System and method for sensor less magnetic field control of a motor
AssigneeAgile Systems Inc.
InventorDavid Kyle MacKay
Life of this patent
Estimating the term…
Abstract
A system and method for sensor less control of a stepper motor is described. The system and method includes estimation of the position of a rotor of the motor by way of sensing circuitry on the windings of the motor, without the use of positional sensors. The system and method of stepper motor control further includes magnetic field optimization for increasing the torque generating component of a magnetic field generated by stators of the motor, and magnetic field weakening for countering some of the effects of back electromotive force generated by the magnetic rotor.
Claims19
A method for controlling a rotor of an electric motor, the motor having a plurality of stators and a winding connected to each stator of the plurality of stators, said motor being responsive to electric current provided to a set of windings of the motor causing the rotor to change position, said method comprising:
- controlling position of said rotor from a present open loop position to an open loop intended position in an open-loop operation mode, by;
- deriving the open loop present position of the rotor from a back electromotive force (EMF) based on at least one of current and voltage conditions of the windings;
- determining an electric current to move said rotor from said open loop present position to said open loop intended position;
- providing said electric current to said set of windings to move said rotor towards said open loop intended position;
- and
- determining a present open loop velocity of said rotor from said at least one of current and voltage conditions;
- transitioning control of the motor from the open-loop operation to a phase-locked loop operation when the present rotor velocity reaches a transition velocity;
- and
- controlling a subsequent velocity of said rotor via a phase-locked loop operation after said transition velocity is reached, said subsequent velocity determined by a phase-locked position of said rotor and an intended phase-locked position of said rotor, by;
- deriving a phase-locked electrical phase for said phase-locked position by;
- determining a back EMF flux value induced over each winding connected to each stator of the plurality of stators from said at least one of current and voltage conditions, including;
- determining a current back EMF value from said at least one of current and voltabe condition, and
- integrating values of the current back EMF and previously determined back EMF over each said winding using integration constants with values determined from the back EMF value at the time of transition;
- determing a phase error representing the difference between a present electrical phase of said rotor and an intended electrical phase representing said intended phase-locked position;
- and
- providing an adjustable phase-locked electric current to said set of winding to move the rotor towards the intended phase-locked position, said current being adjustable to track said phase error to adjust said subsequent velocity.
A system for controlling the position of a magnetic rotor of an electric motor, the motor having a plurality of stators for causing rotation of the rotor upon magnetization of at least one stator of the plurality of stators, and a winding connected to said each stator for magnetizing said each stator when electric current flows through the winding, said motor responding to current control signals to adjust electric current flowing through one or more of said windings to cause the rotor to rotate towards an intended position, said system comprising:
- a sampling circuit electrically connected to each winding for measuring at least one of the current and voltage on each winding;
- a processing circuit in communication with said sampling circuit for determining a present position of the rotor from the at least one of current and voltage on each winding, said processing circuit receiving input control signals based on said input control signals and any difference between the present position and the intended position of the rotor, said processing circuit communicating with said motor to cause an adjustment in the current control signals to cause the rotor to rotate toward the intended position based on the adjusted input control signals;
- a control module to selectively control said motor via phase-lock loop operation and open loop operation,
- wherein
- said open loop operation
- derives a present position of the rotor from a back electromotive force (EMF) based on at least one of current and voltage conditions of the windings;
- derives a present rotor velocity from said at least one of current and voltage conditions;
- and
- adjusts the current control signals to induce movement of the rotor towards an intended position based on the derived present position of the rotor;
- and
- said phase-locked loop operation
- derives a present electrical phase representing said present position of the rotor and an intended electrical phase representing said intended position, said deriving a present electrical phase including determining a back EMF flux value induced over each said winding connected to each stator of the plurality of stators from said at least one of current and voltage conditions, including determining a current back EMF and integrating values of the current back EMF and previously determined back EMF values over each said winding, wherein said integrating includes, at the time of transition, seeding integration constants for said integrating with values determined from the back EMF value at a time of transition between open loop operation and phase-locked loop operation;
- determines a phase error representing the difference between the present electrical phase and the intended electrical phase;
- and
- adjusts said current control signals to control said electric current to track said phase error to provide movement of the rotor towards the intended position;
- and
- said control module selectively engages said open loop operation if the rotor is rotating below a transition velocity of the motor, and said phase-locked loop operation if the rotor is rotating at or above the transition velocity.
Dependencies are inferred from the claim text.