Abstract: A brushless permanent magnet motor has a phase winding, an inverter for applying voltage vectors to the phase winding, and a controller for controlling the inverter. The inverter has a plurality of high side switches and a plurality of low side switches. The controller is configured to divide an electrical cycle of the motor into a first portion and a second portion different to the first portion, apply a first set of voltage vectors to the phase winding in the first portion of the electrical cycle, and apply a second set of voltage vectors to the phase winding in the second portion of the electrical cycle. The second set of voltage vectors is different to the first set of voltage vectors. The controller is configured to turn on a low side switch to apply each voltage vector of the first set of voltage vectors, and turn off all low side switches to apply a zero-voltage vector of the second set of voltage vectors.

Abstract: A method is described for controlling a three-phase permanent-magnet motor. The method includes sequentially exciting and freewheeling phases of the motor. The phases are freewheeled when a magnitude of phase current rises to an upper threshold, and freewheeling continues for either a fixed period of time or until the magnitude of the phase current decreases to a lower threshold. The method further includes measuring a parameter that corresponds to either the magnitude of the phase current during or at the end of freewheeling, or an interval between a start and end of freewheeling or a start and end of excitation. A saturation event is determined to have occurred when the measured parameter is less than a saturation threshold. In response to the saturation event, the phases are commutated.

Abstract: A method of controlling a brushless permanent magnet motor having a plurality of phase windings and an inverter for applying voltage vectors to the plurality of the phase windings, the method including monitoring phase current flowing through a first phase winding to determine a zero-crossing point of the phase current flowing through the first phase winding. The method includes predicting a polarity of phase current flowing through a second phase winding based on the determined zero-crossing point of the phase current flowing through the first phase winding, and determining a timing of a control signal to control switches of the inverter to apply a voltage vector to the phase windings. The timing of the control signal is determined using the predicted polarity of phase current flowing through the second phase winding.

Abstract: A drive circuit for a brushless motor is described. The drive circuit includes a converter for connection to a phase winding of the motor, and a controller. The converter includes a plurality of switches and the controller controls the states of the switches to configure the converter in one of a plurality of configurations. In a first configuration, current is permitted to flow through the phase winding in a first direction and in a second opposite direction. In a second configuration, current is permitted to flow through the phase winding in the first direction and is prevented from flowing through the phase winding in the second direction. The controller includes an input for receiving a signal indicative of current in the converter, and the controller configures the converter from the first configuration to the second configuration in response to a characteristic of the current.

Abstract: A method of determining a position of a rotor of a brushless permanent magnet motor includes measuring a current value indicative of current flowing through a phase winding of the motor and providing a reference voltage value indicative of a voltage applied to the phase winding of the motor. The method includes calculating a phase of back EMF induced in the phase winding using the measured current value and the reference voltage value, and 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 generating a rotor position signal based on the determined zero-crossing point.

Abstract: A stator assembly including at least one pair of c-shaped stator cores, each c-shaped stator core having a bobbin, and a winding wound around each bobbin, wherein the windings on each adjacent pair of c-shaped stator cores are wound in opposite directions.

Abstract: A stator assembly comprising at least one pair of c-shaped stator cores, each c-shaped stator core having a bobbin, and a winding wound around each bobbin, wherein the windings on each adjacent pair of c-shaped stator cores are wound in opposite directions.