Electric bus retrofit - deceleration test - data analysis
The preliminary analysis of the data allowed us to assess the validity of the data and post-processing tools, showing the weaknesses of the single band GPS equipment. In particular, Racelogic's Vbox equipment showed some noise and a delay of 1.6s compared to other equipment.
Also in terms of location, single band GPS has a CEP of around 2.5m (with data from 6 satellites) while multiband equipment can make use of data from 10 satellites to achieve accuracies of around 50cm.
The Garmin and Ublox multiband GNSS equipment showed a high degree of agreement and reliability, showing only slight discrepancies when stationary vehicle.
On the other hand, due to an installation affected by some vibration, whose intensity is proportional to the aerodynamic resistance, the microwave radar speed sensor, despite some noise, showed its reliability, eliminating the well-known "lag" in the response of GNSS-based systems when the vehicle is close to the stationary state or in the vicinity of high speed gradients.
Nevertheless, employing the classical procedures for the analysis of deceleration profiles in the absence of acceleration data from the vehicle's CAN, which exclude the initial instants of the deceleration process, as well as information relating to speeds below 2 km/h [0.55 m/s] where truncation effects in the data acquisition of some systems may give rise to errors greater than 10%, the degree of agreement of the various data sources (which use different operating principles) ensure a high degree of confidence in the results to be obtained and allow the preparation of the next tests to be performed at CTMFA, during which the challenging SORT tests will be carried out, a standard in the bus industry with regard to determining energy consumption in standard conditions.
By aggregating the data from the various tests carried out, with both buses, it is possible to immediately observe the impact of the wind that was felt during the tests, giving rise to two distinct groups of speed profiles, one for each set of tests carried out in opposite directions.
The next few days will be days of detailed study and analysis of the data produced to validate what appears to be the correct predictive dimensioning of the energy storage system designed for the definitive version of eBUS, reconverted by Barraqueiro Transportes, S.A.
