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Grid forming control applied to power converters termed as grid forming converters (GFC) interfacing storage and renewable generation has been identified as a potential solution to facilitate a more significant penetration of converter-based renewable generation in the power system. The emulated electromechanical model in the GFC is also the synchronization unit which typically utilizes measured output active power from the GFC as the feedback variable. However, this feature has opened up a concern on the transient stability due to loss of synchronism under significant transient events in the power systems, which include frequency change, phase jump, and voltage dips. This paper presents a quantitative and illustrative analysis of the impact of the current limit in GFC on the transient stability of a system comprising of GFC. Furthermore, a solution based on virtual active power is proposed to improve the transient stability margin of the GFC when the GFC enters the current limit. Finally, the analysis and the proposed method to enhance the transient stability are verified by Power hardware in the loop (PHIL) experimental tests.

Traditional VSC control is of the “Grid Following Type” (GFL), where the turn-on pulses to the converter switches are determined based on fast synchronization with the external grid voltage phasor. GFL VSC has difficulty operating in very weak ac networks. In contrast, GFM-controlled VSC maintains an internal voltage phasor and has the potential to maintain system stability under such challenging network conditions. One important aspect of VSM type control of a VSC is that it imparts artificial inertia and damping behaviour to the VSC, which can have a significant impact on the VSMs ability to survive frequency events triggered by transient mismatch between generation and loads. This research investigates the disturbance ride through, stability and inertia support of using Virtual Synchronous machine (VSM) Grid-Forming (GFM) control on Voltage-Sourced Converters (VSC) High Voltage direct current (HVdc) transmission system. An adaptive fault ride-through control mode is proposed for VSM to improve its post-fault recovery transient and voltage phase angle jump ride-through performance. The EMT simulation shows the disturbance ride-through performance of VSM GFM with cascaded or switchable current control can be optimized by transiently changing the active power order and the damping coefficient in its power synchronization loop. Linearized models of the VSM with inertia and damping parameters are developed and validated using detailed EMT simulation for system small-signal stability analysis and controller parameter design under different system strengths. A current limiting feature is a necessity in any VSC due to the limited overcurrent ratings of the VSC’s power electronic switches. However, eigenvalue analysis reveals that the VSM can experience instability when connected to strong ac networks with the inclusion of the in-line cascaded current limiting. However, with proper controller tuning, a single suitable gain parameter set can nevertheless be found to allow

Traditional VSC control is of the “Grid Following Type” (GFL), where the turn-on pulses to the converter switches are determined based on fast synchronization with the external grid voltage phasor. GFL VSC has difficulty operating in very weak ac networks. In contrast, GFM-controlled VSC maintains an internal voltage phasor and has the potential to maintain system stability under such challenging network conditions. One important aspect of VSM type control of a VSC is that it imparts artificial inertia and damping behaviour to the VSC, which can have a significant impact on the VSMs ability to survive frequency events triggered by transient mismatch between generation and loads. This research investigates the disturbance ride through, stability and inertia support of using Virtual Synchronous machine (VSM) Grid-Forming (GFM) control on Voltage-Sourced Converters (VSC) High Voltage direct current (HVdc) transmission system. An adaptive fault ride-through control mode is proposed for VSM to improve its post-fault recovery transient and voltage phase angle jump ride-through performance. The EMT simulation shows the disturbance ride-through performance of VSM GFM with cascaded or switchable current control can be optimized by transiently changing the active power order and the damping coefficient in its power synchronization loop. Linearized models of the VSM with inertia and damping parameters are developed and validated using detailed EMT simulation for system small-signal stability analysis and controller parameter design under different system strengths. A current limiting feature is a necessity in any VSC due to the limited overcurrent ratings of the VSC’s power electronic switches. However, eigenvalue analysis reveals that the VSM can experience instability when connected to strong ac networks with the inclusion of the in-line cascaded current limiting. However, with proper controller tuning, a single suitable gain parameter set can nevertheless be found to allow

The grid integration of renewable energy sources interfaced through power electronic converters is undergoing a significant acceleration to meet environmental and political targets. The rapid deployment of converters brings new challenges in ensuring robustness, transient stability, among others. In order to enhance transient stability, transmission system operators established network grid code requirements for converter-based generators to support the primary control task during faults. A critical factor in terms of implementing grid codes is the control strategy of the grid-side converters. Grid-forming converters are a promising solution which could perform properly in a weak-grid condition as well as in an islanded operation. In order to ensure grid code compliance, a wide range of transient stability studies is required. Time-domain simulations are common practice for that purpose. However, performing traditional monolithic time domain simulations (single solver, single domain) on a converter-dominated power system is a very complex and computationally intensive task. In this paper, a co-simulation approach using the MOSAIK framework is applied on a power system with grid-forming converters. A validation workflow is proposed to verify the co-simulation framework. The results of comprehensive simulation studies show a proof of concept for the applicability of this co-simulation approach to evaluate the transient stability of a dominant grid-forming converter-based power system., Intelligent Electrical Power Grids

The grid integration of renewable energy sources interfaced through power electronic converters is undergoing a significant acceleration to meet environmental and political targets. The rapid deployment of converters brings new challenges in ensuring robustness, transient stability, among others. In order to enhance transient stability, transmission system operators established network grid code requirements for converter-based generators to support the primary control task during faults. A critical factor in terms of implementing grid codes is the control strategy of the grid-side converters. Grid-forming converters are a promising solution which could perform properly in a weak-grid condition as well as in an islanded operation. In order to ensure grid code compliance, a wide range of transient stability studies is required. Time-domain simulations are common practice for that purpose. However, performing traditional monolithic time domain simulations (single solver, single domain) on a converter-dominated power system is a very complex and computationally intensive task. In this paper, a co-simulation approach using the MOSAIK framework is applied on a power system with grid-forming converters. A validation workflow is proposed to verify the co-simulation framework. The results of comprehensive simulation studies show a proof of concept for the applicability of this co-simulation approach to evaluate the transient stability of a dominant grid-forming converter-based power system., Intelligent Electrical Power Grids