Method and Apparatus for Estimating Rotor Position in a Sensorless Synchronous Motor

A method of estimating a rotor position in a synchronous motor comprising the steps of:

• determining a current drawn by and a voltage applied to the synchronous motor during operation of the synchronous motor;
• obtaining a q axis inductance for the synchronous motor;
• applying the motor current and voltage signals as an input to a model of the synchronous motor to obtain an observed value of motor current output to the motor, the model being a function of the q axis inductance and a controller gain and being independent of motor speed and d axis inductance;
• and
• determining the estimated rotor position based on the difference between the observed value of motor current and the measured current.

The method of estimating the rotor position of claim 12 wherein the model of the synchronous motor is of the form:

• [
• i
• ^
• α
• .
• i
• ^
• β
• .
• ]
• =
• 1
• L
• q
• 
• [
• v
• α
• v
• β
• ]
• -
• K
• SM
• L
• q
• +
• [
• sign
• 
• (
• i
• ^
• α
• -
• i
• α
• )
• sign
• 
• (
• i
• ^
• β
• -
• i
• β
• )
• ]
• where:
• {circumflex over ({dot over (i)}α is the alpha component of the derivative of the observed current drawn by the motor;
• {circumflex over ({dot over (i)}β is the beta component of the derivative of the observed current drawn by the motor;
• îα is the alpha component of the observed current drawn by the motor;
• îβ is the beta component of the observed current drawn by the motor;
• iα is the alpha component of the current drawn by the motor in the stationary reference frame;
• iβ is the beta component of the current drawn by the motor in the stationary reference frame;
• vα is the alpha component of the voltage supplied to the motor in the stationary reference frame;
• vβ is the beta component of the voltage supplied to the motor in the stationary reference frame;
• Lq is the q axis inductance of the motor;
• and
• KSM is a constant observer gain.

A motor drive system for a multi-phase synchronous motor having an input voltage source comprising:

• a power conversion section configured to convert an input voltage to an output voltage for the synchronous motor;
• at least one current sensor configured to provide a current signal corresponding to a current output to the motor;
• a memory device;
• a program stored in the memory device;
• a processor receiving the current signals, the processor configured to execute the stored program to:
• obtain a motor resistance and a q axis inductance for the synchronous motor;
• obtain an amplitude of the output voltage;
• obtain the voltage and current signals at a predetermined time interval, the time interval being selected such that a change in speed of the synchronous motor during the time interval is approximately zero;
• apply the motor current and voltage signals as an input to a model of the synchronous motor to obtain an observed value of motor current output to the motor, the model being a function of the motor resistance, the q axis inductance, and a controller gain and being independent of motor speed and d axis inductance;
• determine the estimated rotor position based on the difference between the observed value of motor current and the measured current signal;
• and
• provide at least one command signal to the power conversion section to control the conversion of the input voltage to the output voltage based on the estimated rotor position.

A method of estimating a rotor position in a synchronous motor comprising the steps of:

• measuring a current drawn by the synchronous motor while commanding rotation of the motor at a desired speed;
• determining a voltage applied to the synchronous motor while commanding rotation of the motor at a desired speed;
• obtaining a q axis inductance for the synchronous motor;
• determining an observed value of the current output to the motor during motor rotation as a function of the current drawn by the synchronous motor, the voltage applied to the synchronous motor, and the q axis inductance;
• and
• determining the estimated rotor position as a function of the observed value of the motor current output to the motor, wherein the estimated rotor position is independent of the commanded speed to the synchronous motor and independent of a d axis inductance of the synchronous motor.