Abstract: The flux linkage of permanent magnet synchronous machines(PMSM) is sensitive to ambient temperature and stator currents. The relationship among power, torque and flux of SPMSM and IPMSM with i_d=0 control method was studied. A flux estimation strategy based on power closed-loop was proposed. This strategy could lead to a more accurate torque control. The results of simulations and experiments show that the estimated flux linkage in the proposed strategy can follow the real flux-linkage fast and accurately. This strategy shows a good dynamic performance and anti-interference performance in hybrid electric vehicle (HEV) application.