# Topology Comparison Study of Five-Phase Wound-Field Doubly Salient Fault Tolerant Generators
## 4 Experimental verification  
In order to verify the above theoretical analysis, two five-phase WFDSGs were prototyped and tested, and the WFDSGs are shown in Figure 5\(\alpha_{r}=0.5\).  
Figure 5a,b shows the excitation coil and armature coil on the stators of the two five-phase WFDSGs, respectively, which realize brushless excitation. And without winding and permanent magnet, the rotor structure is simple and suitable to operate in high temperature and high-speed situations. In addition, the windings of each phase on the stator are physically and electromagnetically independent, which enables the WFDSG with isolation and fault tolerance characteristics. In Figure 6, a five-phase rectifier and a regulator are used to output steady DC voltage by adjusting the excitation current.  
With the same parameters as the simulation, the normal and the single-phase open-circuit experiment of the two prototypes were carried out. The no-load EMFs of the two WFDSGs are shown in Figure 7a,b. The phase EMFs and the output EMFs of the one phase open-circuit are shown in Figure 7c,d, which show output DC voltage ripple of the 20/16-pole WFDSG is less than that of the 30/24-pole WFDSG. The experimental waveforms of the phases are consistent with the simulated waveforms.  
With a regulator, in the case of unsaturated excitation, if the 20/16-pole WFDSG has a single-phase open-circuit fault, the regulator automatically increases the excitation current to stabilize the output voltage for charging the battery, as shown in Figure 7e.  
Figure 5: The rotor and stator of the five-phase WFDSGs. (**a**) 30/24-pole; (**b**) 20/16-pole.  
Figure 6: The five-phase rectifier and excitation of the WFDSG.  
If the 30/24-pole and 20/16-pole WFDSGs are connected with the loads of 0.5, 1, 2, 4, and 15 ohm, the external characteristics and output characteristics can be drawn as shown in Figure 8.  
Comparing the external and output characteristics of the two WFDSGs, it can be seen that the output voltage and output power of the 20/16-pole WFDSG are larger than the 30/24-pole when the output current is less than 27A, which is also consistent with the simulation results, and this verifies the increase in the number of poles will deduce the second air gap and increase the leakage coefficient of the WFDSG. When the output current is larger than 27A, the output voltage and output power of the 20/16-pole WFDSG drop sharply due to the large demagnetization effect of the armature reaction because there are more turns of the armature winding around each pole of the 20/16-pole WFDSG. Although the armature reaction sometimes enlarges the excitation flux and sometimes reduces it, in the case of almost saturation excitation, the enlargement is difficult to increase the magnetic density of the core, but the demagnetization of the armature reaction can reduce the magnetic density of the core [36].  
Overall, the experimental results agree well with the simulation results, but the experimental data is slightly lower than the simulation data due to the influence of materials and production.  
Figure 8: External and output characteristics. (**a**) External characteristics and (**b**) output characteristics.  
Figure 7: The normal and one phase open-circuit experiment waveforms. (**a**) Normal no-load EMF of the 30/24-pole WFDSG; (**b**) normal no-load EMF of the 20/16-pole WFDSG; (**c**) no-load EMF with one phase open-circuit of the 30/24-pole WFDSG; (**d**) no-load EMF with one phase open-circuit of the 20/16-pole WFDSG; and (**e**) excitation current with one phase open-circuit.