Apparatus for detecting the rotor position of an electric motor and related method
An apparatus for detecting a position of a rotor of a DC motor with N phases having a plurality of windings. The apparatus includes circuitry to couple at least two of the windings between a supply voltage and a reference voltage according to a first current path and allow the current stored in the two windings to be discharged through a second current path. The circuitry is configured to force the at least two windings at a short circuit condition in the second current path. The apparatus also includes a measurement circuit configured to measure the time period of discharging the current stored in the two windings and a rotor position detector for detecting the rotor position based on the measured time period.
1. An apparatus for detecting a position of a rotor of an electric motor having a plurality of windings, the apparatus comprising:
a circuit having at least two half-bridges coupled between a supply node and a reference node, the at least two half-bridges having central points coupled with two windings of the plurality of windings;
the circuit configured to control a current charge operation of a current passing through the two windings via a first current path;
the circuit configured to drive the at least two half-bridges in a pulse width modulation mode during the current charge operation;
a measurement circuit configured to measure a time period between a peak value of the current and a second value of the current during a current discharge operation, wherein the current passes through the two windings via a second current path during the discharge operation; and
a rotor position detector configured to detect a rotor position based on the measured time period.
2. The apparatus according to claim 1 , wherein the circuit is configured to drive the two half-bridges in a pulse width modulation mode with a duty-cycle lower than 100%.
3. The apparatus according to claim 1 , wherein the circuit is configured to stop the electric motor to detect the rotor position.
4. The apparatus according to claim 1 , wherein the electric motor has three phases and three windings.
5. The apparatus according to claim 1 , wherein the measurement circuit comprises a Hall sensor.
6. The apparatus according to claim 1 , wherein the second value of the current is 50% of the peak value of the current.
7. A method for detecting a rotor position of an electric motor having a plurality of windings by using a circuit comprising at least two half-bridges coupled between a supply node and a reference node and having central points coupled with two windings of the plurality of windings, the method comprising:
charging a current passing through two of the plurality of windings via a first current path;
discharging the current stored in the two windings via a second current path;
driving the at least two half-bridges in a pulse width modulation mode during the charging;
measuring a time period between a peak value of the current and a second value of the current during the discharging; and
detecting a rotor position based on the measured time period.
8. The method according to claim 7 , wherein a duty-cycle is lower than 100% for the driving two half-bridges in the pulse width modulation mode.
9. The method according to claim 7 , wherein a duty-cycle is 50% for the driving two half-bridges in the pulse width modulation mode.
10. The method according to claim 7 , further comprising:
repeating the charging and discharging for each one of pairs of phases of the electric motor;
measuring the time period of each discharging; and
detecting the rotor position based on the measured time periods.
11. The method according to claim 7 , wherein a voltage of the supply node varies during driving the at least two half-bridges.
12. The method according to claim 7 , wherein the second value of the current is 50% of the peak value of the current.