Method and apparatus for standstill recognition when restarting a power converter-fed AC motor without a tachometer generator

摘要

The invention relates to a method and apparatus for recognizing a standstill condition when restarting a power converter-fed AC motor without a tachometer generator. According to an embodiment of the invention, a standstill recognition method includes first and second active phases decoupled by a passive phase. In each phase, time characteristics of the orthogonal current components of a measured motor current are recorded, and the energy component of current from the second active phase is further evaluated to generate an average value. This generated average value and an upper range value are then compared to a limiting value, which will be exceeded when the AC motor is at a standstill. Thus, through application of a current measurement and a simple evaluation, one can quickly determine the actual state of the power converter-fed AC motor when restarting.