Method and system for determining the position of a synchronous motor's rotor

A method for determining a rotor position in a synchronous multi-phase motor, said method comprising the steps of:

• coupling combinations of all but one of a plurality of stator windings to a first voltage;
• coupling remaining ones of the plurality stator windings to a second voltage;
• measuring first times for currents through all combinations of the plurality stator windings to equal a reference current;
• and
• determining a rotor position from the measured first times, wherein the rotor position is within an electrical sector associated with a phase time measurement pair having the largest absolute value of a difference there between.

A method for determining a rotor position in a synchronous three phase motor, said method comprising the steps of:

• coupling first ones of three stator windings to a first voltage;
• coupling second ones of the three stator windings to a second voltage;
• injecting first currents from the first voltage into third ones of the three stator windings when the first ones of three stator windings are not coupled to the first voltage and the second ones of the three stator windings remain coupled to the second voltage;
• measuring first times for the first currents to equal a reference current;
• and
• determining a rotor position from the measured first times, wherein the rotor position is within an electrical sector associated with a phase time measurement pair having the largest absolute value of a difference there between.

A system for determining a synchronous motor's rotor position, said system comprising:

• a microcontroller comprising a digital processor and memory, a charge time measurement unit (CTMU) coupled to the digital processor, a timing capacitor coupled to the CTMU, an analog-to-digital converter (ADC) coupled to the CTMU, an analog comparator coupled to the CTMU, and a voltage reference coupled to a first input of the analog comparator;
• a synchronous motor driven by a power bridge comprising a plurality of power switches for coupling stator windings of the synchronous motor to a power source;
• a current return device coupled between some of the power switches and the power source;
• a second input of the analog comparator coupled to the current return device, wherein the current return device provides a voltage to the second input of the analog comparator proportional to current through the stator windings of the synchronous motor;
• wherein the digital processor causes the power switches to couple combinations of two of the three stator windings to a first voltage from the power source and third ones of the three stator windings to a second voltage from the power source, and
• the CTMU to start charging the timing capacitor;
• the analog comparator compares the voltage from the current return device for each combination of the three stator windings with a reference voltage from the voltage reference, wherein when the voltage from the current return device is substantially the same as the reference voltage the CTMU stops charging the timing capacitor;
• and
• the ADC converts charge voltages on the timing capacitor to digital representations thereof that are coupled to the digital processor, wherein the digital processor compares these digital representations to determine the rotor position of the synchronous motor, wherein the rotor position is within an electrical sector associated with a phase time measurement pair having the largest absolute value of a difference there between.

A system for determining a synchronous motor's rotor position, said system comprising:

• a microcontroller comprising a digital processor and memory, a charge time measurement unit (CTMU) coupled to the digital processor, a timing capacitor coupled to the CTMU, an analog-to-digital converter (ADC) coupled to the CTMU, an analog comparator coupled to the CTMU, and a voltage reference coupled to a first input of the analog comparator;
• a synchronous motor driven by a power bridge comprising a plurality of power switches for coupling stator windings of the synchronous motor to a power source;
• a multiplexer having outputs coupled to respective ones of the stator windings, and an input coupled to a current source;
• a current return device coupled between the current source and the power source;
• a second input of the analog comparator coupled to the current return device, wherein the current return device provides a voltage to the second input of the analog comparator proportional to current through the current return device;
• wherein the digital processor causes the power switches to couple first ones of the stator windings to a first voltage from the power source and second ones of the stator windings to a second voltage from the power source,
• the multiplexer to inject current from the current source into third ones of the stator windings, and
• the CTMU to start charging the timing capacitor;
• the analog comparator compares the voltage from the current return device for each combination of the three stator windings with a reference voltage from the voltage reference, wherein when the voltage from the current return device is substantially the same as the reference voltage the CTMU stops charging the timing capacitor;
• and
• the ADC converts charge voltages on the timing capacitor to digital representations thereof that are coupled to the digital processor, wherein the digital processor compares the digital representations to determine the rotor position of the synchronous motor, wherein the rotor position is within an electrical sector associated with a phase time measurement pair having the largest absolute value of a difference there between.