A Small-signal Stability Study for Open-loop I-f Control of Permanent Magnet Synchronous Machine Drives

This paper deals with stability analysis of open-loop I-f control for permanent magnet synchronous machine (PMSM) drives. The nonlinear system dynamics is linearized at steady state working point for analyzing the local stability of open-loop I-f control for PMSM. The analysis shows that the open-loop I-f control is poorly damped but can achieve stable operation in a wide speed range without the mid-frequency instability issue that commonly exists for the open-loop V/f control. In fact, the open-loop I-f control can operate stably from zero to rated speed under different load conditions. Extensive simulation results are presented to verify the theoretical analysis.