Grid Support in Large Scale PV Power Plants using Active Power Reserves

摘要

Photovoltaic (PV) systems are in the 3rd place in the renewable energy market, after hydro and wind power. The increased penetration of PV within the electrical power system has led to stability issues of the entire grid in terms of its reliability, availability and security of the supply. As a consequence, Large scale PV Power Plants (LPVPPs) operating in Maximum Power Point (MPP) are not supporting the electrical network, since several grid triggering events or the increased number of downward regulation procedures have forced European Network of Transmission System Operators for Electricity (ENTSO-E) to continuously upgrade their Network Codes (NCs), moving their focus to grid stabilization features.Considering the technical challenges present in the nowadays power systems, the work presented in this thesis focuses on frequency and power ramp control strategies provided by LPVPPs with internal generated Active Power Reserves (APRs).LPVPPs with frequency support functions such as Frequency Sensitive Mode (FSM) and Inertial Response (IR) are studied and analyzed, with the main goal of demonstrating their necessity in a system with increased level of penetration. Short-term and mid-term frequency stability analysis, based on time domain and statistical evaluation studies, demonstrate LPVPPs ability to improve the frequency stability during transients and their participation in the regulation process of overall frequency quality parameters. Furthermore, the analysis proves LPVPPs can become active players in the power system, along with the conventional generation, and can share part of their stabilizing responsibilities.Stringent power ramping obligations imposed by TSOs such as Puerto Rico Electric Power Authority (PREPA) with increased levels of renewables, represents the second topic of this thesis. Power fluctuations created by the variable and intermittent nature of the irradiance, are smoothed out by a proposed power ramp limitation (PRL) control architecture, which considers LPVPP spatial distribution and minimizes the power mismatches by using optimal curtailed APRs. The proposed PRL method targets the limitation of power fluctuation directly at the production site and, consequently, reduces the ramping stress of the participating plants.The aforementioned ancillary services rely on the use of APRs, a crucial element in their security of the supply. The thesis examines the use of internal generated APRs, realized by curtailment, and their deployment during frequency and irradiance transients. The reserves are dynamically yielded in accordance with meteorological conditions present at the production site and in accordance with the requirements imposed by the ENTSO-E.In order to validate the performance of the frequency support functions, a flexible grid model with IEEE 12 bus system characteristics has been developed and implemented in RTDS. A power hardware-in-the-loop (PHIL) system composed by 20 kW plant (2 x 10 kW inverters and PV linear simulator) and grid simulator (RTDS) has been developed and used to validate the frequency support functions.