Abstract: A control system for a multiphase electric motor comprises processing means arranged to determine a pattern of PWM voltage waveforms to be applied to respective phases of the motor, the processing means assigning different PWM patterns for use with different motor positions. In use for a given rotational position of the motor the processing means is normally adapted to apply PWM waveforms according to the assigned PWM pattern unless a different PWM pattern is currently in use at that time, except that in the event that the demanded voltage waveforms cannot be achieved with the current PWM pattern the processing means is adapted to force the PWM pattern to change. Upon the rotor moving into a different position associated with a different assigned pattern the processing means forces the PWM pattern to change to the assigned PWM pattern.

Abstract: A control system for an electric motor comprises a controller which receives as an input a demanded motor current and produces at an output an intermediate voltage demand signal, a voltage demand signal correction means arranged to generate a voltage demand correction signal, and a combining means arranged to combine the intermediate voltage demand signal and the voltage demand correction signal to produce an actual voltage demand signal that is applied to the motor by pulse width modulation of the switches of a motor bridge driver. The correction signal compensates for unwanted non-linearities caused by interlock delays in the switching of the motor bridge switches.

Abstract: A method of determining an electrical angle offset of a motor position sensor mounted to a multi-phase electric motor, the method comprising rotating a rotor of the multi-phase electric motor at a motor velocity using an external drive system, measuring a motor phase voltage of each phase of the multi-phase electric motor, the motor phase voltage comprising a back-EMF generated by the rotation of the motor, converting the motor phase voltage to a DQ reference frame to form a DQ motor phase voltage and calculating the electrical angle offset from the DQ motor phase voltages.

Abstract: A method of determining an electrical angle offset of a motor position sensor mounted to a multi-phase electric motor, the method comprising rotating a rotor of the multi-phase electric motor at a motor velocity using an external drive system, measuring a motor phase voltage of each phase of the multi-phase electric motor, the motor phase voltage comprising a back-EMF generated by the rotation of the motor, converting the motor phase voltage to a DQ reference frame to form a DQ motor phase voltage and calculating the electrical angle offset from the DQ motor phase voltages.

Abstract: A method of controlling a motor of an electric power assisted steering system, the motor having a plurality of phases, the method comprising taking as an input an input signal indicative of a desired assistance torque and determining from the desired assistance torque a voltage to be applied to each of the phases of the motor, in which the step of determining the voltage to be applied to each of the phases comprises limiting the voltage determined to be applied to each of the phases of the motor dependent upon the voltage provided by a power supply to the motor.

Abstract: A control system for an electric motor comprises a current controller which produces a set of voltage demands for the motor, a current sensing means arranged to produce a current sensing output indicative of electric current in the motor, and a current signal processing means arranged to process the current sensing output signal to produce a modified current signal in which at least one harmonic component present in the current sensing output signal due to inaccuracies in the current measurement is removed or substantially reduced. The modified current signal is combined with a demanded motor current to provide the input to the current controller.

Abstract: A motor control circuit for an electric motor of an electric power assisted steering system of the kind in which a measurement of torque carried by a part of the steering system is used to produce a torque demand signal indicative of a torque to be applied to the steering system by the motor. The motor control circuit includes a current controller is responsive to an error signal that represents the difference between a current demand signal and an actual current signal, and a noise reduction circuit adapted to identify an operating condition of the system in which the motor is stationary or rotating at a very low speed, and in the event that the operating condition is identified the noise reduction circuit is adapted to reduce the response of the controller to variations in the error signal.

Abstract: A control system for an electric motor comprises a controller which receives as an input a demanded motor current and produces at an output an intermediate voltage demand signal, a voltage demand signal correction means arranged to generate a voltage demand correction signal, and a combining means arranged to combine the intermediate voltage demand signal and the voltage demand correction signal to produce an actual voltage demand signal that is applied to the motor by pulse width modulation of the switches of a motor bridge driver. The correction signal compensates for unwanted non-linearities caused by interlock delays in the switching of the motor bridge switches.

Abstract: A control strategy for an electric motor of an electric power assisted steering system of the kind in which a control means produces motor current demand signals that are fed to a motor drive means, the demand signals being dependent on the amount of assistance torque demanded from the motor, the motor drive means being arranged to cause currents to flow in each phase of the motor as required to meet the demanded assistance torque, the control strategy comprising limiting the rate of change of current that is drawn from the electrical supply of the vehicle by the motor in the event that it would otherwise exceed a threshold rate of change.

Abstract: A rotary encoder assembly comprises an annular track comprising an alternating pattern of at least two different encoding regions; a first detector and a second detector each arranged to produce a respective alternating output signal as the track of encoding regions rotates about its axis past the detector, the combined values of the two output signals assuming a plurality of unique states with the states changing from one to another as the encoder rotates. A memory stores compensation values, each value being associated with a respective one of the possible state changes that can occur when the combined values of the two output signals change upon movement of the encoder track, and each indicative of an average error in the position at which the corresponding change of state occurs.

Abstract: A control system for an electric motor comprises a current controller which produces a set of voltage demands for the motor, a current sensing means arranged to produce a current sensing output indicative of electric current in the motor, and a current signal processing means arranged to process the current sensing output signal to produce a modified current signal in which at least one harmonic component present in the current sensing output signal due to inaccuracies in the current measurement is removed or substantially reduced. The modified current signal is combined with a demanded motor current to provide the input to the current controller.

Abstract: A control system for an electric motor comprises a current sensing means arranged to produce a current sensing output indicative of electric current in the motor, current control means arranged to receive the current sensing output and to output a voltage demand indicative of voltages to be applied to the motor, and current sensing correction means arranged to monitor the voltage demand to measure distortion in the current sensing output and to generate a correction signal which is arranged to correct the distortion.

Abstract: A method of estimating the position of a rotor of an electric motor comprises producing an output signal indicative of motor position using a position sensor which comprises a detector and at least one encoder which rotates along with the rotor of the motor and includes a plurality of encoding regions, the output signal of the sensor varying in a stepwise fashion as the encoding regions move past the detector, and passing the output of the sensor through a smoothing algorithm to produce an estimated position signal, the algorithm being arranged to smooth the transition between the steps in the output of the sensor by causing the estimated position signal to lag behind the output of the sensor following a step change in the output of the sensor.

Abstract: A rotary encoder assembly comprises an annular track comprising an alternating pattern of at least two different encoding regions; a first detector and a second detector each arranged to produce a respective alternating output signal as the track of encoding regions rotates about its axis past the detector, the combined values of the two output signals assuming a plurality of unique states with the states changing from one to another as the encoder rotates. A memory stores compensation values, each value being associated with a respective one of the possible state changes that can occur when the combined values of the two output signals change upon movement of the encoder track, and each indicative of an average error in the position at which the corresponding change of state occurs.

Abstract: A method of controlling a motor of an electric power assisted steering system, the motor having a plurality of phases, the method comprising taking as an input an input signal indicative of a desired assistance torque and determining from the desired assistance torque a voltage to be applied to each of the phases of the motor, in which the step of determining the voltage to be applied to each of the phases comprises limiting the voltage determined to be applied to each of the phases of the motor dependent upon the voltage provided by a power supply to the motor.

Abstract: A motor control circuit for an electric motor of an electric power assisted steering system of the kind in which a measurement of torque carried by a part of the steering system is used to produce a torque demand signal indicative of a torque to be applied to the steering system by the motor, the control circuit comprising a switching circuit comprising a plurality of electrical switches, and a motor current controller that generates voltage demand signals to be passed to a drive circuit for the switches that in turn generates pulse width modulated switching signals for the switching circuit that cause the switches to selectively connect the phases to a power supply so as to cause current to flow through the phases of the motor.

Abstract: A control system for a multiphase electric motor comprises processing means arranged to determine a pattern of PWM voltage waveforms to be applied to respective phases of the motor, the processing means assigning different PWM patterns for use with different motor positions. In use for a given rotational position of the motor the processing means is normally adapted to apply PWM waveforms according to the assigned PWM pattern unless a different PWM pattern is currently in use at that time, except that in the event that the demanded voltage waveforms cannot be achieved with the current PWM pattern the processing means is adapted to force the PWM pattern to change. Upon the rotor moving into a different position associated with a different assigned pattern the processing means forces the PWM pattern to change to the assigned PWM pattern.

Abstract: A method of estimating the position of a rotor of an electric motor comprises producing an output signal indicative of motor position using a position sensor which comprises a detector and at least one encoder which rotates along with the rotor of the motor and includes a plurality of encoding regions, the output signal of the sensor varying in a stepwise fashion as the encoding regions move past the detector, and passing the output of the sensor through a smoothing algorithm to produce an estimated position signal, the algorithm being arranged to smooth the transition between the steps in the output of the sensor by causing the estimated position signal to lag behind the output of the sensor following a step change in the output of the sensor.

Abstract: A control strategy for an electric motor of an electric power assisted steering system of the kind in which a control means produces motor current demand signals that are fed to a motor drive means, the demand signals being dependent on the amount of assistance torque demanded from the motor, the motor drive means being arranged to cause currents to flow in each phase of the motor as required to meet the demanded assistance torque, the control strategy comprising limiting the rate of change of current that is drawn from the electrical supply of the vehicle by the motor in the event that it would otherwise exceed a threshold rate of change.

Abstract: A control system for an electric motor comprises a current sensing means arranged to produce a current sensing output indicative of electric current in the motor, current control means arranged to receive the current sensing output and to output a voltage demand indicative of voltages to be applied to the motor, and voltage demand correction means arranged to generate a correction signal and to use the correction signal and the voltage demand to produce a corrected voltage demand.