Abstract: A drive system for a three phase brushless AC motor is arranged to optimize the transistor switching pattern to improve power output whilst allowing current measurement in all of the phases using a single sensor. This is achieved by defining voltage demand vectors x where more than two states are required to meet a minimum state time requirement determined by the single sensor method, and calculating three or more state vectors which produce the demanded vector x whilst still allowing single current sensing. Various methods of optimising the PWM pattern so as to give maximum output whilst using single current sensing are also disclosed.

Abstract: A drive system for a multi-phase brushless motor comprises a single current sensor drive circuit, including switch means 16, switchable between a plurality of states. A controller is arranged to provide pulse width modulated drive signals to control the switch means 16 so as to control the time that the drive circuit switches between said states in each of a series of pulse width modulation periods, and to: determine a demanded voltage parameter set, identify PWM periods during which the demanded voltage parameter set is such that neither two nominal corresponding state times, nor a higher number of equivalent state times producing the same net voltage, in a single PWM period, would allow a predetermined minimum time to be spent in a predetermined number of active states sufficient for current sensing.

Abstract: A drive system for a three phase brushless motor uses an algorithm for position sensing which measures the inductance in the motor phases and determines the position from the measured inductances. In order to reduce acoustic noise, the inductances are measured during test periods Tsd, which are conducting states added to the PWM pattern in each PWM period. The test periods have net voltage of zero and therefore do not affect the output of the motor, but are sufficiently long to allow inductance measuring as well as the use of a single current sensor for current sensing.

Abstract: A drive system for a three phase brushless motor uses an algorithm for position sensing which measures the inductance in the motor phases and determines the position from the measured inductances. In order to reduce acoustic noise, the inductances are measured during test periods Tsd, which are conducting states added to the PWM pattern in each PWM period. The test periods have net voltage of zero and therefore do not affect the output of the motor, but are sufficiently long to allow inductance measuring as well as the use of a single current sensor for current sensing.

Abstract: An angular velocity sensor for a rotor (2) and method of determining angular velocity in which the position at which event generation means (4) pass sensing means (5) is determined using information from the times at which the event generation means (4) passed the sensing means (5) during at least one previous complete revolution to of the rotor (2). Especially applicable to use of Hall Effect Sensors to detect commutation points of a brushless permanent magnet rotor in an Electric Power Assisted Steering apparatus.

Abstract: A drive system for a three phase brushless AC motor that is operative to optimize a transistor switching pattern to improve power output while allowing current measurement in all of the phases using a single sensor. This is achieved by defining a voltage demand vector where more than two states are required to meet a minimum state time requirement determined by the single sensor and calculating three or more state vectors that produce the demand vector while still allowing single current sensing.

Abstract: An angular velocity sensor for a rotor (2) and method of determining angular velocity in which the position at which event generation means (4) pass sensing means (5) is determined using information from the times at which the event generation means (4) passed the sensing means (5) during at least one previous complete revolution to of the rotor (2). Especially applicable to use of Hall Effect Sensors to detect commutation points of a brushless permanent magnet rotor in an Electric Power Assisted Steering apparatus.