In a method and device for monitoring speed, in particular for monitoring
the rotation speed of an electric machine, two processors are employed
which monitor the speed using different checking modes and cross-compare
results. The first processor executes a conventional control algorithm and
checks on the basis of an estimated or measured value of the speed whether
a speed limit has been exceeded. The second processor determines the
actual output frequency, which is also indicative of the speed, of a
converter either from actual current values, which are measured anyway, or
by reconstructing the voltage from control signals of transistors. Both
processors thus monitor if a rotation speed limit has been exceeded and/or
execute corresponding response actions. The method also recognizes faults
in the power section based on the evaluation of the phase current. The
system can also be designed to manage pulling loads.
