The voltage boost capability of conventional single Z-source three-level neutral point clamped (NPC) inverter based on space vector pulse width modulation (SVPWM) is analyzed. If the duty time of a shoot through vector is less than that of a particular effective vector, the maximum voltage gain of the inverter will be just 1.15. The inverter has no voltage boost capability. On that basis, the SVPWM method is modified, this results in higher voltage gain which is identical to that of a two-level Z-source inverter. In order to further improve voltage boost capability, an enhanced Z-source network is proposed. Two switched-inductor (SL) units are connected to the positive bus and negative bus respectively to improve the voltage boost gain. This new topology can achieve lower voltage press of Z-source capacitors than the conventional three-level Z-source inverter when they have identical voltage gains, and it makes it possible to implement neutral-point potential balancing control. And then, Multicell SL enhanced Z-source network is proposed, which has stronger voltage boost capability than that of SL based topology. Simulation results show that both the improved SVPWM methods and the new topologies can improve the voltage boost capability of Z-source three-level NPC inverter effectively.