Electric bus retrofit - deceleration test - data analysis
On March 31st 2021, the work team from the Engineering and Planning Office (GEP) of Barraqueiro Transportes, S.A. (BT), with the precious collaboration of the LCEC (Low Carbon Energy Conversion Lab) of the Lisbon Higher Institute of Engineering (ISEL), carried out a series of tests with the electric bus on the runway of Air Base No. 2 of the Portuguese Air Force, located in Ota, municipality of Alenquer.
The tests were accompanied by the Municipality of Alenquer (CMA), represented by João Coelho Sousa, from the Energy, Innovation and Sustainability area of CMA's Environment Division and manager of the Alenquer LVpD project.
This first day of track tests, of the project to analyze the technical and economic feasibility of converting minibuses from their conventional thermal propulsion to a new electric propulsion system, had as main objective to evaluate the performance of the vehicle at high speeds and experimentally determine the drag coefficients (aerodynamic and rolling), as well as the efficiency losses along the vehicle's kinematic chain. In order to maximize the amount of data collected during the 3 dynamic test sessions, the tests involved not only the converted electric bus, based on the Mercedes Sprinter Chassis, but also a base model vehicle used in the conversion, currently operating at TUT (Transportes Urbanos Torrejanos), in Torres Vedras, kindly provided by Barraqueiro Oeste.
In parallel, in order to assess the accuracy of the various systems used and their operating principles, 4 different data acquisition systems were used, 3 proprietary - single band GNSS (GPS) and multiband - and an inertial system with multiband GNSS assistance - and a high precision system consisting of a microwave radar speed sensor from Corrsys Datron (Kistler) and data acquisition system from Natioinal Instruments, used in numerous research projects and kindly provided by the VP Lab (Vehicle and Propulsion Systems Laboratory) of the Instituto Superior Técnico (IST) to ISEL for the tests.
Based on these results it will be possible to model more realistically the dynamic performance and the associated energy consumption, based on the VSP methodology combined with the laboratory mapping of the efficiency of the electric motor + inverter set. This will allow a more rigorous and objective dimensioning of the needs of the energy storage system to be installed on board the vehicles, according to the different models and operational contexts, in order to ensure the desired autonomy for each route and profile of type operations.
The operations plan included a complex logistical operation, consisting of the transport, by trailer, of the electric vehicle from the premises of the Barraqueiro Group Laboratory, in Camarate, accompanied by two mechanics from ESEVEL, the Barraqueiro Group (GB) workshop located in Frielas, Loures. At the same time, the diesel vehicle was driven from Torres Vedras by a Barraqueiro Oeste driver to the facilities of the Air Force Military and Technical Training Center (CFMTFA) in Ota, which kindly made its facilities available for the tests.
After the friendly welcome by Lieutenant Colonel Paula Pires, who led the entire work team to the track, work began on installing the equipment for recording and monitoring the tests, including the speed sensor, provided by IST, installed and operated by Professor Gonçalo Duarte (ISEL), who generously accompanied the BT's work team in this day of testing. Additionally, the LCEC team from ISEL, represented in the tests by Paulo Almeida, a fundamental partner in this project, continuously monitored and tuned the parameters of the electric traction system, including energy consumption profiles, which allowed preliminary analysis and discussion of the results, in real time, with the Barraqueiro Transportes, S.A. team.
After the equipment installation period, including the necessary tests and parameterization, the first test session, during the morning, allowed to perform about 13 km in the electric vehicle, with multiple cycles and acceleration and natural deceleration tests, having reached a maximum speed of over 56 km/h.
In the afternoon, the session started with the tests of the diesel vehicle, which performed about 21 km, at an average of 37.6 km/h, reaching a maximum speed of about 100 km/h. In parallel, the BT work team, together with Paulo Almeida, reprogrammed the electric traction system controller, having tested the new electric vehicle parameterization on the taxiway.
With the conclusion of the diesel vehicle tests, the second test session with the electric vehicle began, this time with even more satisfactory results. During the afternoon the electric vehicle traveled more than 17 km, at an average speed of 43.9 km/h and a top speed of 87 km/h, above the 85 km/h that was set as the target maximum speed for the project.
With the test batteries, whose current capacity is only 20kWh, of the now electric vehicle exhausted, the satisfaction of the entire work group was reflected on their faces, even after a long and challenging day of work, as well as the gratitude for the commitment of everyone involved in this day of testing, whose results will make an unquestionably valuable contribution to the advancement of this project.
After the complex transportation logistics associated with the transport of electric vehicles, back to the lab, it's time to recharge the vehicle and prepare it for the next challenges and analyze the data.
The following day, BT's GEP team installed a charging monitoring equipment, which allows a continuous and remote monitoring of the car's charging, having registered about 21 kWh of injected energy, with a charging efficiency of about 93.5%, which allowed to charge the batteries with about 19.7 kWh.
Find a preliminary analysis of the data here: