Stator and rotor resistance identifier using high frequency injection

An apparatus for estimating a motor stator resistance in a three phase motor characterized by a stator leakage inductance and driven by a pulse width modulator that is linked to the motor via three supply lines, the apparatus for use with a system that receives a high frequency voltage command signal and causes high frequency voltages to be injected into each of the three motor phases at the high frequency, the apparatus comprising:

• an identifier for identifying a high frequency command angle;
• a first summer for subtracting an current lag angle estimate from the high frequency command angle to generate a high frequency current angle;
• a sensor for obtaining feedback currents from the supply lines;
• a converter for converting the feedback currents into two phase currents;
• a second summer for negating a first of the two phase currents to generate a current lag angle estimate;
• and
• a determiner for using the current lag angle estimate as a voltage-current lag angle estimate to generate the stator resistance estimate.

An apparatus for estimating a motor stator resistance in a three phase motor characterized by a stator leakage inductance and driven by a pulse width modulator that is linked to the motor via three supply lines, the apparatus for use with a system that receives a high frequency voltage command signal and causes high frequency voltages to be injected into each of the three motor phases at the high frequency, the apparatus comprising:

• means for converting the high frequency command signal into a high frequency command angle;
• means for subtracting a voltage-current lag angle estimate from the high frequency command angle to generate a high frequency current angle;
• means for obtaining feedback currents from the supply lines;
• means for converting the feedback currents into two phase currents;
• means for negating a first of the two phase currents to generate a voltage-current lag angle estimate;
• and
• means for using the voltage-current lag angle estimate to generate the stator resistance estimate.

A method for estimating both a motor stator resistance and a rotor resistance in a three phase motor characterized by a stator leakage inductance and driven by a pulse width modulator that is linked to the motor via three supply lines, the method for use with a system that receives a high frequency voltage command signal and causes high frequency voltages to be injected into each of the three motor phases at the high frequency, the method comprising the steps of:

• identifying and storing an initial voltage-current lag angle estimate;
• identifying an initial rotor resistance estimate;
• converting the high frequency command signal into a high frequency command angle;
• subtracting a current lag angle estimate from the high frequency command angle to generate a high frequency current angle;
• obtaining feedback currents from the supply lines;
• converting the feedback currents into two phase currents including a torque producing current and a flux producing current;
• negating the torque producing current;
• stepping up the negated torque producing current to generate the current lag angle estimate and using the current lag angle estimate as a voltage-current lag angle estimate;
• determining the cotangent of the voltage-current lag angle estimate to generate a cotangent value;
• multiplying the high frequency command signal in radian per second value, the cotangent value and the stator leakage reactance to generate the stator resistance estimate;
• dividing the initial voltage-current lag angle estimate by the voltage-current lag angle estimate to generate a stator resistance ratio;
• and
• multiplying the initial rotor resistance estimate by the stator resistance ratio to generate the rotor resistance estimate.

A method for estimating both a motor stator resistance and a rotor resistance in a three phase motor characterized by a stator leakage inductance and driven by a pulse width modulator that is linked to the motor via three supply lines, the method for use with a system that receives a high frequency voltage command signal and causes high frequency voltages to be injected into each of the three motor phases at the high frequency, the method comprising the steps of:

• identifying an initial voltage-current lag angle estimate;
• identifying an initial rotor resistance estimate;
• determining the tangent of the initial voltage-current lag angle estimate and storing the initial tangent value;
• converting the high frequency command signal into a high frequency command angle;
• subtracting a current lag angle estimate from the high frequency command angle to generate a high frequency current angle;
• obtaining feedback currents from the supply lines;
• converting the feedback currents into two phase currents including a torque producing current and a flux producing current;
• negating the torque producing current;
• stepping up the negated torque producing current to generate the current lag angle estimate;
• determining the tangent of ninety degrees less the voltage-current lag angle estimate to generate a tangent value;
• multiplying the high frequency command signal in radians per second value, the tangent value and the stator leakage reactance to generate the stator resistance estimate;
• dividing the initial tangent value by the tangent value to generate a stator resistance ratio;
• and
• multiplying the initial rotor resistance estimate by the stator resistance ratio to generate the rotor resistance estimate.