04-08-2012, 11:29 AM
KINETIC ENERGY RECOVERY SYSTEM BY MEANS OF FLYWHEEL ENERGY STORAGE
2KINETIC ENERGY.pdf (Size: 831.19 KB / Downloads: 599)
Abstract:
This paper deals with the design of Kinetic Energy Recovery Systems (KERS) by
means of Flywheel Energy Storages (FES). KERS by means of FES are currently under
development both for motor sport and road hybrid vehicles. The aim of the work is the
optimalization and implementation to the hybrid and electric road vehicles. Testing equipment
for the experimental analysis of the simplified FES was designed.
INTRODUCTION
Introduction to Regenerative Braking
A regenerative brake is a mechanism that reduces vehicle speed by converting some of
its kinetic energy into another useful form of energy - electric current, compressed air.
This captured energy is then stored for future use or fed back into a power system
for use by other vehicles. For example, electrical regenerative brakes in electric railway
vehicles feed the generated electricity back into the supply system.
In battery electric and hybrid electric vehicles, the energy is stored in a battery or
bank of twin layer capacitors for later use. Other forms of energy storage which may be
used include compressed air and flywheels.
Regenerative braking utilizes the fact that an electric motor can also act as a
generator.
The vehicle's electric traction motor is operated as a generator during braking and
its output is supplied to an electrical load [Fig. 1.].
It is the transfer of energy to the load which provides the braking effect.
Introduction to Flywheel Energy Storage
Kinetic storages, also known as Flywheel Energy Storages (FES), are used in many
technical fields.
While using this technical approach, inertial mass is accelerating to a very high
rotational speed and maintaining the energy in the system as rotational energy. The
energy is converted back by slowing down the flywheel. Available performance comes
from moment of inertia effect and operating rotational speed.
29
Flywheel mass is either mechanically driven by CVT (Continuously Variable
Transmission) gear unit [Fig. 4.] or electrically driven via electric motor / generator
unit [Fig. 5.].
Safety Concept
Safety concept concerning Control System is following:
Control unit limits rotational speed by a hardware lock in the output stage. Control
system monitors all security parameters. During idle operation is no voltage induced.
In case of error messages or breakdown, control system discharge KERS.
Controlled and safe discharge of the system is possible by converting rotational energy
in thermal energy. In the flywheel storage system, the critical energy is reduced by
using several small storages, coolant ducts and channels in stator [Fig. 14.], [Fig. 15.].
FES is designed as a reluctance motor and its resulting safety benefits are
following:
Inner flywheel rotor is designed as homogenous flywheel mass without any additional
coil former, windings, magnets or rotor cage. Laminated rotor consists of sheetmetal
packet, incl. disc spring and rotor shaft equipped with hybrid bearing [Fig. 17.].
CONCLUSION
Comparison with other storage technologies
In comparison with other battery storage technologies, KERS offers:
• Cycle durability [Fig. 25.] - 90% efficiency of flywheel (including power electronics)
in both directions during KERS reference duty cycle.
• Extensive operating temperature range [Fig. 26.].
• Steady voltage and power level [Fig. 27.], which is independent of load, temperature
and state of charge.
• High efficiency at whole working speed range.
• No chemistry included, thus no environmental pollution and great recycling
capability