Search

In response to the issue that traditional energy storage VSGs （virtual synchronous generators） cannot simultaneously possess good disturbance resistance and rapid dynamic response capabilities， a control strategy for energy storage VSGs is proposed， optimizing the dynamic synchronizer using RBF （radial basis function） neural networks. First， a mathematical model for VSG is established， analyzing the impact of rotor inertia and damping coefficient configuration on VSG performance. This analysis reveals the conflicting relationship between parameter configuration and dynamic response versus system dynamic stability. Subsequently， the transient unbalanced power of the rotor is taken as input for a three-layer forward structure RBF neural network algorithm. Through online learning with the RBF neural network algorithm， the optimal transient compensation power is obtained to dynamically adjust the input power of VSG， thereby reducing unbalanced rotor torque and enhancing the transient stability of VSG. Finally， simulation and comparative experiments are conducted to validate the effectiveness of the proposed control strategy.

Abstract The energy exchange between series and shunt converters is the basis for the powerful functioning of the unified distributed power flow controller, which can be realized through the 3rd harmonic current. In this paper, based on the established 3rd harmonic equivalent network of unified distributed power flow controller power system, the influence of the additional loss caused by the 3rd harmonic current on the line transmission capacity is analysed. The mathematical relationship between the neutral point voltage of the transformer and the 3rd harmonic current is constructed, and it is simplified according to the different 3rd harmonic currents. By analysing the power relationship of the 3rd harmonic equivalent network, it is found that there is a contradiction between improving the 3rd harmonic output efficiency of the shunt single‐phase converter and reducing the neutral point insulation voltage of the transformer. The constraint conditions of the 3rd harmonic current are simulated by the advanced digital power system simulator. Finally, the method of obtaining the economical and safe 3rd harmonic current value range is summarized, which provides a theoretical basis and reference for the device parameter design.

Redox flow batteries (RFBs) are one of the most promising techniques to store and convert green and renewable energy, benefiting from their advantages of high safety, flexible design and long lifespan. Membranes with fast and selective ions transport are required for the advances of RFBs. Remarkably, two‐dimensional (2D) materials with high mechanical and chemical stability, strict size exclusion and abundantly modifiable functional groups, have attracted extensive attentions in the applications of energy fields. Herein, the improvements and perspectives of 2D materials working for ionic transportation and sieving in RFBs membranes are presented. The characteristics of various materials and their advantages and disadvantages in the applications of RFBs membranes particularly are focused. This review is expected to provide a guidance for the design of membranes based on 2D materials for RFBs. [ABSTRACT FROM AUTHOR]

The regenerated LiNi0.6Co0.1Mn0.3O2 (NCM613) cathode material was synthesized from electrode scraps through separation, impurity removal, and relithiation. ICP, XRD, SEM, and electrochemical performance were used to study the composition, crystal phase structure, and surface morphology of commercial, cycled, and regenerated NCM613. After separation and impurity removal, the regenerated NCM613 was obtained by using lithium supplement and calcined at 950 °C for 11 h. At 0.1 C, the discharge capacity reaches 201.7mAh/g. After 200 cycles, the capacity is still maintained 175.6mAh/g at 1C, capacity retention is 95.1%. The results show that the regenerated NCM613 has high capacity and excellent cycle stability. This method provides a method for the recovery of spent lithium ion batteries. [ABSTRACT FROM AUTHOR]

LiNi0.5Co0.2Mn0.3O2 (NCM523) has become one of the most popular cathode materials for current lithium-ion batteries due to its high-energy density and cost performance. However, the rapid capacity fading of NCM severely hinders its development and applications. Here, the single crystal NCM523 materials under different degradation states are characterized using scanning transmission electron microscopy (STEM). Then we developed a neural network model with a two-sequential attention block to recognize the crystal structure and locate defects in STEM images. The number of point defects in NCM523 is observed to experience a trend of increasing first and then decreasing in the degradation process. The space between the transition metal columns shrinks obviously, inducing dramatic capacity decay. This analysis sheds light on the defect evolution and chemical transformation correlated with layered material degradation. It also provides interesting hints for researchers to regenerate the electrochemical capacity and design better battery materials with longer life. [ABSTRACT FROM AUTHOR]

Commutation failures (CFs) in inverter stations disturb the power system greatly. Open-conductor fault (OCF) is a longitudinal fault. When it occurs in the alternating current (AC) system, the three-phase voltages are unbalanced. Under this circumstance, it is generally considered that inverters can maintain normal commutation order for the voltage support provided by other transmission lines in normal operation. In this paper, the possibility of the inverter CF during OCF is established. The sensitivities of the CF to the AC voltage disturbances caused by the changes of the AC superposition voltage are analyzed. It is concluded that the sensitivities of the CF with different transformer wiring schemes and fault types are diverse. Before the CF happens in the inverter station during OCF, the CF may occur in other inverter stations of the multi-terminal direct current systems with the constant current and constant extinction angle control strategies. Simulation studies are performed in the PSCAD/EMTDC software (Copyright(C)2006, Manitoba HVDC Research Centre, Canada), and the theoretical analysis is validated by the simulation results. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a new concept for the grid integration of large-scale offshore wind farms. In the offshore wind farm, the wind turbines are integrated into the offshore DC collector grid by a cascaded converter. The high-voltage level for the high-voltage direct current (HVDC) transmission purpose is built by series connections of low voltage modules, without the use of an offshore step-up substation. The output power of each module is controlled by the switching of the related half-bridge, and a modified straightforward voltage balancing strategy is proposed to balance the storage capacitor voltages in the turbines. Supplementary balancing strategies are also presented to assist in balancing the capacitor voltages, when the differences in the wind velocities flowing to the turbines become larger. Because of the stable capacitor voltages, self-commutated voltage source converter (VSC) is adopted as the onshore inverter station connecting the HVDC link and the onshore AC grid. The VSC station not only regulates the DC-bus voltage of the HVDC link, but also provides reactive power compensation to the onshore grid. The time-domain simulation results show that the proposed offshore wind-power collection and transmission system provides a new option for integrating large-scale offshore wind farms. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]