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Electrical excitation doubly salient (EEDS) machines and electrical excitation flux-switching (EEFS) machines, both of which have simple and robust rotor structure and good flux regulation capability, are suitable for use as generators in dc power systems that need high reliability and good constant-power operating capability. In this paper, the basic design dimensions and electromagnetic performance of the EEFS machines are analyzed and those of the EEDS machines are also given for comparison. Compared with the EEDS machine, the EEFS machine exhibits bipolar stator flux-linkage and sinusoidal back-EMF waveforms as well as larger torque density. Then, control schemes of the two machines for voltage regulation of dc power systems are discussed, and in order to improve the steady state and dynamic performance of the EEFS generator dc power system, an improved direct torque control scheme is presented. It develops the strictly linear relationship between the torque and sinusoidal value of the torque angle, and can regulate the instantaneous torque directly and smoothly without current loop. Besides, the flux weakening control of the proposed scheme is also studied. The EEFS generator dc power system with excellent dynamic performance and lower flux and torque ripple has been achieved experimentally. [ABSTRACT FROM AUTHOR]