In continuation to understand the impact of Electrification of vehicles on vehicle testing, (you can refer last blog on Understanding E in EV) today we have picked the most favourite question of consumers- What is the electric vehicle mileage? Answer to this question is not simply a number for an Electric Vehicle, as user has to gain the new understanding of energy replenishment (refuel/recharge) and new method to represent mileage (range). Electric Vehicle range is the distance it can cover in one full charge measured in km or miles. Consumption rate is the important parameter for mapping the performance and behaviour of the vehicle, measured in Wh/km or Wh/mile. Electric vehicle range always troubles the driver with the thought of whether he will be able to make it to the destination without running out of battery(charge) hence the term Range Anxiety was coined.
Effective Electric Vehicle range evaluation methods are continuously developing with development in Electric Vehicle technology. And we will be focusing on these methods in this blog. But first let’s see where are we today on Electric Vehicle range.
Current Electric Vehicle Range Benchmarks
Below table provides a glimpse on current ranges available with various category of vehicles.
* Range is variable depending on the variant
*** Approximate price
These values show how electric vehicle range and its price are directly related. Thus, it becomes important to understand the parameters affecting electric vehicle range.
Major Parameters That Affect Electric Vehicle Range
Electric vehicle range depends on the way energy is gained and the way energy is consumed.
Major Parameters That Affect Consumption
Powertrain and its energy source are the main differentiator between an Electric Vehicle and an Internal Combustion Engine (ICE) vehicle. If consumption is considered, the parameters affecting it have not gone under a drastic change. They majorly stay similar for electric vehicle range and are mentioned below: -
- Vehicle Speed
- Driving Style
- Auxiliary Loads
- Vehicle Weight
- Ambient Temperature
We will look into each of these parameters one by one.
Vehicle Speed and Driving Style
Even though consumption trend is similar for enthusiastic and economical driving in EV and ICEs but rate of consumption varies drastically and still requires lot of research.
The graph given below shows the variation in battery consumption rate & the electric vehicle range against different vehicle speeds.
From the above graph it can be seen that at lower speeds (20 kph to 40 kph), the consumption is low, but at even lower speeds the consumption is slightly more than the minimum consumption. This rise in the consumption at very low speeds is high as more power is required to overcome the rolling resistance and to pull the vehicle weight. Consumption increases with speed as the aerodynamic drag increases and more power is required to drive the motor for an electric vehicle.
Similarly, electric vehicle range at constant speeds is inversely proportional to the consumption at those speeds
Below graph with demo data gives a glimpse of energy consumption for various PPS.
The above graph shows how the consumption varies with change in pedal position. Different Pedal position (PPS) demands different consumption rate and hence higher speed is achieved faster with 100% PPS as compared to when pedal is pressed less. The max speed of the electric vehicle reduces for lower PPS resulting in lower acceleration.
Auxiliary Loads, Aerodynamics and Weight
Efficiency of an IC Engine vehicle drops when driven loaded, same goes for an Electric Vehicle as well. But impact of auxiliaries is critical and its effect on electric vehicle range can be seen in the graph below:
Similarly, aerodynamics impact becomes more critical for EV range as they have more impact on efficiency of battery consumption due to limitation in battery capacity and its cost. For reference: - Tesla claims that the use of new Aero wheels in Model 3 can increase the range by 10%. (https://electrek.co/2018/01/19/tesla-model-3-aero-wheels-explained/, https://insideevs.com/model-3-aero-wheels-efficiency-10-claims-tesla-vp-engineering/ )
Ambient Temperature and cooling
Temperature is one parameter though, which affects the range much more so in an EV rather than ICE vehicle. Following graph shows how power consumption is dependent on ambient temperature. As the ambient temperature increases up to certain range, the consumption rate decreases which in turn reduces total power consumption. With this decrease in the consumption, range of the vehicle increases.
Here you can see the effect of temperature on the range of the vehicle. With increase in the ambient temperature, the range of the vehicle increases. Range tends to reduce in cold and hot areas as the use of ancillary loads increases which demand energy from the battery. Batteries perform well in an optimal temperature range and can produce the required energy efficiently. To keep the battery in the optimum temperature, battery cooling systems needs to work at maximum efficiency.
Challenges in Electric Vehicle Range Extension
Range extension is dependent on two critical parameters- Battery Capacity and Battery charging.
1. Improvement in Battery Capacity-
One way of improving the EV Range is to provide a battery with higher capacity which will increase the range, but increasing battery capacity also adds to the weight of the car which can affect range and this will add to the cost of the vehicle. A balance has to be found for improving range of the vehicle to maintain affordability and efficiency output for battery Power.
2. Battery Charging-
There are different ways in which an Electric Vehicle can be charged and are categorized as follows:
- Level 1: Regular household outlet which will charge at a slower rate and takes longest to charge the battery to 100% SOC. Typically AC charging.
- Level 2: Electric Vehicle Charging Stations- These charging stations operate on a higher voltage then level 1 type of charging and can charge the battery to full in a shorter time. Typically, AC charging
- Level 3: DC Fast Charging as the name suggests, it charges the Electric Vehicle at very fast pace as it connects directly to the battery bypassing the onboard converter offloading the conversion to off-board converter allowing it to provide any amount of power required. These charge Electric Vehicles the fastest and are typically available at public stations.
Another challenge which the industry is facing is with regard to the number of electric vehicle charging stations and its network. Currently there is very less development in the charging infrastructure, and range anxiety is the most significant factor standing in the way of electric vehicles.
Next challenge is to map and understand impact of these parameters on electric vehicle efficiency for various user drive cycles, weather and ambient conditions. This can be done by combining learnings from the testing procedures used to map user profiles with new capability to measure the power consumption from battery.
Electric Vehicle Range Measurement Methodology
Since electric vehicles are still in initial phase of development so it is important to understand the drive cycle for each electric vehicle and then use specific tests for Electric Vehicle range estimation. This helps in understanding the demands for Electric V charging infrastructure and thus to improve electric vehicle range and reach.
Various other tests can be carried out for complete benchmarking of an Electric Vehicle which were covered in our previous blog: Understanding “E” in EV (Electric Vehicle).
Electric Vehicle Range- Measurement and Analysis
Measurement can be done generally for
- DC power measurements at battery terminals.
- Battery temperature pack cooling efficiency measurement.
- CAN bus messages measurement.
From the above measured parameters various analysis are done to obtain: -
- Consumption Rate: wrt speed and its variation with change in ambient temperature.
- Regenerated Power: when the vehicle is subjected to braking and allowed to coast.
- Consumed power: wrt speed and temperature
- SOC level: Coulomb counting is one of the most used method for estimating the SOC level and the same would be used here at ASI.
- Peak power out of battery: Peak power varies with speed and during various accelerations. This can be understood and behaviour can be analysed.
- Braking performance at various SOC level: Braking of the vehicle may vary with change in SOC in terms of distance and regenerated power.
- Power consumption by auxiliaries: This can be measured at the auxiliary battery and consumption by auxiliary loads can be mapped.
All the above parameters give us an insight on behaviour of the vehicle and how the Battery Management System (BMS) is designed to deliver the desired performance to improve electric vehicle range.
Note: All the values in the graphs are for representational purposes. Data is manipulated for confidentiality.