As a typical multilevel topology, the modular multilevel converter (MMC) has been extensively studied by the academia and industry for its unique advantages, such as high modularity, fault tolerant capability and high-quality output. With the rapid development of transportation electrification, the application of MMC in electric vehicle (EV) systems has also been continuously investigated in recent years. Compared with current power electronic solutions, the ability of integrating function of motor drive, cell state-of-charge (SOC) equalizer and on-board charger in one single converter makes MMC a promising candidate for EV applications. Although having a series of advantages, current harmonics generated by the operation of MMC will flow through battery cells in EV, leading to additional power losses and eventually, reduced battery lifetime. In past research on MMC for EV applications, there is no relevant study solving this problem. To make the application of MMC in EV systems feasible, it is necessary to propose specific methods to suppress harmonics flowing through batteries. This thesis focuses on researching current harmonic suppression strategies for MMCs in EV systems. The configuration, modeling of main circuit and battery and commonly used modulation techniques of MMC for EV applications are first introduced. The battery SOC balancing control of MMC is then analyzed in detail. To suppress battery current harmonics, a circulating current injection method is proposed in this thesis, reducing the root mean square (RMS) value of cell current harmonics, and mitigating the negative effect on battery lifetime. The rationale of the suppression method is analyzed. Optimal magnitude and frequency of injected current are also derived. To verify the effectiveness of the proposed method, simulations in the MATLAB/Simulink environment as well as experiments based on a single-phase MMC prototype are carried out. This thesis proposes a voltage injection method as well, to mitigate negative effects on battery health of current harmonics by equivalently increasing the frequency of initial harmonic components. To eliminate the injected voltages on the AC side of MMC, a hybrid MMC topology is also proposed. Simulation results again validate the effectiveness of the proposed method and hybrid topology.
Il convertitore modulare multilivello (MMC) è stato ampiamente studiato dal mondo accademico e industriale per i suoi vantaggi: alta modularità, elevata tolleranza ai guasti e bassa distorsione armonica della tensione di uscita. Con la progressiva elettrificazione dei sistemi di trasporto, l'utilizzo del MMC nei veicoli elettrici (EV) è stato anch’esso oggetto di particolare interesse negli ultimi anni. Confrontato con le attuali soluzioni di elettronica di potenza, la capacità del MMC di integrare le funzioni di azionamento del motore, equalizzatore dello stato di carica (SOC) delle celle e caricatore di bordo, rende lo stesso convertitore un valido candidato per le applicazioni in ambito EV. Nonostante abbia diversi vantaggi, le armoniche di corrente che circolano nei moduli dell'MMC comportano perdite di potenza aggiuntive e un maggicr degrado delle batterie utilizzate nei veicoli elettrici, riducendo così la loro vita utile. Nelle passate ricerche sugli MMC per applicazioni EV, non ci sono studi per la soluzione di questo problema. Per rendere realizzabile l'utilizzo dei MMC nei veicoli elettrici, metodi specifici per la soppressione delle armoniche che fluiscono attraverso le batterie devono essere definiti. Questa tesi si concentra sulla ricerca di strategie di soppressione delle armoniche per gli MMC nei sistemi EV. La configurazione, la modellazione del circuito principale e della batteria e le tecniche comuni di modulazione per gli MMC in applicazioni EV vengono introdotte per prime. Il controllo del MMC sul bilanciamento dello stato di carica delle celle viene poi analizzato in dettaglio. Per sopprimere le armoniche di corrente nelle batterie, un metodo di iniezione di corrente di circolazione viene proposto in questa tesi. Esso riduce il valore efficace delle armoniche di corrente e mitiga quindi l'effetto negativo sulla vita utile della batteria. Nella tesi è stato analizzato il principio di funzionamento metodo di soppressione delle armoniche proposto. I valori ottimali del modulo e della frequenza delle correnti iniettate vengono anch'essi analizzati. Per verificare l'efficacia del metodo proposto, sono state effettuate simulazioni in ambiente MATLAB/Simulink ed esperimenti basati su un prototipo di un MMC monofase. La tesi propone anche un metodo di iniezione di tensione per mitigare gli effetti negativi delle armoniche di corrente sullo stato di salute della batteria, incrementando la frequenza delle componenti armoniche iniziali. Per eliminare queste iniezioni di tensione sul lato AC del MMC, una topologia ibrida del MMC è stata proposta. I risultati della simulazione validano, di nuovo, l'efficacia del metodo proposto e della topologia ibrida.
Battery current harmonic suppression strategies for modular multilevel converters in electric vehicle applications
WANG, DI
2019/2020
Abstract
As a typical multilevel topology, the modular multilevel converter (MMC) has been extensively studied by the academia and industry for its unique advantages, such as high modularity, fault tolerant capability and high-quality output. With the rapid development of transportation electrification, the application of MMC in electric vehicle (EV) systems has also been continuously investigated in recent years. Compared with current power electronic solutions, the ability of integrating function of motor drive, cell state-of-charge (SOC) equalizer and on-board charger in one single converter makes MMC a promising candidate for EV applications. Although having a series of advantages, current harmonics generated by the operation of MMC will flow through battery cells in EV, leading to additional power losses and eventually, reduced battery lifetime. In past research on MMC for EV applications, there is no relevant study solving this problem. To make the application of MMC in EV systems feasible, it is necessary to propose specific methods to suppress harmonics flowing through batteries. This thesis focuses on researching current harmonic suppression strategies for MMCs in EV systems. The configuration, modeling of main circuit and battery and commonly used modulation techniques of MMC for EV applications are first introduced. The battery SOC balancing control of MMC is then analyzed in detail. To suppress battery current harmonics, a circulating current injection method is proposed in this thesis, reducing the root mean square (RMS) value of cell current harmonics, and mitigating the negative effect on battery lifetime. The rationale of the suppression method is analyzed. Optimal magnitude and frequency of injected current are also derived. To verify the effectiveness of the proposed method, simulations in the MATLAB/Simulink environment as well as experiments based on a single-phase MMC prototype are carried out. This thesis proposes a voltage injection method as well, to mitigate negative effects on battery health of current harmonics by equivalently increasing the frequency of initial harmonic components. To eliminate the injected voltages on the AC side of MMC, a hybrid MMC topology is also proposed. Simulation results again validate the effectiveness of the proposed method and hybrid topology.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/164986