This paper presents a grid-forming control (GFC) scheme for two-stage photovoltaic (PV) systems that maintains power reserves by operating below the maximum power point (MPP). The PV plant in GFC mode behaves like a voltage source that supports the grid during disturbances in full or limited gridforming mode as per the reserve availability. This is a model-free method that avoids the estimation of MPP power in real-time commonly done in the literature, which makes it simpler and more reliable. The proposed control also features an enhanced current limitation scheme that guarantees containment of the current overshoots during faults, which is not trivial in voltage-sourced GFC inverters. A thorough investigation is done, exploring various generation mixtures of synchronous machines (SM), GFC and grid-following (GFL) inverters, and all common disturbances, e.g., load change, faults and irradiance transients. The results show very favorable dynamic performance by the GFC inverters, far superior to GFL inverters and directly comparable to SMs. It is found that replacing SMs with GFC inverters may improve the frequency profile and terminal voltage during disturbances, despite losing out in the mechanical inertia and the strict inverter overcurrent limits.

This paper presents a grid-forming control (GFC) scheme for two-stage photovoltaic (PV) systems that maintains power reserves by operating below the maximum power point (MPP). The PV plant in GFC mode behaves like a voltage source that supports the grid during disturbances in full or limited gridforming mode as per the reserve availability. This is a model-free method that avoids the estimation of MPP power in real-time commonly done in the literature, which makes it simpler and more reliable. The proposed control also features an enhanced current limitation scheme that guarantees containment of the current overshoots during faults, which is not trivial in voltage-sourced GFC inverters. A thorough investigation is done, exploring various generation mixtures of synchronous machines (SM), GFC and grid-following (GFL) inverters, and all common disturbances, e.g., load change, faults and irradiance transients. The results show very favorable dynamic performance by the GFC inverters, far superior to GFL inverters and directly comparable to SMs. It is found that replacing SMs with GFC inverters may improve the frequency profile and terminal voltage during disturbances, despite losing out in the mechanical inertia and the strict inverter overcurrent limits.

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<p>This paper presents a systematic approach for a detailed positive sequence dq domain modeling and simulation of low inertia power systems for system stability and transients analysis. It aims to reduce the computational complexities while maintaining simulation accuracy comparable to electromagnetic transient (EMT) programs. The proposed approach integrates the detailed models of various components of inverter-based power systems. A computationally efficient voltage source model is proposed for the synchronous machine behind the sub-transient reactance considering stator transients, which makes the direct interface of SM model with the network feasible without affecting the accuracy. A method is presented to obtain explicit dynamic voltages of typical nodes that do not have a shunt capacitance. Furthermore, a method is proposed to simulate three-phase symmetrical faults in dq domain followed by the line tripping with and without current zero interruption. Matlab/Simulink numerical simulations with three bus and WSCC 9-bus test systems under various disturbances validate the  effectiveness and adequacy of the proposed method as compared to the EMT approach. </p>