Error Analysis of Motor-Efficiency Estimation and Measurement

Uncertainties and errors exist in all areas of the scientific and engineering world. Accurate error analysis is needed to justify the correctness of the experimental results and investigate the effects of errors in motor efficiency estimation and measurement. This paper presents the classification and mathematical derivation of the errors in motor efficiency evaluation. An extended motor efficiency error analysis, using the maximum error estimation (MEE), worst-case error estimation (WCEE), and realistic error estimation (REE) techniques, is presented. Two efficiency methods, the direct efficiency measurement and the nonintrusive air-gap torque (NAGT) methods, are analyzed, considering all possible error sources. It is concluded that the REE method provides the most accurate error estimate. For the NAGT method, REE predicts the motor efficiency estimation error to be within plusmn2.25%, which agrees well with the 2.0% error obtained from the experimental results. Another contribution of this paper is that the influence of each error source (motor variable) on the motor efficiency evaluation accuracy can be quantified and ranked. This will greatly facilitate efficiency evaluation method improvement and experimental instruments selection.