSR J1701–3726 was analyzed. It is found that the pulse nulling phenomenon of this pulsar has quasi-periodic, and the quasi-period value approximately is 81.25P, where P is the rotation period, and the pulse nulling ratio NF (Nulling Fraction) is calculated to be 27%±0.97%. Further study on the change of relative energy in the on-pulse region over time shows that there are four different switching modes a, b, c, and d between null state and burst state, among which mode a occurs 23 times, mode b occurs 6 times, mode c occurs 5 times, and mode d occurs 79 times, indicating that there may be some randomness in state transitions.

Large-scale power electronic converters contain numerous energy storage devices, contributing to high dimensions of system state-space equations. Electromagnetic transient (EMT) simulation involving these large systems presents a significant challenge. This paper proposes a high-order exponential integrator (El) with network decoupling strategy to achieve rapid simulation of power electronic systems using a variable step-size switching-event driven algorithm. The proposed exponential integrator with network decoupling reduces the size of system matrices to accelerate EMT simulation, while making precomputation of key matrix terms feasible. The proposed EI technique uses high-order derivatives of state-space equations to accommodate large, variable step-sizes. EI is inherently L-stable, making the proposed algorithm well suited for stiff or non-stiff systems alike. A large-scale power electronic system case study is used to demonstrate the numerical accuracy and efficiency of the proposed EL The simulation runtime of the EI demonstrates a 32-fold speedup, compared to a popular simulation toolbox, i.e., Simulink/Simscape Electrical toolbox.

Virtual power plant (VPP) operation entails multi-stage data acquisition, dispatch, and market clearing across distributed energy resources; any data tampering or loss compromises decision fidelity and may induce systemic risk.To systematically address these trust issues, we propose a chain-of-trust-based trustworthy network architecture spanning the entire VPP lifecycle, embedding a trust-quantification scheme into its evaluation framework. The model decomposes trust into subjective and objective dimensions, integrates a Gaussian confidence kernel with dynamic weight adaptation, and yields a multi-attribute credibility metric. Time-decay and evolution factors enable adaptive, real-time assessment of node behavior. Simulations on the IEEE 30-bus system and Network Attack Simulator (NASim) platform under multi-intensity scenarios validate end-to-end trust computation. Finally, to counter feedback delay, sluggish weight updates, and poor malicious-node detection, we introduce incentive mechanisms, accelerated trust refresh, enhanced anomaly detection, multi-attribute fusion, and layered defense, furnishing a holistic security solution for VPPs under sophisticated attacks.

Solid-state transformers (SST) merit attention due to their flexibility and high efficiency. They are now being used in medium voltage distribution systems for renewable integration, electric vehicle charging, and in data centers. SSTs have a multi-phase, multi-stage, and multi-port structure combining AC-DC converters and DC-DC converters to handle both AC and DC inputs and outputs. Hardware-in-the-loop (HIL) testing with real-time simulation is essential for validating the control and protection systems of the SST. Simulating the SST in real-time is challenging due to the large number of switches present as well as their high switching frequency. To this end, an FPGA-based high-fidelity real-time model for accurate simulation of SSTs is presented in this paper. The developed FPGA model is both flexible and scalable to simulate different SST topologies with a combination of H-bridges, and dual active bridges (DAB) in real-time. These units can be connected in different ways (cascaded, series, parallel) to fit diverse converter topologies. Up to 64 DABs can be simulated in a single FPGA with simulation timesteps as low as 40 ns. Real-time simulation results are presented to validate the development of this FPGA-based model using a representative AC-DC SST topology.