Synchronous Condensers (SynCons) are widely used in the voltage source converter (VSC) integrated weak grid for voltage support and oscillation suppression. Whereas recent research suggests that the SynCon may accelerate and lose transient rotor angle stability due to the excessive active power injected by nearby VSCs during metallic faults. However, the transient stability of the SynCon cannot be guaranteed even if it decelerates during non-metallic faults. To reveal this phenomenon, the transient stability of SynCon during non-metallic faults is investigated in this paper. After deriving power-angle characteristics in different operating conditions, a novel transient instability mechanism is discovered, and the effect of the system parameters is analyzed based on the Equal Area Criterion (EAC). It reveals that inertia, excitation, VSC size, and voltage support during FRT all contribute to such transient instability. To mitigate unbalanced active power during faults and improve transient stability, an adaptive fault ride-through (FRT) strategy is proposed. The electromagnetic transient (EMT) simulations based on the PSCAD/EMTDC are carried out to validate the effectiveness of the theoretical analysis and the proposed adaptive control strategy.

High penetration of renewable energy resources is widely connected to the grid via grid-following converters, which may threaten the transient voltage stability of the system. However, most researchers only pay attention to the transient voltage stability of inductive motors in the electromechanical transient time scale, and the electromagnetic dynamics of voltage source converters (VSCs) are ignored for simplicity. Therefore, the potential transient voltage instability risk of the system in the electromagnetic transient time scale is concealed. To fill this gap, the transient voltage instability mechanisms for grid-following VSCs with various control strategies are revealed, which can be concluded that the positive-feedback process after the state variable exceeds the unstable equilibrium point is the main cause. Then, the effect of the current limitation of VSCs on the transient voltage stability and transient performance of the system is theoretically illustrated. On this basis, the indexes for transient voltage stability margin considering the active power recovery process are presented, and a robust current limitation based stability enhancement scheme is proposed to stabilize the system. Simulation results verify the correctness of the theoretical analysis and the effectiveness of the proposed control strategies.

Deployment of Synchronous Condensers (SynCons) has become one popular solution in accommodating large-scale renewable energy resource (RER) for existing power systems. In  this paper, rotor angle instability of SynCon is investigated. To  derive intuitive understandings and quantitative analysis, the  swing equations of the equivalent synchronous generators (ESG)  are derived. The Lyapunov’s direct method is employed to analyze  the attraction domain for a typical benchmark system. Based on  that, a rotor angle stability margin index is developed and an  adaptive low voltage ride through (LVRT) control strategy is  proposed for assessment and enhancement of rotor angle stability.  The criterion and effectiveness are verified with on EMT  simulations, respectively.

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 control lagging of converters. 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 methodology 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. The intent of this concept is 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 methodologies.