A multidimensional variable band flux modulator for four-phase-leg voltage source inverters

This paper presents a multidimensional flux modulator for closed-loop control of the output voltage of a four-phase-leg inverter. The proposed strategy uses flux regulated hysteresis with a rectangular bounding cube in the synchronous d-q-o reference frame, and a simple set of switching rules to ensure the selection of only the nearest active space vectors to the target reference phasor. In addition, the inherent optimal sequencing and central placement of active vectors between successive s result in the modulator having an improved performance as compared to other reported hysteresis schemes. A further enhancement is achieved by adjusting the dimensions of the bounding cube to restrict the switching process to the nearest three active vectors (and vectors) within a constant switching period. Under this constraint, the modulator achieves a harmonic performance virtually identical to the well-known open-loop space vector modulation. But since the modulator is a closed-loop system, it also exhibits excellent robustness to system parameter variations. The performance and practicability of the modulator have been verified both in simulation and experimentally.