Wavelet Analysis for Frequency Disturbance Characterization in an Electric Vehicle

Reduction of CO₂ emission is a mandatory objective for every actor in the field of automotive transport, and electric vehicles (EV's) are increasingly becoming an effective option for both OEMs and customers. However, components development and vehicle integration for EV's present new challenges that must be faced and new issues which need to be solved. In particular electric motor control systems are developed to achieve the same comfort conditions as in conventional vehicles. IDIADA developed a prototype electric commercial vehicle in which both the motor and driveline were integrated. The electric motor output shaft delivers the torque to the transmission under a certain level of load variation and with torque irregularities that must be smoothed out in the transmission components. This paper studies the results of the testing of the prototype vehicle carried out to improve the overall NVH behavior of the powertrain. The test results revealed that abrupt change in frequency content must be limited in order to avoid torque irregularities from the motor to the transmission. The abrupt change in current from the inverter to the motor was also studied by means of the wavelet analysis to reduce a given frequency range of load irregularities. This methodology permits a very accurate study in the frequency and time domain allowing the detection of the changes in time of the signals even for slight deviations and helps to properly specify the motor control characteristics. This study enabled the definition of the powertrain specifications and the electric motor control system for the entire vehicle speed range.