Deployment of Synchronous Condensers (SynCons) has become one popular solution in accommodating large-scale renewable energy source (RES) for existing power systems. However, as a rotating device, SynCon may lose transient rotor angle stability caused by injected active power from nearby RES after a fault. To reveal this phenomenon, the transient stability of SynCon is investigated in this article. To derive intuitive mechanism and assist quantitative analysis, the equivalent synchronous generators (ESG) model is proposed to characterize the transient behavior of SynCon and co-located RES. The Lyapunov's direct method is employed for the assessment of transient stability by analyzing attraction domain for a typical benchmark system. On this basis, an index of transient stability margin against grid strength and an adaptive low voltage ride through (LVRT) control strategy are proposed for further assessment and enhancement of transient stability. The accuracy and effectiveness of the proposed methods are verified with EMT simulations of a typical windfarm configuration.

Temporary overvoltage (TOV) is becoming one challenge for the integration of significant power electronics resources into a power system. To assess the risk of TOV in a Multi-Infeed Power Electronic System (MIPES), a worst-case estimation approach is proposed to assess TOV risk. The paper starts with analyzing the mechanism of TOV, which reveals that TOV is dominated by excessive reactive power resulting from comprehensive control laggings. Then, the principle of approximating the TOV for a Voltage Source Converter (VSC) connecting to an infinite bus is introduced within the context of the RMS model. After that, a method based on the concept of generalized short-circuit ratio for overvoltage (gSCR-TOV) is introduced to quantify the risk of TOV in a multi-bus system. This concept intends to permit screening to identify those nodes at greatest need for further EMT assessment. To localize these nodes, a concept of weighted sensitivity matrix is further proposed to pinpoint the bus subject to highest TOV in a MIPES. Finally, case studies of EMT time-domain simulations are carried out and verifies the effectiveness of the proposed methods.

Temporary overvoltage (TOV) severely restricts the development and utilization of renewable power resources (RPRs), especially when RPRs are delivered through the line commutated converter-based high voltage direct current (LCC-HVDC) system. To reveal the TOV mechanism for the sending system during commutation failures (CFs), the transient process of the system is partitioned into different stages, where the evolution of the system trajectories is analyzed. On this basis, the variation of AC voltage and DC current considering complex dynamic interactions between LCC-HVDC and renewable energy Plants (REPs) during repetitive CFs (RCFs) is clearly quantified. After revealing the impact of control parameters of both REPs and the LCC-HVDC on the TOV during RCFs, a collaborative optimization method for control parameters is proposed for TOV suppression. Moreover, when the blocking after the RCF tends to be inevitable, the optimal blocking moment is determined to inhibit the TOV caused by HVDC blocking. The accuracy and effectiveness of the proposed methods are verified with EMT simulations of a typical benchmark system.

With the integration of large-scale renewable energy sources into the power grid, the interconnection between Grid-Forming (GFM) Voltage Source Converters (VSCs) and Grid-Following (GFL) VSCs has become a prominent trend in the power system. However, significant differences in the synchronization mechanisms between GFM VSCs and GFL VSCs have led to unclear small-signal synchronization stability characteristics in interconnected systems. To address the gap, this paper employs the concept of a synchronous generator that simultaneously controls the dq internal potential components for a better physical understanding, constructing an equivalent structure capable of unifying GFM-VSC and GFL-VSC. Mathematically, a synchronization stability analysis model for interconnected systems based on current sources is established. Furthermore, a quantitative indicator for the small-signal synchronization stability margin in interconnected systems is introduced based on the generalized Nyquist criterion, and a concise analysis is presented regarding the impact of control parameters on small-signal synchronization stability. In addition, an optimization method for GFM-VSCs parameters and configuration based on participation factor iteration is proposed. Finally, simulation examples are built in MATLAB/Simulink to verify the rationality of the theoretical analysis.

Synchronous condensers (SynCons) are widely used in supporting the integration of renewable power plants (RPPs) in weak grids. However, recent research suggests that a SynCon co-located with RPPs may be prone to transient rotor angle instability due to the excessive active power injected by nearby RPPs during metallic faults. This paper further discovers that the transient stability of the SynCon may be lost even it generates electrical power during high-resistance faults. This novel mechanism of instability is investigated by deriving power-angle characteristics in different fault scenarios, and then the effect of the system parameters on the stability is analyzed via a proposed index based on the critical clearance time (CCT). It reveals that inappropriate parameters of SynCons, weak grid, and voltage support during fault ride-through (FRT) all contribute to such transient instability. To mitigate such instability, an adaptive FRT strategy is proposed. The electromagnetic transient (EMT) simulations based on the PSCAD are carried out to validate the effectiveness of the theoretical analysis and the proposed adaptive control strategy.

The proliferation of renewable power generation units (RGUs) deteriorates the physical inertia of the system, making the evaluation of unit-level frequency support capability (FSC) and system-level frequency stability increasingly important. However, the prior-art approaches lack a standardized framework for FSC assessment, and the non-disclosure of RGU information by manufacturers exacerbates this challenge. To address these issues, this paper proposes a unified transfer function structure (UTFS) model and its parameter solving method based on impedance measurement, enabling a unified assessment of both the unit-level FSC and system-level frequency stability. The unit-level UTFS can be obtained through frequency-domain approaches, e.g., xy-impedance measurements. Moreover, the system-level UTFS can be acquired through the simple aggregation of unit-level UTFS. Without detailed models or post-event data, the proposed framework uniformly represents the FSC of various RGUs through three key indicators: effective inertia, damping, and primary frequency regulation (PFR). Furthermore, the proposed method analytically derives system frequency indicators: frequency nadir, rate of change of frequency (RoCoF), and steady-state frequency deviation. Numerical simulations and analysis of the operational data of a provincial power grid are provided to validate the proposed method.