Power System in Autonomous Driving Cars
Power System in Autonomous Driving Cars
Source: https://innovator.news/chinas-drive-to-dominate-autonomous-cars-84894b95961f
What is a Self-Driving Car?
Although current Advanced Driver-Assistance Systems (ADAS) provide important safety functions such as pre-collision warnings, steering assistance, and automatic braking, self-driving vehicles take these technologies to the next level by completely removing the need for a driver.
As a matter of fact, there are “levels” to autonomy, which breaks down as follows:
Level 0: The automated system has no control over the vehicle, but may prompt the driver of hazards
Level 1: The driver and the automated system share control of the vehicle. Examples of this can be found in most cars equipped with ADAS
Level 2: The automated system is capable of taking full control of the vehicle; however, the driver must be ready to intervene if the system fails to recognize a potential hazard
Level 3: The Automated system takes full control of the vehicle and the passenger can safely take their attention away from driving tasks; however, they must still be able to intervene
Source: https://www.landmarkdividend.com/wp-content/uploads/2018/05/Self-Driving-Gif.gif
Level 4: Driver can safely divert all attention away from driving tasks and let the automated system take full control. This functionality is currently limited to specific “geofenced” areas and other relatively controlled environments1
Level 5: No human intervention is required
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. How the addition of automated driving sensors affects the auxiliary load and the electrical distribution network of the vehicle.
VEHICLE ELECTRIC LOADS
Currently, vehicles have a multitude of sensors and electronics that are not directly related to the powertrain of the vehicle, called auxiliary loads. Depending on the size of these auxiliary loads, they can make a significant difference in the range of an electric vehicle. These auxiliary loads include heaters, fans, lighting, power steering, infotainment systems, and the air conditioning unit. The heating, ventilation, and air conditioning (HVAC) system is one of the largest auxiliary loads on an EV. Research has shown the HVAC electrical load is highly dependent on the ambient temperature, and HVAC systems can have up to a 35% impact on the range of the vehicle at extreme temperatures.
Source : https://www.energy.gov/eere/vehicles/vehicle-technologies-office-electric-drive-systems
It can be inferred from these references that at least 500 W of auxiliary load are used for HVAC on average, and the remaining auxiliary loads consume around 500 W of power, independent of ambient temperature. The absolute minimum auxiliary load required to keep a standard non-automated EV operating was reported to be approximately 200 W. Additional auxiliary power will be needed to supply energy to sensors and computer processors for an automated vehicle to drive. The above fig. shows a general wiring diagram of an EV. The HVAC is connected directly to the high voltage battery due to its large voltage input and potential power demand. All other auxiliary components, including additional auxiliary loads used for vehicle automation, are powered by the 12 V bus running throughout the vehicle or by a DC/DC converter connected to the 12 V bus. The 12 V bus must have sufficient charge to engage the relays and connect the high voltage battery to the motor drive to start the EV.
Power for Automation Vehicle
The total power required for a midsize car to achieve a high level of automation is almost 200W. The main additional electrical load on autonomous vehicles is the computer, and the computer is one of the main crossing points between the two. Due to the need to deal with more practical situations and also have safety against failures, the automation level should be set to 3–5. Most companies will not raise concerns about the reliability of electric vehicles. Increasing the load on the self-driving sensors can increase the total load on the 12V battery bus by almost 50%. Although the 12V battery is continuously charged by the high voltage battery via the DC / DC converter, the vehicle still relies on the 12V battery to start.
These additional charges can shorten battery life and have a small but significant impact on the overall range of the electric vehicle. Although HVAC will have a greater impact on the driving range of automatic electric vehicles, adding automatic car sensors may affect 2–3% of the electric vehicle driving range.
POWER DIVISION
Central Power and Computing Source
The first and simplest energy system structure includes computing energy and electrical energy in a single space of a vehicle. In this configuration, the high-voltage battery, low-voltage battery, and computing hardware are located in the same overall space in the vehicle. This configuration can allow localized computing and redundancy in the functional space; however, due to the centralized placement of all critical power, computing, and control resources without providing power and control redundancy for the sensors, the design is not fail-safe.
Source: Diagram of the sensors and wiring paths required for an automated vehicle
Distributed Power Sources
Another solution that can be used to distribute power to the vehicle’s automatic sensors is to install two separate 12V batteries at each end of the vehicle. General Motors has already mentioned the use of this technology and has demonstrated multiple sensor power supplies in its autonomous vehicles. Some power sources are scattered over an area and each power source is assigned multiple loads. If one power source is no longer working, there is redundancy to allow other sources to compensate for the dysfunctional power source or cables.
For the sake of integrity, the lines of communication between the centralized or distributed computer system and the autonomous driving sensors must also be redundant. The power supply is scattered throughout the vehicle, which will require additional costs and wiring. However, due to its redundancy, this configuration is more secure than the centralized configuration.
Challenges to deployment
1. Price of autonomy
Some people suggest that if it is produced in 2020, the 4th and 5th tier cars may cost 75,000 to 100,000 US dollars more than ordinary cars. To be honest, this number may even be too low, because the total cost may exceed $100,000 when considering the number of sensors required to reach the Tier 4 and Tier 5 ranges. Consumers can afford it. The high price may mean that the first truly self-driving car deployments are part of the mobility as a service (MaaS), carpooling, or robotaxi fleet. By replacing the expense of human drivers and driving higher vehicle utilization rates than consumers, these entities can build business models that can support these more expensive vehicles.
2. Is Level 3 a deployable reality?
Level 3 is the first step in the transition from ADAS to autonomy. However, there is currently some controversy regarding level 3 autonomy and the requirements for vehicles and drivers. Successfully deployed level 3 autopilot requires the driver to remain alert when the vehicle’s autopilot function is activated. This raises an interesting question because we as drivers instinctively think that we no longer need to pay attention as we let go and can happily send emails, text messages, etc. This requires our eyes and our eyes. Our ideas are not in the way.
Source: https://spectrum.ieee.org/transportation/self-driving/accelerating-autonomous-vehicle-technology
However, when using Level 3, the car may ask you to regain control of the car at any time. This raises the question of how quickly a distracted driver can get behind the wheel and regain control of the vehicle to alleviate the situation that the autonomous car cannot handle. Some automakers are currently discussing skipping level 3 as a way to overcome this challenge. Also, from a liability perspective, skipping level 3 will make it easier to determine whether the driver is controlling the vehicle or driving automatically. There is also a discussion on the use of in-cab cameras and advanced software algorithms to determine if the driver is alert and appropriate for the advanced driving monitoring system to regain control, rather than triggering the appropriate warnings to restore the driver. driver to a fully prepared state. Even if the automaker decides to skip this level, the technical complexity required to go from level 3 to 4 is much greater.
3. Processing needs of dramatically increased sensor complexity
Moving from ADAS to autonomous driving requires a deeper understanding of everything around the car. To achieve this goal, the number of sensors in automobiles has increased dramatically, and multiple LiDAR sensors, cameras, and radars are needed to replace and fundamentally improve human vision and situational awareness.
Source: https://spectrum.ieee.org/transportation/self-driving/accelerating-autonomous-vehicle-technology
These sensors are not only expensive, but the processing required to understand “what they see” and the development of conditions outside the car is very different from the calculation methods required for simple ADAS functions such as adaptive cruise control or emergency braking.
5. Safe deployment of autonomous vehicles
Safety is a key part of many automotive systems. Strict safety standards and certifications apply to any function that must operate reliably when required by the driver, such as braking, steering, etc. When we increase the mileage of a car, we are actually using a complex computer system to replace the safety decision of a human driver. The computer system contains many heterogeneous computing elements and, as mentioned above, has a billion lines of code.
Source: https://spectrum.ieee.org/transportation/self-driving/accelerating-autonomous-vehicle-technology
With the integration of functions on powerful multicore SoCs, it is also necessary to support mixed-critical applications on a single SoC. This is why certain applications require the highest level of functional safety when performing life-critical functions, combined with applications running at lower criticality levels. Trying to achieve the highest level of functional safety for all software is impossible, so a computer and software architecture is needed to support these different levels of safety without having to allocate a separate SoC for each application.
Conclusion :
Automated vehicles are now being rapidly pushed into consumers' hands. However, many steps need to be taken before full automation will be implemented on roadways. This Blog reviewed some of the major requirements for a vehicle to reach a high level of automation. The wiring architecture necessary to power these additional automated vehicle sensors has also been discussed, and consideration has been given to communication and power wires along with potential hardware fail-safe measures. Highly automated vehicles still need improvement from a sensor, legislative, and computing standpoint before they become a commercial method of transportation.
References :
https://www.osti.gov/servlets/purl/1474470
https://www.landmarkdividend.com/self-driving-car/
Siddharth Deshetti
Saurabh Ghodake
Sonali Jagtap
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