Power over Ethernet is a technology that allows the transmission of power over the lines of a communication network, i.e. Ethernet cables. In this way one can avoid the use of a power cable, that takes up space and requires an extra port on the powered device. The Automotive and Aerospace sectors are increasingly employing PoE technology because of the higher number of smart devices and sensors on board that need to be both powered and communicate with the central control unit. The manufacturers in these industries are pushing for architectures that allow more power to be transmitted on the cable maintaining a high bandwidth (1 Gb/s). This thesis focuses on the analysis of one such architecture. Section 1 contains an introduction on PoE that discusses main applications, the functioning principle and future development. Various PoE circuit architectures are presented and the one that is analysed for the rest of the thesis is chosen. In order to understand the functioning of the circuit under analysis, initially an ideal and perfectly balanced circuit is considered. This is done in section 2; the matrices of the terminal conditions of both transmission side and receiving side are defined for the ideal case. The voltages at the receiving end are then calculated by combining the matrix expressions. Also the modal transformation matrix T is calculated and four ideal modal circuits are defined: Two differential modes and two common modes. The two differential modes are named transmission mode 1 and transmission mode 2, while the two common modes are named power mode and common mode. In section 3 an unbalance in the balun center-tap is considered and studied through a parameter delta. The effect of delta is isolated thanks to the superposition principle and seen as an additive component to the ideal case. These effects are shown both in the physical circuits and in the modal circuits and are plotted as a function of frequency in MATLAB environment. Section 4 introduces an unbalance in the impedance matrix of the dc/dc converter, lambda, and the conducted emission currents that originate from a typical dc/dc converter. The procedure followed is the same as that in section 3. In section 5, non-ideal behaviour is assumed for the balun transformers, i.e. unbalance of the center-taps, imperfect magnetic coupling and exhibiting a magnetizing current. The resulting expressions are complex, so various approximations are proposed and compared using MATLAB. Finally the circuit is compared in MATLAB and Spice environments to validate the assumptions made thus far. The study of the transmission lines is performed in section 6. The p.u.l parameters are calculated from geometrical characteristics of the wires and a Spice equivalent model for coupled multi-conductor transmission lines is proposed. The complete circuit is then tested on Spice and MATLAB to validate the proposed model. In section 7 a sensitivity analysis is performed on each parameter accompanied by a Monte Carlo analysis of the physical and modal circuits. Finally some final considerations are presented in chapter 8.
Power over Ethernet è una tecnologia che permette la trasmissione di potenza su linee di comunicazione, in particolare su cavo Ethernet. In questo modo si può evitare l'utilizzo del cavo di potenza che occupa spazio e richiede un ulteriore porta sul dispositivo. I settori dell’automotiva e dell'aerospazio ricorrono sempre più spesso a configurazioni PoE a causa del crescente numero di sensori e di dispositivi smart presenti sul veicolo. Questi devono sia essere alimentati, sia comunicare con l'unità di controllo centrale. Perciò vi è una crescente domanda per nuove architetture che permettono la trasmissione di maggiore potenza, mantenendo una larga banda di comunicazione (1 Gb/s). Questa tesi si focalizza sull'analisi di una tale architettura. Il capitolo 1 presenta una introduzione sul PoE che discute le principali applicazioni, il principio di funzionamento e lo sviluppo futuro. Vengono presentati vari circuiti e dopodiché viene scelto e giustificato quello che verrà studiato per il resto della tesi. Per poter capire come funziona l'architettura scelta, il circuito viene inizialmente considerato ideale e completamente bilanciato. Questo circuito viene analizzato nel capitolo 2, dove vengono definite le matrici di impedenza che caratterizzano i terminali di trasmissione e ricezione del segnale. Dopodiché vengono calcolate le tensioni ai terminali di ricezione combinando le espressioni matriciali trovate. Inoltre vengono definiti la matrice modale T e i rispettivi quattro circuiti modali: due modi comuni e due modi differenziali. I due modi differenziali sono definiti transmission mode 1 e transmission mode 2, mentre i due modi comuni power mode e common mode. Il capitolo 3 considera uno sbilanciamento di uno dei balun attraverso il parametro delta. Grazie alla linearità del sistema, l'effetto di delta può essere isolato e considerato come un componente additivo al caso ideale. Gli effetti di delta sono studiati sia sui circuiti modali, sia sul circuito fisico utilizzando MATLAB. Il capitolo 4 introduce uno sbilanciamento nella matrice di impedenza del dc/dc converter e le emissioni condotte che orginano da un tipico convertitore. La procedura seguita è la stessa del capitolo 3. Nel capitolo 5, viene ipotizzato un comportamento non ideale dei baluns, ovvero un accoppiamento magnetico non perfetto e una corrente di magnetizzazione non nulla. Le espressioni risultanti sono abbastanza complesse perciò vengono proposte alcune approssimazioni. Queste sono poi confrontate usando MATLAB. Infine il circuito è simulato su MATLAB e su Spice per validare le considerazioni fatte. Il capitolo 6 presenta uno studio delle linee di trasmissione. I parameteri per unità di lunghezza (p.u.l) vengono calcolati a partire dalle caratteristiche geometriche dei cavi. Un modello Spice equivalente per linee lunghe mutuamente accoppiate viene proposte e usato per simulare il circuito completo. Nel capitolo 7 viene svolta una simulazione di Monte Carlo e un'analisi di sensibilità di delta e lambda, sia sui circuiti modali sia sul circuito fisico. Infine nel capitolo 8 vengono presentate le conclusioni.
Analysis of a typical PoE circuit configuration with coupled transmission wires
MONOPOLI, TOMAS
2018/2019
Abstract
Power over Ethernet is a technology that allows the transmission of power over the lines of a communication network, i.e. Ethernet cables. In this way one can avoid the use of a power cable, that takes up space and requires an extra port on the powered device. The Automotive and Aerospace sectors are increasingly employing PoE technology because of the higher number of smart devices and sensors on board that need to be both powered and communicate with the central control unit. The manufacturers in these industries are pushing for architectures that allow more power to be transmitted on the cable maintaining a high bandwidth (1 Gb/s). This thesis focuses on the analysis of one such architecture. Section 1 contains an introduction on PoE that discusses main applications, the functioning principle and future development. Various PoE circuit architectures are presented and the one that is analysed for the rest of the thesis is chosen. In order to understand the functioning of the circuit under analysis, initially an ideal and perfectly balanced circuit is considered. This is done in section 2; the matrices of the terminal conditions of both transmission side and receiving side are defined for the ideal case. The voltages at the receiving end are then calculated by combining the matrix expressions. Also the modal transformation matrix T is calculated and four ideal modal circuits are defined: Two differential modes and two common modes. The two differential modes are named transmission mode 1 and transmission mode 2, while the two common modes are named power mode and common mode. In section 3 an unbalance in the balun center-tap is considered and studied through a parameter delta. The effect of delta is isolated thanks to the superposition principle and seen as an additive component to the ideal case. These effects are shown both in the physical circuits and in the modal circuits and are plotted as a function of frequency in MATLAB environment. Section 4 introduces an unbalance in the impedance matrix of the dc/dc converter, lambda, and the conducted emission currents that originate from a typical dc/dc converter. The procedure followed is the same as that in section 3. In section 5, non-ideal behaviour is assumed for the balun transformers, i.e. unbalance of the center-taps, imperfect magnetic coupling and exhibiting a magnetizing current. The resulting expressions are complex, so various approximations are proposed and compared using MATLAB. Finally the circuit is compared in MATLAB and Spice environments to validate the assumptions made thus far. The study of the transmission lines is performed in section 6. The p.u.l parameters are calculated from geometrical characteristics of the wires and a Spice equivalent model for coupled multi-conductor transmission lines is proposed. The complete circuit is then tested on Spice and MATLAB to validate the proposed model. In section 7 a sensitivity analysis is performed on each parameter accompanied by a Monte Carlo analysis of the physical and modal circuits. Finally some final considerations are presented in chapter 8.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/153498