Analysis of On- and Off-Line Optimized Predictive Current Controllers for PWM Converter Systems

This paper treats 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. There the ac voltage represents (according to the directions of the energy flow which is possible in both directions) either the counter emf of an ac machine or the three-phase power supply system (mains). The following control concepts are investigated by digital computer simulation: 1) a simple hysteresis controller: 2) a predictive controller with ON-line optimization (optimization with respect to minimum switching frequency) and 3) a controller based on OFF-line optimization (using a switching table). It is shown that for the system analyzed here, the relatively involved (concerning its realization) predictive controller can he replaced by a switching table of very limited size. For rating of the treated controllers the switching frequency (at the same rms value of the current control error) as a function of the rms voltage of the ac system and the other system parameters is used.