Search

Energy storage system based on grid-forming converter (GFMC) is regarded as the key equipment in photovoltaic (PV) system for energy consumption and inertia improvement. However, the design of GFMC aiming at stability improvement of PV & energy storage system (PVESS) is still open to public. Hence, this study takes the PVESS composed of photovoltaic grid-following converter (GFLC) and energy-storage GFMC as the research object, explores the impact of GFMC on the PVESS stability under different operating conditions, and proposes a stability-oriented parameter design method for GFMC. Firstly, the impact of operating conditions on the output impedance of GFLC and GFMC in PVESS is analyzed. Secondly, by treating the GFMC and the grid as an equivalent grid (i.e., an equivalent subsystem) and taking into account the operating status of PVESS, the system stability under different operating conditions is discussed in detail. Results show that the PVESS stability is the worst when the PV output is maximum, and, because the output impedance of GFMC in low-to-mid frequency range is dominated by its filter inductor, the strength of the equivalent grid is seriously affected by the GFMC filter inductor. Hence, as the key factor affecting the PVESS stability, the GFMC filter inductor deserves a careful selection. Subsequently, a comprehensive design for GFMC filter and control parameters is proposed, which can effectively improve the PVESS stability under the weak grid. Hardware-in-the-loop (HIL) experiments are conducted to verify the effectiveness of the proposed method.

VSG is a pivotal control strategy for GFM, designed to enhance the damping and inertia of power systems, thereby bolstering their stability. Despite its benefits, VSG can induce a QEO due to dynamic interactions between the GFM and the power system. This QEO, is different from control issues, contrasts with the EO associated with conventional SG, which is rooted in electromechanical factors. To address this phenomenon, the influence mechanism of VSG on QEO of the system is studied. First, a comprehensive control model for the VSG is established and its efficacy in providing damping and inertia is assessed. Subsequently, a small-signal model for the VSG when connected to the grid is developed. Utilizing this model, the system’s characteristic roots and the trajectories of principal state variables, elucidating the impact of VSG control parameters on QEO are analyzed. The validity of the models and the underlying mechanisms are confirmed through extensive simulations. Furthermore, for the key problems that need to be solved urgently in the application of VSG in power system with renewable energy, further thinkings are prospected.

Power systems around the globe are undergoing a transformation characterized by a massive deployment of converter-interfaced generation (CIG) to effectively combat climate change. However, achieving a seamless transition from current power systems dominated by synchronous generators (SGs) to future ones with high levels of CIG requires overcoming several technical challenges. From a frequency stability perspective, reduced system inertia increases the frequency nadir after a loss of generation thereby endangering frequency stability. In this context, this paper proposes a novel methodology for determining control requirements to impose on CIG as their penetration in the network increases. Results of a case study based on the Chilean grid projected for the year 2046 show that, if only grid-following converters without frequency control capability are deployed, a maximum CIG penetration level of 75% can be achieved without threatening frequency stability. The Chilean system can reach a 99% CIG penetration, provided that the remaining CIGs are deployed in grid-following with frequency support capability. Finally, we show that if the last SG is replaced with a grid-forming converter, the system can still sustain frequency stability and exhibits a good dynamic performance. These results demonstrate that, at least from a frequency stability viewpoint, achieving a 100% based CIG system is technically possible. The proposed methodology can be used by energy regulators to define the control requirements necessary to impose on CIG for achieving renewable energy targets in a secure way. Although the obtained results are particular for the Chilean system, the proposed methodology can be applied to any power system.

This paper deals with the development of a control technique for the control of voltage source converters (VSCs) as an interface between renewable energy sources (RESs) and power grids. The lack of inertia in converter-based generators and their unconventional dynamic behavior increase the negative impacts on the power grid, unlike the operation of the conventional synchronous generators (SGs). In this sense, the proposed control technique emulates the behavior of SGs in the control loop of the interfaced converter acting as a grid-forming power generator. Thus, supportive functionalities for enhancing electric grid stability (e.g., frequency oscillation damping) will be provided by interfaced converter as a virtual synchronous generator (VSG). The main targets of the proposed control technique include virtual inertia emulation, frequency oscillation damping, primary and secondary frequency regulation, and voltage regulation. The main contribution of this work over the existing methods is that the optimal values for swing equation parameters are employed to ensure well-designed damping feature of the VSG-based converter which adapts grid-connected and islanded operating modes, enabling a smooth resynchronizing to the grid as its plug-and-play capability requirement. The control structure is evaluated through simulation in MATLAB/Simulink.