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21 pages, 6063 KiB

Open AccessArticle

Characteristics and Protection Methods for Double-Circuit HVDC Transmission Lines on the Same Tower Considering DC Line-Touching Faults

by Yan Tao, Junchao Zheng, Xiangping Kong, Lei Gao, Jinjiao Lin and Chenqing Wang

Electronics 2024, 13(24), 4924; https://doi.org/10.3390/electronics13244924 - 13 Dec 2024

Viewed by 536

Abstract

In heavily loaded regional power grids, some AC transmission lines are confronting escalating pressures due to excessive short-circuit currents. To optimize AC channels, most research advocates for retrofitting existing AC lines into multi-line-commutated converter-based high-voltage direct current (LCC-HVDC) lines. However, there is a [...] Read more.

In heavily loaded regional power grids, some AC transmission lines are confronting escalating pressures due to excessive short-circuit currents. To optimize AC channels, most research advocates for retrofitting existing AC lines into multi-line-commutated converter-based high-voltage direct current (LCC-HVDC) lines. However, there is a contradiction between limited land area for AC stations and the relatively large footprint of passive filters in LCC-HVDC; this paper introduces self-adapted LCC (SLCC) by replacing passive filter groups with a static var generator (SVG). Secondly, the reactive power compensation, harmonic filtering control methods of SVGs, and operation characteristics of the SLCC system are explored, and the harmonics of the grid-side current are reduced by nearly 14.6%. Then, to fill the gap of previous studies on solely AC or AC-DC line touching, inspired by emerging DC line-touching risks in double-circuit (LCC and SLCC) lines on the same tower, the equivalent models are formulated to elucidate the evolution mechanisms of voltage/current and extract fault features in various line-touching faults; it finds that the longitudinal differential current during line-touching faults can be capitalized. Based on the current feature, an effective protection algorithm tailored for the identification of DC line-touching faults is proposed. Finally, simulations are conducted to validate the efficacy of proposed control and protect methods, demonstrating the potential to enhance the reliability of AC to DC conversion projects. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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14 pages, 3643 KiB

Open AccessArticle

The Supplementary Damping Method for CLCC HVDC Based on Projective Control Theory

by Feifei Zhao, Zhenjian Xie, Wenjia Zhang, Wanchun Qi, Hui Cai, Sixuan Xu, Xingning Han and Quanquan Wang

Electronics 2024, 13(16), 3261; https://doi.org/10.3390/electronics13163261 - 16 Aug 2024

Viewed by 860

Abstract

This paper proposes a design method for an additional damping reduced-order controller based on the projective control theorem. Improvements are made to the projective theorem to achieve additional damping control through Controllable-Line-Commutated Converter (CLCC)-based High Voltage Direct Current (HVDC), which suppresses low-frequency oscillations. [...] Read more.

This paper proposes a design method for an additional damping reduced-order controller based on the projective control theorem. Improvements are made to the projective theorem to achieve additional damping control through Controllable-Line-Commutated Converter (CLCC)-based High Voltage Direct Current (HVDC), which suppresses low-frequency oscillations. Using small disturbance identification techniques, the system’s linear model is first identified, and the state feedback control law of the system is then determined using the state-space pole assignment control method. Then, by retaining the dominant oscillation modes of the closed-loop system through the improved projective theorem, the state feedback is converted into output feedback. Ultimately, the sixth-order state feedback controller is reduced to a second-order one and applied in the CLCC HVDC additional damping strategy to suppress low-frequency oscillations. Simulation results based on the electromagnetic transient simulation software PSCAD demonstrate that the designed CLCC HVDC additional damping reduced-order projective control exhibits good suppression performance, strong robustness, and low order, which are of significant importance for engineering practice. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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19 pages, 4270 KiB

Open AccessArticle

Neural Network-Based Aggregated Equivalent Modeling of Distributed Photovoltaic External Characteristics of Faults

by Kuan Li, Qiang Huang, Rongqi Fan, Shuai Gao, Anning Wang, Tao Huang and Ruichen Sun

Electronics 2024, 13(16), 3232; https://doi.org/10.3390/electronics13163232 - 15 Aug 2024

Viewed by 803

Abstract

Distributed power networks have a large number of photovoltaic power sources. The bidirection of power flow, different transient control strategies, and installation locations make the transient characteristics highly complex and unpredictable. The vast network of the distribution system makes it almost impossible to [...] Read more.

Distributed power networks have a large number of photovoltaic power sources. The bidirection of power flow, different transient control strategies, and installation locations make the transient characteristics highly complex and unpredictable. The vast network of the distribution system makes it almost impossible to predict the electrical quantities of each branch. Reasonable aggregation modeling of the distribution network can greatly simplify the network topology, facilitating transient control and the setting of relay protection settings. An aggregated equivalent modeling method based on the LSTM neural network for distributed PV fault external characteristics is proposed. This method equates the complex distribution network to a highly nonlinear but controllable current source. The method can output the I–V curves of equivalent PV system parallel points under any output power and is able to predict the fault characteristics of the equivalent system after a voltage drop at the parallel point. Compared to traditional mechanistic modeling, this method does not require specific modeling of complex physical systems and is able to accurately map the strong nonlinear inputs and outputs of distribution networks. The established LSTM model first uses a one-dimensional convolutional layer for feature extraction of the PV power coefficients (input), and then two hidden layers are utilized to process the sequence data; the vectors are mapped into a sequence of external characteristic curves (output) in a fully connected layer. A typical distribution network is built based on the traditional PV power model, and a large number of different output combinations are selected for simulation to provide an effective training set and validation set data for LSTM model training. By using the training set data, the weights and offset coefficients of each layer of the LSTM are continuously optimized until the model with the smallest overall error is obtained, which is the optimal model. Finally, the optimal model is utilized to establish an equivalent distribution network system, different degrees of voltage drops are set up at the grid-connected points, the fault characteristics are compared with those of the complete model, and the simulation results can prove the reliability and practicality of the proposed method. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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18 pages, 4018 KiB

Open AccessArticle

The Coordination Control Strategy for Improving Systems Frequency Stability Based on HVDC Quota Power Support

by Guojiang Zhang, Yongyong Jia and Qian Zhou

Electronics 2024, 13(16), 3218; https://doi.org/10.3390/electronics13163218 - 14 Aug 2024

Viewed by 530

Abstract

This paper aims to improve the recovery characteristics of the receiving grid during DC blocking failures through DC emergency power support, revealing the mechanism of improving the power angle stability of the receiving grid through timely DC power increase and decrease. Based on [...] Read more.

This paper aims to improve the recovery characteristics of the receiving grid during DC blocking failures through DC emergency power support, revealing the mechanism of improving the power angle stability of the receiving grid through timely DC power increase and decrease. Based on the transmission pattern of “north-to-south power transmission” in a certain provincial power grid, the actual maximum long-term overload capacity of multiple DC lines is calculated, considering multiple constraints such as the strength of the receiving grid, the stability limit of AC evacuation channels, and DC overload capacity. A multi-DC emergency power support strategy after DC blocking is developed, avoiding the risk of AC transmission channel overload caused by power flow transfer, reducing the impact of large-capacity DC blocking and inappropriate DC power increases on the receiving grid, and achieving coordination between AC and DC systems. The effectiveness of the proposed strategy is verified through simulation. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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17 pages, 5175 KiB

Open AccessArticle

An AC-DC Coordinated Scheme for Cascaded Hybrid High-Voltage Direct Current to Suppress Wind Power Fluctuations

by Tingshan Zhou, Qian Li, Yufeng Xu, Yizheng Zhao, Deming Liu and Dong Liu

Electronics 2024, 13(14), 2847; https://doi.org/10.3390/electronics13142847 - 19 Jul 2024

Viewed by 660

Abstract

Given power fluctuations from near-land offshore wind farms, this article designs a coordinated control strategy for cascaded hybrid DC transmission. To suppress the frequency disturbances when wind power varies, supplementary active power control schemes are proposed, in which the coordinated DC voltage control [...] Read more.

Given power fluctuations from near-land offshore wind farms, this article designs a coordinated control strategy for cascaded hybrid DC transmission. To suppress the frequency disturbances when wind power varies, supplementary active power control schemes are proposed, in which the coordinated DC voltage control strategy is also considered in order to keep DC voltage stable when the supplementary control prompts a voltage-sourced converter overload. Simultaneously, to further improve wind farm-side AC voltage stability, a dynamic limiter is added in the coordinated control, which can make a voltage-sourced converter release more reactive power when a fault happens. Thereby, the stability of DC-side voltage and active power and AC-side frequency and voltage can all be enhanced through the proposed coordinated scheme. Finally, the electromagnetic transient model of the hybrid high-voltage direct current with renewable power is established using PSCAD X4.6.2 software, and the simulation example is carried out with the model to verify the scheme proposed in this article. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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15 pages, 4614 KiB

Open AccessArticle

Distributed MPC-Based Voltage Control for Active Distribution Networks Considering Uncertainty of Distributed Energy Resources

by Chao Ma, Wenjie Xiong, Zhiyuan Tang, Ziwei Li, Yonghua Xiong and Qibo Wang

Electronics 2024, 13(14), 2748; https://doi.org/10.3390/electronics13142748 - 12 Jul 2024

Cited by 4 | Viewed by 959

Abstract

Due to the uncertainty of distributed energy resources (DERs), the effectiveness of voltage control in distribution networks faces significant challenges. Aiming at this problem, a novel distributed stochastic model predictive control (DSMPC) scheme was proposed in this paper to achieve voltage regulation considering [...] Read more.

Due to the uncertainty of distributed energy resources (DERs), the effectiveness of voltage control in distribution networks faces significant challenges. Aiming at this problem, a novel distributed stochastic model predictive control (DSMPC) scheme was proposed in this paper to achieve voltage regulation considering the uncertainty of DERs. In the proposed control scheme, based on the photovoltaic (PV) prediction error model, multiple operation scenarios are selected to characterize the uncertainty of PV generation. Then, based on these selected scenarios, a DSMPC approach is developed to minimize the cost of control actions by coordinating the PV inverters and battery energy storage systems. Simulation involving the modified IEEE 34-bus verified that the proposed method can work effectively under the uncertainty of DERs and achieves a comparable control performance with a well-designed centralized controller. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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17 pages, 7470 KiB

Open AccessArticle

Research on the Quantitative Assessment Method of HVDC Transmission Line Failure Risk during Wildfire Disaster

by Bo Zhou, Xinwei Sun, Yunyang Xu and Wei Wei

Electronics 2024, 13(11), 2119; https://doi.org/10.3390/electronics13112119 - 29 May 2024

Cited by 1 | Viewed by 791

Abstract

It is increasingly important to effectively predict the failure of HVDC transmission lines caused by wildfire disasters. On the basis of comprehensively considering the distribution of fire points, the characteristics of wildfire propagation, and the failure factors of the transmission line, a method [...] Read more.

It is increasingly important to effectively predict the failure of HVDC transmission lines caused by wildfire disasters. On the basis of comprehensively considering the distribution of fire points, the characteristics of wildfire propagation, and the failure factors of the transmission line, a method for calculating the probability of failure in HVDC transmission lines during wildfire disasters is proposed to quantify the risk of HVDC transmission line failures caused by wildfire disasters. Using the ArcGIS 10.7. platform, the study examined the quantity of fire points within the buffer zone of each HVDC transmission line from 2001 to 2022. The results indicate significant variations in the number of fire incidents in the buffer zones of various transmission lines. Notably, there has been a noticeable increase in the number of fire incidents along several HVDC transmission lines, including Xizhe, Baihetan-Jiangsu, Baihetan-Zhejiang, and Fufeng, in recent years. Based on the number of fire points in the buffer zone obtained through ArcGIS processing and the proposed failure probability calculation model, six HVDC hydropower transmission channels in the Sichuan Province were analyzed. At the same time, the proposed probability calculation model was simplified, and a corresponding linear evaluation index was introduced. The regression analysis results indicate that the proposed index can effectively assess the failure risk of HVDC transmission lines during wildfire disasters. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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23 pages, 7828 KiB

Open AccessArticle

Fault Ride-Through Method for Interline Power Flow Controller Based on DC Current Limiter

by Jiajun Li, Huabo Shi, Baohong Li, Qin Jiang, Yue Yin, Yingmin Zhang, Tianqi Liu and Chang Nie

Electronics 2024, 13(6), 1038; https://doi.org/10.3390/electronics13061038 - 11 Mar 2024

Cited by 2 | Viewed by 1024

Abstract

The interline power flow controller (IPFC) based on a modular multilevel converter with a half-bridge configuration can control the active and reactive power flows of multiple alternating current (AC) lines. However, it forms a multiterminal system on the direct current (DC) side, which [...] Read more.

The interline power flow controller (IPFC) based on a modular multilevel converter with a half-bridge configuration can control the active and reactive power flows of multiple alternating current (AC) lines. However, it forms a multiterminal system on the direct current (DC) side, which leads to DC faults. To reduce the protection and clearance requirements on the DC side of IPFCs, this paper proposes a hybrid current limiter topology suitable for generating a DC-side fault ride-through scheme. The current limiter employs a low-loss branch in steady-state conditions; when the fault occurs, a commutation capacitor and controllable power electronic devices are used to transfer the fault current to the current-limiting branch. To clarify the operating principles of the current limiter, the working states of each stage and electrical stress of each device are analyzed. Different components with varying limiter parameters are also discussed, and optimal parameters to achieve the best limitation effect are discussed. PSCAD simulations show that the proposed limiter can limit the overcurrent effectively, and DC-side fault clearance can be achieved easily with this fault ride-through strategy. Full article

(This article belongs to the Special Issue The Hybrid AC-DC Power System Coordinated Control and Operation Technology, 2nd Edition)

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