Differential Efficiency Testing Method for Power Drive Systems With Measurement Uncertainty Analysis

Absolute efficiency measurements in power drive systems (PDSs) require low-uncertainty instrumentation, making them costly and impractical for properly characterizing small incremental performance gains. Differential measurements offer a practical alternative by focusing on variations between operating points and attenuating systematic uncertainties. This article proposes a structured method for differential efficiency measurement in PDSs and derives equations for the quantification of the measurement uncertainty in the proposed method. The results are presented in a general way, so best practices are highlighted to improve the applicability of differential measurements in different PDS configurations, motor types, and industrial applications. The proposed method is evaluated in an experimental case study considering several switching frequencies in a frequency converter, and the results show that the method enables the reliable characterization of efficiency variations of the order of 0.05%, even when using instrumentation with insufficient accuracy for absolute efficiency assessments.