Overmodulation and six-step mode for observer-based V/Hz control

Abstract

This thesis deals with the control of electrical machines in the overmodulation range. The goal is to have a stable control system able to exploit the full potential voltage of the inverter. After a brief explanation of the system model, the overmodulation algorithm is described. This method allows to have a smooth transition between the linear operation to the extreme operating condition in which the maximum voltage is produced. A synchronized PWM approach is adopted in order to reduce the harmonic spectrum throughout the whole operation.

A scalar control based on a flux observer is considered thanks to its stability and its compatibility with the maximum voltage operation.

Results show the feasibility of the overall system, six-step mode is able to increase the reachable speed while lowering the currents.