A variable band universal flux/charge modulator for VSI and CSI modulation

This paper presents an integrated approach for closed-loop control of the output voltage of a voltage-source inverter and the output current of a current-source inverter, using hysteresis with a rectangular bounding box in the synchronous d-q reference frame and a simple set of switching rules. The modulator is constrained to only select from the two nearest active space vectors to the target reference, and hence achieves a significantly improved harmonic performance compared to Sigma-Delta and other stationary frame hysteresis modulators. A further refinement then adjusts the dimensions of the bounding box to restrict the switching process to two active space vectors (and null vectors) only within a constant switching period. This achieves a harmonic performance similar to open-loop space-vector modulation. Discontinuous modulation can also be implemented using an alternative dimension-varying strategy and, since the modulator is a closed-loop system, it exhibits excellent robustness to parameter variations and other system disturbances. The practicability and performance of the modulator under various modulation conditions have been verified both in simulation and experimentally.