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

This paper presents an integrated approach to the closed-loop control of output voltage for a voltage source inverter and output current for 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. Also, since the modulator is a closed loop system, it exhibits excellent robustness to parameter variations and other system disturbances. The performance and practicability of the modulator have been verified both in simulation and experimentally.