Research

13 pages, 5111 KiB

Open AccessArticle

Research on a Three-Phase Energy Mutual-Aid Strategy for a Grid-Connected Inverter Based on Constructed Negative Sequence Current Control

by Zhenao Sun, Dazhong Ma and Qiuye Sun

Appl. Sci. 2023, 13(23), 12863; https://doi.org/10.3390/app132312863 - 30 Nov 2023

Viewed by 520

Abstract

With the increased grid-connected capacity of a single-phase distributed power supply, three-phase power unbalance is more likely to occur in a power grid. Three-phase power unbalance can further lead to three-phase voltage unbalance, which can have adverse effects on power quality and power [...] Read more.

With the increased grid-connected capacity of a single-phase distributed power supply, three-phase power unbalance is more likely to occur in a power grid. Three-phase power unbalance can further lead to three-phase voltage unbalance, which can have adverse effects on power quality and power supply reliability. Therefore, there is a need to build a three-phase power transmission channel to realize power exchanging among phases. In this paper, a novel grid-connected inverter control strategy for three-phase power exchanging is proposed based on constructed negative sequence current control. A completed negative sequence current control loop is added to a conventional three-bridge inverter to realize the decoupling control of three-phase grid current, and then three-phase power exchanging is realized. On this basis, this paper further puts forward a strategy for three-phase power exchanging aimed at three-phase voltage balance. Correspondingly, the three-phase grid current is controlled according to the feedback of the three-phase voltage. Then, three-phase voltage balance is achieved by three-phase power exchanging. The simulation and experimental results show that the proposed strategy is suitable for a three-phase unbalanced power grid, which can realize three-phase power exchanging, and further, can achieve three-phase voltage balance. The proposed strategy can help to improve power quality and supply reliability. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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17 pages, 4373 KiB

Open AccessArticle

A Robust Design Method for Ultra-Low-Frequency Oscillation Suppression Control in Hydro–Photovoltaic Complementary Systems

by Xueyang Zeng, Gang Chen, Huabo Shi, Sijia Wang and Peng Shi

Appl. Sci. 2023, 13(19), 11066; https://doi.org/10.3390/app131911066 - 08 Oct 2023

Viewed by 766

Abstract

Aiming at the problem of ultra-low-frequency oscillation (ULFO) in power systems, with an oscillation frequency lower than 0.1 Hz, an oscillation suppression control method is proposed. Firstly, the mathematical modeling of the system is carried out, and a cascade correction control method of [...] Read more.

Aiming at the problem of ultra-low-frequency oscillation (ULFO) in power systems, with an oscillation frequency lower than 0.1 Hz, an oscillation suppression control method is proposed. Firstly, the mathematical modeling of the system is carried out, and a cascade correction control method of the governor of hydropower generators is proposed. Secondly, using the ability of photovoltaic (PV) active power to adjust the system frequency, an additional controller for PV active power is proposed. Then, a unified frequency model considering the two controllers is established for multi-hydro and multi-PV systems, and the structural singular value method is used to coordinate the design of the parameters of the hydropower and PV generator controllers to achieve robust performance. Finally, based on a time-domain simulation of single-hydro and single-PV systems and an actual demonstration system located in Sichuan Province, China, the results show that the control method proposed in this paper has a good suppression effect on ultra-low-frequency oscillation under different working conditions, and meets the requirements of robust performance. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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22 pages, 9340 KiB

Open AccessArticle

Investigation of Impulse Aging of Energy-Absorption Elements for Hybrid DC Circuit Breakers

by Xinyi Wang, Yiying Liu, Yilei Lv, Jinru Sun, Xueling Yao, Xinyu Wang and Zhihan Li

Appl. Sci. 2023, 13(17), 9784; https://doi.org/10.3390/app13179784 - 29 Aug 2023

Viewed by 503

Abstract

The state of the energy-absorption branch MOV in the hybrid DC circuit breaker (DCCB) has a very important impact on the short fault breaking operation of the circuit breaker. Therefore, it is necessary to evaluate the state of the MOV, which is also [...] Read more.

The state of the energy-absorption branch MOV in the hybrid DC circuit breaker (DCCB) has a very important impact on the short fault breaking operation of the circuit breaker. Therefore, it is necessary to evaluate the state of the MOV, which is also called the “sleep component”. Due to DCCB being placed indoors, the aging is mainly caused by short-circuit impulse current. Therefore, this paper mainly focuses on the study of the short-circuit impulse aging characteristics of the energy-absorption branch MOV. The dynamic simulation system of a hybrid DCCB was built to investigate the impulse of short-circuit current on the MOV of the energy-absorption branch during the circuit breaking process. Then, an accelerated impulse aging test platform was built and the accelerated impulse aging tests of the MOV were conducted. The aging characteristics of the MOV were analyzed in detail and detailed analysis was conducted of the macroscopic parameters and microstructure changes. The results indicate that the nonlinear coefficient α could be emphasized as a basis for judging the “sleeping” component states and aging degree of the hybrid DC circuit breaker, and can be expected to be applicable to MOV condition monitoring of BCCB in the future. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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16 pages, 4103 KiB

Open AccessArticle

An Improved Arc Fault Location Method of DC Distribution System Based on EMD-SVD Decomposition

by Liuming Jing, Lei Xia, Tong Zhao and Jinghua Zhou

Appl. Sci. 2023, 13(16), 9132; https://doi.org/10.3390/app13169132 - 10 Aug 2023

Viewed by 898

Abstract

The influence of the control strategy of the power electronic converter obscures the fault characteristics of DC distribution networks. The existence of arc faults over an extended period of time poses a grave threat to the security of power grids and may result [...] Read more.

The influence of the control strategy of the power electronic converter obscures the fault characteristics of DC distribution networks. The existence of arc faults over an extended period of time poses a grave threat to the security of power grids and may result in electric shock, fire, and other catastrophes. In recent years, the method of fault localization based on the traveling wave method has been a popular topic of research in the field of DC distribution system protection. In this paper, the fault localization principle of the traveling wave method is described in depth, and the propagation characteristics of the traveling wave of fault current in the online mode network are deduced. We present a method for wave head calibration that combines empirical mode decomposition (EMD) and singular value decomposition (VMD). After the fault-traveling current signal has been subjected to EMD, the first eigenmode function is extracted and subjected to singular value decomposition (SVD). After SVD, the detail component can reflect the singularity of the signal. The point of the maximum value of the detail component signal corresponds to the moment when the faulty traveling wave head reaches the monitoring point. Finally, the DC distribution system is modeled based on the PSCAD/EMTDC simulation environment, and the fault location method is verified. The simulation results show that the method can effectively realize fault localization. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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15 pages, 2973 KiB

Open AccessArticle

An Efficient Method for the Reliability Evaluation of Power Systems Considering the Variable Photovoltaic Power Output

by Haojie He, Liweiyong Guo, Peidong Han, Changzheng Shao and Tan Xu

Appl. Sci. 2023, 13(16), 9053; https://doi.org/10.3390/app13169053 - 08 Aug 2023

Viewed by 769

Abstract

The operational reliability of power systems is threatened by the random failure of components and uncertain power output of renewable energies, such as photovoltaics. Under such circumstances, reliability evaluation is necessary for maintaining a continuous and stable energy supply. However, traditional reliability evaluation [...] Read more.

The operational reliability of power systems is threatened by the random failure of components and uncertain power output of renewable energies, such as photovoltaics. Under such circumstances, reliability evaluation is necessary for maintaining a continuous and stable energy supply. However, traditional reliability evaluation methods are usually extremely time-consuming, considering the numerous system states that need to be analysed. Hence, the reliability evaluation process cannot follow up the dynamic changes in PV output, which makes the timeline of the evaluation disappointing. This paper proposes an efficient reliability evaluation method for power systems with PV integration. The method reveals the analytical relationship between the reliability levels of the power system and the uncertainty factors that influence the reliability, such as the PV output. In this way, the dynamic reliability evaluation is achieved, and the evaluation results can be updated timely when the output of PV changes. First, a Gaussian mixture-hidden Markov model (GMM-HMM) is used to model the distribution characteristics of PV output. Then, the state enumeration and the hyperbolic truncated polynomial chaos expansion method are used to determine the analytical relationship between the reliability indices and PV output. Lastly, based on the analytical function, the operational reliability of the power systems is dynamically evaluated considering the real-time PV output. The effectiveness of the proposed method is verified using the modified IEEE 30 system as an example. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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31 pages, 8634 KiB

Open AccessArticle

Probabilistic Forecasting of Available Load Supply Capacity for Renewable-Energy-Based Power Systems

by Qizhuan Shao, Shuangquan Liu, Yigong Xie, Xinchun Zhu, Yilin Zhang, Junzhou Wang and Junjie Tang

Appl. Sci. 2023, 13(15), 8860; https://doi.org/10.3390/app13158860 - 31 Jul 2023

Viewed by 671

Abstract

In order to accurately analyze the load supply capability of power systems with high penetration of renewable energy generation, this paper proposes a probabilistic available load supply capability (ALSC) forecasting method. Firstly, the optimal input features are selected by calculating the maximal information [...] Read more.

In order to accurately analyze the load supply capability of power systems with high penetration of renewable energy generation, this paper proposes a probabilistic available load supply capability (ALSC) forecasting method. Firstly, the optimal input features are selected by calculating the maximal information coefficient (MIC) between the input features and the target output. Based on this, a stacking ensemble learning model is applied for the prediction of wind power, photovoltaic power and load power. Secondly, the distributions of the forecasting objects are obtained based on forecasting errors and the error statistics method. Finally, the forecasting distributions of wind power, photovoltaic power and load are set as the parameters of a power system, and then probabilistic ALSC is calculated using Latin hypercube sampling (LHS) and repeated power flow (RPF). In order to simulate a more realistic power system, multiple slack buses are introduced to conduct two types of power imbalance allocations with novel allocation principles during the RPF calculation, which makes the ALSC evaluation results more reasonable and accurate. The results of probabilistic ALSC forecasting can provide a reference for the load power supply capacity of a power system in the future, and they can also provide an early warning for the risk of ALSC threshold overlimit. Case studies carried out on the modified IEEE 39-bus system verify the feasibility and effectiveness of the proposed methods. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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21 pages, 13211 KiB

Open AccessArticle

Design of Energy Recovery Control for General Virtual Synchronous Machines Based on Various Forms of Energy Storage

by Haigang Liu, Chu Sun, Xiaolin Zhang, Na Wang and Juncheng Wang

Appl. Sci. 2023, 13(14), 8059; https://doi.org/10.3390/app13148059 - 10 Jul 2023

Cited by 1 | Viewed by 840

Abstract

The reduced inertia in the power system due to renewable energy integration introduces operation challenges in frequency stability and control. The current options for virtual inertia and frequency support are limited by the energy resources and the power electronic interface. Considering the demand [...] Read more.

The reduced inertia in the power system due to renewable energy integration introduces operation challenges in frequency stability and control. The current options for virtual inertia and frequency support are limited by the energy resources and the power electronic interface. Considering the demand on response speed and energy capacity, a general virtual synchronous machine (VSM) control based on various forms of energy storage systems (ESS) is proposed. The steady-state energy variation of energy storage is found to be proportional to the virtual damping or governor gain, while inversely proportional to the integral gain of system frequency control. It is found that the size of energy storage can be at the second time scale (for example, 6.8 p.u.·s) for VSM implementation, which is significantly smaller than the conventional hour-scale energy storage in the power system. Based on energy dynamic analysis, stability requirement, and bandwidth separation rules, an energy recovery control is designed to maintain constant state of charge (for example, 50%) while avoiding conflicts with frequency regulation. The time scale of the designed energy recovery control loop (for example, hundreds of seconds) is longer than the secondary frequency control. The effectiveness of the proposed control is verified through comprehensive case studies. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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21 pages, 4119 KiB

Open AccessArticle

Optimization of a Virtual Synchronous Control Parameter for a Wind Turbine Generator Considering the Physical Constraint Boundary of Primary Frequency Regulation

by Junying Cao, Peng Sun, Zhaoyang Chen and Zhentao Qin

Appl. Sci. 2023, 13(9), 5569; https://doi.org/10.3390/app13095569 - 30 Apr 2023

Viewed by 860

Abstract

The wind turbine generator participates in the primary frequency regulation of the power system by releasing kinetic energy from the rotor. It is necessary to ensure that the rotor speed and converter capacity are within the safe range during the frequency regulation process; [...] Read more.

The wind turbine generator participates in the primary frequency regulation of the power system by releasing kinetic energy from the rotor. It is necessary to ensure that the rotor speed and converter capacity are within the safe range during the frequency regulation process; otherwise, it will have serious negative effects on the frequency stability of the power system. As an important primary frequency regulation parameter, the dead zone affects the evaluation of the frequency regulation ability of WTG. Therefore, the influence of the dead zone should also be further considered. In order to evaluate the frequency regulation capability of wind turbine generators more comprehensively and accurately, this paper proposes an optimized method for the parameter of virtual synchronous control for wind turbine generators by considering the dead zone and physical constraint boundary of primary frequency regulation. After establishing the time domain expression by considering the frequency regulation dead zone, the real-time frequency regulation capacity of the wind turbine generator is quantified by considering the speed limit of the rotor and the capacity limit of the converter. Furthermore, the optimal value of the frequency regulation coefficient can be derived. Simulation results show that the proposed method can effectively reduce the frequency deviation and frequency change rate of the power system, which can also keep the response within the physical constraint boundary. Consequently, the proposed method can fully utilize the ability for frequency regulation of the wind power generation system and effectively improve the frequency stability of the power system. Full article

(This article belongs to the Special Issue Advances and Challenges in Power Systems with High Penetration of Renewable Energies)

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