## 3 Phase Current Analysis  
Interior Permanent Magnet Synchronous Motors (IPMSMs) have a rated torque of 1134 Nm and a peak torque of 1660 Nm. Considering the motor's speed range, control strategy (Maximum Torque Per Ampere (MTPA) or field weakening control) and magnetic saturation characteristics, four operating points (1000 rpm, 1660 Nm; 3200 rpm, 1660 Nm; 3200 rpm, 1134 Nm; 6000 rpm, 588 Nm) were selected. Their phase currents and internal magnetic fields were analyzed. Among them, the working points were 1000 rpm, 1660 Nm and 3200 rpm, 1134 Nm was controlled by MTPA, and the other two points were controlled by a weak magnetic field. Based on the SVPWM control model, the dq-axis currents at different operating points of the motor with and without the magnetic saturation effect were calculated  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline Rated power/kW & 380 & Rated speed/rpm & 3200 \\ Maximum power/kW & 550 & Maximum speed/rpm & 6000 \\ Rated torque/Nm & 1134 & Rated AC voltage/V & 440 \\ Outer diameter of stator/mm & 482 & Silicon steel sheet & B20 AT1500 \\ Insulation class & H & Cooling system & Water \\ \hline \hline \end{tabular}
\end{table}
Table 1: The main parameters of the outer rotor PMSM.  
separately, and then Park inverse transformation was performed on the direct axis and quadrature axis (dq-axis) current to obtain the phase current of the motor in one electrical cycle, as shown in Figure 2. When the motor adopted MTPA control, the internal magnetic saturation of the stator was relatively high, and the phase current obtained was larger than the phase current without considering the magnetic saturation. In weak field control, the magnetic saturation was low, and the phase current was smaller than the phase current without considering the effect of magnetic saturation [15; 16; 17; 18; 19; 20; 21; 22; 23].  
Figure 2: _Cont._  
The A-phase current shown in Figure 2 was Fourier decomposed to get its harmonic amplitudes, as shown in Figure 3.  
The phase current obtained by inverter space vector pulse width modulation, the main harmonic order of its waveform was \((2\mathrm{i}-1)\mathrm{fc/f}\pm 2\), \((2\mathrm{i}-1)\mathrm{fc/f}\pm 4\), \(2\mathrm{ifc/f}\pm 1\), \(2\mathrm{ifc/f}\pm 5\) (i = 1, 2, 3,... ). Among them, fc is the inverter carrier frequency, and f is the fundamental frequency. The carrier frequency of the controller was 8 kHz, when the PMSM was working at 1000 rpm, fc/f = 80, then the main harmonic orders were \(80\pm 2\), \(80\pm 4\), \(160\pm 1\), \(160\pm 5\),... The current harmonic orders at 3200 rpm were mainly \(25\pm 2\), \(25\pm 4\), \(50\pm 1\), \(50\pm 5\), \(75\pm 2\), \(75\pm 4\),... The current harmonic orders at 6000 rpm were mainly \(13\pm 2\), \(13\pm 4\), \(26\pm 1\), \(26\pm 5\), \(39\pm 2\), \(39\pm 4\),...  
Figure 2: Phase current and dq-axis current under different working points of the motor.  
A large number of current harmonics were generated by the motor's SVPWM. The current harmonic total distortion (\(THD\)) rate was used to reflect the harmonic content of the phase current, and its calculation Equation can be expressed as:  
\[THD=\frac{\sqrt{\sum_{n=2}^{\infty}I_{n}^{2}}}{I_{1}}\times 100\% \tag{3}\]  
Based on Equation (3), the harmonic distortion rate of the phase current of the motor with and without the magnetic saturation effect was calculated separately, as shown in Table 2. After considering the magnetic saturation effect, the dq-axis flux linkage of the motor changed nonlinearly with the  
Figure 3: A-phase harmonic current amplitude under different working points of the motor.  
current, and the harmonic content of the phase current was higher than the harmonic content without considering the magnetic saturation effect.