*2.1. Proposed Topology*

The proposed high-harmonic injection-based WFSM topology is presented in Figure 2. This topology employs two inverters, namely inverter-1 and inverter-2. Inverter-1 provides the regular three-phase input armature currents (*Iabc*1) to the armature winding (*ABC*) of the machine, whereas inverter-2 injects the single-phase high-harmonic current (*IH*) i.e., *6th* harmonic current in this case, to the neutral-point of the Y-connected *ABC* winding. The input armature currents of inverter-1 are responsible for the fundamental-harmonic current of the armature winding that produces the fundamental MMF in the air gap. However, the single-phase *6th* harmonic input current of inverter-2 is responsible for generating a high-harmonic current component of the armature winding. This current develops the high-harmonic MMF in the air gap. Although the fundamental and high-harmonic MMF components are produced by the same armature winding, the difference in their frequencies

makes them uncoupled. On the rotor side, the rotor has two windings, namely excitation winding and field winding. Both windings are electrically connected by an uncontrolled rectifier. The fundamental MMF component produces the main armature magnetic field, whereas the high-harmonic MMF component induces the harmonic current in the rotor excitation winding. The induced harmonic current is rectified to inject DC to the field winding of the rotor to produce the rotor main field. The produced rotor field interacts with the equal number of stator poles to produce torque. A 4-pole 24-slot (4p24s) machine is utilized to validate the operation of the proposed high-harmonic injection-based WFSM topology. This machine is adopted from [16]. The structure of the employed machine along with its armature and rotor winding configurations are presented in Figure 3. As seen in the figure, the stator core is equipped with 4-pole, 24-slot, double-layered armature winding whereas the rotor is fitted with 4 rotor main teeth and 8 rotor sub-teeth to accommodate the excitation and field windings. The parameters of the armature winding used for the employed machine are presented in Table 1, which shows that the winding factor of the winding is 0.933. The winding factor and the three-phase MMF for the different harmonic numbers generated for armature winding used for the employed machine are presented in Figure 4a,b, respectively. The winding configuration used for the armature of the machine is chosen from the various options available on online tool named as Emetor-Electric motor winding calculator [21].

**Figure 2.** Proposed brushless WFSM topology.

**Figure 3.** Two-dimensional machine layout and its winding configuration.


**Table 1.** Winding parameters for the employed machine.

**Figure 4.** (**a**) Winding factor and (**b**) three-phase MMF for different harmonic numbers generated for the armature winding used for employed machine [21].
