Research

15 pages, 2292 KiB

Open AccessArticle

Research on Voltage Sag Loss Assessment Based on a Two-Stage Taguchi Quality Perspective Method

by Cheng Guo, Xinyuan Zhang, Mi He, Linling Wang and Xuanming Yang

Symmetry 2024, 16(3), 328; https://doi.org/10.3390/sym16030328 - 08 Mar 2024

Viewed by 619

Voltage sags resulting from symmetrical or asymmetrical faults pose a significant threat to power quality. In response to this challenge, a voltage sag loss assessment method based on a two-stage Taguchi quality perspective approach is proposed to address the quantitative analysis of voltage [...] Read more.

Voltage sags resulting from symmetrical or asymmetrical faults pose a significant threat to power quality. In response to this challenge, a voltage sag loss assessment method based on a two-stage Taguchi quality perspective approach is proposed to address the quantitative analysis of voltage sag economic losses. Initially, using the Taguchi quality perspective method, single-index quality loss functions are separately established for voltage sag magnitude and fault duration. Subsequently, by introducing a comprehensive load tolerance curve, sensitivity parameters within the quality loss function are accurately calculated. This yields a deterministic model for voltage sag assessment. Building upon this, the relative impact of the two indices on voltage sag loss is evaluated using the quality loss function. Consequently, a comprehensive loss model under the influence of multiple indices is formed by integrating two single-index evaluation models. The simulation results indicate that this method can effectively assess the economic losses of voltage sags under the combined influence of multiple factors. Compared to the original economic loss assessment method, it improves quantitative accuracy by approximately 3.72%. Moreover, the method reduces the computational complexity of loss assessment through the consolidation of intervals with similar sensitivity parameters. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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15 pages, 2663 KiB

Open AccessArticle

A New Method for the Analysis of Broadband Oscillation Mode of New Energy Stations

by Cheng Guo, Lingrui Yang, Jianbo Dai, Bo Chen, Ke Yin and Jing Dai

Symmetry 2024, 16(3), 278; https://doi.org/10.3390/sym16030278 - 28 Feb 2024

Viewed by 585

Abstract

The accurate identification of the broadband oscillation mode is the premise of solving the resonance risk of new energy stations. Reviewing the traditional Prony algorithm, the problems of the high model order and poor noise immunity in broadband oscillation mode are identified. The [...] Read more.

The accurate identification of the broadband oscillation mode is the premise of solving the resonance risk of new energy stations. Reviewing the traditional Prony algorithm, the problems of the high model order and poor noise immunity in broadband oscillation mode are identified. The accuracy and running time of the Variational mode decomposition (VMD) is a symmetric trade-off problem. An improved strategy based on VMD is proposed. Firstly, the optimal value of the number of modes and penalty factors obtained by a particle swarm optimization algorithm is input into VMD to decompose the signal into multiple modes. Then, combined with the energy threshold method, the denoising and signal reconstruction of each mode component after decomposition are carried out. Finally, the Prony algorithm is used to identify the oscillation mode of the original signal and the reconstructed signal, respectively. The Signal-to-noise ratio (SNR) and model order are compared and analyzed. Through the analysis of the example and simulation data, it is shown that the proposed method effectively solves the problem of poor engineering adaptability of the traditional Prony algorithm. It also can accurately obtain the time-domain characteristics of broadband oscillation, which has a promising future in the engineering application. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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20 pages, 7639 KiB

Open AccessArticle

Adaptive Virtual Inertia Control Strategy for a Grid-Connected Converter of DC Microgrid Based on an Improved Model Prediction

by Feng Zheng, Minghong Su, Baojin Liu and Wanling Liu

Symmetry 2023, 15(11), 2072; https://doi.org/10.3390/sym15112072 - 15 Nov 2023

Viewed by 872

Abstract

Aiming at the problem that the bus voltage in a low-inertia DC microgrid is prone to be affected by internal power fluctuations, an adaptive virtual inertia control strategy for a grid-connected converter of a DC microgrid based on an improved model prediction is [...] Read more.

Aiming at the problem that the bus voltage in a low-inertia DC microgrid is prone to be affected by internal power fluctuations, an adaptive virtual inertia control strategy for a grid-connected converter of a DC microgrid based on an improved model prediction is proposed. Firstly, the adaptive analog virtual synchronous generator (AVSG) is introduced into the voltage outer loop by combining the inertial parameters with the voltage change rate, and the flexible adjustment of the inertial parameters is realized. Secondly, the improved model predictive control is introduced into the current inner loop to realize the fast-tracking of the given current value and improve the dynamic characteristics of the control system. Finally, a system model is established based on Matlab/Simulink for simulation. The results show that compared with the traditional virtual inertia control strategy, the proposed control strategy has smaller bus voltage fluctuation amplitude and better dynamic performance; when a 10 kW load mutation occurs, the magnitude of bus voltage drop is reduced by 60%, and the voltage recovery time is shortened by 30%. The proposed control strategy can effectively improve the stability of DC bus voltage and the operation ability of the system under asymmetric conditions. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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15 pages, 7649 KiB

Open AccessArticle

Research on Optimal Scheduling Strategy of Microgrid Considering Electric Vehicle Access

by Zhimin Wu, Yang Zou, Feng Zheng and Ning Liang

Symmetry 2023, 15(11), 1993; https://doi.org/10.3390/sym15111993 - 28 Oct 2023

Cited by 1 | Viewed by 790

Abstract

The random output of renewable energy and the disorderly grid connection of electric vehicles (EV) will pose challenges to the safe and stable operation of the power system. In order to ensure the reliability and symmetry of the microgrid operation, this paper proposes [...] Read more.

The random output of renewable energy and the disorderly grid connection of electric vehicles (EV) will pose challenges to the safe and stable operation of the power system. In order to ensure the reliability and symmetry of the microgrid operation, this paper proposes a microgrid optimization scheduling strategy considering the access of EVs. Firstly, in order to reduce the impact of random access to EVs on power system operation, a schedulable model of an EV cluster is constructed based on the Minkowski sum. Then, based on the wavelet neural network (WNN), the renewable energy output is predicted to reduce the influence of its output fluctuation on the operation of the power system. Considering the operation constraints of each unit in the microgrid, the network active power loss and node voltage deviation are taken as the optimization objectives, and the established microgrid model is equivalently transformed via second-order cone relaxation to improve its solution efficiency. Based on network reconfiguration and flexible load participation in demand response, the economy and reliability of system operation are improved. Finally, the feasibility and effectiveness of the proposed method are verified based on the simulation examples. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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16 pages, 4731 KiB

Open AccessArticle

Optimal Location and Sizing of Photovoltaic-Based Distributed Generations to Improve the Efficiency and Symmetry of a Distribution Network by Handling Random Constraints of Particle Swarm Optimization Algorithm

by Muhammad Abid Ali, Abdul Rauf Bhatti, Akhtar Rasool, Muhammad Farhan and Ebenezer Esenogho

Symmetry 2023, 15(9), 1752; https://doi.org/10.3390/sym15091752 - 13 Sep 2023

Cited by 1 | Viewed by 865

Abstract

Distributed generators (DGs) are increasingly employed in radial distribution systems owing to their ability to reduce electrical energy losses, better voltage levels, and increased dependability of the power supply. This research paper deals with the utilization of a Particle Swarm Optimization algorithm by [...] Read more.

Distributed generators (DGs) are increasingly employed in radial distribution systems owing to their ability to reduce electrical energy losses, better voltage levels, and increased dependability of the power supply. This research paper deals with the utilization of a Particle Swarm Optimization algorithm by handling its random constraints to determine the most appropriate size and location of photovoltaic-based DG (PVDG) to keep the asymmetries of the phases minimal in the grid. It is thus expected that this algorithm will provide an efficient and consistent solution to improve the overall performance of the power system. The placement and sizing of the DG are done in a way that minimizes power losses, enhances the voltage profile, i.e., bringing symmetry in the voltage profile of the system, and provides maximum cost savings. The model has been tested on an IEEE 33-bus radial distribution system using MATLAB software, in both conditions, i.e., with and without PVDG. The simulation results were successful, indicating the viability of the proposed model. The proposed PSO-based PVDG model further reduced active power losses as compared to the models based on the teaching–learning artificial bee colony algorithm (TLABC), pathfinder algorithm (PFA), and ant lion optimization algorithm (ALOA). With the proposed model, active power losses have reduced to 17.50%, 17.48%, and 8.82% compared to the losses found in the case of TLABC, PFA, and ALOA, respectively. Similarly, the proposed solution lessens the reactive power losses compared to the losses found through existing TLABC, PFA, and ALOA techniques by an extent of 23.06%, 23%, and 23.08%, respectively. Moreover, this work shows cost saving of 15.21% and 6.70% more than TLABC and ALOA, respectively. Additionally, it improves the voltage profile by 3.48% of the power distribution system. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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14 pages, 1287 KiB

Open AccessArticle

Utilizing Full Degrees of Freedom of Control in Voltage Source Inverters to Support Micro-Grid with Symmetric and Asymmetric Voltage Requirements

by Akhtar Rasool, Fiaz Ahmad, Muhammad Salman Fakhar, Syed Abdul Rahman Kashif and Edwin Matlotse

Symmetry 2023, 15(4), 865; https://doi.org/10.3390/sym15040865 - 05 Apr 2023

Viewed by 981

Abstract

This article proposes a novel equivalent control method for voltage source inverters (VSI) with disturbance observers (DOB) to support the symmetric and asymmetric voltage requirements of a micro-grid (MG) while also matching the MG output power requirements. The method leverages the degrees of [...] Read more.

This article proposes a novel equivalent control method for voltage source inverters (VSI) with disturbance observers (DOB) to support the symmetric and asymmetric voltage requirements of a micro-grid (MG) while also matching the MG output power requirements. The method leverages the degrees of freedom (DOF) of the VSI under symmetric and asymmetric MG voltage conditions by utilizing the mean-point voltage of the MG, which is often overlooked in literature studies due to this being grounded. The method enables the three-phase inverter to generate voltages as needed by the MG inconsistently due to changing loads in the MG circuits or phases. The method is also insensitive to disturbances because of the DOB, being part of the controller. The proposed method is validated under both the balance and imbalance voltage demands of the MG. The mean voltage of the MG is used as a set-point to be corroborated as a mean voltage at the inverter’s output, in addition to active-reactive power references. The novel model is developed by augmenting the new, mean-point voltage as part of the system dynamics. The proposed method is simulated in MATLAB/Simulink^® and is verified for its hardiness and effectiveness. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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16 pages, 4088 KiB

Open AccessArticle

Research on the Fault-Transient Characteristics of a DC Power System Considering the Cooperative Action of a Flexible Current-Limiting Device and a Circuit Breaker

by Feng Zheng, Yaling Peng, Weidong Wang and Song Zheng

Symmetry 2023, 15(1), 134; https://doi.org/10.3390/sym15010134 - 03 Jan 2023

Viewed by 1156

Abstract

As an effective carrier of a new energy collection, the DC power grid has low inertia and weak damping characteristics, making it essential to limit fault current and isolate the DC system. To quickly and effectively suppress fault current, a flexible current-limiting device [...] Read more.

As an effective carrier of a new energy collection, the DC power grid has low inertia and weak damping characteristics, making it essential to limit fault current and isolate the DC system. To quickly and effectively suppress fault current, a flexible current-limiting device (FCLD) is proposed, which can realize transient fault self-recovery without circuit breaker action and permanent and quick isolation of a fault. It improves the operational ability of the DC system under an asymmetric condition. First, a rectifier provides a set-slope current to each cascade inductor, so the voltage of the inductor can be clamped. Second, a controlled current source (CCS) is applied to generate inverse flux to prevent the inductor from magnetic saturation. The protection action time of the DC circuit breaker is reformulated. Finally, by considering the synergistic action of the current-limiting device, the circuit breaker, and the transient characteristics of the DC grid fault, the protection scheme of the multi-terminal flexible DC system can be formulated. To verify the validity of the proposed flexible current-limiting device, a multi-terminal flexible DC simulation platform is established, and the faults of DC lines are simulated and analyzed. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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14 pages, 2085 KiB

Open AccessArticle

Modern Active Voltage Control in Distribution Networks, including Distributed Generation, Using the Hardware-in-the-Loop Technique

by Beshoy Nabil Fahmy Fanos, Mohammad H. Soliman, Hossam E. A. Talaat and Mahmoud A. Attia

Symmetry 2023, 15(1), 90; https://doi.org/10.3390/sym15010090 - 29 Dec 2022

Cited by 2 | Viewed by 1540

Abstract

Voltage constraints usually place restrictions on how distributed generation (DG) can be connected to weak distribution networks. As DG capacity increases, active voltage control techniques are needed. Active approaches can greatly lower connection costs while boosting the capacity of connectable DG when used [...] Read more.

Voltage constraints usually place restrictions on how distributed generation (DG) can be connected to weak distribution networks. As DG capacity increases, active voltage control techniques are needed. Active approaches can greatly lower connection costs while boosting the capacity of connectable DG when used in place of the passive strategy. In this article, a modified active voltage control algorithm is used on an IEEE 33 bus system to test the robustness and reliability of the control algorithm under severe conditions. The simulations are carried out using the hardware-in-the-loop (HIL) method. Real-time simulations are used to test data transfer and the reliability of the control algorithm’s execution. The analysis is based on a three-phase symmetric power system. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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29 pages, 8166 KiB

Open AccessArticle

A State Machine-Based Droop Control Method Aided with Droop Coefficients Tuning through In-Feasible Range Detection for Improved Transient Performance of Microgrids

by Mandarapu Srikanth and Yellapragada Venkata Pavan Kumar

Symmetry 2023, 15(1), 1; https://doi.org/10.3390/sym15010001 - 20 Dec 2022

Cited by 4 | Viewed by 1967

Abstract

The cascaded droop-voltage-current controller plays a key role in the effective operation of microgrids, where the controller performance is critically impacted by the desigheme, a constant value n of the droop controller. Moreover, in critical loading (e.g.: connection/disconnection of large inductive load), the [...] Read more.

The cascaded droop-voltage-current controller plays a key role in the effective operation of microgrids, where the controller performance is critically impacted by the desigheme, a constant value n of the droop controller. Moreover, in critical loading (e.g.: connection/disconnection of large inductive load), the pre-set value of the droop coefficient brings asymmetry in transient performance leading to instability. Hence, to improve symmetry by reducing the trade-off between transient response and stability margin, this paper proposes a state machine-based droop control method (SMDCM) aided with droop coefficients’ tuning through in-feasible range detection. Here, to realize the issues and the role of the droop controller’s dynamics on the microgrid’s stability, a small-signal stability analysis is conducted, thereby, an in-feasible range of droop values is identified. Accordingly, safe values for droop coefficients are implemented using the state machine concept. This proposed SMDCM is compared with the conventional constant droop control method (CDCM) and fuzzy logic-based droop control method (FLDCM) in terms of frequency/power/voltage characteristics subjected to different power factor (PF) loading conditions. From the results, it is seen that CDCM failed in many metrics under moderate and poor PF loadings. FLDCM is satisfactory under moderate PF loading, but, showed 54 Hz/48 Hz as maximum/minimum frequency values during poor PF loading. These violate the standard limit of ±2%, but SMDCM satisfactorily showed 50.02 Hz and 49.8 Hz, respectively. Besides, FLDCM levied an extra burden of 860 W on the system while it is 550 W with SMDCM. System recovery has taken 0.04 s with SMDCM, which completely failed with FLDCM. Similarly, voltage THD with FLDCM is 58.9% while with SMDCM is 3.08%. Peak voltage due to capacitive load switching is 340V with FLDCM and 150 V with SMDCM. These findings confirm that the proposed SMDCM considerably improved the transient performance of microgrids. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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18 pages, 11929 KiB

Open AccessArticle

Research on a Non-PLL Control Strategy for a Flexible Fault Current Limiter and Its Application in Improving the FRT Capability of Microgrids

by Feng Zheng, Guojing Wu, Bo Qu, Xingyao Xiang and Song Zheng

Symmetry 2022, 14(12), 2652; https://doi.org/10.3390/sym14122652 - 15 Dec 2022

Viewed by 895

Abstract

Aiming to achieve fault ride-through (FRT) in a microgrid under the condition of an asymmetric power grid, this paper proposes a scheme that applies the cascaded H-bridge flexible fault current limiter to realize both voltage regulation and current limiting at the point of [...] Read more.

Aiming to achieve fault ride-through (FRT) in a microgrid under the condition of an asymmetric power grid, this paper proposes a scheme that applies the cascaded H-bridge flexible fault current limiter to realize both voltage regulation and current limiting at the point of common coupling (PCC). In order to overcome the instability of phase-locked loop (PLL) and its other problems, in the double-synchronous rotating coordinate system, the dq-axis components of each sequence electric quantity can be extracted without PLL by setting the rotational angular frequency of the coordinate axis to a given value. To eliminate the deviation between the set frequency and the actual frequency of the power grid, the calculation formula for the frequency correction amount is deduced, and, based on this, an iterative correction method for the set frequency of the rotating coordinate system is proposed. In this way, the set frequency can adaptively follow the actual frequency of the power grid, which ensures the effectiveness of the non-PLL scheme. Based on this, a sequence decomposition and compensation control strategy for the CHB-FFCL is presented. Finally, through the MATLAB/Simulink platform simulation, the effectiveness of the proposed strategy is verified and thereby shown to improve the FRT capability of microgrids under complex grid conditions. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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9 pages, 1139 KiB

Open AccessArticle

A Residual Voltage Data-Driven Prediction Method for Voltage Sag Based on Data Fusion

by Chen Zheng, Shuangyin Dai, Bo Zhang, Qionglin Li, Shuming Liu, Yuzheng Tang, Yi Wang, Yifan Wu and Yi Zhang

Symmetry 2022, 14(6), 1272; https://doi.org/10.3390/sym14061272 - 20 Jun 2022

Cited by 2 | Viewed by 1319

Abstract

Voltage sag is the most serious power quality problem in the three-phase symmetrical power system. The influence of multiple factors on the voltage sag level and low computational efficiency also pose challenges to the prediction of residual voltage amplitude of voltage sag. This [...] Read more.

Voltage sag is the most serious power quality problem in the three-phase symmetrical power system. The influence of multiple factors on the voltage sag level and low computational efficiency also pose challenges to the prediction of residual voltage amplitude of voltage sag. This paper proposes a voltage sag amplitude prediction method based on data fusion. First, the multi-dimensional factors that influence voltage sag residual voltage are analyzed. Second, these factors are used as input, and a model for predicting voltage sag residual voltage based on data fusion is constructed. Last, the model is trained and debugged to enable it to predict the voltage sag residual voltage. The accuracy and feasibility of the method are verified by using the actual power grid data from East China. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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14 pages, 7469 KiB

Open AccessArticle

Cascaded Multilevel Inverter-Based Asymmetric Static Synchronous Compensator of Reactive Power

by Martynas Šapurov, Algirdas Baskys, Raimondas Pomarnacki, Artūras Serackis, Mindaugas Jankauskas, Van Khang Huynh, Vytautas Bleizgys, Aldas Dervinis, Edvardas Bielskis, Sarunas Paulikas, Nerijus Paulauskas and Darius Guršnys

Symmetry 2022, 14(3), 483; https://doi.org/10.3390/sym14030483 - 26 Feb 2022

Cited by 2 | Viewed by 1632

Abstract

The topology of the static synchronous compensator of reactive power for a low-voltage three-phase utility grid capable of asymmetric reactive power compensation in grid phases has been proposed and analysed. It is implemented using separate, independent cascaded H-bridge multilevel inverters for each phase. [...] Read more.

The topology of the static synchronous compensator of reactive power for a low-voltage three-phase utility grid capable of asymmetric reactive power compensation in grid phases has been proposed and analysed. It is implemented using separate, independent cascaded H-bridge multilevel inverters for each phase. Every inverter includes two H-bridge cascades. The first cascade operating at grid frequency is implemented using thyristors, and the second one—operating at high frequency is based on the high-speed MOSFET transistors. The investigation shows that the proposed compensator is able to compensate the reactive power in a low-voltage three-phase grid when phases are loaded by highly asymmetrical reactive loads and provides up to three times lower power losses in the compensator as compared with the situation when the compensator is based on the conventional three-level inverters implemented using IGBT transistors. Full article

(This article belongs to the Special Issue Advanced Technologies in Power Quality and Power Disturbance Data Application)

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