Abstract
Owing to rapid increase in PV penetration without inherent inertia, there has been an unremitting deterioration of the effective inertia of the existing power systems. This may pose a serious threat to the stability of power systems during disturbances if not taken care of. Hence, the problem of how to emulate Synthetic Inertia (SI) in PV Systems (PVS) to retain their frequency stability demands attention. Super Capacitor (SC)-based storage become an attractive option over the other energy storage types because of its high-power density, burst power handling capability, faster response and longer life cycle. Considering this, the authors here propose a novel PV-SC Cascaded Topology (PSCT) as a cost-effective approach to emulate SI by integrating a low voltage SC to a high voltage grid-connected PVS. The proposed PSCT helps in operating the SC as a voltage source rather than a current source. Thus, it eliminates the high gain requirements of the SC interfacing converters. The aim is to target two main frequency response services, i.e., Primary Frequency Response (PFR) and Synthetic Inertial Response (SIR), using a novel common control scheme, but without affecting any other energy intensive services. The authors introduced a Droop-Inspired (DI) method with an adjustable inertia constant to emulate dynamic inertia so that a wider range of Rate of Change of Frequency (RoCoF) values can be serviced with a limited storage. A very streamlined analysis was also carried out for sizing of the SC stage based on a simple Three-Point Linearization (TPL) technique and DI technique with a limited knowledge of the disturbance parameters. The whole system was initially validated in a MATLAB Simulink environment and later confirmed with the OPAL-RT Real-Time Simulator. The investigated response was subject to variation in terms of control parameters, changes in solar irradiance, grid frequency variation, etc.
Highlights
In light of increased PV penetration [1,2,3], it is necessary to analyze the requirements and challenges that existing power systems will face in near future
The authors proposed a linear approximation method denoted as the Three-Point Linearization (TPL) method, which does not demand the knowledge of actual complex Primary Frequency Response (PFR) characteristics, but rather, a set of a few parameters, i.e., the fault (T f), f nadir, Fnom and Fo f f, while estimating the size of the storage
If integrated to a PV system of 10 kWp, this method will be capable of emulating the dynamic synthetic inertia in the range of 2 to 9 s based on the Rate of Change of Frequency (RoCoF), which was much better and flexible than the synchronous generators in scale
Summary
In light of increased PV penetration [1,2,3], it is necessary to analyze the requirements and challenges that existing power systems will face in near future. The concept of virtual energy storage approaches has drawn the attention of the research community as an effective solution towards the low lifespan of the BESS involving the mimicking of virtual inertia in PVS to improve the frequency nadir One such approach is the PV reserve method, known as PV delta power control [17] or PV deloaded control [18,19,20,21,22]. In [25], the authors implemented a complex self-adoptive fuzzy logic method to emulate virtual inertia to improve the frequency stability In both studies, the proposed controls were the main concern, but the targeted energy storage types were undisclosed. It is highly uncertain how PV will support the required power to emulate the frequency response during low-insolation and night-time periods Another virtual energy storage-based approach gained popularity in terms of addressing the issues with the PV reserve-type approach.
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