Modulation Error Observation and Regulation for use in Off-line Optimal PWM Fed High Power Synchronous Motors

In synchronous motors, in the range of several mega watts, operated at low switching frequencies, it is advantageous to use off-line optimal PWM, to reduce the switching losses and undesired frequency harmonic components. But low transient performance of the system restricts the use of such commands. Considering the feed-forward structure of PWM modulators, it is tried in this paper to compensate the undesired modulation-error transients that may cause high overcurrents. An 80 kW setup is used to simulate the experiments in laboratory. IGBT based, two-point voltage source inverter is used, and operated at low switching frequencies to simulate GTO-based inverters that are commonly used to feed motors in this power range