Iet Generation Transmission & Distribution最新文献

The grounding circulation current of the sheath and armour of single-core AC submarine cables is high during operation, which can easily cause insulation damage and faults. Traditional methods that only monitor the amplitude of grounding circulation current make it difficult to detect defects in the cables, so further research is needed on the mathematical mechanism and detection methods of grounding circulation current. A mathematical model for the capacitance and impedance coupling of a single-core submarine cable was established, and the influence of factors such as active power, length of armour stripping section, armour resistivity, armour magnetic permeability and grounding resistance on the grounding circulation current was analysed. A method for identifying abnormal grounding circulation current of submarine cables based on the combination of amplitude and phase was proposed.

In a multi-agent active distribution network, each agent schedules its electrical network independently to increase its profit. The high penetration level of renewable energy sources such as wind and solar power, may disturb the electrical balance of supply and demand and cause overvoltage in the grid. This study presents a decentralized scheduling approach for managing energy and reactive power transactions between the agents considering their independence and privacy. Using the proposed framework, the agents can increase their profit by exchanging active and reactive power with their neighbours, while all the technical constraints such as the allowed voltage limit of the buses are satisfied. To prove the effectiveness of the suggested technique, a multi-agent active distribution network including 11 independent agents is simulated with a high penetration of renewable energy. The simulation results illustrate the efficiency of the suggested approach from two technical and economic points of view.

The inherent constraints of grid-forming converters affect their ability to maintain voltage source characteristics within a specific operational range. In response to these limitations, ongoing pilot projects involving grid-forming technology have adjusted their current thresholds up to three times the rated current, significantly exceeding the traditionally threshold of 1.2 times the rated current. This paper aims to investigate the effects of current thresholds on the dynamic responses of grid-forming converters under large disturbances, with the intention of identifying an optimal current threshold that meets the grid's demands for maintaining voltage source characteristics and overall stability. A novel power angle relationship is introduced, integrating current limits and anti-windup voltage controls into the equivalent circuit models of these converters. Analytical expressions for stable and unstable equilibrium points are derived, improving insights into the converters' dynamic behaviour and their resilience to phase jumps across various current thresholds and short-circuit ratios. Findings indicate that higher current thresholds substantially improve phase jump limits and withstand capabilities. The paper concludes with proposed configurations and optimization strategies for current thresholds, all supported by experimental validation.

The carbon capture-transportation-utilization (C-CTU) chain strengthens the coupling between terminal energy consumption and renewable energy resources (RES), achieving carbon emission reduction in power generation sectors. However, the dynamic operation of the C-CTU chain and the uncertainties induced by RES output pose new challenges for the low-carbon operation. To address above challenges, the nonlinear dynamic operation model of C-CTU chain is first proposed in this study. It is further incorporated into the day-ahead operation scheme of the electricity-carbon integrated system considering the stochastic nature of wind power. This scheme is treated as a two-stage stochastic integer programming (TS-SIP) problem with a mixed-integer nonlinear recourse. By means of the polyhedral envelope-based linearization method, this recourse is reformulated into its linear counterpart. To further improve the computational performance of classical decomposition algorithms, a novel Benders decomposition framework with hybrid cutting plane strategies is proposed to obtain better feasible solutions within a limited time. Simulations are conducted on two power system test cases with the C-CTU chain. Numerical results indicate that the engagement of C-CTU chain promotes the low-carbon economic operation of the power system. Also, the proposed decomposition algorithm shows a superior solution capability to handle large-scale TS-SIP than state-of-the-art commercial solvers.

Numerous policies have been implemented to advance the growth of renewable energy. Nonetheless, certain policies have not yielded the anticipated impact on the progression of renewable energy development. In order to maximize the promotion effect of renewable energy policies, this study proposes a capacity allocation optimization method of wind power generation, solar power and energy storage in power grid planning under different policy objectives. First, based on the policy quantification, grey relation analysis (GRA) is used to calculate the correlation degree of the policy indicators on the planning capacity of renewable energy. Further, a multi-objective capacity estimation model for wind, solar and energy storage is comprehensively presented. Some highly correlated policy indicators are transformed into the special constraints. And the economy and the stability of the power grid are integrated as the objective function. Meanwhile, the carbon trading and punishment for wind power and solar power abandonment are considered. Finally, the proposed model is solved by NSGA-II-PSO (particle swarm optimization) algorithm. The novelty of the algorithm is that the crossover operation of NSGA-II is replaced by the position updating of particle swarm. The calculation result of the case study can effectively evaluate the optimal planning capacity of renewable energy under different policies, while ensuring the economic and the stability of the power system. The study can provide the reasonable basis and the valid analytical method for the policy formulation and the renewable energy development.

Autonomous microgrid is known to lack appropriate inertia and damping for grid stabilization. Due to this, virtual synchronous machine (VISMA) has been introduced to provide necessary ancillary services through control of power converters. In a multi-VISMA (n-VISMA) microgrid, relative rotor angle stability of the power system is dependent on the active power balance after small perturbation. Thus, the use of relevant analytical models are essential issues for microgrid stability analysis. This paper presents a comprehensive small-signal stability analysis to study inherent electromechanical oscillations in the virtual rotors. The subsystems of the microgrid consisting of VISMA, network, load and the outer power control were all modelled in Synchronous Reference Frame. The small-signal model (SSM) was tested on IEEE-9 bus system with VISMA replacing electromechanical synchronous machines on the network. To validate the developed numerical analytics, dynamic responses of the SSM are compared with those of the non-linear (NL) system dynamics and the results reveal that the developed linearized SSM is sufficient to accurately characterize behaviour of the VISMA microgrid when operated in autonomous mode. Eigenvalues analysis and parameter sensitivities of the critical modes were investigated. Oscillatory participations of the VISMAs and steady state stability limit of the microgrid have also been investigated.

Harmonic resonance is caused by harmonic source matching resonance frequency and presents the characteristics of decentralization and whole network in modern grids. The current resonance suppression methods mainly focus on reducing the harmonic source, and are suitable for single-site and small-scale grids. This paper presents a new method for suppressing parallel resonance at system level. The holistic harmonic resonance is suppressed by reducing the harmonic impedance. In addition, new resonances are prevented by weakening the coupling between resonance and non-resonance frequencies. The resonance modal analysis and resonance frequency shift (RFS) are employed to optimize harmonic impedance. Simulation results indicate that the capacitance parameter has higher sensitivity and is theoretically more suitable for RFS. Considering the accuracy of modal frequency sensitivity, a variable-limit genetic algorithm for iteration is proposed. The validity of the proposed method was verified using an IEEE 14-bus test network.

For the problem that traditional droop control cannot maintain the maximum output power of photovoltaic (PV) units, this work proposes a self-adaptive communication-free control scheme for the islanded PV-storage AC microgrids. The proposed control enables the maximum power point tracking-based output active powers of PVs by adaptively adjusting P-f/Q-V droop coefficients. It also facilitates adaptive allocations of reactive powers based on the available capacities of PVs and storage modules. The key characteristics of the proposed control strategy are summarized as follows: 1) PV units are controlled as voltage sources, which could participate in the voltage/frequency regulation to a certain extent; 2) maximum power utilization of PVs is obtained; 3) adaptive allocations of reactive powers are realized based on the maximum available capacity of PVs and storage modules. Subsequently, the stability analysis of the proposed self-adaptive communication-free control strategy is verified. Finally, the validity of the proposed self-adaptive communication-free control method is validated through simulations conducted using MATLAB/Simulink.

Islanding detection is a challenging issue in modern grid-connected distributed generation networks (GCDGN). Generally, islanding detection has two categories local and remote, local schemes can be categorized into active, passive, and hybrid schemes. This article proposes a triple-indexed passive islanding detection (TIPID) scheme using an extended Kalman filter (EKF). Initially, the EKF algorithm is applied on voltage signal at the point of the common coupling to estimate the desired fundamental and non-fundamental features. The first index, known as the cumulative voltage logarithmic index, is computed by taking the natural logarithm of the fundamental voltage features to detect any variations in the GCDGN. The second index, known as the voltage differentiation index (VDI), is calculated from the fundamental voltage features, while the third index, known as the odd-order harmonic distortion index (OOHDI), is obtained from the non-fundamental odd-order harmonics of the PCC voltage. Then, the VDI and OOHDI are compared to pre-defined threshold to detect/distinguish islanding events. The proposed TIPID method is validated through extensive simulations on the IEEE 13-bus test bed via MATLAB/Simulink 2022b. Results show that under both balanced/unbalanced load & generation, the proposed TIPID approach detects islanding occurrences with reduced non-detection zone (NDZ) in less than 5 ms.

Under the envisioned smart grid paradigm, there is an increasing demand for a fast, accurate, and efficient power flow solution for distribution system operation and control. Various solution techniques have been proposed, each with its own unique formulation, solution methodology, advantages, and drawbacks. Motivated by challenges associated with the integration of renewable distributed energy resources and electric vehicles into distribution systems and further by the speed and convergence limitations of existing tools, this paper presents a novel graph-based power flow solution for smart grid's real-time operation and control, named Flow-AugmentationPF algorithm. The proposed method formulates a power flow problem as a network-flow problem and solves it by using a maximum-flow algorithm, inspired by the push-relabel max-flow technique. The performance of the proposed algorithm is tested and validated using several benchmark networks of different sizes, topologies, and parameters and compared against the most commonly used solution techniques and commercial software packages, namely PSS/E and PSCAD. The proposed formulation is simple, accurate, fast, yet computationally efficient, as it is based on matrix-vector multiplication, and is also scalable, considering the formulation works as a graph-based method, which, inherently, allows for parallel computation for added computational speed.