# Rotor Position Alignment of FSTPI Based PMSM Drive Using Low Frequency Signal Injection
## 5 Implementation and Experimental Results  
To validate the feasibility of the proposed scheme, an experimental platform of the FSTP inverter for PMSM drive is set up which is shown in Figure 5. Comparative experimental studies of the proposed smooth initial rotor position alignment method and the classical method have been conducted on a 1 kW FSTP inverter fed PMSM drive. The stator resistance and inductance of the PMSM are 3.4 \(\Omega\) and 3.3 mH, respectively. The rotor magnetic flux linkage is 0.095 Wb. The DC-link voltage measurements are performed by Tektronix TPP0200 model passive voltage probes with 300 V max. range and up to 200 MHz bandwidth. The voltage probes are used with the voltage amplifiers. The current probe used in the system is Fluke 80i-110s with \(\pm\)(3% + 50 mA) accuracy at 10 A and \(\pm\)100 A range. Rotor position and speed are obtained by HEDSS ICU4809 incremental encoder with 2500 ppr with up to 120 kHz response frequency. Figures 6-9 illustrate the experimental results of the mechanical rotor positions and DC-link capacitor voltages using conventional and the proposed methods under fan type load, respectively. Figures 10 and 11 represent phase \(a\) current and mechanical rotor speed using the proposed method under \(V_{DC}=400\) V with \(C_{1}\) and \(C_{2}\) are 2200 \(\mu\)F, respectively. In Figure 6, classical rotor alignment with the proper constant \(d\)-axis voltage value using virtual zero angle is applied as a reference with \(q\)-axis voltage is set to zero. The rotor is deviated too much from the desired zero angle from the initial position of 20 mechanical degrees. Its final position is around \(-90\) mechanical degrees, as shown in Figure 6.  
Figure 5: A 1 kW experimental test-bed. Figure 6: Mechanical rotor position of the PMSM drive under classical alignment procedure at start-up. Operating at: 0.25 pu \(d\)-axis voltage and zero \(q\)-axis voltage with 10 kHz switching frequency under fan type loading condition. Figure 7: Mechanical rotor position of the proposed zero angle LFS injection based PMSM drive with FSTP inverter. Operating at: 0.25 pu \(d\)-axis voltage and zero \(q\)-axis voltage with 10 kHz switching frequency under fan type loading condition. Figure 8: DC-link capacitor voltages of the PMSM drive under classical alignment procedure at start-up. Operating at: 0.25 pu \(d\)-axis voltage and zero \(q\)-axis voltage with 10 kHz switching frequency under fan type loading condition. Figure 9: Steady-state DC-link capacitor voltages of the proposed zero angle LFS injection based PMSM drive with FSTP inverter. Operating at: 0.25 pu \(d\)-axis voltage and zero \(q\)-axis voltage with 10 kHz switching frequency under fan type loading condition. It is seen in Figure 7 that under \(f_{LF}=50\) Hz LFS injection with 0.25 pu \(d\)-axis voltage amplitude reference, proper zero angle alignment is successfully achieved. Initial rotor position is set to 20 mechanical degrees. After 1.2 s, the rotor locks to the zero mechanical degree position with the proposed method as opposed to the classical one in which the alignment procedure to zero angle is not successful, as shown in Figure 6. The rotor is aligned to a negative position using the classical alignment method. Since only DC capacitor voltages exist in the classical zero angle alignment method, no current flows through the phase which is mounted to the center point of the capacitors. Therefore, the alignment procedure is unsuccessful. Figure 11: Mechanical rotor speed of the proposed zero angle LFS injection based PMSM drive with FSTP inverter. Operating at: 0.25 pu \(d\)-axis voltage and zero \(q\)-axis voltage with 10 kHz switching frequency under fan type loading condition. Figure 10: Phase \(a\) current at steady-state of the proposed zero angle LFS injection based PMSM drive with FSTP inverter. Operating at: 0.25 pu \(d\)-axis voltage and zero \(q\)-axis voltage with 10 kHz switching frequency under fan type loading condition.