**6.3 Experimental study**

**Parameter Analytical design method FEA** PM flux linkage 1.43 Wb 1.35 Wb Back-EMF 44.8 V 42.4 V Torque 8.4 Nm 7.97 Nm

**Table 6.**

**Figure 28.**

**Figure 29.**

**Figure 30.**

**94**

*Test bed of the FRPMM prototype.*

*Back-EMF waveforms at rated speed 300 rpm: (a) waveform; (b) FFT analysis.*

*Results comparison of the design method and 2D FEA.*

*Direct Torque Control Strategies of Electrical Machines*

*12-slot/17-pole FRPMM prototype: (a) stator; (b) rotor.*

To verify the calculated results by the analytical method and FEA, the FRPMM prototype has been built. Its major parameters are listed in **Table 4**. The structure and test bed of the prototype are shown in **Figures 28** and **29**, respectively.

#### **Figure 31.**

*Output torque vs. phase current.*


**Table 7.** *Result comparison of FEA and experiment of the FRPMM prototype.*

**Figure 30** compares the phase back-EMF waveform and spectrum at 300 rpm. It can be seen that the back-EMF waveforms are very sinusoidal. This is because the total harmonic distortion (THD) of FEA and experiments are only 1.26% and 2.63%, respectively. The sinusoidal back-EMF is inherent without any special design techniques such as skewing or pole shaping. Then, **Figure 31** shows the FEA simulated and experimental results of average torque at different winding current values. In addition, the analytical design value is also plotted as the blue triangle. It indicates that the simulated, analytical and experimental results have reached good agreements. Finally, **Table 7** compares the electromagnetic performances by FEA and experiments. Thus, the feasibility of the analytical design method can be seen.
