SUSTAINABLE HYBRID · Investigating Battery and Capacitor Sizing Problems with More Efficient Power Flow Control Techniques for Sustainable Hybrid Electric Vehicle Development

Investigating Battery and Capacitor Sizing Problems with More Efficient Power Flow Control Techniques for Sustainable Hybrid Electric Vehicle Development

This project is about investigating electric motor control strategies used in Hybrid Electric Vehicles. The results of investigation is to serve understanding the relation between battery behavior and electric motor control. Eventually new control strategies for electric motors will be developed and this yields extended lifetime for battery and DC link capacitors used in motor controller. Furthermore cost reduction of a certain class of Hybrid Electric Vehicles (HEV) is also expected by reducing battery and electrolytic capacitor cost. These two components constitute an important part of the total HEV cost. During the project, following work packages are achieved; -Literature review -Building high fidelity model for all system components including rotating machines, inverters, battery and capacitor. -Investigating inverter modulation techniques and their impact on DC bus current waveform -Investigating DC link current waveform in two-motor drive systems -Analyzing field orientation technique in an effort to correlate direct and quadrature axis current with DC link current ripple in two-motor system -Analyzing pulse width modulation technique in an effort to correlate carrier signal phase shift with DC link current ripple in two-motor system -Establishing an optimal control relation by golden search method to minimize battery losses -Extending research results onto another application which wind energy application In completion of above work steps, following results are obtained; -There is a strong relation between direct/quadrature axis current with DC link current ripple. By controlling direct axis current, we can reduce relatively low-frequency harmonics in the DC link current. The frequency depends on the speed and pole number of the electric machines such that high speed and pole number yield higher frequency. -There is a strong relation between carrier signal phase shift in pulse width modulation scheme and DC link current ripple in two-motor system. There is certain phase shift which minimizes DC link current ripple. The amount of phase shift is operating point dependent and must be varied in the face of varying load levels. With this method, the targeted frequency for elimination from DC link current ripple is rat or around switching frequency. -In Hybrid Electric Vehicle or Electric Vehicle applications, battery along with capacitors forms DC link capacitor. DC link capacitor size can be reduced by adapting two methods mentioned above. -In wind Energy applications, there is usually no battery at DC link and only capacitors are used to form DC link. In this case there is still opportunity to reduce capacitor ripple current and this yields cost and volume reduction in the system. These results will have following impacts, -In automotive industry, battery ripple current reduction yields more efficiency, more compactness. -In automotive industry, capacitor size reduction may be possible and this yields more compact inverters for HEV and EV applications. -In renewable energy industry, in particular wind energy area, capacitor size reduction may be possible and this enables to reduce system cost and volume to a certain extend. -Overall socio-economic impact is on the improvement at vehicle electrification and wind energy conversion. The results of the research can contribute cheaper, more compact and more reliable products in this area. The results may help in spreading of these technologies at a bit faster pace. -The methodology and the results of this research are directly relevant with automotive and renewable energy industries. In particular, strategy developers and engineering teams may have interest. In automotive industry, cost and volume reduction aspects are always appealing subjects in vehicle electrification. In an effort to commercialize and spread the electric vehicle technology, the result of the project can be considered as a significant leap. Similarly, in wind energy industry, cost and volume reduction issues can be revisited by the assistance of the research conducted with this project.

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