Method and apparatus for sensing load current in a motor controller
First Claim
1. In a power controller which powers a multi-phase load from a power supply by employing (a) a power switching matrix connected to the load, and (b) switching control means for generating a switching cycle and a commutation sequence in order to control the power switching matrix, apparatus in combination with the switching control means for sensing current flowing through the load, the current sensing apparatus comprising:
- a resistive element for sensing current connected in series between the power supply and the power switching matrix such that the power supply, switching matrix and current resistive element form an electrical loop;
a capacitive element connected in parallel with the resistive element,an output which provides an output signal representative of the sampled current, said output signal being provided at the capacitive element;
a sampling switch having a control input, installed between the capacitive element and resistive element in order to selectively charge the capacitive element, the sampling switch having an on-resistance, the capacitive element and sampling switch being selected such that
space="preserve" listing-type="equation">T.sub.H.sbsb.min ≈
C.sub.S *R.sub.S.sbsb.s.sub.-ONwhere THmin is a minimum permissible time period for the portion of the switching cycle wherein the load is being actively driven, CS is the capacitance provided by the capacitive element, and RSs-ON is the on-resistance of the sampling switch; and
a sampling switch actuation circuit, operatively connected to the control input, for activating the sampling switch for a time period corresponding to a portion of the switching cycle in each commutation step wherein the power switching matrix is configured to enable current flowing through the load to flow through the resistive element.
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Abstract
The approach to measuring load current in a multi-phase bridge inverter circuit connected to a multiphase load involves placing a single current sense resistor in series with the inverter circuit and power supply. The current flow through the sense resistor is sampled during a portion of the switching cycle wherein the inverter is configured to enable current flowing through the multi-phase load to flow through the sense resistor. Typically, this will occur during a portion of the switching cycle (e.g. PWM cycle) wherein the load is being actively driven. For a 120°, 3-phase, 6-step commutation sequence typically used to control a d.c. brushless servo motor, the sampled current is a time-multiplexed measure of the current flow through each load phase. The same sense resistor is also used for indicating a short circuit condition by comparing the voltage across the resistor to a reference voltage.
90 Citations
22 Claims
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1. In a power controller which powers a multi-phase load from a power supply by employing (a) a power switching matrix connected to the load, and (b) switching control means for generating a switching cycle and a commutation sequence in order to control the power switching matrix, apparatus in combination with the switching control means for sensing current flowing through the load, the current sensing apparatus comprising:
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a resistive element for sensing current connected in series between the power supply and the power switching matrix such that the power supply, switching matrix and current resistive element form an electrical loop; a capacitive element connected in parallel with the resistive element, an output which provides an output signal representative of the sampled current, said output signal being provided at the capacitive element; a sampling switch having a control input, installed between the capacitive element and resistive element in order to selectively charge the capacitive element, the sampling switch having an on-resistance, the capacitive element and sampling switch being selected such that
space="preserve" listing-type="equation">T.sub.H.sbsb.min ≈
C.sub.S *R.sub.S.sbsb.s.sub.-ONwhere THmin is a minimum permissible time period for the portion of the switching cycle wherein the load is being actively driven, CS is the capacitance provided by the capacitive element, and RSs-ON is the on-resistance of the sampling switch; and a sampling switch actuation circuit, operatively connected to the control input, for activating the sampling switch for a time period corresponding to a portion of the switching cycle in each commutation step wherein the power switching matrix is configured to enable current flowing through the load to flow through the resistive element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A multi-phase motor controller, comprising:
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a power switching matrix for selectively powering a multi-phase motor from a power supply; switching control circuitry, including a commutation controller, operatively connected to the power switching matrix for generating a switching cycle in order to control the power switching matrix and providing an m-phase, n-step commutation sequence; a resistive element for sensing current connected in series between the power supply and the power switching matrix such that the power supply, switching matrix and resistive element form an electrical loop; a capacitive element connected in parallel with the resistive element; an output which provides an output signal representative of the sampled current, said signal output being provided across the capacitive element; a sampling switch, having a control input, installed between the capacitive element and resistive element in order to selectively charge the capacitive element, the sampling switch having an on-resistance, the capacitive element and sampling switch being selected such that
space="preserve" listing-type="equation">T.sub.H.sbsb.min ≈
C.sub.S *R.sub.S.sbsb.s.sub.-ONwhere THmin is a minimum permissible time period for the portion of the switching cycle wherein the load is being actively driven, CS is the capacitance provided by the capacitive element, and RSs-ON is the on-resistance of the sampling switch; a sampling switch actuation circuit, operatively connected to the control input, for activating the sampling switch for a time period corresponding to a portion of the switching cycle in each commutation step wherein the power switching matrix is configured to enable current flowing through the load to flow through the resistive element. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method for sensing current supplied to a multi-phase load from a power supply by apparatus which employs a power switching matrix connected to the load and commutation control means for providing switching control signals, having a switching cycle, to the power switching matrix, the method comprising:
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connecting a resistive element for sensing current in series between the power supply and the power switching matrix such that the power supply, switching matrix and resistive element form an electrical loop; connecting a capacitive element in parallel with the resistive element; installing a sampling switch between the capacitive element and resistive element in order to selectively charge the capacitive element, the sampling switch having an on-resistance, the capacitive element and sampling switch being selected such that
space="preserve" listing-type="equation">T.sub.H.sbsb.min ≈
C.sub.S *R.sub.S.sbsb.s.sub.-ONwhere THmin is a minimum permissible time period for the portion of the switching cycle wherein the load is being actively driven, CS is the capacitance provided by the capacitive element, and RSs-ON is the on-resistance of the sampling switch; activating the sampling switch for a time period corresponding to a portion of the switching cycle in each commutation step wherein the power switching matrix is configured to enable current flowing through the load to flow through the resistive element; and reading the voltage or current of the capacitive element during said time period. - View Dependent Claims (21, 22)
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Specification