Integrated Compact Drives for Electric and Hybrid Electric Vehicles

Increased use of electric and hybrid electric vehicles (EVs/HEVs) is one of the most promising ways to reduce carbon dioxide emissions. To develop more competitive solutions, one of the trends in the development of drive systems for EVs/HEVs is to integrate the power electronic converter and the electric motor. This thesis aims to investigate the performance and the operation of modular converters in integrated motor drive systems for EVs/HEVs. Special attention is given to the stacked polyphase bridges converter. In the first part, the concept of integrated modular motor drive systems for EVs/HEVs is introduced. Three suitable modular converter topologies, namely, the stacked polyphase bridges (SPB) converter, the parallel-connected polyphase bridges (PPB) converter and the modular high frequency (MHF) converter, are evaluated and compared with conventional electric drives, based on two-level three-phase converters, in terms of power losses, energy storage requirements, and semiconductor costs. An analytical model for power loss calculation is proposed and experimentally proven to be accurate with less than 1% error above very low current levels. In the second part of the thesis, the harmonic content of the dc-link current of the SPB converter is analyzed. According to the theoretical analysis, harmonics of certain orders can be eliminated by phase shifting the modulation carriers among submodules. By adopting such an interleaving modulation technique the size of the dc-link capacitor can be reduced without increasing the switching frequency, which is beneficial for achieving a compact integrated system. Therefore, the energy storage requirements of the SPB converter with different modulation techniques and switching frequencies have also been investigated. The proposed modulation method allows for around 80% reduction of the dc-link capacitance for vehicle drives, resulting in a significant size reduction of the power converter and improved integration. Finally, a communication-based distributed control system for the SPB converter is presented. This system includes three parts: master controller, slave controller and data network. The serial peripheral interface (SPI) protocol is adopted in this work for the communication interface. The communication delay arising from the serial communication is inevitable, thus a timing analysis is also presented. By using a dynamic model, the sensitiveness of the dc-link stability has been studied. It has been found that stability is maintained even when the baud rate of the SPI communication is lower than 1 Mbps, indicating that other communication protocols with lower bandwidths can also be adopted for this topology. The analytical investigations provided in this thesis are validated by experiments on a four-submodule laboratory prototype. Experimental results verify the correctness of the theoretical analysis, as well as the dynamic performance of the distributed control system, indicating that the results of this thesis will be useful for future industrial implementation.