A Minimum Infinity Norm Based PWM Modulator for Four-Leg Three-Phase Converters

This paper presents a new pulse width modulator dedicated basically for under determined systems. The solution of the under determined problem is performed by minimum l-infinity norm solution. One of known under determined system is a four-leg three-phase converter because four reference signals must be created from three control commands. The infinity norm enables to find proper solution to generate corresponding reference signals for the PWM modulator. The designed modulator is implemented with a control system of the four-leg three-phase converter working as an universal supply unit but the proposed modulator is able to operate in arbitrary application with the four-leg converter, generally for arbitrary under-deteremined systems. It is shown in the paper that the known carrier based PWM algorithm represents a subset of modulators utilizing the minimum l-infinity norm. The theoretical assumptions and the design of the modulator were verified by simulations as well as by experiments on a laboratory prototype of 17 kVA.