27-11-2012, 05:59 PM
Construction of a Hybrid Electrical Racing Kart as a Student
07EPE-Construction_of_a_Hybrid_Electrical_Racing_Kart_as_a_Student_Project.pdf (Size: 448.71 KB / Downloads: 54)
Abstract
In the student project presented here a hybrid racing kart was built on the basis of a conventional kart.
Technical key aspects of the project were the connectional design of the structure, the sizing of the key
components and the implementation of a control strategy. Beside technical aspects, basics of project
management and teamwork were central topics. After a short introduction the students accomplished
all work on their own responsibility. In particular they were responsible for the costs and schedule.
Introduction
Today, hybrid electric vehicles are accepted as a step toward environmentally compatible vehicles.
Due to the high torque of electrical drives, apart from environmental advantages, hybrid propulsion
systems offer also potential for enhancement of driving dynamics [1]. These improved driving
dynamics can be used e.g. for racing karts [2]. Within the project presented in this contribution such a
hybrid racing kart was constructed by students of electrical engineering. Starting point was an existing
conventional kart. This was extended to a hybrid electrical kart using standard components, as used
e.g. in automation industry. Beside technical aspects, the basics of project management were a central
topic.
Curriculum of the Student Project
The student project was divided into a specification, a design and a project conclusion phase. Contents
of the specification phase were the basics of project management, the definition of the project
objectives and the requirement specification. In the design phase a functional specification, the
schedule and the technical realization were done. To supervise the progress of the project milestones
were defined. After finishing the technical realization in the project conclusion phase the achieved
project objectives were evaluated based on the requirement and functional specification. At the end of
the project the functional hybrid racing kart was presented.
The project focus was not the development of new power electronic components or electrical drives,
but the integration of existing components to a functional system. After a short introduction to the
basics of project management the students accomplished all work on their own responsibility. In
particular the students were responsible for the costs and schedule.
Design Phase
The design phase started with the description of the technical realization in a functional specification
subject to the requirement specification. For this purpose, first the students designed a suitable
structure for the hybrid racing kart. A possible structure, which considers the project objectives
Energy Storage
As energy storage for the hybrid racing kart batteries can be considered as well as double layer
capacitors (DLC). Latter were selected because of their high power density and sufficient number of
charge/discharge cycles. The layout of the energy storage had to fulfill two requirements. On the one
hand the energy capacity had to be considered and on the other hand the DLCs had to provide the
required power.
The storage power rating arises approximately from the rated power of the electrical drives (s.
Table II) as 900 W. The energy capacity of the DLC was sized considering that is possible to
accelerate solely electrically from 0-20 km/h. The technical data of the kart listed in Table II, in
particular the voltage limits, result in a necessary capacity for the DLC of 12 F. DLC modules which
were available for the project have a maximum voltage of 15 V, a capacity of 58 F and a maximum
power of 750 W.
To comply with the voltage conditions, a series connection of 3 modules is necessary. This results in
an energy storage with a maximum voltage of 45 V, a capacity of 19 F and a maximum power of
2250 W.
The DLCs are connected to the DC link of the electrical drive inverter without any additional power
electronics (e.g. DC/DC converter). To limit the resulting voltage range of the DC link the DLCs are
operated in a range of 30-40 V so that 35% of the available energy capacity is used.
To operate the kart in different conditions (s. Table I) and to protect the DLCs from overcharge, the
students developed a circuit of relays and resistors shown in Fig. 3. As space on the kart is limited, the
resistors can be connected in different combinations, resulting in the required values for resistance and
power.
With this combination of resistors, it is possible to charge the completely discharged DLC by the
electrical drives with limited charging current, provide resistive braking power of about 1 kW and
offer the possibility to discharge the DLC after use.
An overvoltage protection circuit (OVP) monitors the voltage of the DLC, cutting off the DLC from
the DC link in case of failure of the control of the kart.