**4. Experimental Results**

Figure 14a shows a complete experimental test bench to validate the simulation results presented before. It consisted of a 5.5 kW three-phase SynRM with a 36-slot stator and fourpole rotor as in case 4. The stator and the rotor are shown in Figure 14b. The three-phase SynRM was coupled with a 10 kW three-phase induction motor. The SynRM implemented in this paper required a control system, as it had no rotor cage. Hence, the desired speed of the three-phase SynRM was achieved using an induction motor, as the three-phase SynRM worked in the mode of torque control. A three-phase inverter based on space vector modulation with a 6.6 kHz switching frequency and 600 V DC bus voltage was

used to control the three-phase SynRM. A digital signal processing (DSP1103) was used to obtain the required switching pulses. Incremental encoder and torque sensor were used to measure the rotor speed and the average torque respectively. The input electrical power for the three-phase SynRM was computed using a power analyzer.

**Figure 14.** (**a**) The complete experimental setup and (**b**) three-phase SynRM stator and rotor.

To validate the implemented simulation model, various measurements were obtained on the prototype. Figure 15 shows the simulated and measured value of the SynRM output torque at half the rated speed and current (speed = 1500 rpm and RMS current= 6.1 A) at different current angles. There was good agreemen<sup>t</sup> between the simulated and average values. The average torque and power factor measured and simulated values at different line currents including overloading to double the rated current, at an optimal current angle, and at one-third the rated speed as shown in Figures 16a and 16b respectively. The torque was linearly varied with the current as shown in Figure 16a. Figure 16b shows that there was a step-change in the power factor. This was due to the change of optimal current angle with line current.

**Figure 15.** Simulated and measured output torque at different current angles at half the rated current and half the rated speed.

**Figure 16.** (**a**) Average output torque and (**b**) power factor at different line currents, at an optimal current angle, and at *Nr* = 1000 rpm.

Figure 17 shows the measured and simulated values for the efficiency and total losses of the SynRM at different line currents, at rated speed, and at an optimal current angle. There was a slight difference between the simulated and measured values of efficiency and losses. This was due to neglecting the effect of mechanical and switching losses and the inaccurate iron loss simulation model parameters. Figure 18 shows the efficiency map of the complete drive system at different rotor speeds and at optimal current angles including the flux weakening region.

**Figure 17.** (**a**) Efficiency, (**b**) SynRM total losses at different line currents, optimal current angle, and at rated speed.

**Figure 18.** Efficiency map of the complete drive system at optimal current angles.
