# Self-Sensing Six-Phase PMSM Drive Based on Back-EMF Measurement
## 5 Operation Mode with the Healthy Speed/Position Sensor  
The healthy operation of the six-phase PMSM drive is presented in Figures 5-10, followed by the back-EMF investigation in the three-phase operation (Figures 11-14). In this case, the speed/position feedback is obtained from the resol  
Figure 4: Simulation of the transformation between phase coordinates D–E–F to the stationary \(\alpha\)–\(\beta\) subspace at the zero-position reference frame: (**a**) basic harmonic with the third harmonic and the DC offset; (**b**) basic harmonic with the fifth harmonic. Figure 5: Phase current during the startup transient of the six-phase operation. Figure 3: Simulation of the transformation between phase coordinates D–E–F to the stationary \(\alpha\)–\(\beta\) subspace at the zero-position reference frame. Figure 8: Double zero-sequence SVM during the steady-state six-phase operation: (**a**) PWM references; (**b**) SVM sectors. Figure 6: Current in transformed subsystems during the startup transient of the six-phase operation: (**a**) \(\alpha\)-\(\beta\) subsystems; (**b**) \(z\)1-\(z\)2 subsystem. Figure 7: Startup transient of the six-phase operation: (**a**) rotor speed; (**b**) current in \(d\)–\(q\) subsystem. Figure 9: Oscilloscopic record of the measured voltage during the steady-state six-phase operation. Figure 11: Phase current during the startup transient of three-phase operation. Figure 12: Oscilloscopic record of the measured voltage during the steady-state three-phase operation. Figure 10: Measured voltages during the steady-state six-phase operation: (**a**) measured phase voltages and their transformed \(\alpha-\beta\) components; (**b**) frequency spectrum of the measured voltage vF. Figure 5:0 Measured voltages during the steady-state three-phase operation: (**a**) measured phase voltages and their transformed \(\alpha-\beta\) components; (**b**) frequency spectrum of the measured voltage vF. Currents of the \(zI\)-\(z2\) subspace are controlled to zero, which eliminates the differences between partial \(\alpha\)-\(\beta\) components (Figure 6a,b). This technique also eliminates the current sharing problem [16] and the harmonic disturbance from the phase current [17], as shown in Figure 5:1  
The startup in the speed loop control from 0 to 3000 rpm is shown in Figure 7a. The maximal current of the machine is 19 A, so the dynamic of the speed controller for the standard six-phase operation can be set higher, as shown in Figure 7b. However, the dynamic has been set according to the three-phase operation, wherein the startup current reaches the maximum, as shown in Figure 5:2  
The dual zero-sequence SVM technique [18] has been utilized for the generation of PWM references (Figure 8). The modulation has been realized using inverse transformation (depicted in Figure 1) with the injection of the third harmonic saw. The third harmonic injection allows us to increase the DC-bus voltage utilization so the machine can reach a higher speed than that of the purely sinusoidal PWM references. The PWM references with the third harmonic are also beneficial in this experiment for the recognition of the source voltage's influence on measured voltages. Voltage measured with an oscilloscope on phase F is shown in Figure 5:3 The DC-bus voltage of the application is 45 V, which corresponds to the PWM pulses measured on the phase connector of the power inverter (vF_1). The voltage signal is then filtered with hardware filters and amplified by an operational amplifier (vF_2). The voltage signal is sampled by a microcontroller (vF), which is shown in Figure 5:4 Measured voltages are a combination of the power supply voltage and the back-EMF voltage, so the estimated position from this operation does not correspond to the actual electrical position of the rotor flux. The three-phase operation is presented in the following part of the paper to investigate the back-EMF behavior in the disconnected system. The second three-phase winding is not supplied to eliminate the influence of the stator voltage on the measured voltage.