Resumen de Large scale photovoltaic power plants: configuration, integration and control
This thesis focuses on the operation and control of Large Scale Photovoltaic Power Plants (LS-PVPPs) according to grid code requirements with a special focus on the basic unit: the PV generator. The aim of this thesis is to study to what extent a PV generator can be controlled to comply with the plant operators requirements considering the capability curves under variable solar irradiance and temperature. In this sense, four challenges were identified: system integration, technical limitations and capability curves, dynamic modelling, and control. These challenges are addressed by a comprehensive literature review, mathematical analysis, and a series of detailed simulations. A thorough literature review of the current technology and topologies used in LS-PVPPs is performed, concluding that the central topology and radial configuration are the layouts most widely used. Additionally, grid codes presented by Germany, Puerto Rico, South Africa, Romania, and China are deeply analysed. A comparison of these grid codes is developed considering: fault ride through capability, frequency and voltage stability supprt as well as active and reactive power management. In addition a broad discussion about the challenges that the LS-PVPPs have to overcome is pesented together with the compliant technology and future trend.According to this review, one of the challenges to overcome is the understanding of the PV generator’s operation in LS- PVPPs. Thus, an analysis of its technical limitations and capability curves is essential in order to improve its control. In this thesis, a mathematical analysis to extract the PV generator’s capability curves is developed. These curves are characterized by four main parameters: solar irradiance, ambient temperature, dc voltage and modulation index. These values are dependent on each other in order to obtain the complete curve. In the case where the dc voltage is equal to a single value, the point of operation is limited by the solar irradiance and temperature. However, when the dc voltage varies in a safe range, the PV generator can work in a wider area for the same solar irradiance and temperature. The validation of these curves is tested in steady state under variable solar irradiance, ambient temperature, dc voltage and modulation index. In addition, this thesis analyses how the dynamic response of a PV generator is affected by its capability curves under quick variations of solar irradiance and different temperature values.Taking into consideration the capability curves and the photovoltaic power plant operation’s requirements, the PV generator’s control of active and reactive power is addressed. In this thesis, power curtailment and the control of power reserves are addressed under variable solar irradiance and temperature. Additionally, the control of reactive power is developed by the variation of the dc voltage and the modulation index value according to the instantaneous capability curve under the specific ambient conditions. The validation of the different studies is developed in DIgSILENT Power Factory. The simulations consider the PV generator performance under variable solar conditions and different references of active and reactive power. The results showed that an adequate control of the active and the reactive power of the PV generator taking into account the capability curves could help to comply with the power plant operator’s requirements.
