The purpose of this thesis is to examine in depth the use of PLL during the insertion operations of an inverter in micro-grids, which allow hooking the generation system without transient current. The electrical system model studied is composed by an inverter connected in parallel to a LCL filter and a voltage generator, which represents the rest of the micro-grid. Starting from this circuital model the PLL has been implemented in support of the control circuit of the inverter in order to execute the parallel of the inverter with the grid. The first part of this work presents the principal PLL typologies already proposed in literature. An analysis of their structure and the execution of tunings have been made in order to implement them in the control circuit of the inverter, to attest their performances. For this reason widely different tunings have been made to compare the output of the PLL different typologies and establish the best project specifications. A simulation of the insertion of the inverter in the micro-grid, using Simulink, has been done to test the above-mentioned specifications, taking into consideration the different grids conditions. For example, a comparison has been done between insertions made with distorted voltage and different frequencies from the nominal one, conditions that can verify in the micro-grids. From the analysis of such specifications, in the second part of the thesis, a PLL have been developed and proposed to operate in highly disturbed grid conditions. This allows determining the electrical quantities pulsation and consequently determining the phase angle, in the presence of the principal grid disturbance: the inverse sequence, the 5th harmonic and the 7th harmonic. Lastly, in order to complete the study of the insertion of the inverter, the current transient provoked by the droop control have been analysed, reducing it by using the PLL, to obtain a hook to the grid with current values sustained by the components of the electrical system.
Questa tesi si propone di approfondire l’utilizzo del PLL nelle operazioni d’inserzione di un inverter nelle micro reti, permettendo un aggancio del sistema di generazione senza transitori di corrente. Il modello di sistema elettrico studiato è composto da un inverter connesso in parallelo ad un filtro LCL e un generatore di tensione rappresentante il resto della micro rete. Partendo da questo modello circuitale si è implementato il PLL in supporto al circuito di controllo dell’inverter, in maniera tale da eseguire il parallelo dell’inverter con la rete. Nella prima parte della tesi verranno mostrati i principali PLL già proposti in letteratura, analizzandone la struttura ed eseguendo dei dimensionamenti con l’obbiettivo di implementarli nel circuito di controllo dell’inverter, verificandone le prestazioni. Si sono eseguiti per questo motivo dei dimensionamenti molto diversi tra loro, confrontando in questo modo il rendimento delle tipologie di PLL e verificando quali fossero le migliori specifiche di progetto. Tali verifiche si sono effettuate simulando, tramite simulink, l’inserzione dell’inverter nella micro rete, considerando diverse condizioni di rete. Per esempio si sono confrontati i risultati d’inserzioni effettuate con tensioni distorte e frequenze diverse da quella nominale, condizioni che si possono verificare nelle micro reti. Dallo studio di tali applicazioni, nella seconda parte della tesi, si è sviluppato un PLL proposto per funzionare in condizioni di rete molto disturbata. Questo permette di determinare la pulsazione delle grandezze elettriche, e di conseguenza l’angolo di fase, in presenza dei principali disturbi di rete: la sequenza inversa, la 5⁰ armonica e la 7⁰ armonica. Infine, per completare lo studio dell’inserzione dell’inverter, si è analizzato il transitorio di corrente provocato dal controllo di droop, riducendolo, utilizzando il PLL, fino ad ottenere un aggancio alla rete con valori di corrente sostenibili dalle componenti del sistema elettrico.
Studio e implementazione del PLL per l'inserzione di un inverter nelle micro reti
FORMENTI, LUCA
2015/2016
Abstract
The purpose of this thesis is to examine in depth the use of PLL during the insertion operations of an inverter in micro-grids, which allow hooking the generation system without transient current. The electrical system model studied is composed by an inverter connected in parallel to a LCL filter and a voltage generator, which represents the rest of the micro-grid. Starting from this circuital model the PLL has been implemented in support of the control circuit of the inverter in order to execute the parallel of the inverter with the grid. The first part of this work presents the principal PLL typologies already proposed in literature. An analysis of their structure and the execution of tunings have been made in order to implement them in the control circuit of the inverter, to attest their performances. For this reason widely different tunings have been made to compare the output of the PLL different typologies and establish the best project specifications. A simulation of the insertion of the inverter in the micro-grid, using Simulink, has been done to test the above-mentioned specifications, taking into consideration the different grids conditions. For example, a comparison has been done between insertions made with distorted voltage and different frequencies from the nominal one, conditions that can verify in the micro-grids. From the analysis of such specifications, in the second part of the thesis, a PLL have been developed and proposed to operate in highly disturbed grid conditions. This allows determining the electrical quantities pulsation and consequently determining the phase angle, in the presence of the principal grid disturbance: the inverse sequence, the 5th harmonic and the 7th harmonic. Lastly, in order to complete the study of the insertion of the inverter, the current transient provoked by the droop control have been analysed, reducing it by using the PLL, to obtain a hook to the grid with current values sustained by the components of the electrical system.File | Dimensione | Formato | |
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2016_12_Formenti.pdf
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Descrizione: Testo della tesi
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https://hdl.handle.net/10589/127141