## 5 Experimental Results  
The mathematical models and simulation results are verified by experiments performed on a dual-axis motor drive system. The block diagram of the experimental setup is shown in Figure 13.  
Figure 11: The dc-link capacitor current (**a**) and frequency spectrum of it (**b**): (red) zero rad phase difference; (blue) \(\pi/2\) rad phase difference. Figure 12: The dc-link capacitor current for varying speeds of PMSM-2. The motor driver unit consists of two main parts: the dual VSIs circuit and the microcontroller circuit. The switching signals of the three-phase inverters are generated by using the FOC algorithm and SVPWM technique implemented in the real-time microcontroller. The dual VSIs circuit consists of the gate drivers and switches as the MOSFET. Since the input voltage is 48 V and low, and the switching frequency is 10 kHz, MOSFETs are the most compatible switches for this application. A switching frequency of 10 kHz is selected to ensure that the MOSFETs do not overheat and that the output current ripple remains within the desired range (5% of the phase current). The insertion of the phase difference between the carrier waves is implemented in the real-time microcontroller. One of the carrier waves is delayed \(\pi/2\) rad in each switching cycle so that there is a \(\pi/2\) rad phase difference between the carrier waves of the VSIs. Since the input voltage of the dual three-phase VSI is low and the switching frequency is 10 kHz, a film capacitor is chosen where its series equivalent resistance is lower than that of an electrolytic capacitor, and therefore its current rating is higher. Four film capacitors were connected in parallel to provide the required current for the dual three-phase VSIs. In addition, dc-link capacitors are connected to the input of the dual three-phase VSIs with a short cable to measure the current on them using a current sensor which is the CWT Rogowski current probe. The accuracy of the current probe is \(\pm 2\%\) of the reading. The measured current is observed by the Tektronix DPO 3034 Digital Phosphor Oscilloscope with a minimum sampling rate of 50 Ms/s. The FFT of the dc-link capacitor current is analyzed by the FFT under the MATH function of the oscilloscope. The RMS under the measurement function of the oscilloscope is used to calculate the RMS value of the dc-link capacitor current. Since cables have self-inductance, they are kept as short as possible so that the inductance between the dc-link capacitor and the dual three-phase VSIs is very low  
Figure 13: Block diagram of the experimental setup. compared to the inductance of the voltage source. As a result, unwanted voltage spikes are minimized and the current of the dc-link capacitor is measured more correctly. The input voltage of the dual three-phase VSIs is the regulated 48 V and is supplied by a Sorensen SGI100-300 DC voltage source. The accuracy of the dc-voltage source is \(\pm\)0.1%. The 48 V voltage source simulates the two series battery banks (24 V + 24 V) used in military applications. There is a 4 m 0 AWG cable between the voltage source and the motor driver unit. The total cable inductance is 5 uH, and the cable resistance is 3 mOhm. Two PMSMs are loaded with MAGTROL HD-825 and HD-810 series hysteresis dynamometers. The dynamometers are controlled by the DSP6001 High-Speed Dynamometer Controller. In addition, PMSMs are driven at constant speed or constant load torque. The accuracy of the speed and load torque is \(\pm\)0.01% and \(\pm\)0.02%, respectively. The parameters of the PMSMs are given in Table 3.  
The desired speed and torque commands are given from the real-time microcontroller interface via the CAN protocol. The load torque is set by the hysteresis dynamometer. At this time, the dc-link capacitor current is measured and observed by the oscilloscope. The oscilloscope data are stored and plotted by the MATLAB-2017b program for different cases. The reduction in the dc-link capacitor current is experimented for three cases similar to those simulated in the previous part.