Grid-Forming Control for Solar PV Systems With Power Reserves

Abstract

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.

Modeling and Simulation of Transients in Low Inertia Power Systems

“…The voltage and current feed-forward terms improve the overall transient response [7], [13]. Two-stage inner loop control structure facilitates current limiting within capacity of the inverter, that is not possible with just grid forming strategy [22].…”

“…3) Current Limitation: The current reference saturation based current limitation scheme proposed in [22] is adopted in this paper (see Fig. 3(d)) to avoid damage to the switches during faults.…”

“…The v-q droop grid support functionality automatically injects high amount of reactive current as the terminal voltage drops. The current limiting mechanism [22] used for GFM inverter as explained in subsection D, is implemented for GFL inverter as well.…”

RPC-based frequency control strategy of LCC-HVDC sending end power system with renewable energy

“…10.3389/fenrg. 2022.1037825 In order to analyze and solve the frequency stability problems brought by high proportion of renewable energy, Xiong et al (2022) compared and analyzed typical frequency control strategies for renewable energy systems; Xiong et al (2020) modeled and analyzed the stability of highproportion renewable energy systems connected by voltage source converters (VSCs) and summarized the key techniques; Pawar et al (2021) proposed a grid-connected control scheme for two-stage photovoltaic systems, which can effectively improve frequency stability; Morren et al (2006) used the power reserve of the wind turbine to provide virtual inertia to support the primary frequency regulation of the grid. However, most of the above methods require the renewable energy generation side to reserve power, which leads to its inability to operate at the maximum power point, affecting the economical operation of the system and increasing the generation cost of the renewable energy system.…”

Dual-port grid-forming control of MMCs and its applications to grids of grids

“…Replacing synchronous generators with converter-interfaced resources results in significantly different power system dynamics and challenges standard operating paradigms. In particular, while power converters have limited inertia and reduced overload capability, they are fully controllable and enable a fast and flexible response as long as their limitations are considered [1]- [3].…”