The introduction of environmentally friendly energy policies, including decarbonisation objectives has led to an increasing penetration of Non-Programmable Renewable Energy Source-based (NPRES) electricity generation. Solar and wind energy represent the most promising because their larger exploita- tion potential. However, the foreseen massive integration of NPRES in the networks raises concerns about reliable, stable and secure power system operation, due to their aleatory nature which impacts the ability of providing stable voltage levels and elec- trical frequency in the whole electric system. Following the footsteps of the EU-funded project Twenties, this thesis is focused on the participation of o shore wind farms, especially the ones connected to onshore AC grids by High Voltage Direct Current (HVDC) links, in Primary Frequency Control (PFC) of the onshore AC grids themselves. Many recent studies propose control strategies enabling high-capacity wind farms to successfully provide active power reserves for frequency control. However, most of them lack an adequate modelling of the involved diverse apparatuses. This thesis tries to bridge the gap by a design of the main participating actor, the wind turbine, from the ground up and by a rather detailed dynamic model of its aerodynamical, mechanical and electrical components. Here, a wind turbine with a gearless Permanent Magnet Synchronous Generator, equipped with a back-to-back Voltage Source Converter (VSC) in a three-level neutral-point clamped con guration, is considered. A typical hierarchical approach is followed for control design: there are inner loops controlling currents in the VSC by means of a sinusoidal Pulse Width Modulation technique, and outer loops allowing to control active power, AC voltage and DC voltage according to high-level purposes. Major focus is put on the property of robustness given the non-perfect knowledge of the controlled devices. The undertaken path begins with the detailed design process of a wind turbine and go through the definition of suitable control systems enabling low- level and high-level functionalities. The work culminates with the simulation of PFC provisioning from the wind turbines demonstrating the ability of the wind turbine to comply with Transmission System Operator requirements under critical wind conditions.
La realizzazione di politiche transnazionali rispettose dell’ambiente, comprensive di obiettivi di decarbonizzazione, ha portato in tutta l’UE a una crescente penetrazione della generazione da Fonti Energetiche Rinnovabili Non Programmabili (FERNP). Le fonti solare ed eolica sono particolarmente interessanti, per il loro maggior potenziale di sfruttamento rispetto alle altre FERNP. Tuttavia, la prevista massiccia integrazione di FERNP nelle reti è critica per l’affidabilità, la stabilità e la sicurezza del sistema elettrico: la loro aleatorietà impatta sulla stabilità dei livelli di tensione e della frequenza dell’intero sistema. Sulle orme del Progetto UE Twenties, questa tesi si focalizza sulla partecipazione delle centrali eoliche offshore, specialmente se connesse a reti AC sulla terraferma mediante collegamenti in corrente continua ad alta tensione (HVDC), alla Regolazione Primaria di Frequenza (RPF) di tali reti AC. Molti studi recenti propongono strategie di controllo che permettono a grandi centrali eoliche di fornire efficacemente riserve di potenza attiva per la regolazione di frequenza. Tuttavia, spesso in essi manca una modellistica adeguata dei diversi apparati. Questa tesi cerca di contribuire con un progetto completo del principale attore, la turbina eolica, e con un modello dinamico dettagliato dei suoi componenti aerodinamici, meccanici ed elettrici. Si considera una turbina eolica con generatore sincrono a magneti permanenti gearless, con un convertitore a tensione impressa (VSC) a tre livelli neutral-point clamped in configurazione back-to-back. Per progettare il controllo, si segue un tipico approccio gerarchico: gli anelli interni controllano le correnti nel VSC mediante Pulse Width Modulation sinusoidale, quelli esterni permettono di controllare potenza attiva, tensione AC e tensione DC secondo obiettivi di alto livello. Si pone molta attenzione alla proprietà di robustezza, data la non perfetta conoscenza dei dispositivi controllati. Tra le funzionalità di alto livello, si simula la fornitura di RPF, mostrando la capacità della turbina eolica di rispettare i requisiti dei Gestori di Reti di Trasmissione in condizioni di vento critiche.
Dynamic analysis of offshore wind farms. A focus on support to primary frequency control
ZARFATI, EMANUELE
2014/2015
Abstract
The introduction of environmentally friendly energy policies, including decarbonisation objectives has led to an increasing penetration of Non-Programmable Renewable Energy Source-based (NPRES) electricity generation. Solar and wind energy represent the most promising because their larger exploita- tion potential. However, the foreseen massive integration of NPRES in the networks raises concerns about reliable, stable and secure power system operation, due to their aleatory nature which impacts the ability of providing stable voltage levels and elec- trical frequency in the whole electric system. Following the footsteps of the EU-funded project Twenties, this thesis is focused on the participation of o shore wind farms, especially the ones connected to onshore AC grids by High Voltage Direct Current (HVDC) links, in Primary Frequency Control (PFC) of the onshore AC grids themselves. Many recent studies propose control strategies enabling high-capacity wind farms to successfully provide active power reserves for frequency control. However, most of them lack an adequate modelling of the involved diverse apparatuses. This thesis tries to bridge the gap by a design of the main participating actor, the wind turbine, from the ground up and by a rather detailed dynamic model of its aerodynamical, mechanical and electrical components. Here, a wind turbine with a gearless Permanent Magnet Synchronous Generator, equipped with a back-to-back Voltage Source Converter (VSC) in a three-level neutral-point clamped con guration, is considered. A typical hierarchical approach is followed for control design: there are inner loops controlling currents in the VSC by means of a sinusoidal Pulse Width Modulation technique, and outer loops allowing to control active power, AC voltage and DC voltage according to high-level purposes. Major focus is put on the property of robustness given the non-perfect knowledge of the controlled devices. The undertaken path begins with the detailed design process of a wind turbine and go through the definition of suitable control systems enabling low- level and high-level functionalities. The work culminates with the simulation of PFC provisioning from the wind turbines demonstrating the ability of the wind turbine to comply with Transmission System Operator requirements under critical wind conditions.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/120471