Linear Operating Range and Extension of Three-Dimensional Active Zero-State PWM for Open-End Winding Drive

Active zero-state PWM (AZSPWM) finds a wide application for its merits of reducing common mode voltage (CMV). However, as to the modulation index (MI) and the possible over-modulation algorithms are still not clear, especially in the applications of the open-end winding drive with common mode connected DC links or with a single DC link, where the low-order components of CMV is actively used to control the zero-sequence-current (ZSC) dynamically in the common mode loops. To this end, the available MI range and the negative effects enforced by the CMV required are analyzed firstly. Then three possible algorithms are proposed to deal with voltage saturation effectively. As a result, the CMV still can be produced faithfully even in the saturation cases. Especially, the differential-mode voltage allowed is increased in volt-second sense when combined them with the proposed compensation scheme, i.e., an overmodulation scheme. For clarity, three dimensional (3D) diagrams are used to make illustration and the modulation is correspondingly referred to as a 3D-AZSPWM. At last, an open-end winding drive with common mode connected DC links, more applicable to electric vehicles, is used to confirm the analysis and the proposed reduction and overmodulation algorithms.