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 grid-forming 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.

中文翻译：

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具有备用电源的太阳能光伏系统的并网控制

本文提出了一种用于两级光伏 (PV) 系统的并网控制 (GFC) 方案，该系统通过在最大功率点 (MPP) 以下运行来保持功率储备。GFC 模式下的光伏电站就像一个电压源，根据备用可用性，在完全或有限电网形成模式的干扰期间支持电网。这是一种无模型方法，避免了文献中通常进行的实时 MPP 功率估计，这使其更简单、更可靠。所提出的控制还具有增强的电流限制方案，可确保在故障期间抑制电流过冲，这在电压源 GFC 逆变器中并非微不足道。进行了彻底的调查，探索了同步电机 (SM)、GFC 和并网 (GFL) 逆变器的各种发电组合，以及所有常见的干扰，例如负载变化、故障和辐照瞬变。结果表明 GFC 逆变器的动态性能非常好，远远优于 GFL 逆变器，可直接与 SM 相媲美。发现用 GFC 逆变器替换 SM 可以改善干扰期间的频率分布和端电压，尽管会失去机械惯性和严格的逆变器过流限制。