Methods of determining initial position of a rotor and systems thereof

1. A drive system comprising:

a motor including a rotor, the motor configured to receive a measured current;

a controller configured to generate a voltage for the motor at a stationary reference frame, the generated voltage having a frequency and the measured current being based on the voltage;

a filter configured to obtain position information of the rotor based on the measured current; and

a nonlinear observer configured to estimate a rotor position of the motor during the stationary reference frame based on the position information,

the controller being further configured to control the motor based at least in part on the estimated rotor position.

2. The drive system of claim 1 , wherein the nonlinear observer is configured to sample the measured current at a frequency of less than 10 kHz.

3. The drive system of claim 2 , wherein the nonlinear observer is configured to sample the position information at approximately 5 kHz.

4. The drive system of claim 1 , wherein the controller is configured to generate the voltage to have a frequency of 500 Hz.

5. The drive system of claim 1 , wherein the generated voltage dissipates a voltage across a direct current (DC) bus capacitor.

6. The drive system of claim 5 , wherein the nonlinear observer is configured to estimate the rotor position during one discharging cycle of the DC bus capacitor.

7. The drive system of claim 1 , further comprising:

an inverter configured to supply a three-phase current to the motor based on pulse width modulation (PWM).

8. The drive system of claim 7 , wherein the nonlinear observer is configured to estimate the rotor position at a sampling frequency relatively greater than a PWM frequency.

9. The drive system of claim 1 , wherein the filter includes,

a matched filter configured to filter noise from the measured current; and

a synchronous reference frame filter configured to extract the position information of the rotor from the filtered measured current.

10. The drive system of claim 9 , wherein the matched filter is configured to maintain a fundamental energy of a waveform of the measured current.

11. The drive system of claim 9 , wherein the matched filter is configured to maintain a sinusoidal shape of a waveform of the measured current.

12. A method of estimating a rotor position in a motor, the method comprising:

generating a voltage for the motor at a stationary reference frame, the generated voltage having a frequency;

obtaining a measured current for the motor, the measured current being based on the generated voltage;

filtering the measured current to obtain position information of the rotor; and

determining an estimate of the rotor position during the stationary reference frame based on the position information.

13. The method of claim 12 , wherein the determining an estimate includes sampling the position information at a frequency of less than 10 kHz.

14. The method of claim 13 , wherein the determining an estimate includes sampling the position information at approximately 5 kHz.

15. The method of claim 12 , wherein the generating a voltage generates the voltage to have a frequency of 500 Hz.

16. The method of claim 12 , wherein the generated voltage dissipates a voltage across a direct current (DC) bus capacitor.

17. The method of claim 16 , wherein the determining an estimate of the rotor position estimates the rotor position during one discharging cycle of the DC bus capacitor.

18. The method of claim 12 , wherein the filtering includes,

filtering noise from the measured current; and

extracting, by a synchronous reference frame filter, the position information of the rotor from the filtered measured current.

19. The method of claim 18 , wherein the filtering noise maintains a fundamental energy of a waveform of the measured current.

20. The method of claim 18 , wherein the filtering noise maintains a sinusoidal shape of a waveform of the measured current.

21. A method of determining a polarity in a magnet of a permanent magnet synchronous machine (PMSM), the method comprising:

generating alternating positive and negative DC voltages for a plurality of switching periods for the PMSM;

determining first and second current responses of the PMSM based on the generated positive and negative DC voltages, respectively; and

determining the polarity of the magnet based on the first and second current responses.

22. The method of 21 , wherein the polarity is based on a highest current response of the first and second current responses.