Suppression of short-circuit current in halt sequence to stop two-level inverter connected to PMSM during regeneration mode

This paper discusses an approach to suppress the rise of the short-circuit current in a halt sequence which is named “Flux-weakening Short-circuit halt sequence (FSHS)”. When grid faults stop a back-to-back system which has a DC-link capacitor with a small capacitor while in regeneration, the DC-link voltage increases rapidly due to regeneration current. FSHS interrupts the regeneration current to stop the two-level inverter and suppresses the rise of the DC-link capacitor voltage without a dynamic brake circuit. However, FSHS cannot suppress the rise of short-circuit current caused by the q-axis current which rises during the short-circuit mode when the regeneration current is low or PMSM with small synchronous inductance is driven. The improved FSHS suppresses the rise of the short-circuit current in low-load region by maintaining the q-axis current around zero until before the mode is changed to Sequence II at zero-crossing point of the current. In the experiment, it is confirmed that the improved FSHS suppresses to 85% of the short-circuit current when the regeneration current is low.