Analysis of Uncertainty in Efficiency of an Automotive Electric Machine with Active Rectifier

This paper outlines a method for calculating the uncertainty in efficiency of an electric generator and active rectifier using frequency analysis of voltages and currents. Since the accuracy of instrumentation varies greatly with the frequency of the measured signal, ascertaining measurement uncertainty in a system with composite signals presents a challenge. This research evaluates uncertainties for individual frequency components of the measured voltages and currents using accuracy values listed in the datasheets for the data acquisition units and current sensor, in order to better account for frequency-dependent error. The uncertainties associated with the measured speed and torque are also evaluated. Uncertainty values associated with the input quantities are propagated to obtain uncertainty in the power values and then uncertainty in the calculated machine, rectifier, and system efficiencies. The measurement data for the analysis is obtained from an experiment with a 125 kW automotive motor and a 250 kW SiC inverter.