How is Electric Vehicle Range Tested?
Range anxiety is one of the biggest concerns of consumers when it comes to looking to purchase an electric vehicle (EV). Because of this, manufacturers of EVs need to have accurate range predictions to build trust and quell range anxiety.
The determination of range for battery electric vehicles (BEV) has been historically tested using the 2-cycle test methodology from the SAE J1634 standard in North America. The 2-cycle test procedure, like the single-cycle test (SCT) and multi-cycle test (MCT), generally includes standalone or sometimes a combination of city and highway speed profiles.
The Five-Cycle Testing Guidelines for Electric Vehicles
The single-cycle test (SCT) is a full-deplete test, meaning that the vehicle is driven in a repeating city or highway drive cycle until the battery dies. This can take a long time and consumes significant resources, placing significant logistical strains on test facilities. Also, additional test cycles beyond the SCT are needed to better characterize the effects of temperature and accessory loads on EV range performance.
These constraints led the Environmental Protection Agency (EPA) to adopt new methodologies for testing and determining the range of BEVs called the multi-cycle test (MCT), short-multi cycle test (SMCT+), and 5-cycle test procedures. The MCT and SMCT are full-deplete tests and combine standard dynamic drive cycles (UDDS, HFEDS, or US06) with constant-speed driving phases. The goal of using the standard dynamic drive cycles is to determine the energy consumption associated with specific and established driving patterns. and the goal of the constant speed profiles is to rapidly discharge the battery energy consuming less time and resources compared to the SCT. The standard MCT procedure consists of four UDDS cycles and two HFEDS cycles in a specified sequence including mid-test and end-of-test constant speed “battery discharge phases” (CSC) which vary in duration depending on the vehicle and the size of its battery pack. The speed profile for MCT is shown in Fig1.
The SMCT includes AC energy consumption in its range determination by means of a shorter test as compared to the MCT. It accomplishes this by changing the order of the cycles and including a US06 cycle. SMCT is not a full-deplete test unlike MCT, and the remaining battery energy must be depleted separately in the case of the SMCT, which is often done by simply driving the vehicle at a steady-state speed (called SMCT+).
Lastly, the EPA 5-cycle procedure encompasses high vehicle speeds, aggressive vehicle accelerations, use of climate control system, and cold ambient conditions in addition to the standard City and Highway drive cycles used in SCT, MCT, or SMCT+. The 5-cycle test does a better job of reflecting typical driving conditions and styles. It produces energy consumption ratings that are more representative of a vehicle’s on-road range. Different testing options for 5-cycle EV certification are shown in Fig3.
Leveraging the Adjustment Factor to Improve EV label-range
Every original equipment manufacturer (OEM) is required to run at least 2-cycle to certify range for EVs in North America, but the drive cycles under consideration in 2-cycle tests are low-speed tests that aren’t truly representative of the real world. This forces the EPA to use an adjustment factor to yield a more realistic customer that experiences range. The default adjustment factor is 0.7, which reduces the raw range by 30% when an OEM opts to certify the range with just a 2-cycle methodology. For example, a car that achieves 500 miles of range during a 2-cycle test ends up with a 350-mile label range by using the default adjustment factor. However, the EPA allows manufacturers the option to run three additional drive cycles (US06, SCO3, and FTP cold drive cycle) and use those results to earn a more favorable adjustment factor. The adjustment factor can never be less than 0.7, in the case that the estimated adjustment factor from the 5-cycle test is less than 0.7 then a default adjustment factor of 0.7 can be applied.
Using GT-SUITE to predict the 5-cycle adjustment factor
GT-SUITE, a multi-physics simulation software, is used to automate the entire 5-cycle process outlined in SAE J1634 regulation to predict the adjustment factors for various vehicle configurations, leaving users with testing options to choose for EV range certification. In addition, GT will help users eliminate the iterative steady-state calculations involved in the MCT and manual extraction of energy consumption data required to estimate the adjustment factor by using a python script. The test condition and cycle information for the MCT and the standalone 5-cycle test are highlighted in Fig4.
Fig4: Range testing driving profile and test conditions
The BEV range test procedure outlined in SAE J1634 involves varying test conditions and drive cycles to estimate the final range. GT offers users the chance to streamline the entire EV range estimation process and takes it a step further to automate the required drive cycles to compute the adjustment factor.
Learn More About our Battery Simulation Capabilities
Stay tuned for Part 2 of this blog series, where we will discuss more about the implementation and automation of various 5-cycle test conditions in GT-SUITE to calculate the 5-cycle adjustment factor in EVs.
If you are interested in learning more about battery simulation, check out our battery modeling page and learn more about our hybrid and electric simulation solutions. Also, check our top 15 battery-related topics blogs in this list!