The electronic converters are used more and more these days and new regulations impose more stringent limits on current harmonics injected into the grid. In addition, several applications demand the capability of power regeneration to the power supply. This thesis aims to realize a bidirectional converter working as active front end (AFE); thus, the studied converter must absorb a current in phase with the grid voltage and with low harmonic content (unitary power factor operation). The focus will be on the development of the control that runs on such type of converter. In the first chapter, an excursus on different type of electronic converters acting as rectifier will be done: their main characteristics are highlighted. The topologies to realize two AFE converters (for single-phase and three-phase operations), will be selected, namely the full bridge VSC (Voltage Source Converter) and the three phase VSC. Then, the modelling of such converters is done, using the sliding average theory, the sliding harmonics theory and the dq transformation. After that, a possible implementation in MATLAB Simulink of the control schemes, acting on the dq variables, is presented. Moreover, since the single-phase dq control shows some criticalities, an alternative control scheme based on proportional-resonant controller is created. The tuning of the controller parameters is done mainly experimentally, using also the “pidtune” function in MATLAB to get first-guess values. All the proposed control systems are tested in MATLAB Simulink to verify the dynamic performances and the unitary power factor operation. Moreover, the impact of the main system parameters on the AC current THD (Total Harmonic Distortion) and the DC voltage ripple is investigated. Then, the proportional resonant control and the three phase dq control are tested in a small-scale experimental setup. These two controls show good performance both in term of unitary power factor operation and dynamic responses to load or voltage variation. Thus, they are suitable to realize an electronic converter working as active front end.
I convertitori elettronici sono sempre più utilizzati e le nuove regolamentazioni impongono limiti stringenti in termini di contenuto armonico delle correnti assorbite dalla rete. Inoltre, molte applicazioni richiedono la capacità di invertire il flusso di potenza del convertitore. L’obbiettivo di questa tesi è realizzare un convertitore bidirezionale “active front end (AFE)”, ovvero un convertitore bidirezionale che assorbe una corrente in fase con la tensione di rete e con un basso THD. Il focus sarà sulla realizzazione del sistema di controllo. Nel primo capitolo, sarà fatto un excursus dei diversi tipi di convertitori elettronici che possono fungere da raddrizzatori, evidenziando le loro caratteristiche principali. Inoltre, saranno selezionate le topologie per realizzare due AFE, monofase e trifase, che sono rispettivamente il VSC (Voltage Source Converter) trifase e il VSC full bridge. Successivamente, questi due convertitori saranno modellizzati usando le teorie “sliding average” e “sliding harmonics”, oltre che la trasformata dq. A questo punto, verrà presentata un’implementazione in Simulink dello schema di controllo che agisce sulle variabili dq. Inoltre, siccome il controllo in assi dq monofase ha mostrato delle criticità, verrà creato uno schema di controllo alternativo, basato sui controllori proporzionali-risonanti. La taratura dei controllori è stata fatta principalmente in modo sperimentale, aiutandosi anche con la funzione “pidtune” di MATLAB. Tutti i sistemi di controllo sono stati testati in simulazione con l’ausilio di Simulink per verificare le prestazioni dinamiche, il THD della corrente e il fattore di potenza. Inoltre, è stato verificato l’impatto delle principali specifiche del convertitore sul THD e sul ripple della tensione lato DC. Successivamente, il controllo proporzionale risonante monofase e il controllo in assi dq trifase sono stati testati in un setup sperimentale in scala ridotta. Queste due tipologie di controllo si sono dimostrati validi dal punto di vista delle prestazioni dinamiche e per ottenere l’operatività a fattore di potenza unitario. Di conseguenza, sono adatte per realizzare convertitori elettronici che operano da AFE.
Study and design of a bidirectional AC/DC converter working as an active front end
Tagliaretti, Riccardo
2021/2022
Abstract
The electronic converters are used more and more these days and new regulations impose more stringent limits on current harmonics injected into the grid. In addition, several applications demand the capability of power regeneration to the power supply. This thesis aims to realize a bidirectional converter working as active front end (AFE); thus, the studied converter must absorb a current in phase with the grid voltage and with low harmonic content (unitary power factor operation). The focus will be on the development of the control that runs on such type of converter. In the first chapter, an excursus on different type of electronic converters acting as rectifier will be done: their main characteristics are highlighted. The topologies to realize two AFE converters (for single-phase and three-phase operations), will be selected, namely the full bridge VSC (Voltage Source Converter) and the three phase VSC. Then, the modelling of such converters is done, using the sliding average theory, the sliding harmonics theory and the dq transformation. After that, a possible implementation in MATLAB Simulink of the control schemes, acting on the dq variables, is presented. Moreover, since the single-phase dq control shows some criticalities, an alternative control scheme based on proportional-resonant controller is created. The tuning of the controller parameters is done mainly experimentally, using also the “pidtune” function in MATLAB to get first-guess values. All the proposed control systems are tested in MATLAB Simulink to verify the dynamic performances and the unitary power factor operation. Moreover, the impact of the main system parameters on the AC current THD (Total Harmonic Distortion) and the DC voltage ripple is investigated. Then, the proportional resonant control and the three phase dq control are tested in a small-scale experimental setup. These two controls show good performance both in term of unitary power factor operation and dynamic responses to load or voltage variation. Thus, they are suitable to realize an electronic converter working as active front end.File | Dimensione | Formato | |
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Executive_Summary_Tagliaretti_10607751.pdf
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Tesi_Tagliaretti_10607751.pdf
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https://hdl.handle.net/10589/197275