A Novel Low-Frequency Virtual Space Vector Modulation With the Improved Continuity of Output Average-Voltage and Bus Voltage Utilization for Single-Phase Neutral Point Clamped Three-Level Inverter

In the high-power superconducting fusion converter, the single-phase neutral point clamped (NPC) three-level converter is applied to replace the traditional thyristor converter using an integrated gate-commutated thyristor (IGCT) as a power device. The operating frequency of IGCT is usually lower, only a few hundred Hz. An optimized hybrid space vector pulsewidth modulation (SVPWM)-8H is proposed to solve the problems of discontinuous output average voltage, low dc bus voltage utilization rate, dead time compensation, and neutral point potential balance. The new sectors are inserted to make the range of output average voltage of adjacent sectors intersect, which improves the continuity of output average voltage. Furthermore, some sectors are composed of four vectors to reduce the minimum working time of redundant small vectors, improving the dc bus voltage utilization ratio and the converter's performance. Moreover, by analyzing the influence of dead time on redundant small vectors, redundant vectors are rearranged to make redundant small vectors' working time synchronously in sector and sector switching, which reduces the influence of dead time on neutral point potential balance. Finally, by analyzing the influence of dead time on the output average voltage, dead time compensation is applied, which reduces the difficulty of compensation implementation. Simulations and experiments verify the rationality of the optimized hybrid SVPWM-8H.