# US 12,015,368 B2 · Method of determining a position of a rotor of a brushless permanent magnet motor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,015,368 B2 - Document ID: US12015368B2 - Status: Granted - Kind: B2 - Application number: 17/598,174 - Filed: 2020-03-19 - Published: 2022-11-03 - Granted: 2024-06-18 - Earliest claimed: 2019-03-28 - Assignees: Dyson Technology Limited - Applicants: Dyson Technology Limited - Inventors: Nikita Shmidt - Web page: https://patentgrep.com/patent/US12015368B2 ## CPC - H02P 6/182: using back-emf in windings - H02P 6/181: {using different methods depending on the speed} - H02P 6/21: Open loop start - H02P 25/04: Single phase motors, e.g. capacitor motors - H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS ## Abstract A method of determining a position of a rotor of a brushless permanent magnet motor includes measuring phase current flowing through a phase winding of the motor during excitation of the phase winding, and measuring voltage applied to the phase winding of the motor during excitation of the phase winding. The method includes calculating a phase of back EMF induced in the phase winding using the measured phase current and the measured voltage. The method includes determining a zero-crossing point of the back EMF induced in the phase winding using the calculated phase of back EMF induced in the phase winding. The method includes determining an aligned position of the rotor of the brushless permanent magnet motor when the back EMF induced in the phase winding is at the zero-crossing point. ## Claims ### Claim 1 A method of determining a position of a rotor of a brushless permanent magnet motor, the method comprising: measuring instantaneous phase current flowing through a phase winding of the motor during excitation of the phase winding; measuring voltage applied to the phase winding of the motor during excitation of the phase winding; calculating a phase of back EMF induced in the phase winding using the measured instantaneous phase current and the measured voltage; determining, using the calculated phase of back EMF induced in the phase winding, a zero-crossing point of the back EMF induced in the phase winding of the motor; and determining, based on when the back EMF induced in the phase winding is at the zero-crossing point, an aligned position of the rotor of the brushless permanent magnet motor. ### Claim 2 (depends on 1) The method as claimed in claim 1, wherein the phase of back EMF induced in the phase winding is calculated using the equation E = L ⁢ d ⁢ I dt + IR - V PH , where E is the back EMF induced in the phase winding, L is the inductance of the phase winding, I is the phase current flowing through the phase winding, R is the resistance of the phase winding, and VPH is the voltage across the phase winding. ### Claim 3 (depends on 1) The method as claimed in claim 1, wherein the method comprises measuring phase current over a plurality of excitation pulses applied to the phase winding. ### Claim 4 (depends on 3) The method as claimed in claim 3, wherein the method comprises measuring phase current over each excitation pulse applied to the phase winding. ### Claim 5 (depends on 1) The method as claimed in claim 1, wherein measuring current flowing through the phase winding of the motor comprises measuring average phase current flowing through the phase winding of the motor and/or measuring instantaneous phase current flowing through the phase winding of the motor. ### Claim 6 (depends on 1) The method as claimed in claim 1, wherein measuring voltage applied to the phase winding of the motor during excitation of the phase winding comprises measuring average DC voltage and/or measuring instantaneous DC voltage applied to the phase winding of the motor during excitation of the phase winding. ### Claim 7 (depends on 1) The method as claimed in claim 1, wherein the method comprises commutating the phase winding relative to the determined zero-crossing point of back EMF induced in the phase winding. ### Claim 8 (depends on 1) The method as claimed in claim 1, wherein determining a zero-crossing point of the back EMF induced in the phase winding may comprise utilising any or any combination of a calculated phase of back EMF induced in the phase winding, an amplitude representative of the amplitude of back EMF induced in the phase winding, and a frequency representative of the frequency of back EMF induced in the phase winding. ### Claim 9 (depends on 1) The method as claimed in claim 1, wherein calculating a phase of back EMF induced in the phase winding comprises integrating the equation E = L ⁢ dI dt + IR - V PH to obtain a relationship representative of integrated back EMF. ### Claim 10 (depends on 9) The method as claimed in claim 9, wherein calculating a phase of back EMF induced in the phase winding comprises equating integrated back EMF to an integral of a sinusoidal waveform representative of back EMF induced in the phase winding. ### Claim 11 (depends on 10) The method as claimed in claim 10, wherein calculating a phase of back EMF induced in the phase winding comprises equating a relationship representative of integrated back EMF with an integral of a sinusoidal waveform representative of back EMF induced in the phase winding. ### Claim 12 (depends on 1) The method as claimed in claim 1, wherein calculating a phase of back EMF induced in the phase winding comprises calculating at least one instantaneous back EMF value using the measured instantaneous phase current and the measured voltage. ### Claim 13 (depends on 12) The method as claimed in claim 12, wherein instantaneous back EMF values are calculated using the equation E = L ⁢ dI dt + IR - V PH . ### Claim 14 (depends on 1) The method as claimed in claim 1, wherein calculating a phase of back EMF induced in the phase winding comprises integrating calculated instantaneous back EMF values. ### Claim 15 A brushless permanent magnet motor, comprising a controller configured to: measure instantaneous phase current flowing through a phase winding of the motor during excitation of the phase winding; measure voltage applied to the phase winding of the motor during excitation of the phase winding; calculate a phase of back EMF induced in the phase winding using the measured instantaneous phase current and the measured voltage; determine, using the calculated phase of back EMF induced in the phase winding, a zero-crossing point of the back EMF induced in the phase winding of the motor; and determine, based on when the back EMF induced in the phase winding is at the zero-crossing point, an aligned position of the rotor of the brushless permanent magnet motor. ### Claim 16 A data carrier comprising machine readable instructions for the operation of a controller of a brushless permanent magnet motor to: measure instantaneous phase current flowing through a phase winding of the motor during excitation of the phase winding; measure voltage applied to the phase winding of the motor during excitation of the phase winding; calculate a phase of back EMF induced in the phase winding using the measured instantaneous phase current and the measured voltage; determine, using the calculated phase of back EMF induced in the phase winding, a zero-crossing point of the back EMF induced in the phase winding of the motor; and determine, based on when the back EMF induced in the phase winding is at the zero-crossing point, an aligned position of the rotor of the brushless permanent magnet motor. ### Claim 17 (depends on 1) The method of claim 1, wherein the phase winding is one of a plurality of phase windings of the motor. ### Claim 18 (depends on 1) The method of claim 1, wherein measuring the voltage applied to the phase winding of the motor comprises measuring a direct current voltage applied to the phase winding of the motor. ### Claim 19 (depends on 15) The brushless permanent magnet motor of claim 15, wherein: the phase winding is one of a plurality of phase windings of the motor; and the voltage applied to the phase winding is a direct current voltage. ### Claim 20 (depends on 16) The data carrier of claim 16, wherein: the phase winding is one of a plurality of phase windings of the motor; and measuring the voltage applied to the phase winding of the motor comprises measuring a direct current voltage applied to the phase winding of the motor.