In recent years, the quick technological improvement that involved the power electronic devices has increased the spread of renewables sources exploitation. Wind power is among the world's fastest growing renewable sources and Wind Energy Conversion Systems (WECSs) play a pivotal role in contributing to the total power production in today’s world. This thesis proposes a particular WECS based on a multi-modular (MM) machine with Nm modules, which allows to reach high generation power keeping the same radial length of the module. The machine under study is a three-module axial flux permanent magnet synchronous generator (AFPMSG) that is directly driven (DD) by the wind turbine. The three modules are fastened on the same shaft and aligned with one another. Each module is connected to a two-level converter with sinusoidal pulse width modulation (PWM). All the machine-side converters are connected in series at the DC bus to allow to reach the usual levels for HVDC transmission. The connection to the grid is made through a single two-level grid-side converter with sinusoidal PWM and a distribution transformer. A mathematical analysis is carried out in order to develop the machine-side and the grid-side control system. A control strategy for the regulation of each machine-side DC bus voltage and the overall grid-side one is presented. In particular, the main interest of the thesis is the regulation of the DC bus voltage at the terminals of each machine-side capacitors and of the grid-side one, exploiting the interaction between the machine-side and grid-side control systems. Basically, it is needed to implement the DC bus voltage controller in the machine-side converters because, without DC bus midpoint connections, the grid-side converter is able to control only the overall DC bus voltage and not each DC bus voltage at the machine-side. To that end, the proposed control strategy consists in introducing an additional q-axis current reference contribution in the control system of (Nm-1) machine-side converters. In this way, (Nm-1) machine-side DC bus voltages are controlled by the respective converters, while a rectified voltage remains fluctuating in order to avoid a hyperstatic system, but controlled through the action of the grid-side converter, which controls the overall DC bus voltage. The effectiveness of the proposed DC bus voltage control strategy is proved through simulations in Matlab/Simulink environment.
Negli ultimi anni, il rapido miglioramento tecnologico che ha coinvolto i dispositivi dell’elettronica di potenza ha aumentato la diffusione dello sfruttamento delle fonti rinnovabili. L'energia eolica è tra le fonti rinnovabili più in rapida crescita al mondo e i sistemi di conversione dell'energia eolica (WECS) svolgono un ruolo fondamentale nel contribuire alla produzione totale di energia nel mondo di oggi. Questa tesi propone un particolare WECS basato su una macchina multi-modulare (MM) a Nm moduli, che permette di raggiungere un'elevata potenza di generazione mantenendo la stessa lunghezza radiale del modulo. La macchina in esame è un generatore sincrono a magneti permanenti a flusso assiale (AFPMSG) a tre moduli azionato direttamente (DD) dalla turbina eolica. I tre moduli sono fissati sullo stesso albero e allineati tra loro. Ogni modulo è collegato ad un convertitore a due livelli con modulazione di larghezza di impulso sinusoidale (PWM). Tutti i convertitori lato macchina sono collegati in serie al bus DC per consentire di raggiungere i livelli usuali per la trasmissione HVDC. La connessione alla rete avviene tramite un unico convertitore lato rete a due livelli con modulazione PWM sinusoidale e trasformatore di distribuzione. Viene eseguita un'analisi matematica per sviluppare il sistema di controllo lato macchina e quello lato rete. L'interesse principale della tesi è la regolazione della tensione del DC bus ai terminali di ciascun condensatore lato macchina e di quello lato rete, sfruttando l'interazione tra i sistemi di controllo lato macchina e lato rete. Essenzialmente, è necessario introdurre il controllo della tensione del bus DC nei convertitori lato macchina poiché, senza nessuna connessione del punto medio del bus DC, il convertitore lato rete è in grado di controllare solo la tensione totale del DC bus e non le singole tensioni DC lato macchina. A tal fine, la strategia di controllo proposta consiste nell'introdurre un ulteriore contributo alla corrente di riferimento dell'asse q nel sistema di controllo di (Nm-1) convertitori lato macchina. In questo modo, (Nm-1) tensioni del bus DC lato macchina sono controllate dal rispettivo convertitore, mentre una tensione rimane fluttuante, per evitare un sistema iperstatico, ma controllata dall’azione del convertitore lato rete, che controlla la tensione del bus DC complessiva. L'efficacia della strategia di controllo della tensione del bus DC proposta è dimostrata attraverso risultati della simulazione.
DC bus voltage control in a multi-modular off-shore wind energy conversion system in a back-to-back configuration with a grid connection
Cespuglio, Alfredo
2019/2020
Abstract
In recent years, the quick technological improvement that involved the power electronic devices has increased the spread of renewables sources exploitation. Wind power is among the world's fastest growing renewable sources and Wind Energy Conversion Systems (WECSs) play a pivotal role in contributing to the total power production in today’s world. This thesis proposes a particular WECS based on a multi-modular (MM) machine with Nm modules, which allows to reach high generation power keeping the same radial length of the module. The machine under study is a three-module axial flux permanent magnet synchronous generator (AFPMSG) that is directly driven (DD) by the wind turbine. The three modules are fastened on the same shaft and aligned with one another. Each module is connected to a two-level converter with sinusoidal pulse width modulation (PWM). All the machine-side converters are connected in series at the DC bus to allow to reach the usual levels for HVDC transmission. The connection to the grid is made through a single two-level grid-side converter with sinusoidal PWM and a distribution transformer. A mathematical analysis is carried out in order to develop the machine-side and the grid-side control system. A control strategy for the regulation of each machine-side DC bus voltage and the overall grid-side one is presented. In particular, the main interest of the thesis is the regulation of the DC bus voltage at the terminals of each machine-side capacitors and of the grid-side one, exploiting the interaction between the machine-side and grid-side control systems. Basically, it is needed to implement the DC bus voltage controller in the machine-side converters because, without DC bus midpoint connections, the grid-side converter is able to control only the overall DC bus voltage and not each DC bus voltage at the machine-side. To that end, the proposed control strategy consists in introducing an additional q-axis current reference contribution in the control system of (Nm-1) machine-side converters. In this way, (Nm-1) machine-side DC bus voltages are controlled by the respective converters, while a rectified voltage remains fluctuating in order to avoid a hyperstatic system, but controlled through the action of the grid-side converter, which controls the overall DC bus voltage. The effectiveness of the proposed DC bus voltage control strategy is proved through simulations in Matlab/Simulink environment.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/171282