Current measuring apparatus for use with electric motors
AssigneeTRW Inc.
InventorErnest Henry Introwicz
Life of this patent
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Abstract
A current measuring circuit for an electric motor provides an output indicative of the change in the current di/dt flowing in a phase of the electric motor over a measurement period of time. The circuit includes a current measurement element having a resistance; a switch which in use selectively permits transmission of a voltage dependent upon the instantaneous value of the voltage dropped across the current measurement element to a part of the circuit; and a switch controller which is adapted to operate the switch in response to timing signals supplied by the switch controller so as to define the measurement period of time.
Claims15
A current measuring circuit adapted to provide an output indicative of the change in the current flowing in at least one phase of an electric motor over a measurement period of time, the current measurement circuit including:
- a current measurement element having a resistance in series with at least one phase of the motor;
- a switch which, in use, selectively permits and prevents transmission of a voltage that is indicative of the instantaneous value of the voltage dropped across the current measurement element to a part of the current measurement circuit that measures the change in the voltage dropped across the current measurement element during the measurement period of time;
- and
- a switch controller which is adapted to operate the switch in response to timing signals supplied by the switch controller so as to define the measurement period of time,
- in which the current measurement circuit is adapted to provide an output indicative of the change in the current flowing in the at least one phase during the measurement period of time, wherein the measurement period of time either starts after the leading edge of a pulse and ends before the next trailing edge of the pulse or starts after a trailing edge of the pulse and before the next leading edge of a pulse, the voltage applied to the phase being constant during the measurement period of time, and to determine therefrom the inductance of at least one of the phases thereby to determine the rotational position of the motor from a known variation of inductance with motor position.
A drive system for a multi-phase brushless electric motor comprising a plurality of phases, the system comprising:
- a drive circuit including phase switching means for varying the phase voltage applied across each of the plurality of phases, and
- control means arranged to control the phase switching means so as to provide PWM control of the phase voltages to control the mechanical output of the multi-phase brushless electric motor, measure a rate of change of current in at least one of the plurality of phases during a test period and to determine therefrom the inductance of at least one of the plurality of phases thereby to determine the rotational position of the multi-phase brushless electric motor,
- the control means determining the change of current using the output of a current measurement circuit comprising:
- a current measurement element in series with at least one phase of the motor;
- a switch which, in use, selectively permits and prevents transmission of a voltage that is indicative of the voltage dropped across the current measurement element to a part of the current measurement circuit that measures the change in the voltage dropped across the current measurement element during the measurement period of time;
- and
- a switch controller which is adapted to operate the switch in response to timing signals supplied by the switch controller so as to define the measurement period of time
- in which the current measurement circuit is adapted to provide an output indicative of the change in the current flowing in the at least one phase during the measurement period of time, wherein the measurement period of time either starts after the leading edge of a pulse and ends before the next trailing edge of the pulse or starts after a trailing edge of the pulse and before the next leading edge of a pulse, the voltage applied to the phase being constant during the measurement period of time, and to determine therefrom the inductance of at least one of the phases thereby to determine the rotational position of the motor from a known variation of inductance with motor position.
Dependencies are inferred from the claim text.