Robust optimal power flow considering uncertainty in wind power probability distribution

This paper proposes an optimal power flow model that takes into account the uncertainty in the probability distribution of wind power. The model can schedule controllable generators under any possible distribution of wind power to ensure the safe and economic operation of the system. Firstly, considering the incompleteness of historical wind power data, the paper models the uncertainty of wind power using second-order moments of probability distribution and their fluctuation intervals. Subsequently, a robust optimal power flow model based on probability distribution model and joint chance constraints is established. The Lagrangian duality theorem is then employed to eliminate random variables from the optimization model, transforming the uncertainty model into a deterministic linear matrix inequality problem. Finally, a convex optimization algorithm is used to solve the deterministic problem, and the results are compared with traditional chance-constrained optimal power flow model. The feasibility and effectiveness of the proposed method are validated through case study simulations

Influence of the DC frequency limit controller on the frequency characteristics of the multi-area asynchronous interconnected power grid with renewable energy integration

To systematically analyze the impact of the DC frequency limit controller (FLC) configuration scheme on the frequency characteristics of asynchronous interconnected power grids with renewable energy integration, a comprehensive frequency analysis model for three-area asynchronous interconnected power grids including the FLC is proposed. The model is based on the SFR model considering renewable energy integration and includes a simplified model of the DC FLC. A rigorous validation of the rationality and stability of the model is achieved through detailed mathematical calculations and pole-zero analysis. Taking the local power grids as an example, the established model is used to study the difference between single- and double-sided configuration of the DC FLC, the relationship between the increase in the renewable energy penetration rate and the frequency characteristics of each regional power grid, and the influence of DC FLC configuration on the maximum acceptance ratio of renewable energy. Through data comparison and theoretical analysis, the influence of FLC configuration on the frequency characteristics of each region of the asynchronous power grid under renewable energy integration is obtained. The results show that the configuration of a bilateral FLC on the DC line has more advantages in alleviating the complementary power disturbance at both ends and obvious limitations on the non-complementary power disturbance at both ends. Compared with the configuration of the bilateral FLC, the configuration of a unilateral FLC on the weak grid has a larger proportion of renewable energy acceptance. When the DC FLC power transmission capacity is sufficient, the weak grid and the adjacent two asynchronous grid DC tie lines are configured with a single-sided FLC, and the weak grid is theoretically connected to the renewable energy penetration rate of up to 100%

Adaptive compound power quality disturbance detection via OMD and improved networks for renewable energy systems

In the evolving landscape of power systems, the integration of various renewable energy resources (RERs) introduces complex challenges, particularly in maintaining power quality, which are paramount for system stability. To address this issue, an adaptive power quality disturbance (PQD) detection framework is implemented in this paper. First, the optimal mode decomposition (OMD) is developed to decompose the compound PQDs into sub-ingredients to make them more visible based on the optimal energy ratio. Subsequently, we propose an improved attention convolutional neural network (IACNN), an advanced neural network architecture that leverages an enhanced attention mechanism to expedite the identification of PQDs. Importantly, the sub-ingredients can be strengthened based on the established PQD detection framework. Finally, a series of experiments are conducted under different noise levels and various types of PQDs. The results demonstrate that the proposed framework has profound detection effectivity with about 99.2% accuracy under the simulation condition of 20 dB noise level. In addition, the experimental verification analysis proves a satisfactory real-time performance. This underscores the potential of the proposed framework as a significant advancement in the realm of power quality management, offering a robust solution to the challenges posed by the integration of RERs into modern power systems

Two basic ways to realise DC circuit breakers

As a key element of the DC grid, the technology of DC circuit breakers (DCCBs) still have difficulty to be widely used due to its large cost and volume. This paper studies the basic principle and its realisation methods for DCCBs. First, two basic ways of breaking the fault current are discussed, including the way by inserting a metal oxide varistor (MOV) to force the fault current to zero and the way by inserting capacitor to change the nature of the fault current. Second, a new approach to realise the DCCB has been proposed based on the inserting capacitor way. According to this new approach, three topologies of DCCB are proposed, including the single-branch DCCB with inserted capacitor (SB-DCCB-C), the double-branch DCCB with inserted capacitor (DB-DCCB-C) and the triple-branch DCCB with inserted capacitor (TB-DCCB-C). All these three DCCBs are proved to be able to deal with DC faults effectively according to the simulation results in PSCAD/EMTDC. Finally, the economy of four circuit breaker structures are compared

DC Fault Analysis and Clearance Solutions of MMC-HVDC Systems

In this paper, the DC short-circuit fault and corresponding clearance solutions of modular multilevel converter-based high-voltage direct current (MMC-HVDC) systems are analyzed in detail. Firstly, the analytical expressions of DC fault currents before and after blocking the MMC are derived based on the operation circuits. Before blocking the MMC, the sub-module (SM) capacitor discharge current is the dominant component of the DC fault current. It will reach the blocking threshold value in several milliseconds. After blocking the MMC, the SM capacitor is no longer discharged. Therefore, the fault current from the AC system becomes the dominant component. Meanwhile, three DC fault clearance solutions and the corresponding characteristics are discussed in detail, including tripping AC circuit breaker, adopting the full-bridge MMC and employing the DC circuit breaker. A simulation model of the MMC-HVDC is realized in PSCAD/EMTDC and the results of the proposed analytical expressions are compared with those of the simulation. The results show that the analytical DC fault currents coincide well with the simulation results

Electromechanical Transient Modeling and Control Strategy of Decentralized Hybrid HVDC Systems

This paper studies the electromechanical transient model and the control strategy of line commutated converter (LCC) and modular multilevel converter (MMC) based decentralized hybrid High Voltage Direct Current (HVDC) Transmission systems. The decentralized hybrid HVDC system is a new type of topology, and the related electromechanical transient model and control strategy have not been studied well. In this paper, the electromechanical transient model of a decentralized hybrid HVDC system is devloped through mathematical deduction. This model can be easily implemented in electromechanical transient simulation software and meet the time domain simulation requirements of large-scale systems. Then, in order to ensure the safe absorption of the DC power under various conditions, an optimal power flow model considering the decentralized hybrid HVDC system is proposed. Finally, the electromechanical transient model proposed in this paper is verified by the electromagnetic transient model, and the control strategy is validated in a modified New England 39-bus system

Advances in Urban Power Distribution System

The urban power distribution system is one of the most complex artificial systems in the world [...

Study on frequency characteristics of receiving power system with large-scale offshore wind power generation

With the rapid development of offshore wind power and large-scale grid connection, the mechanical inertia and frequency regulation ability of the power system are greatly reduced, which seriously affects the frequency stability of the receiving end power grid. Aiming at the frequency stability analysis of large-scale offshore wind power connected to the receiving end power grid, this paper proposes a frequency response aggregation model which includes the frequency limiting controller (FLC) and the wind turbine generator (WTG) with frequency modulation (FM) capability. The rationality of model aggregation and the stability of transfer function are proved by theoretical analysis. Taking a southern province in China as an example, the effects of wind turbine generator access form and DC block capacity on different frequency response indexes are analyzed by using the proposed frequency response aggregation model. Through theoretical and simulation analysis, the correlation of system inertia, FM capacity and DC FLC capacity with frequency deviation nadir and quasi-steady state frequency index is obtained, and the relevant conclusions affecting frequency stability indexes are drawn. Finally, through the model simulation method, the improvement of the system frequency stability when the wind turbine provides inertia and primary FM support is analyzed. This paper concludes that when the wind power penetration is in the range of 10%∼40% and the wind power assisted frequency modulation capacity reaches 5% of the installed capacity, the minimum frequency of the system can be maintained above 49.5 Hz

Study on the Method for Analyzing Electric Network Resonance Stability

With the increasing utilization of power electronic equipment in power systems, there has been an increase in the occurrence of oscillatory behavior from unknown sources in recent years. This paper puts forward the concept of electric network resonance stability (ENRS) analysis and tries to classify the above-mentioned oscillations into the category of ENRS. With this method, many complex power system oscillations can be analyzed with the linear network theory, which is mathematically mature. The objective of this paper is to establish a systematic approach to analyze ENRS. By introducing the s-domain nodal admittance matrix (NAM) of the electric network, this paper transforms the judgment of ENRS into the zero-point solution of the determinant of the s-domain NAM. First, the zero-points of the determinant of the s-domain NAM are proved to correspond to the eigenvalues of the system. Then, a systematic approach is proposed to analyze ENRS, which includes the identification of the dominant resonance region and the determination of the key components related to resonance modes. The effectiveness of the proposed approach for analyzing ENRS is illustrated through case studies