Abstract: For forming an electric voltage signal which is proportional to a flux component of a rotating-field machine, a voltage associated with the flux component is fed to the input of an integrator, and a voltage signal proportional to the flux component is taken off of the integrator. The input of a zero-controller for suppressing the DC component of this voltage signal is connected to the output of the integrator and the output of the zero-controller is connected to a summing point at the input of the integrator. This integrator circuit can be used to determine the position of the flux of a rotating field machine, with the correct phase and amplitude, and independently of frequency, while the zero-controller remains engaged at speeds from the beginning of localization of standing rotor position up to the nominal frequency of the machine. The zero-controller has a P-controller and an I-controller whose output signals are fed to the summing point.

Abstract: A drive for a rotating field machine which has two AC voltage integrators of identical design for forming two electric voltage signals each of which is proportional to a flux component in the machine. Each voltage integrator includes an integrator and a zero-controller having negative feedback for suppressing the DC component of input voltages fed to a summing point of the integrator. Each integrator, is fed, as one input voltage, a voltage proportional to the phase-voltage belonging to the flux component and a voltage proportional to the corresponding stator current in a machine supply lead, for compensating the ohmic stator voltage drop. A second voltage, also depending on the phase current, is processed to compensate for the inductive stator voltage drop.