Abstract
EVO Electric has designed, built and tested the DuoDrive hybrid system based on proprietary axial flux motor technology, and installed it in a London Taxi Cab. The DuoDrive switchable series/parallel hybrid system has demonstrated a 60% improvement in fuel economy compared to a conventional taxi when operated over an urban drive cycle. As with many hybrid vehicles, a large part of this improvement is attributed to effective and efficient recapture of braking energy. The amount of braking energy that can be recovered, and the efficiency with which it can be returned to the road will therefore have a significant impact on the overall fuel economy of the vehicle. One factor that limits the amount of energy that can be recovered is the allowable charge rate of the battery, as braking events are usually high power and in a hybrid vehicle the battery size is generally small. The vehicle described in this paper has an energy storage system comprised of high power ultra-capacitors and a high energy lithium ion battery connected through a DC/DC converter. This allows efficient, high power transfer under regenerative braking and acceleration, and similarly efficient energy storage over longer timescales. Managing the power flow through the DC/DC converter and therefore the ultra-capacitor voltage, is a key control parameter that affects the efficiency of the overall system. This paper presents the energy storage system layout and demonstrates how different DC/DC converter control strategies can affect the system energy efficiency.
Highlights
Hybridising a conventional internal combustion engine by adding an electric motor is a proven method of improving fuel economy of vehicles driven over an urban i.e. stop start drive cycle [1]
During regeneration of the braking energy, when the ultracapacitor voltage rises above a certain value, the DC/DC converter transfers energy back to the batteries; Case2 – The DC Bus target voltage is dependent on vehicle speed
EVO Electric have designed, built and tested the DuoDrive hybrid system using a London Taxi as a vehicle platform and demonstrating 60% improvement in fuel economy in urban driving
Summary
Hybridising a conventional internal combustion engine by adding an electric motor is a proven method of improving fuel economy of vehicles driven over an urban i.e. stop start drive cycle [1]. The basic system architecture shown in figure 1 has a novel feature in that the energy storage system is comprised of a lithium ion battery pack and an ultracapacitor array This is in order to minimise component sizes and preserve the life of the battery. The most important part of the system is the hybrid control software This has been developed at EVO Electric using Matlab-Simulink software and is a rules rather than cost-function based system designed around the following requirements; minimising the number of engineon events in urban driving; operating the engine as close as possible to the peak efficiency point when it is on; maximising the amount of vehicle kinetic energy that can be recovered; minimizing the transfer of power in both directions between the batteries and ultracapacitors
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