Position sensorless drive system and method for permanent magnet motors

Abstract

A position sensorless drive systems for a permanent magnet motors are disclosed. An embodiment includes a square wave voltage source connectable to an input of a permanent magnet motor. At least one current sensor is connectable to the motor, wherein the current sensor is configured to sense the current in at least one power line to the motor in response to the square wave input to the motor. The position of the rotor relative to the stator may be determined based on the current resulting from the square wave voltage.

What is claimed is: 
     
         1 . A position sensorless drive system for a permanent magnet motor, the motor comprising a rotor and a stator, the drive system comprising:
 a square wave voltage source connectable to an input of a permanent magnet motor;   at least one current sensor connectable to the motor, wherein the current sensor is configured to sense the current in at least one power line to the motor in response to the square wave input to the motor;   wherein the position of the rotor relative to the stator may be determined based on the current resulting from the square wave voltage.   
     
     
         2 . The drive system of  claim 1 , wherein the system is adapted to determine the position of the rotor when the rotor is stationary relative to the stator, and further comprising a position observer, wherein the position observer is adapted to determine the position of the rotor relative to the stator based on the current input resulting from the injected square wave. 
     
     
         3 . The drive system of  claim 1 , wherein the position observer is adapted to determine that the rotor is in a first orientation when the current input resulting from the square wave voltage is greater than an average current, and wherein the position observer is adapted to determine that the rotor is in a second orientation when the current input resulting from the square wave voltage is less than the average current. 
     
     
         4 . The drive system of  claim 1 , wherein the position of the rotor relative to the stator may be determined when the rotor is moving relative to the stator by analyzing reflected current ripples resulting from the square wave voltage. 
     
     
         5 . The drive system of  claim 4 , wherein the square wave voltage is adapted to be injected into the d-axis of the motor. 
     
     
         6 . The drive system of  claim 4 , wherein the position of the rotor relative to the stator may be determined by analyzing the current ripples in the q-axis of the motor. 
     
     
         7 . A position sensorless drive system for a permanent magnet motor, the motor comprising a rotor and a stator, the drive system comprising:
 a voltage input for the q-axis of the motor;   a voltage input for the d-axis of the motor;   a square wave voltage source adapted to generate an injected voltage, to be added to the voltage input for the d-axis of the motor;   at least one current sensor adapted to measure the current in at least one power line to the motor, the current being generated in response to the injected voltage;   an extraction device coupled to the at least one current sensor that is adapted to generate an error signal based on current in the d-axis and current in the q-axis; and   a position observer coupled to the extraction device, wherein the position observer is adapted to determine the position of the rotor based on the error signal.   
     
     
         8 . The drive system of  claim 7  further comprising a dq/abc device coupled between the first and second inputs and the motor, wherein the dq/abc device is adapted to transform the voltage inputs for the q-axis and the d-axis into a three phase input signal to drive the motor. 
     
     
         9 . The drive system of  claim 8 , wherein the at least one current sensor is adapted to measure the current on at least one of the three phases of the three phase input signal. 
     
     
         10 . The drive system of  claim 8 , wherein the position of the rotor as determined by the position sensor is adapted to be input to the dq/abc device. 
     
     
         11 . The drive system of  claim 7  further comprising an abc/dq device coupled between the motor and the extraction device, wherein the abc/dq device monitors the current measured by the at least one current sensor and generates currents representative of the current in the d-axis and current in the q-axis. 
     
     
         12 . The drive system of  claim 11  further comprising a filter coupled between the abc/dq device and the extraction device, wherein the filter is adapted to pass high frequency components of the currents representative of the current in the d-axis and the current in the q-axis to the extraction device. 
     
     
         13 . The drive system of  claim 13  wherein the filter is adapted to pass low frequency representations of the current in the d-axis and the current in the q-axis, wherein the representation of the current in the d-axis is at least partially adapted to generate the voltage input for the d-axis and wherein the representation of the current in the q-axis is at least partially adapted to generate the voltage input for the q-axis. 
     
     
         14 . The drive system of  claim 11  wherein the position of the rotor as determined by the position observer is adapted to be input to the abc/dq device. 
     
     
         15 . The drive system of  claim 7 , wherein the currents representative of the current in the d-axis and the current in the q-axis are reflected ripple currents generated in response to the injected voltage. 
     
     
         16 . The drive system of  claim 15 , wherein the currents representative of the current in the d-axis and the current in the q-axis are second harmonics of reflected ripple currents generated in response to the injected voltage. 
     
     
         17 . The drive system of  claim 7 , wherein the error signal is proportional to the amplitude of the injected voltage multiplied by the ratio of the difference in inductance in the q-axis and the d-axis over the difference between the average inductance squared and the difference in inductance in the q-axis and the d-axis squared. 
     
     
         18 . The drive system of  claim 7 , wherein the position observer is adapted to generate a first signal of the error signal multiplied by the proportional constant of the motor and second signal of the error signal multiplied by the integral constant of the motor and integrated, and wherein the first signal and the second signal are added together. 
     
     
         19 . A method of determining the position of a rotor in a permanent magnet motor, the method comprising:
 injecting a square wave voltage into the motor;   monitoring the input current in response to the injected square wave when the rotor is not moving, wherein the average current is greater than the differential current when the rotor has a first orientation and wherein the average current is less than the differential current when the rotor has a second orientation.   
     
     
         20 . The method of  claim 19  further comprising:
 measuring current reflected from the motor in response to the square wave when the rotor is rotating at a low speed; and 
 determining the position of a rotor based on the reflected current.