Space Harmonics Elimination for Fractional-Slot Windings With Two-Slot Coil Pitch

Abstract

Recently, fractional-slot windings with two-slot coil pitch are receiving more and more attention due to their lower space harmonic contents in stator magnetomotive force (MMF) compared with the widely-used fractional-slot nonoverlapping counterparts. To further reduce the detrimental space harmonics for this type of winding, various solutions featured by varied coil turn ratios are investigated in this paper. Firstly, all the feasible slot and pole number combinations for fractional-slot windings with twoslot coil pitch are discussed. Secondly, two types of Slot Harmonic Only Windings (SHOW), i.e., SHOW I and SHOW II, are illustrated on the 18-slot/10-pole (18S10P) and 24S10P windings, through which only the main harmonic and its slot harmonics will be present in stator MMF harmonics. Then, to overcome the drawback of reduced main harmonic magnitude owing to both the decreased winding factor and poor slot area utilization associated with the SHOW, two solutions, i.e., 6-0 solution and 5-1 solution for 18S10P and four alternatives, i.e., 7-1 solution, 6-2 solution, 5-3 solution and 4-4 solution for 24S10P, are proposed based on the SHOW I or SHOW II. It is found that the 5-1 solution for 18S10P and 5-3 solution for 24S10P winding are the most desirable ones considering the tradeoff between larger main harmonic magnitude and lower harmonic contents. Furthermore, electromagnetic performance comparisons are carried out between 24S10P permanent magnet (PM) machines with 5-3 solution and 12S10 two layer and 24S10P two layer machines. Although the average torque of the 24S10P machine with 5-3 solution has a slight decrease, its torque ripple and radial magnetic force density rotor eddy-current losses are greatly suppressed compared with the two layer counterparts. INDEX TERMS Fractional-slot winding, slot harmonic only, space harmonic, two-slot coil pitch.

Comparative study of dual 3‐phase permanent magnet machines with coil span of two slot‐pitches

“…It can be seen that the winding factors for the two PM machines are exactly the same, that is, 0.958. Besides, from Table 2, although the winding factor of the single 3-phase PM machine (0.925) is relatively lower [8,9,12] with coil span of two slot-pitches…”

“…The average torque electromagnetic torque can be obtained as [12]. $$${T}_{avg}=\frac{{e}_{a1}{i}_{a1}+{e}_{b1}{i}_{b1}+{e}_{c1}{i}_{c1}}{{\omega }_{r}}+\frac{{e}_{a2}{i}_{a2}+{e}_{b2}{i}_{b2}+{e}_{c2}{i}_{c2}}{{\omega }_{r}}$$$ where T avg is the average torque, ω r is the rotor mechanical angular speed, e a1 , e b1 , e c1 , e a2 , e b2 , e c2 are the back‐EMFs for each phase, and i a1 , i b1 , i c1 , i a2 , i b2 , i c2 are the input phase currents for each phase, respectively.…”

“…It is noted that among the above techniques, the multilayer windings, different turns per coil side, flux‐barriers, etc., can only be effective for the reduction of sub‐harmonics, while super‐harmonics cannot be effectively suppressed [5–7]. In contrast, by doubling the stator slot number with coil span of two slot‐pitches, it is found in [8–13] that both the sub‐ and super‐harmonics of the stator MMF can be significantly suppressed. Through examples in [8, 9], it is observed that compared to a typical 12‐slot/10‐pole machine, the 24‐slot/10‐pole PM machine has much less MMF harmonic distortions, and consequently reduced PM eddy current losses, increased machine efficiency, and reduced torque ripple, etc.…”

A Novel 24-Slot/10-Pole Dual Three-Phase Fractional-Slot Overlapped Winding for Low Non-Working Space Harmonics and Stator Modularization

“…In [35], the sub-harmonics existing in TSP windings can be further reduced by altering the turn numbers of some coils. To remove more non-working harmonics without excessive loss of the working harmonic, [36] further improved TSP winding using coils with different number of turns. This improved TSP winding was successfully applied in 18-slot/10-pole and 24-slot/10-pole machines.…”

Modular Permanent Magnet Synchronous Machine with Low Space Harmonic Content

“…In [33], the technique of using coils with different turns was applied to TSPWs with various slot/pole combinations. Reference [34] investigated various TSPWs with varied coil turns and managed to increase their winding factors of the working harmonics.…”