Motor control
AssigneeTRW Lucas Varity Electric Steering Ltd.
InventorsAndrew James Stephen Williams, Anthony Walter Burton
Life of this patent
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Abstract
A method of monitoring the operation of a brushless motor is disclosed. The method comprises the steps of monitoring the current flowing into or out of the windings of the motor using a current measurement circuit to produce an output signal indicative of the current; measuring the output of the current measurement circuit when the instantaneous current flow through the current measurement circuit is known to be substantially zero; and producing a modified output signal which is compensated for any differences between the actual measured output signal value and an ideal output signal value. The method enables any drift in the output signal to be compensated “on-line” whilst the is running.
Claims24
A method of monitoring the operation of a brushless motor comprising a number of phases, each of said phases comprising one or more windings connected in a bridge circuit, said bridge circuit comprising a number of arms with one of said arms for each phase, each said arm comprising a top switching device connected between said phase and a first supply voltage and a bottom switching device connected between said phase an a second, different, supply voltage, each of said switching devices being switchable from an on state to an off state wherein the method comprises the steps of:
- monitoring current flowing into or out of said windings using a current measurement means to produce an output signal indicative of said current;
- controlling said motor by applying suitable signals to each switching device such that the instantaneous current flow through said current measurement means is substantially zero;
- measuring the value of an output signal of said current measurement means when said instantaneous current flow through said current measurement means is substantially zero;
- and producing a modified output signal which is compensated for any differences between the measured value and that indicative of zero current.
A method of controlling a motor comprising a number of phases, each phase being connected to a first voltage through a top switching device and to a second voltage through a bottom switching device, the method comprising the steps of:
- calculating a respective phase voltage demand value for each phase of said motor indicative of a net voltage to be applied to said phase;
- calculating a duty period value of a pulse width modulated signal for said top switching device and a duty period value of a pulse width modulated signal for said bottom switching device of each phase needed to apply a net voltage to said phase corresponding to said phase voltage demand value;
- processing said duty period value to define for each phase a time delay between a first switching edge for said top switching device where it is switched from an off state to an on state and a second switching edge for said top switching device where it is switched back to the off state and a time delay between a third switching edge for said bottom switching device where it is switched from an on state to an off state and a fourth switching edge for said bottom switching device where it is switched back to said on state, the position of said edges defining a cycle of a PWM signal;
- calculating the positions of said edges of said signals for one phase relative to said edges of said signals for said other phases so that at a first instance a current flowing into or out of said motor is indicative of the current in a single phase and at a second instance the current flowing in said motor is indicative of the current flowing in a second, different, phase;
- and
- modulating each switching device with its respective PWM signal.
Dependencies are inferred from the claim text.