Hybrid Virtual Vector Modulation With Improved Power Factor Range and Active Capacitor Voltage Balancing for Eight-Switch Three-Phase Three-Level Inverter

As the demand of low cost in photovoltaic (PV) applications, an eight-switch three-phase three-level inverter (TP-TLI) has been proposed. However, it can only operate under high power factor (PF) with the previously proposed modulation strategies. This article proposes a hybrid virtual space vector modulation (HVSVM) with improved PF range, which contains three basic VSVMs with different PF ranges and output performances. The union of PF ranges for these three basic VSVMs can cover the full range of inverting operation. The proposed HVSVM not only can adaptively switch these three VSVMs by detecting the polarities of three-phase current in each sector, but also guarantees the output quality as much as possible. Compared to the previously proposed methods, the proposed HVSVM expands the operation range of PF angle from about [−30°, 30°] to [−90°, 90°], which greatly expands the application range of the eight-switch TP-TLI. Moreover, an active neutral-point voltage control (NPVC) method using a unified NPVC model is also proposed for the HVSVM. The highlight of this method is the NPV can be actively adjusted for any PF angle over full range of modulation index. The proposed strategies are verified by experiment results with a 3-kVA prototype.