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The ultra‐low frequency oscillation (ULFO) imposes an emerging stability challenge to the high proportion of hydropower grids. To suppress ULFO without reducing the primary frequency regulation of the hydro governor, a novel idea to exploit the voltage regulation effect of load is implemented. First, the additional damping controller is designed and configured in static var compensator (SVC), and the frequency analysis model considering the configuration of SVC as well as damping controller is established. Based on the model, the specific influence of SVC and controller on ULFO is analysed through eigenvalue calculation. In addition, the influence of various load models and SVC location on the damping level are further studied. Consequently, a parameter optimization design method for SVC additional damping control is proposed, it is modelled as the optimization problem of damping ratio in ULFO mode under multi‐operation conditions, which is solved by a particle swarm optimization algorithm. Finally, the effectiveness of the designed SVC additional damping controller is verified in the improved four‐machine two‐area power system and the actual power grid in China. [ABSTRACT FROM AUTHOR]

Fault ride-through is a prerequisite for ensuring continuous operation of a variable-speed pumped storage unit with a full-size converter (FSC-VSPU) and providing support for the renewable energy and power grid. This paper proposes low-voltage ride through (LVRT) and high-voltage ride through (HVRT) strategies for FSC-VSPU to address this issue. Firstly, the structure of FSC-VSPU and its control strategy under power generation and pumping conditions are described. Subsequently, the fault characteristics of the FSC-VSPU under different operating conditions are analyzed. More stringent fault ride-through technical requirements than those for wind turbines are proposed. On this basis, the fault ride-through strategies of combining fast power drop, rotor energy storage control, power anti-regulation control, dynamic reactive current control, low power protection, and DC crowbar circuit are proposed. Simulation case studies conducted in PSCAD/EMTDC verify the correctness of the theoretical analysis and the effectiveness of the LVRT and HVRT strategies in this paper. [ABSTRACT FROM AUTHOR]

In a hydropower-dominated power grid, the primary frequency regulation (PFR) capability of hydropower units is typically compromised to suppress ultra-low frequency oscillations (ULFOs). However, as renewable wind power is further integrated, a practicable solution to damp ULFOs has emerged, which is to adjust the frequency control parameters of wind turbine (WT) units. Driven by the goals of overall damping enhancement and ULFO suppression, this paper first establishes an extended unified frequency model (EUFM) of a hydro–wind power sending system. Based on EUFM, the damping torque of the hydro–wind power sending system is derived, and the specific impact of WT control parameters on ULFOs and PFR characteristics is investigated. Then, a novel optimization objective function considering damping in the ultra-low frequency band and PFR is formulated and solved using an intelligence algorithm. By optimizing the parameters of the WT to suppress ULFOs, the PFR capability of hydropower units can be released. Finally, simulation results verify that the optimized WT parameters can simultaneously address the ULFO problem and guarantee PFR performance, thereby enhancing the frequency dynamic stability of the sending system. [ABSTRACT FROM AUTHOR]

Subsynchronous oscillation (SSO) is the resonance between a new energy generator set and a weak power grid, and the resonance frequency is usually the sub-/super-synchronous frequency. The eigensystem realization algorithm (ERA) is a classic algorithm for extracting modal parameters based on matrix decomposition. By leveraging the ERA's simplicity and low computational cost, an enhanced methodology for identifying the key parameters of SSO is introduced. The enhanced algorithm realizes SSO angular frequency extraction by constructing an angular frequency fitting equation, enabling efficient identification of SSO parameters using only a 200 ms synchrophasor sequence. In the process of identification, the fitting-based ERA effectively addresses the limitation of the existing ERA. The accuracy of SSO parameter identification is improved, thereby realizing that SSO parameter identification can be carried out using a 200 ms data window. The fitting-based ERA is verified using synthetic and actual data from synchrophasor measurement terminals. The research results show that the proposed algorithm can accurately extract fundamental and subsynchronous or supersynchronous oscillation parameters, effectively realizing dynamic real-time monitoring of subsynchronous oscillations. [ABSTRACT FROM AUTHOR]

Conventional grid-forming control often destabilizes voltage source converters (VSCs) in stiff grids, and transient synchronization instability will occur in the grid fault condition. Therefore, power self-synchronization control (PSSC) is first introduced for enhancing the small-signal stability of grid-forming control in the case of a short circuit ratio ranging from 1 to infinity. Meanwhile, the transient synchronization instability for the grid-forming converter with PSSC in the grid fault condition is analyzed by the phase portrait, and a transient stability enhancement control (TSEC) scheme is combined with a PSSC-based VSC, which can efficiently eliminate the risk of losing synchronization in the arbitrary SCR. Finally, experimental results are provided to confirm the theoretical analysis. [ABSTRACT FROM AUTHOR]

The novel "How to Do It" narrates the story of female college student Xu Jingjing's repeated setbacks and heartache in order to realize her career dream of taking root in the provincial capital, with the theme of the difficulty of college students' employment. The novel describes the pressure of power and capital on the bottom, and constructs a thick barrier in front of ordinary students from the bottom. How to break through becomes a test and challenge, but also a pain point. Adhering to faith and not violating moral principles means enduring more difficult tests, having more outstanding talents, being able to withstand more complex temptations, and living a dignified and valuable life. The novel repeatedly asks the question of "How to Do It" at the intersection of good and evil, beauty and ugliness, and kindness and cruelty'. On the one side, there are thorns everywhere, It is difficult to move forward, and may even draw blood, but it achieves a stronger self while surmounting difficulties; on the other side, it is a smooth road, but it may be increasingly far away from the true self. The protagonist chooses to fight, grow, inspire and surpass, which is highly enlightening. With a heart towards the sunshine, you can dilute the mist and realize the noble value of life. [ABSTRACT FROM AUTHOR]

To make clear the influence of renewable energy on ultra-low-frequency oscillation (ULFO) in a hydro-dominant system via an high voltage direct current (HVDC) transmission system, this paper studies the damping characteristics when wind power is integrated into the sending power system. The damping torque method is applied for the mechanism study and risk evaluation of ULFO. The study of the inner cause and outer performance proves that ULFO belongs to frequency oscillation rather than conventional power oscillation. According to the theoretical analysis, the suggested control mode is identified to reduce the risk of ULFO. Moreover, a robust controller is designed for wind units based on mixed H2/H∞ robust control theory, and the control method makes use of the fast response ability of the converter without compromising the primary frequency regulation ability. Finally, a simulation model of a hydro-dominant sending power system with wind integration is established in PSCAD Version 4.6 software. The simulations verify the proposed control can suppress ULFO effectively. [ABSTRACT FROM AUTHOR]

Amino‐functionalized magnetic zirconium alginate beads with an interpenetrating network (Fe3O4/PAM/SA–Zr) were prepared, characterized, and then tested as a novel biomass adsorbent for phosphate removal and recovery. The hydrogel beads exhibited outstanding thermostability and possessed a magnetic response. The effects of the pH, dosage, initial phosphate concentration, interference ions, and temperature on the removal of phosphate were investigated. The kinetics, isotherms, and thermodynamics of the adsorption were studied. Notably, the adsorption of phosphate was endothermic, feasible, and spontaneous with a maximum uptake capacity of 42.23 mg‐P/g at an optimized pH of 2.0. The phosphate could be desorbed effectively with a 0.2 mol/L NaOH solution, and the adsorbent exhibited a good reusability. The possible adsorption mechanisms were verified by zeta potential, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy analyses. Continuous phosphate‐adsorption tests were conducted in a fixed‐bed columns packed with Fe3O4/PAM/SA–Zr, and the breakthrough curves were predicted by the Adams–Bohart, Thomas, and Yoon–Nelson models, respectively. The suitability of the hydrogel beads for the treatment of real wastewater was also tested. These hydrogel beads should be a promising adsorbent for phosphate removal and recovery from aqueous solutions, with the advantages of a high uptake capacity, good reusability, and easy magnetic separation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46897. [ABSTRACT FROM AUTHOR]