Field Orientated Control with Subordinated Pulse Pattern Generation of PWM Converter Fed Induction Machines

Abstract

A field orientated control strategy with subordinated pulse pattern generation, for induction machines fed by PWM converters with low switching frequencies, is presented. The control circuit supplies the fundamental waveforms of the stator currents, while the current harmonics are optimized by the voltage control scheme. The whole control system is digitally implemented, by means of a microcomputer system.After describing the function of the PWM-modulator the control concept is shown. The signal processing strategy, which includes the applied machine model, the coordinate transformations and the embedding of the modulator is explained. The acquisition of the quantities to be measured, speed and stator currents, is depicted in detail.The controller functions are mainly performed by software. After classifying these tasks according to their priority the software section is described, which comprises the control and pulse pattern generation algorithms.By means of measurements on a test drive the principles of operation of the presented concept, the independent execution of closed loop control and pulse pattern generation is documented.