01-01-2013, 11:21 AM
REGENERATIVE BRAKING IN AN ELECTRIC VEHICLE
REGENERATIVE BRAKING.pdf (Size: 547.37 KB / Downloads: 189)
Abstract:
Electric vehicles have been attracting unprecedented attention in light of the volatile market prices
and prospect of diminishing supplies of fuel. Advances in battery technology and significant improvements in
electrical motor efficiency have made electric vehicles an attractive alternative, especially for short distance
commuting. This paper describes the application of Brushless DC (BLDC) motor technology in an electric
vehicle with special emphasis on regenerative braking. BLDC motors are being encountered more frequently
in electric vehicles due to their high efficiency and robustness; however a BLDC motor requires a rather complex
control to cope with the reversal of energy flow during the transition from motoring regime to regenerative
braking. In an electric vehicle, regenerative breaking helps to conserve energy by charging the battery,
thus extending the driving range of the vehicle. There is a number of different ways to implement regenerative
braking in a BLDC motor. This paper describes the Independent Switching scheme for regenerative braking
[1] as applied to a developmental electric vehicle at the University of South Australia.
Electric vehicles and regenerative
braking
In recent times, electric vehicles (EVs) have received
much attention as an alternative to traditional
vehicles powered by internal combustion
engines running on non-renewable fossil fuels.
This unprecedented.focus is mainly attributable
to environmental and economic concerns linked
to the consumption of fossil-based oil as fuel in
internal combustion engine (ICE) powered vehicles.
With recent advances in battery technology and
motor efficiency, EVs have become a promising
solution for commuting over greater distances.
Plug-in EVs utilise a battery system
which can be recharged from standard power
outlets. Since performance characteristics of
electric vehicles have become comparable to, if
not better than those of traditional Internal
Combustion Engine (ICE) vehicles, EVs present
a realistic alternative.
BLDC motor
Principally, a brushless DC (BLDC) motor is an
inside-out permanent magnet DC motor, in
which the conventional multi-segment commutator,
which acts as a mechanical rectifier, is replaced
with an electronic circuit to do the commutation. [6]. Consequently, a BLDC motor requires
less maintenance and is quite robust [7].
A BLDC motor has a higher efficiency than a
conventional DC motor with brushes [6]. However,
a BLDC motor requires relatively complex
electronics for control.
BLDC motor control
Two separate modules (stages) are required in
order to control a BLDC motor: a power module
and a control module.
A BLDC motor requires a DC source voltage to
be applied to the its stator windings in a sequence
so as to sustain rotation. This is done by
electronic switching using an inverter as shown
in Figure 2. The inverter circuit employs a half
H-Bridge for each stator winding [8].
BLDC regenerative braking
Regenerative braking can be achieved by the
reversal of current in the motor-battery circuit
during deceleration, taking advantage of the
motor acting as a generator, redirecting the current
flow into the supply battery. The same
power circuit of Figure 2 can be used with an
appropriate switching strategy. One simple and
efficient method is independent switching in
conjunction with pulse-width modulation
(PWM) to implement an effective braking control
[9].
In independent switching, all electronic
switching devices are off while applying regenerative
braking. The bottom switching devices
are on for the 120 degree portion of the cycle,
corresponding to the flat top part of the phase
EMF, as illustrated in Figure 4. All top switches
are kept turned off.
Conclusion
The regenerative braking system described in
the paper hss been successfully type-tested. The
system employs the Independent Switching
strategy to control the flow of current during
various stages of the cruise profile. The work is
in progress to fit TREV with the commercial
BLDC motor and a commercial power supply
together with the controller developed in-house.