This paper presents an integration algorithm for stator flux estimation of direct torque control (DTC). This algorithm only contains a fifth-order low-pass filter (LPF), a high-pass (HP) filter, and a simple logical calculation part, where the fifth-order LPF and the HP filter can effectively filter out HF harmonics and the dc drift in the back EMF, respectively. The alpha- and beta-axis back EMFs passing through the two filters will obtain beta-axis stator flux linkage and opposite polarity a-axis stator flux linkage, respectively, and then by the logical calculation part can finally achieve alpha- and beta-axis stator flux linkages. At any synchronous angular frequency, the amplitude-and phase-frequency characteristics of this algorithm are same as those of the pure integrator, and meanwhile its dc gain is zero. The proposed algorithm with high estimation accuracy behaves well in both steady state and dynamic performance when used in a DTC-based electrical excitation flux-switching generator dc power system, which is verified by experimental results.