Siemens Aktiengesellschaft

Hans-Dieter Heining

Michael Braun

Albert Wick

A method of operating a three-step inverter that supplies a polyphase machine whose electric output variables are formed by scanning two zero-shifted setpoint signal sets with triangular modulation signal, in a space vector representation using double modulation. A first or second interval value is formed between the maximum or minimum value of phase signal waveforms of the setpoint signal sets and an upper or lower scanning limit. The first and second interval values are added or subtracted from the phase signal waveforms of the first and second setpoint signal sets, to thereby increase the linear control range of the inverter and reduce the harmonic spectrum in the inverter output signals.

Method of operating a three-step inverter

For establishing the field direction without mechanical pickup upon startup of a rotating field machine, e.g., in permanent excitation, a high-frequency component (iz*) is impressed on the stator current or on the stator voltage. Thereby high-frequency voltage components (or current components) are coupled into the stator windings, the envelope curves of which are correlated to the position of the field axis of rotor axis. Preferably the components of a model vector (FM) which also contain high-frequency components are calculated by a flux computer (60). The high frequency components isolated in a filter (61) are correlated in a means value former (62) to the components of the direction vector (fx). Thereby a field-oriented operation of a synchronous machine is possible.

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Nuremberg, Germany

Hans-Dieter Heining