**5. Experimental Results**

Experiments were performed on the setup, as shown in Figure 11. A 7.5 kW spindle motor was used, and its parameters are shown in Table 1. The DC generator was used as a load in the high-speed region. The output torque can be obtained by the torque transducer, which was equipped between the spindle motor and the DC generator. A DSP TMS320F28377D (Texas Instruments, Texas, USA), which is a two core MCU was used to realize the proposed algorithm and IRFOC algorithm. A CPLD EPM240T100C5N (Altera, California, USA) was used to realize PWM. In the experiment, the PWM frequency was 10 kHz. The current sample and control frequency was 20 kHz. The phase currents were obtained by the two current sensors on the power converter board.

**Figure 11.** Experiment setup. (**a**) is the induction machine and load. and (**b**) is the control and power board.

In the experiment, the maximum q-axis current was set to 3√2*irated*. As the simulation shows, the q-axis current was not proportional to the load at the same flux level when the field-oriented angle is inaccurate. The q-axis current comparative experiment results are given in Figure 12 at 1200 rpm with different loads. The torque was applied by a DC generator. The q-axis current was calculated by the DSP and stored in RAM. Therefore, the q-axis current of the experiment was read by the DSP and transferred to a computer. The experimental results are similar to the simulated results shown in Table 2. After compensating for the rotor flux oriented angle error, the q-axis current is proportional to the load torque and is almost the same regardless of which rotor resistance was used to calculate the slip angular velocity.

**Figure 12.** Q-axis current at 1200 rpm with 30 Nm, and 60 Nm loads. (**a**) *R*∗ *<sup>r</sup>* = 0.5*Rr*; (**b**) *R*<sup>∗</sup> *<sup>r</sup>* = 0.8*Rr*; (**c**) *R*∗ *<sup>r</sup>* = 1.5*Rr*.

If the field-oriented angle is not accurate, the maximum torque will decrease, especially in the flux weakening region. The maximum output torque at different speeds was recorded, as shown in Figure 13. The maximum torque decreased with increasing speed when the rotor resistance used in the slip angular velocity calculation was not accurate. After compensation, the output torque was increased.

**Figure 13.** Maximum output torque from 1000 rpm to 6000 rpm.
