Method and system for cranking an internal combustion engine

A method for cranking an internal combustion engine, the engine coupled to a permanent magnet machine comprising a rotor having a plurality of permanent magnets poles, and a stator having a plurality of phase windings disposed on the stator, each phase winding including a plurality of coils, the method comprising the steps of:

• (a) receiving a start signal;
• (b) determining an initial position of the rotor with respect to a stator phase winding;
• (c) applying a pulse-width-modulated (PWM) signal to the stator winding corresponding to determined initial position of the rotor;
• (d) determining a threshold value of the stator current variation;
• (e) measuring current of the stator winding in response to applied pulse-width-modulated signal to determine current variation;
• (f) if current variation is more than the threshold value:
• determining updated rotor position, applying a pulse-width-modulated signal to the stator winding corresponding to the updated rotor position;
• and repeating steps (d)-(f);
• and
• (g) if current variation is less than the threshold value:
• applying a pulse-width-modulated signal to the stator winding corresponding to the last updated rotor position and repeating steps (d)-(g),
• wherein the step of determining an initial position of the rotor with respect to a stator phase winding comprises:
• (a) selecting a pair of stator phase windings;
• (b) applying a voltage signal across the selected pair of stator phase windings for a predetermined period of time;
• (c) measuring the current flowing through the selected windings;
• (d) repeating steps (a)-(c) for a newly selected pair of stator phase windings;
• and
• (e) determining position of the rotor based on the pair of stator phase windings for which the measured current is maximum.

A system for cranking an internal combustion engine, the engine coupled to a permanent magnet machine comprising a rotor having a plurality of permanent magnets poles, and a stator having a plurality of phase windings disposed on the stator, each phase winding including a plurality of coils, the system comprising:

• a control unit coupled to the permanent magnet machine and configured to:
• (a) receive a start signal;
• (b) determine an initial position of the rotor with respect to a stator phase winding;
• (c) apply a pulse-width-modulated (PWM) signal to the stator winding corresponding to determined initial position of the rotor;
• (d) determine a threshold value of the stator current variation;
• (e) measure current of the stator winding in response to applied pulse-width-modulated signal to determine current variation;
• (f) if current variation is more than the threshold value:
• determine updated rotor position, apply a pulse-width-modulated signal to the stator winding corresponding to the updated rotor position;
• and repeat steps (d)-(f);
• and
• (g) if current variation is less than the threshold value:
• apply a pulse-width-modulated signal to the stator winding corresponding to the last updated rotor position and repeat steps (d)-(g);
• and
• a power supply connected to the control unit,
• wherein, to determine the threshold value of the stator current variation, the control unit is further configured to:
• measure instantaneous or average battery voltage;
• measure instantaneous or average engine speed;
• measure stator current substantially at the beginning of a PWM cycle and substantially at the end of the PWM cycle;
• and
• determine the threshold value based on the measured battery voltage, engine speed and stator current.