Effect of voltage sags on the Z-source adjustable-speed drives

This paper presents a critical evaluation of the effect of voltage sags on Z-source adjustable speed drives (ZSASD), analyzes the behaviour of Z-source adjustable speed drives under the balanced and unbalanced sags. The voltage-tolerance curves are obtained to assess the sensitivity of the ZSASD under the balanced voltage sags. In particular the capacitor voltage variation under unbalanced voltage sag and its dependence on source impedance, Z-source network inductance and capacitance, and shoot-through duty cycle is computed. It is shown that for larger Z-source network capacitance and inductance, the capacitor voltage variation under the voltage sag is small and decreases the susceptibility of a ZSASD. The proposed representation can be established for any other three-phase equipment and used for sensitivity assessment. By controlling the shoot-through duty cycle, the ZSASD system provides ride-through to voltage sags, both balanced and unbalanced sags. Analysis and simulation results will be demonstrate these features.