Explore the vast range of titles available.

This paper explores how different control strategies—grid-forming and grid-following—impact the transient stability of modular multilevel converters (MMCs) interfacing with AC power grids. By employing electromagnetic transient simulation tools (PSCAD/EMTDC) on an adapted IEEE three-machine, nine-bus system, various scenarios are analyzed, including faults of differing types and locations. In the simulation, traditional synchronous generators (SGs) are replaced by MMCs configured under distinct control modes. Results indicate that grid-forming (GFM) control enhances the receiving-end grid’s transient stability by providing superior phase support and extended fault-clearing times compared to grid-following (GFL) control, with hybrid approaches yielding intermediate performance. These findings underline the importance of converter control selection in achieving robust dynamic operation in modern power systems with a high penetration of renewable energy.

In practical engineering, it has been observed that increasing local generators’ capacity in receiving-end power grids can lead the system to transition from voltage instability to power angle instability after a fault. This contradicts the typical engineering experience, where increasing the generators’ capacity at the receiving end is expected to enhance voltage stability, making it challenging to define an appropriate pre-control range for generators. This paper aims to quantify the impact of local generators on the stability of AC/DC receiving-end power grids. First, the paper describes the instability phenomena observed under different generators’ capacity conditions in actual AC/DC receiving-end power grids. Next, by using a simplified single-machine-load-infinite-bus model, the paper explores how the system’s instability characteristics evolve from being dominated by load instability to being driven by generator instability as the ratio of local generators to load varies. This study conducts an in-depth analysis of the coupling mechanism between power angle stability and voltage stability. For the first time, it quantitatively characterizes the stable operating region of the system using power angle and induction motor slip as dual constraint conditions, providing a new theoretical framework for power system stability analysis. Additionally, addressing the lack of quantitative research on the upper limit of generator operation in current systems, this study constructs post-fault power recovery curves for loads and DC power sources. Based on the equal-area criterion, it proposes a quantitative index for the upper limit of local generator operation, filling a research gap in this field and providing a crucial theoretical basis and reference for practical power system operation and dispatch.

The advent of large-scale renewable energy and High voltage direct current (HVDC) transmission has resulted in stability problems in frequency and voltage. Grid-forming (GFM) strategies are characterized by excellent voltage and frequency support properties. Nevertheless, it is not feasible to precisely delineate the precise mathematical relations between GFM converter capacity and the associated stability margin. This paper addresses the optimal configuration of GFM converters in a large receiving-end power grid scenario with a significant proportion of renewable energy and HVDC feed-in. It presents a GFM converter evaluation method constrained by static voltage and frequency security. Firstly, the GFM converter technology based on virtual synchronous machine control is introduced, with a detailed explanation of its control frame. Secondly, the principles of how GFM control improves the static stability limit and frequency dynamic response characteristics are analyzed in depth, and a comprehensive assessment of GFM converter requirements is conducted by combining static stability margin constraints and frequency security constraints. Finally, the effectiveness of the proposed method is verified through a modified IEEE 39-bus model based on the Matlab/Simulink platform.

The incorporation of renewable energy on a broad scale into power grids increases the complexity to the issue of transient voltage stability in power systems. This research presents a rapid evaluation technique for assessing the stability of voltage fluctuations in power grids that receive electricity from photovoltaic sources. At first, a receiving‐end system model was developed, which includes photovoltaics, and an alternative circuit of the virtual induction motor (IM) is obtained by utilizing the Thevenin equivalent. Second, the torque balance equation and the Kirchhoff voltage equation are interconnected to determine the unstable slip of the IM following a malfunction. Finally, by merging the unstable slip with the conventional transient stability discriminant index, the effects of different photovoltaic outputs, IM ratios, and system contact impedances on transient voltage stability are investigated. The proposed method avoids the computational burden of solving the differential‐algebraic equations describing the complex transient processes of the IM. It also obviates the necessity of iteratively modifying the receiving load or fault clearance time in the simulation platform to achieve the constrained stability condition of the system’s transient voltage. The transient stabilization of voltage results is efficiently obtained by directly solving algebraic equations.

High-voltage direct current (HVDC) blocking disturbance leads to large power losses in the receiving-end power grid, and the event-driven emergency frequency control (EFC) is an important measure to prevent large frequency deviation. By aggregating controllable distributed energy resources (DERs) on the demand side, a virtual power plant (VPP) could quickly reduce its power and can be a new fast response resource for EFC. Considering both the VPP and the traditional control resources, this paper proposes an optimized EFC strategy coordinating multiple resources for the receiving-end power grid with multi-infeed HVDC. The approximate aggregation model of the VPP response process is constructed, based on which the EFC strategy, aiming at minimizing the total control cost while meeting constraints on rotor angle stability and frequency deviation security, is proposed. The electromechanical transient simulation combined with particle swarm optimization (PSO) is utilized to solve the model, and parallel computation is utilized to accelerate the solving process. The effectiveness of the proposed EFC strategy is verified by a provincial receiving-end power grid with multi-infeed HVDC. The detailed simulation results show that VPP could dramatically reduce the control cost of EFC while maintaining the same stability margin.

For a receiving-end power grid with multi-infeed LCC-HVDC systems, simultaneous commutation failures may seriously threaten the safe and stable operation of the system. To evaluate the impact of commutation failure and improve the voltage stability of the commutation buses in multi-infeed HVDC systems, this paper proposes a method for evaluating the voltage stability of commutation buses and a reactive power coordination control (RPCC) method for commutation failure of multiple HVDC systems. Firstly, three indicators and the entropy weight method are adopted to comprehensively evaluate the voltage stability of commutation buses. Then, an RPCC method is proposed to resist commutation failure. The proposed RPCC method uses the voltage interaction factor (VIF) to screen out DC systems that are strongly related to dynamic reactive power compensation devices and activates the devices to provide RPCC to the DC systems through an auxiliary controller. Finally, the effectiveness of the proposed method is verified through a practical example of the Jiangsu power grid.