Electric power steering system for a vehicle
First Claim
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1. A system (1) being powered by a battery which delivers a voltage V, and (2) effective for operation in a vehicle, comprising:
- a) a two-phase electric motor havingi) a stator of the synchronous type andii) two stator phases;
b) a field-oriented controller for controlling voltages applied to the phases, whereini) full battery voltage is available for application across each phase;
ii) all phase voltages are independently controllable; and
iii) a continually rotating stator vector is generated, of selected phase with respect to the rotor and of selected magnitude.
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Abstract
A control system for an electric motor. Field Oriented Control, FOC, uses a digital control system, and attempts to maintain the rotating stator magnetic field ninety degrees ahead of the rotor field, in order to maximize torque. However, if a three-phase motor is used, which is very common, large amounts of computation are required, to convert from a three-phase coordinate system to an orthogonal coordinate system. The invention replaces the three-phase motor with a two-phase motor, which has been found to impose certain additional costs, but also provides benefits.
34 Citations
34 Claims
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1. A system (1) being powered by a battery which delivers a voltage V, and (2) effective for operation in a vehicle, comprising:
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a) a two-phase electric motor having i) a stator of the synchronous type and ii) two stator phases; b) a field-oriented controller for controlling voltages applied to the phases, wherein i) full battery voltage is available for application across each phase; ii) all phase voltages are independently controllable; and iii) a continually rotating stator vector is generated, of selected phase with respect to the rotor and of selected magnitude. - View Dependent Claims (2, 3, 4, 5, 32)
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6. A method for operation in a vehicle being powered by a battery which delivers a voltage V, comprising:
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a) maintaining a two-phase electric motor having i) a stator of the synchronous type and ii) two stator phases; b) maintaining a field-oriented controller for controlling voltages applied to the phases, which maintains a continually rotating stator field which is (1) of selected magnitude and (2) in selected phase relation with a rotor field, which i) applies full battery voltage across each phase; and ii) provides independently controllable voltages to all phases. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A system (1) for operation in a vehicle having a power steering system, and (2) being powered by a battery which delivers a voltage V, comprising:
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a) a two-phase electric motor having i) a stator of the synchronous type and ii) two stator phases; b) a field-oriented controller for controlling voltages applied to the phases, which maintains a continually rotating stator field which is (1) of selected magnitude and (2) in selected phase relation with a rotor field, wherein i) full battery voltage is available for application across each phase; and ii) all phase voltages are independently controllable, wherein pulse-width modulation, PWM, is used to control magnitude of current in each phase, the PWM applied to one phase need not be synchronized with the PWM applied to the other phase, and voltage V is available for application to each phase.
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13. A method (1) for operation in a vehicle having a power steering system, and (2) being powered by a battery which delivers a voltage V, comprising:
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a) providing a two-phase electric motor having i) a stator of the synchronous type and ii) two stator phases; b) providing a field-oriented controller for controlling voltages applied to the phases, which maintains a continually rotating stator field which is (1) of selected magnitude and (2) in selected phase relation with a rotor field, wherein i) full battery voltage is available for application across each phase; and ii) all phase voltages are independently controllable, wherein pulse-width modulation, PWM, is used to control magnitude of current in each phase, the PWM applied to one phase need not be synchronized with the PWM applied to the other phase, and voltage V is available for application to each phase. - View Dependent Claims (19, 21, 23)
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14. In an electric motor which has a rotor having a rotor field and stator coils which produce a rotating stator field vector, and which is controlled by a control system implementing Field Oriented Control, which maintains a continually rotating stator field which is (1) of selected magnitude and (2) in selected phase relation with the rotor field, a method comprising:
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a) deriving data concerning behavior of the coils; and b) based on the data, computing position of the stator field vector, without translating from an N-phase reference frame of the stator to an orthogonal reference frame, wherein N is greater than two. - View Dependent Claims (15, 16, 17)
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18. For an electric motor which has a rotor having a rotor field and stator coils which produce a continually rotating stator field vector, and which is controlled by a control system implementing Field Oriented Control, which maintains the stator field (1) at a selected magnitude and (2) in a selected phase relation with the rotor field, a system comprising:
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a) means for deriving data concerning behavior of the coils; and b) means for receiving the data and computing position of the stator field vector, without translating from an N-phase reference frame of the stator to an orthogonal reference frame, wherein N is greater than two. - View Dependent Claims (20, 22)
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24. A system comprising:
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a) a motor comprising a two-phase stator of the synchronous type; and b) a control system which implements Field Oriented Control, which maintains a continually rotating stator field which is (1) of selected magnitude and (2) in selected phase relation with the rotor field, wherein the only coordinate transformations undertaken are (1) from a stationary system to a rotating system and (2) from the rotating system to the stationary system. - View Dependent Claims (25)
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26. A method comprising:
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a) providing a motor comprising a two-phase stator of the synchronous type; and b) providing a control system which implements Field Oriented Control, which maintains a continually rotating stator field which is (1) of selected magnitude and (2) in selected phase relation with the rotor field, wherein the only coordinate transformations undertaken are (1) from a stationary system to a rotating system and (2) from the rotating system to the stationary system. - View Dependent Claims (27)
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28. A method, comprising:
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a) in a vehicle, maintaining an electric motor having a stator of the synchronous type; b) generating currents in coils of the stator, said currents producing a rotating stator field vector; and c) obtaining an expression for orthogonal components of the stator field, without computing said components. - View Dependent Claims (29)
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30. A system, comprising:
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a) a vehicle; b) a power source—
power receiver pair comprisingi) an electrical power source in the vehicle, and ii) a mechanical device to be powered, the power source-power receiver having the characteristic that, when a 3-phase electric motor and Field Oriented Control implemented in a DSP are used to convert power from the source to the receiver, a computer program having N lines of code is required, and c) means for converting power from the source to the receiver which requires 0.75 N, or fewer, lines of code. - View Dependent Claims (31)
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33. A system (1) being powered by a battery which delivers a voltage V, and (2) for operation in a vehicle, comprising:
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a) a two-phase electric motor having i) a stator of the synchronous type and ii) two stator phases; b) a field-oriented controller for controlling voltages applied to the phases, wherein i) full battery voltage is available for application across each phase; ii) all phase voltages are independently controllable; iii) wherein A) two duty cycles needed for synthesis of two sinusoids, one for each coil, are computed based on rotor angle and voltage magnitude; and B) one duty cycle is computed as product of voltage magnitude and sine(rotor angle plus phase term) and the other duty cycle is computed as product of voltage magnitude and cosine(rotor angle plus the phase term).
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34. A method for operation in a vehicle being powered by a battery which delivers a voltage V, comprising:
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a) maintaining a two-phase electric motor having i) a stator of the synchronous type and ii) two stator phases; b) maintaining a field-oriented controller for controlling voltages applied to the phases, which i) applies full battery voltage across each phase; and ii) provides independently controllable voltages to all phases wherein (A) two duty cycles needed for synthesis of two sinusoids, one for each coil, are computed based on voltage magnitude and rotor angle and (B) one duty cycle is computed as product of voltage magnitude and sine(rotor angle plus phase term) and the other duty cycle is computed as product of voltage magnitude and cosine(rotor angle plus the phase term).
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Specification