Power-split operation strategy for series hybrid electric buses based on a cost function

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Power-split operation strategy for series hybrid electric buses based on a cost function

Richter, Michael / Stiegeler, Markus / Kabza, Herbert

The series hybrid technology with a motor generator unit (MGU) and a separate electric motor/generator used as a drive unit has been widely adapted in buses. Because of the many acceleration and deceleration processes in the operation mode of the bus this hybrid concept has several benefits. In this paper we present an analytic power split operation strategy based on the cost of the battery energy and the efficiency of the MGU. On the basis of these costs it is decided when and in which operation point it is most efficient to operate the MGU. This paper shows that a minimal fuel consumption and a widely constant SOC can be achieved with the power split operation strategy. Additionally we compared a new and an aging battery in the power-split operation strategy with a single-point strategy. The analytical cost function-based operation strategy provides a good and easy-to-implement operation strategy for series hybrid buses. By the coupling of the cost function to the power splitting and the SOC the operation strategy guarantees, that the SOC can be kept in a narrow area during the whole cycle and deep discharge can be avoided. Also we showed the interrelations between the required power, the electric base cost factor and the resulting driving mode. In addition, we could show that with a new battery the MGU is operating in the best efficiency area. The comparison to a single-point operation strategy shows that with the power-split strategy remarkable fuel savings can be obtained even with an aging battery if an intelligent charging of the battery and an proper splitting of the required energy between battery and MGU is implemented.