A POWER SYSTEM IN AUTOMATIC DRIVING VEHICALS
A POWER SYSTEM IN
AUTOMATIC DRIVING VEHICALS
I.
INTRODUCTION
:
Automated vehicles have
drawn increasing attention in recent years, where certain companies are pushing
automated vehicles into consumers’ hands. However, these vehicles are not fully
automated, and to reach higher levels of automation, more sensors and systems
must be implemented to control the vehicle in all real-world circumstances. The
addition of advanced driver assistance systems (ADAS) to a vehicle is a task in
itself.
A vehicle has limited
space for sensors, wiring, power supplies, and computer processors.
Additionally, all these new components, added to make a vehicle automated,
consume power while individual sensors might not be large loads, the power
drawn by a multitude of sensors can compound to be significant. Most new
studies about automated vehicle systems use an electric vehicle (EV) instead of
an internal combustion engine (ICE) vehicle. EVs are inherently easier to
control using automated driving sensors and systems, because control is
accomplished electrically rather than mechanically. Furthermore, EVs have fewer
moving parts than ICE vehicles, which can lead to improved reliability, and
government regulations and policies in the U.S. are leading towards an all-EV
future.
II.POWER
AND RANGE OF VEHICLE:
Table.1/Fig.1.sensor
power requirements for an automated vehicle
Fig.
2. Diagram of the sensors and wiring paths required for an automated vehicle.
The total power required for a mid-size sedan
to reach a high level of automation with the setup shown in Fig.2 is almost 200
W, as shown in Table I. Although only one design is shown here most other
automated vehicle sensor layouts are around 200 W and only make minor
adjustments, such as replacing RADAR with LiDAR on the front and rear of the
vehicle and utilizing different cameras. The main additional electrical load
for an automated vehicle is the computer, and the computer is one of the main
stepping points between levels 3-5 of automation, due to the need to handle
more real-world circumstances and also be fail-safe. Most companies do not
release the electrical power requirements of their computer packages, while
others speculate the power demand will be at least a few kilowatts, thus making
comparisons difficult. Therefore, this section will focus mainly on the sensors
and the total estimated power consumption of an automated EV from the data
provided. Passenger entertainment loads are also expected to increase for fully
automated vehicles. For higher levels of automation, when a person is not
responsible for monitoring the environment or fall-back performance of the
automated vehicle, it is reasonable to assume passengers will want to be on
electronic devices while they are waiting to arrive at their destination. These
additional loads, such as a laptop or entertainment system, can range from
50–100 W in some cases. Therefore, two or three of these passenger-induced
loads could double the amount of power calculated in this paper to have a
highly automated vehicle.
Fig.
3. LiDAR circuit schematic and waveform of one laser pulse. When the threshold
voltage is applied to the FET, the small capacitor is shorted to ground causing
a current spike that emits a laser pulse via the laser diode.
A.
CENTRAL
POWER AND COMPUTING SOURCE :
The first and simplest power architecture contains
the computational power and electrical power within a single space in the
vehicle. In this configuration, the high voltage battery, low voltage battery,
and computation hardware all lie in the same general space within the vehicle.
The configuration could allow for redundancies within the localized computing
and power space; however, this design falls short of being fail-safe due to the
central positioning of all critical power, computing, and control resources
while not providing power and control redundancies to the sensors.
Fig.
4. Diagram of the sensors and wiring paths required for an automated vehicle.
B. DISTRIBUTED POWER SOURCES:
Another solution that could be implemented to
distribute power to the automated vehicle sensors is to have two separate 12 V
batteries on either end of the vehicle. General Motors has mentioned using this
technique and shows multiple power sources for sensors in their automated
vehicle the topology could function similarly to the grid. A few power sources
are scattered across a region with multiple loads assigned to each energy
source. In the event that an energy source is no longer operational,
redundancies are in place to allow the other sources to compensate for the
dysfunctional power source or wire. To be complete, there would also need to be
a redundancy in communication lines between a centralized or distributed
computing system and the automated driving sensors. Power sources are scattered
throughout the vehicle, which would require additional costs and wiring.
However, this configuration is more fail-safe than the centralized
configuration due to its redundancies.
Fig.
5. Diagram of the sensors and wiring paths required for an automated vehicle
with two separated power sources and backup power sources located with each
sensor indicated by yellow lightning bolts.
Another approach is to have two separate low voltage
power sources, as in the last approach, with a small amount of energy storage
located next to each sensor, as seen in Fig. 5. This would enable the sensors
to operate even if there is a wire fault in the immediate vicinity of a sensor.
A sensor could then operate independent of any physical connections for a short
amount of time while the vehicle could divert to a safe location to further
analyse a disturbance in the vehicle. Powering the sensor is only part of the
challenge— data must still be transferred between the central computer and the
sensors in order to obtain positioning information. This could be accomplished
by wireless communication. The additional power sources, along with wireless
communication, would add to the cost of the system; however, it would make the
system more fail-safe.
III.SENSOR
POWER MEASUREMENTS:
To confirm the data sheet power consumption values
for the sensors shown in Table I, a test bench platform was built to test the
power requirement for some of the automated driving sensors and determine if
they had any effect on the 12 V bus. The results are shown in Table II.
Table
II/Fig.1.sensor power requirements data sheet vs measured results
LiDAR was initially discussed as a concern due to its high sampling rate and fast, high current pulses. However, experimental results show that the voltage harmonics on the DC bus did not pose an issue. This was likely due to a good filtering system designed by the manufacturers. Other measurements showed slightly lower power consumption compared to data sheet values. In addition, measurements taken on RADAR and LiDAR sensors indicated their power consumption does not vary significantly when objects are moving around them. For example, the power is constant if there are multiple moving objects or if all objects are stationary around the LiDAR sensor. Moreover, the IMU with GNSS did not vary significantly while the vehicle was moving.
VI.IMAGE CREADIT:
[1]. https://www.osti.gov/servlets/purl/1474470
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