Patent ID: 9431936
Filing Date: 2016-08-30
CPC Classification: B60L,G01R,H02M,H02P

Claim Text:
1. A method for diagnosing a frequency converter, the frequency converter having a positive and negative DC link voltage which is applied via bridges of switching elements in an alternating sequence to phases of a motor, wherein pulse width modulation (PWM) signals drive the switching elements for a respective one of the phases, and wherein current sensors capture phase currents, the method comprising: a) applying PWM signals as test patterns to the switching elements; b) picking up sensor signals of the current sensors; and c) ascertaining a presence of the DC link voltage upon a displacement current being recognized in the sensor signals at each of the flanks of the PWM signals applied as the test patterns, the displacement current being recognized by detecting discrete current spikes occurring in the sensor signals and determining whether each respective one of the current spikes temporally coincides with each respective one of the flanks of the test patterns.