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This editorial discusses the need for clean and reliable energy sources in response to increasing electricity consumption and environmental concerns. The integration of wind and solar power into the existing power grid presents challenges due to their variability and dependence on weather conditions. The research presented in this collection focuses on key technologies for planning and operating hybrid energy systems, which combine wind and solar power with controllable sources like hydropower, thermal power, and battery storage. The articles cover topics such as wind turbine control, market decision-making methods, optimization models, and short-term prediction models. These studies propose innovative approaches and models to improve the reliability, efficiency, and sustainability of hybrid energy systems. [Extracted from the article]

This paper presents an open‐access Matlab/Simulink‐based power system simulation toolbox (MatPSST) for research and education. In MatPSST, dynamic modeling is implemented by Simulink. Only the initialization process is coded in Matlab. This structure makes full use of Simulink, enabling users to fully use the rich solvers and built‐in toolboxes in Matlab/Simulink, such as small‐signal analysis, without additional programming. The interaction with real‐time platforms like RTLAB and dSPACE in MatPSST is convenient through the Simulink interface. In addition, MatPSST provides a uniform interface and flexible framework for user‐defined functions. Users do not need to consider the interaction between models and dynamic solvers when implementing state‐of‐the‐art user‐defined models. To avoid the heavy work (replicate units and change parameters) in modeling detailed wind farm or photovoltaic station with hundreds of renewable generation units, the idea of the vector‐variable‐based model is proposed with MatPSST. Case studies introduce some selected application examples of MatPSST in research and education and demonstrate its accuracy by the comparisons with Simscape and PSAT. The cases reveal the advantages of MatPSST in promoting power system research and education. [ABSTRACT FROM AUTHOR]

Although the harmonics interaction plays a vital role in causing commutation failure (CF) in an ultra HVDC (UHVDC) system with hierarchical connection, it has not been sufficiently considered in previous work. In this paper, the electric interaction among the inverter valves of the UHVDC system with hierarchical connection during receiving system fault transient process is demonstrated. Moreover, the mechanism of CFs in UHVDC system with hierarchical connection is also investigated via the analysis of harmonics interaction. After the AC fault occurs, the appearance processes of the local commutation failure (LCF) and concurrent commutation failure (CCF) are divided into several stages and interpreted by schematic diagrams. And the characteristics of each stage are also concluded. In addition, a coordinated CF prevention scheme based on harmonics and DC current detection is proposed to mitigate the CFs in UHVDC system with hierarchical connection. Finally, the effectiveness of the proposed scheme is verified via a $\pm 1100$ kV UHVDC transmission system under various short circuit ratio values and AC-side coupling strengths. [ABSTRACT FROM AUTHOR]

Commutation failure (CF) is an inherent drawback of line-commutated converter high-voltage DC (LCC-HVDC) system. And CF prevention (CFPREV) control is widely applied in UHVDC lines to mitigate the subsequent CF. However, the formation of a multi-infeed UHVDC system induces power exchange and voltage interaction between AC buses during the transient process, making the behaviors and mitigation of CFs more complex. Consequently, exploring the impact of CFPREV control on adjacent stations and optimizing the CFPREV control to adapt to the interaction characteristics in a multi-infeed system is necessary. Considering the interaction characteristics, the impact of CFPREV control on the commutation process of inverters in a multi-infeed system is analyzed through formula derivation and simulation verification. It is found that although CFPREV control can effectively mitigate the CFs of the inverter near the fault, it will further increase the risk of concurrent CF (CCF) of remote inverters due to the interaction on the AC side. To solve this problem, a coordinated control scheme of CFPREV controls in a multi-infeed UHVDC system is proposed. The output of the CFPREV control of the inverter near the fault can be adjusted adaptively according to the commutation margins of remote inverters. And the probability of CCF caused by CFPREV control is consequently decreased. Case studies are conducted based on Henan provincial multi-infeed UHVDC system in China to verify the analysis result and the effectiveness of the coordinated control scheme of CFPREV controls. [ABSTRACT FROM AUTHOR]

This paper proposes an additional reactive power control strategy and an emergency control strategy for ±1100 kV ultra-high voltage direct current (UHVDC) system with a hierarchical connection mode, in which the inverter station connect to two AC systems with different voltage levels. Firstly, the relationship between reactive power and DC voltage is analysed. Then, an additional reactive power control strategy is proposed to solve the voltage fluctuation caused by reactive power disturbance. Next, the reactive power emergency control strategy is proposed when a short-circuit fault occurs. Reactive power compensation devices will be inputted into the fault-free AC system to provide reactive power support through coupling relationship between two AC systems in the inverter side. Simulation results show that the additional reactive power control strategy can suppress reactive power disturbances without affecting the active power. Moreover, the reactive power emergency control strategy can reduce the probability of commutation failure in converters connected to the fault AC system while a short-circuit fault occurs. [ABSTRACT FROM AUTHOR]

With increasing wind farm scale, dynamic modeling and simulating the low-voltage ride-through (LVRT) process of wind farms are time- and source-consuming. Thus, a dynamic equivalent model of a wind farm considering the LVRT process is necessary and vital for power system analysis. However, the crowbar status of each doubly-fed induction generator (DFIG), voltage, and wind speed differences among will influence the LVRT process and equivalent results. To consider these three factors comprehensively and eliminate the error, this paper proposes a three-stage dynamic equivalent modeling approach, using accurate crowbar identification and voltage differences among DFIGs. Stage I: DFIGs are divided by crowbar status. A new accurate crowbar identification method is proposed to consider the interference from other DFIGs, using the experimental two-machine system and several dynamic simulations to correct fault voltage. Stage II: The often-overlooked voltage differences are considered, and DFIGs are divided into different clusters for accurate fault dynamics. Stage III: To eliminate errors resulting from wind speed differences, the DFIG active power reference is corrected based on the analytical function of the wind farm LVRT process. The proposed model can accurately identify crowbar status and consider the voltage and wind speed differences without detailed model simulation results, improving the accuracy. Case studies are undertaken on a wind farm with fifty DFIGs. Simulation results indicated that the proposed model can match the detailed model under different wind scenarios and fault voltages, and it also increases simulation efficiency, which is suitable for studying the effect of LVRT on power systems. [Display omitted] • A three-stage dynamic equivalent method is proposed to model the wind farm. • Fault voltage is corrected to identify crowbar status given DFIGs' mutual impact. • Voltage differences among wind turbines are considered to reduce equivalent error. • The simulation results demonstrate the effectiveness of proposed equivalent method. • The proposed model can capture the LVRT process of large-scale wind farm. [ABSTRACT FROM AUTHOR]