Evaluating drive cycle current for better battery pack design

Evaluating drive cycle
current for better
battery pack design

Vineet Dravid

Founder, CEO oorja & Expertise

oorja’s drive cycle current app predicts the current in each battery cell, allowing for accurate battery design and enabling accurate calculation of battery degradation and temperature rise

While evaluating battery pack performance during the design phase, information on drive cycles for which the battery is being designed is critical. A drive cycle is basically a vehicle usage pattern representative of how an “average” user uses the vehicle. Whether you are optimizing the pack for thermal runaway or evaluating degradation, it is important to investigate how the pack will behave for any given drive cycle.

Further, regulatory requirements mandate that the vehicle meet requirements for certain well established drive cycles, certified as being representative of standard user behaviour by certification agencies. Some of these standard drive cycles include the US 06, MIDC (modified Indian Drive Cycle) and WLTC (World Harmonized Light Duty Test Cycle) (Fig 1). It is a requirement that users validate their designs for one such drive cycle and submit reports.

Drive Cycle Velocity Profiles

Fig 1: Drive Cycle Velocity Profiles for MIDC, US06, WLTC Standards

How does one now account for all these variables and convert a traditional drive cycle into one which is EV analysis compliant?

In internal combustion (IC) engines, the primary application of driving cycles was to identify the performance characteristics of a vehicle, such as exhaust emissions and fuel consumption. In electric vehicles, understanding the behaviour of the battery across various drive cycles is extremely valuable since it allows for optimal battery design in terms of battery capacity and power requirements.

‘Drive cycles’ are essentially a series of data points that plot vehicle speed against time under various driving conditions. For instance, drive cycles for urban intra-city commutes vary from those for highway driving.

Understanding drive cycles for a variety of conditions is crucial to get a better understanding of battery behaviour. Driving cycles may be impacted by a number of driving profile characteristics, including the average, maximum, and minimum values as well as the standard deviations of speed, acceleration, and delay. For instance, you might only be able to travel at 35 km/hr in a city, yet you could reach 90 km/hr on a highway.

Computing the drive cycle behaviour for IC vehicles is easier given the availability of huge volumes of open data. However, the data available is mapped to velocity versus time. This data is inaccurate and fairly complex to analyse battery behaviour for drive cycles, because of the non-linear nature of cell behaviour.

Further, traditional methods for calculation that involve copious amounts of Excel-based transactions are not only tedious but also lacking in accuracy.

While it can be difficult to obtain precise data to estimate current, oorja’s drive cycle current generator app provides all the essential details about the vehicle, the type of terrain it will be travelling on, and other factors.

One stop solution to estimate drive cycle current

With oorja’s Drive Cycle Current App, users can add or choose vehicle-related characteristics like terrain type, class of user, conversion efficiency, battery information, cell type, pack configuration. The power calculation is based on parameters such as frontal area, mass, friction coefficients etc.

MIDC Drive Cycle Current for Two Wheelers

Fig 2: Two-Wheeler Velocity and Current Profiles for MIDC with Terrain Type: Flat and Uniform 10o Inclination

It aids better design since it can account for phenomena such as regenerative braking. It can also help deduce battery pack configuration. For example, if the battery discharges before the drive cycle is complete, then it is an indication that the battery pack is not adequate for that particular drive cycle.

The output from this can serve as an input for other oorja apps for calculation of capacity fade and thermal management.

US06 Current Profile for Four Wheeler, Flat Terrain

Fig 3: Four-Wheeler Current Profile for US06 Standard, Terrain Type: Flat

WLTP: Drive Cycle: Current Profile of Four Wheeler, Flat Terrain

\Fig 4: Four-Wheeler Current Profile for WLTP Class-2 Standard, Terrain Type: Flat

The ability to accurately predict a vehicle’s driving cycle current is becoming more crucial in today’s intelligent transportation systems, especially for managing energy in hybrid electric vehicles, regulating energy consumption in electric vehicles, and planning the trajectory of autonomous terrestrial vehicles. Oorja’s engineering solutions can help accurately assess the drive cycle current parameters of a battery pack and achieve optimal outcomes.

Write to us at prajakta.sabnis@oorja.energy and explore how oorja can help you with accurate range predictions. Alternately, visit https://oorja.energy to book a demo.