Analysis of DC Motor Current Waveforms Affecting the Accuracy of “Sensorless” Angle Measurement

Abstract

A typical approach for “sensorless” angle or speed measurement of dc machines is to evaluate periodic oscillations in the electrical motor signals which is also known as ripple counting. This method is usually applied to the current signal and very susceptible to counting errors due to different waveforms caused by various influences. In this article, the steady-state current waveforms of a small dc machine are investigated to identify the causes leading to incorrect counting results. The focus is on production tolerances and changes over the service life of the motor. This is done both by the experimental and simulative investigations and analysis of the signals in the time and frequency domains. For the simulative investigation, much attention is paid to suitable modeling for this particular task and parameter variations are performed to separate the influences on the current signal. The goal is a better understanding of the different waveforms and their causes as a basis for the development of future error-free counting algorithms.