<p>Flux modulation motors (FMMs) are a good choice for many applications due to their high torque density. These brushless motors have various structures, which can be divided into four groups according to their excitation. The excitation includes rotor permanent magnet (PM) excitation, stator PM excitation, direct current winding excitation, and hybrid excitation. These types of excitations are reviewed first, along with their principles of operation using winding function theory. In some applications, electric motors must operate at a wide speed range and require appropriate torque-speed characteristics. The flux-weakening capability (FWC) is introduced as an advantage, equivalent to having an appropriate torque-speed characteristic. However, FWC is directly related to the parameters of the motors, and their high values correspond to the low values of other specifications, such as the torque density and power factor. Therefore, to specify the best torque-speed characteristics, the performance of the mentioned FMMs from startup to five times the rated speed is investigated and compared. Furthermore, designs such as hybrid motors and motors with switched windings, which have been proposed to improve torque-speed characteristics, are also examined and compared. The results are extracted using Ansys Maxwell software. Finally, a prototype of a surface PM FMM has been fabricated, and its experimental results are presented.</p>