# Design of External Rotor Ferrite-Assisted Synchronous
## 5 Experimental Results  
The proposed 3.7 kW five-phase external rotor Fe-PMaSynRM has been fabricated and tested to validate the torque generation and back-emf simulation results. The fabricated five-phase Fe-PMaSynRM is shown in Figure 16 where the stator laminations are shown in Figure 16, rotor laminations are in Figure 16. The stator has 25 slots, and the stator coils are distributed with a span of 2 slots. The rotor has 12 poles that are distinguishable by the arc-shaped Y32H-2 grade Fe magnets. Both stator and rotor cores contain 50 PN600 steel to support the high torque density objective and to avoid the saturation. The weight of active materials of the initial model and optimal prototype Fe-PMaSynRM model have been shown in Table 6.  
The fabricated Fe-PMaSynRM has been mounted on a 5 HP dynamo testbed to validate the design properties and support the high power density operation shown in Figure 17. The dynamo is built with a DC machine as the prime mover and a digital electronic load. The test setup is shown in Figure 17a and the controller block diagram to drive the motor is shown in Figure 17b An indirect field-oriented control method has been adopted. An in-house five-phase inverter has been developed. The control algorithm is developed and implemented in the digital signal processor (TI DSP F28335). As shown in Figure 17b the five-phase currents are sensed to transform it to 2D vector quantities namely d-q axes components. Conventional PI regulators were designed to perform the closed-loop control of d-q currents followed by inverse park-transformation and generation five-phase voltages at the output terminals of the voltage source inverter. Field-oriented control utilizing MTPA and FW strategies were chosen to conduct the tests.  
First, no-load tests of the prototype are performed to observe the back-EMF and cogging torque. The back-EMF curve at 1800 rpm rotor speed has been shown in Figure 18. It is observed that the back-emf of the proposed Fe-PMaSynRM has a peak voltage of 62.75 V and an RMS voltage of 58.6 V, which nearly matches the FEA results shown in Figure 13. The cogging torque of the external rotor Fe-PMaSynRM is shown in Figure 19. To measure this quantity the Fe-PMaSynRM was connected to an induction machine which acted as the prime mover. The prime mover was spun at a speed of 2.5 Hz. A torque transducer was used on the shaft of the motor to capture the torque. It is observed that the peak-to-peak cogging torque of the proposed five-phase external rotor Fe-PMaSynRM is only 0.024 Nm, which  
Figure 17: The experimental setup to test the external rotor Fe-PMaSynRM prototype.  
was predicted to be 0.19 Nm as per FEA results. Although, the difference is significant, both values are reasonably small. The difference might have occurred from a reasonably small error in measured torque data of the dyno setup.  
Second, experimental test for full excitation is also carried out on the fabricated prototype to compare the generated torque under load. During this test, the prime mover was running at rated speed of 1800. A vector control using MTPA algorithm was implemented to generate the maximum torque with minimum current. The torque was captured using torque transducer. A position sensor was utilized to get the rotor information utilizing an incremental encoder. Before the test, the optimal angle offset was calculated to ensure MTPA method. Figure 20a shows the output torque of the five-phase external rotor Fe-PMaSynRM. The test result shows the average torque developed under rated excitation by the five-phase external rotor Fe-PMaSynRM is 19.4 Nm. The predicted torque from the FEA data was 19.2 Nm which is very close to the test data.  
Figure 19: Cogging torque of the proposed Fe-PMaSynRM.  
Figure 20: Proposed motor results (**a**) developed electromagnetic torque (**b**) phase A currents.