# Current Harmonic Suppression Algorithm for Asymmetric Dual Three-Phase PMSM
## 6 Experimental Verification  
The effectiveness of the proposed current harmonic suppression algorithm is verified by the implementation in an ADT-PMSM experimental platform (Siemens, Munich, Germany). The experimental setup is shown in Figure 12, which is composed of a DC machine mechanically coupled to the ADT-PMSM acting as a loading motor. The loading motor is controlled in speed control mode. The ADT-PMSM is supplied by using a two-level VSI (Infineon, Munich, Germany) configured for six-phase operation. A DC power supply is used to provide the DC-link voltage of 12V to the VSI. The complete control algorithm is implemented in a control board using Infineon TC277 (Infineon, Munich, Germany, 2017). The switching frequency is 10 kHz with 1 \(\mu\)s of dead time provided by the hardware in the VSI (Infineon, Munich, Germany, 2017). To provide the current display at higher resolution, a current probe (CP150, Lecroy, New York, America, 2013) and Teledyne Lecroy oscilloscope (WaveSurfer 3024, Lecroy, New York, America, 2016) are used. The data of the phase currents are saved as Excel files with the help of an oscilloscope. Figure 11: Double zero-sequence injection pulse width modulation (PWM) strategy. Figure 12: Experimental platform for ADT-PMSM. The parameters for ADT-PMSM are given in Table 1, and the specifications of VSI are given in Table 2.  
Four cases are listed below to compare the performances. Case 1: The algorithm is implemented without feedforward voltage compensation and a resonant controller;  
Case 2: The algorithm is implemented with feedforward voltage compensation only;  
Case 3: The algorithm is implemented with resonant controller only;  
Case 4: The algorithm is implemented with both feedforward voltage compensation and a resonant controller. Figure 13 shows the experimental results without employing feedforward voltage compensation and a resonant controller, which is equivalent to Case 1. Here, the command currents \(i_{d}\) and \(i_{q}\) are set to be 0 A and 35 A, respectively. The ADT-PMSM is operating under a current control loop and the speed is maintained at 500 rpm and 1000 rpm by the loading motor, respectively. Without the current closed-loop control strategy in the \(x\)-\(y\) subspace and feedforward voltage compensation method, \(u_{x}\) and \(u_{y}\) are set to be 0 in order to avoid injecting extra harmonic voltages. It is obvious that the phase currents are severely distorted due to the dead-time effects and some other factors. A fast Fourier transform is conducted on the phase A current waveform as illustrated in Figure 14. From the figure, one can see that the phase current contains dominant fifth and seventh current harmonics and the total harmonic distortions (THD) are 20.53% and 17.98% respectively. Besides, it can be seen that the system is more sensitively influenced by the error voltage at low speed than at high speed, because the voltage error caused by dead time accounts for a large proportion at low speed. Figure 15 depicts the experimental results after adopting the proposed feedforward voltage compensation which is equivalent to Case 2. The compensating voltages are calculated based on Equations (4), (5), and (6). The reference voltages are synthesized based on the proposed SVPWM method illustrated in Section 5. The waveforms of the phase currents have been improved a lot. The fifth and seventh current harmonics are significantly reduced. The THDs of the phase A current are reduced to 4.60% and 4.11% respectively with the proposed feedforward voltage compensation method, as shown in Figure 16.