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With the development of the new power system with a high proportion of new energy and a high proportion of power electronic equipment, various problems caused by high-frequency oscillation will seriously affect the daily normal operation of the power system. For the existing active oscillatory suppression strategies, the impedance characteristics of other frequency bands will be affected, which may cause new oscillation problems in other frequency bands, namely the negative effect of oscillatory suppression strategy. In response to such phenomena, we conducted research on the mechanism of negative effects and optimize the control strategies accordingly. First, an analysis model of the grid-connected inverter was established. The concept of the damping factor was proposed based on the relationship between passive damping and active damping. The feasibility of the oscillation suppression mechanism based on the damping factor was demonstrated, and the negative effect mechanism of the oscillation suppression strategy was clarified. Secondly, a control strategy based on the superposition of active damping was proposed, which not only solved the negative effect of the oscillation suppression strategy but also avoided the shift of the inherent resonance point. Finally, the theory was verified based on the MATLAB R2022a/Simulink simulation platform.

Voltage source converter-based high-voltage direct current (VSC-HVDC) systems integrated into weak AC grids may exhibit oscillation-induced instability, posing significant threats to power system security. With increasing structural complexity and diverse control strategies, the stability characteristics of VSC-HVDC system require further investigation. This paper focuses on the stability of a receiving-end VSC-HVDC system consisting of a DC voltage-controlled VSC parallel-connected to a power-controlled VSC, under various operating conditions. First, small-signal models of each subsystem were developed and a linearized full-system model was constructed based on port relationships. Then, eigenvalue and participation factor analyses were utilized to evaluate the influence of control strategy, asymmetrical grid strength, power flow direction, and tie line on the system’s small-signal stability. A feasible short-circuit ratio (SCR) region was established based on joint power–topology joint, forming a stable operating space for the system. Finally, the correctness of the theoretical analysis was validated via MATLAB/Simulink time-domain simulations. Results indicate that, in comparison to the power control strategy, the DC voltage control strategy was more sensitive to variations in the AC system and demands a strong grid, and this disparity was predominantly caused by the DC voltage control. Furthermore, the feasible region of the short-circuit ratio (SCR) diminished with the increase in the length of the tie-line and alterations in power flow direction under the mutual-support power mode, leading to a gradual reduction in the system’s stability margin.

Affected by the nonlinear time-varying factors due to fault scenarios, protection relaying, and control measures, the dynamic behaviors of a power system may be significantly different from the results of previous methods. In order to analyze the oscillation characteristics of complex power systems more accurately and suppress the low frequency oscillation more effectively, this paper improves the trajectory section eigenvalue method. Firstly, the time response of a system is obtained by numerical simulation in a given fault scenario. Secondly, the algebraic variables are substituted to the differential equations along the trajectory. Thus, the original time-varying differential-algebraic equations are approximated by a set of linear ordinary differential equations, which can be updated along the trajectory. On this basis, this paper proposes a method to extract instantaneous features of the oscillation from the micro perspective. The non-equilibrium points with strong nonlinearity or critical eigenmodes are identified by the proposed method. The simulation test results of the IEEE 3-machine 9-bus system and the New England system illustrate the validity of the proposed method.

Transforming the existing key HVAC transmission lines into High Voltage Direct Current (HVDC) transmission systems is a new type of transmission capacity expansion scheme that has been applied in power systems in Germany, the United Kingdom and other regions. After the occurrence of AC/DC intersystem faults, the fault characteristics are complex, and the protection adaptability will be affected. At present, there is no specific protection scheme for AC/DC intersystem faults. In this paper, a protection scheme based on the same side current similarity characteristics of AC and DC transmission lines is proposed, and the Hausdorff distance algorithm is introduced to measure two sets of current waveforms under different fault scenarios. The proposed protection scheme can complete the fault identification within a few milliseconds after the fault and has good rapidity and application prospects, and the effective value of the scheme is verified on the simulation platform.

As flexible and controllable resources, PV and wind power can provide effective cooperative voltage support in renewable-rich distribution networks. This paper proposes a multi-resource cooperative voltage support strategy based on an improved particle swarm optimization (PSO) algorithm to coordinate heterogeneous controllable resources for optimal reactive power allocation and enhanced voltage stability. The proposed PSO integrates a sensitivity-matrix-guided initialization to improve feasibility and accelerate early-stage convergence, together with an adaptive parameter adjustment mechanism to enhance search efficiency and robustness. The method is validated on an IEEE 69-bus distribution network implemented in MATPOWER. Simulation results show that the proposed strategy increases the voltage qualification rate from 86.96% to 100% and reduces the average voltage deviation by 61.3%.

The AC/DC transmission system is an important component of the power system, and the cross-circuitry Fault diagnosis of the AC/DC transmission system plays an important role in ensuring the normal operation of power equipment and personal safety. The traditional AC/DC transmission detection methods have the characteristics of complex detection processes and low fault line identification rates. Aiming at such problems, this paper proposes a new method of cross-circuitry Fault diagnosis based on the AC/DC transmission system based on a blind signal separation algorithm. Firstly, the method takes the typical cross-circuitry Fault scenario as an example to construct the topology diagram of the AC/DC power transmission system. Then, the electrical signals of the AC system and the DC system of the AC/DC power transmission system are collected, and the collected signals are extracted by the blind signal separation algorithm. Then, aiming at the cross-circuitry Fault problem of the DC system, the electrical quantities of the positive and negative poles on the rectifier side and the inverter side are collected, and the characteristics of the electrical quantities are analyzed by wavelet to determine the fault. At the same time, aiming at the problem of the cross-circuitry Fault of the AC system, three fault types of cross-circuitry Fault, ground fault, and intact fault are set up, and the electrical quantities of A, B, and C are collected on the same side, and the characteristics of three-phase electrical quantities are analyzed by wavelet. Finally, the cross-circuitry Fault judgment interval of the AC/DC system is set as the basis of fault judgment. After experimental verification, the relative error of the model is 1.4683%. The crossline fault identification method of the AC/DC transmission system based on the blind source separation algorithm proposed in this paper can accurately identify the crossline fault location and identify the fault type. It also provides theoretical and experimental support for power system maintenance personnel to maintain equipment.

Due to the negative resistance effect of power electronic devices, power systems with a high proportion of renewable energy face a significant resonance risk. To address this, this paper proposes a resonance-suppression strategy for high-penetration renewable energy systems based on an active amplitude and phase corrector (APC). Firstly, by considering its internal dynamics and complete control loops, the impedance model of the APC is derived. Next, the similarities and differences between resonance stability and harmonic resonance are analyzed using the s-domain and frequency-domain admittance matrices, concluding that resonance suppression for low-damping s-domain modes can be handled in the frequency domain. Then, a supplementary APC control strategy in the abc-frame is proposed, which improves impedance magnitude at specific frequencies while keeping the phase almost unchanged. Finally, the proposed strategy is validated through case studies on an offshore wind power system in Zhejiang Province.

The DC-side response characteristics of the VSC-HVDC transmission system under AC-side sub-synchronous disturbances may lead to the propagation of AC/DC oscillations, and then there may be non-fundamental frequency oscillation on the DC-side. To clarify the interactive influence mechanism and propagation evolution law of the AC and DC side sub-synchronous oscillations in the VSC-HVDC transmission system, the frequency characteristics of the DC-side oscillation power are investigated by considering the effect of converter control links. First, the AC-side voltage and current frequency responses under single/multiple SSO components are analyzed. Secondly, the frequency characteristics of the DC-side power after the injection of single/multiple SSO components are investigated. Meanwhile, the effect of system control parameters on the sub-synchronous responses of the DC-side power is investigated. Finally, the theoretical analysis is verified with PSCAD/EMTDC simulations. The results show that under the influence of the AC-side SSO components, the DC-side of VSC-HVDC faces the risk of multi-frequency oscillations; when there are multiple SSO components on the AC-side, there is a coupling between the components, and the system control parameters affect the amplitude of the DC-side oscillation power.

It has been well known that inverter-based resources (IBRs) can lead to converter-driven stability issues under weak grid connections. However, as the number of IBRs increases, instabilities can also occur even under strong grid connections. A practical case is presented to demonstrate this conclusion, using large-scale energy storage systems (ESSs) as an example. In this study, the ESSs induce oscillations with a frequency of 150 Hz in the d-q coordinates while providing both capacitive and inductive reactive power support (achieved by ESS functional control loops) to the connected power system. Theoretical analysis reveals that under strong grid connections, the dynamic interactions among power conversion systems (PCSs) of ESSs can be superimposed and intensified as the ESS scale extends, which reduces oscillation damping and leads to system instability. This indicates that ESS functional control loops also have potential instability risks when providing supports to power systems, which should be carefully examined. Finally, major impact factors are identified to mitigate the oscillations, and the conclusions are validated based on the SIMULINK platform. This paper provides valuable practical insights into system instabilities even under strong grid conditions, emphasizing the importance of functional control design and careful planning of the scale for IBR-dominated systems.

•Explored the differences in behavioral performance and neural mechanisms between collaborative cooperation and division of labor cooperation.•Division of labor cooperation contributes to improved cooperative behavior, while collaborative cooperation enhances IBS.•Whether in division of labor or collaborative cooperation, working with friends better IBS compared to strangers.•In division of labor cooperation, there is a significant negative correlation between perspective taking scores and IBS. Collaborative cooperation (CC) and division of labor cooperation (DLC) are two prevalent forms of cooperative problem-solving approaches in daily life. Despite extensive research on the neural mechanisms underlying cooperative problem-solving approaches, a notable gap exists between the neural processes that support CC and DLC. The present study utilized a functional near-infrared spectroscopy (fNIRS) hyperscanning technique along with a classic cooperative tangram puzzle task to investigate the neural mechanisms engaged by both friends and stranger dyads during CC versus DLC. The key findings of this study were as follows: (1) Dyads exhibited superior behavioral performance in the DLC task than in the CC task. The CC task bolstered intra-brain functional connectivity and inter-brain synchrony (IBS) in regions linked to the mirror neuron system (MNS), spatial perception (SP) and cognitive control. (2) Friend dyads showed stronger IBS in brain regions associated with the MNS than stranger dyads. (3) Perspective-taking predicted not only dyads’ behavioral performance in the CC task but also their IBS in brain regions associated with SP during the DLC task. Taken together, these findings elucidate the divergent behavioral performance and neural connection patterns between the two cooperative problem-solving approaches. This study provides novel insights into the various neurocognitive processes underlying flexible coordination strategies in real-world cooperative contexts.