Analysis of on- and off-line optimized predictive current controllers for PWM converter systems

The problem of on-off current control for coupling of a DC voltage system with a three-phase (polyphase) AC voltage system via a pulsewidth modulated (PWM) converter is discussed. The AC voltage represents either the counter EMF (electromotive force) of an AC machine or the three-phase power supply system (mains). The following control concepts are investigated by digital computer simulation: a simple hysteresis controller; a predictive controller with online optimization (optimization with respect to minimum switching frequency); and a controller based on offline optimization (using a switching table). It is shown that the relatively involved predictive controller can be replaced by a switching table of very limited size. For rating of the treated controllers the switching frequency as a function of the RMS voltage of the AC system and the other system parameters is used