CONTROL DEVICE FOR ELECTRIC MOTOR AND CONTROL METHOD FOR ELECTRIC MOTOR

• US 20140042938A1
• Filed: 04/16/2012
• Published: 02/13/2014
• Est. Priority Date: 04/21/2011
• Status: Active Grant

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Nakamura, Hideo, Shoji, Mitsuhiro
• Granted Patent: US 9,203,335 B2
• Time in Patent Office: Days
• US Class Current: 318/400.02
• CPC Class Codes: H02P 21/0085 specially adapted for high speeds, e.g. above nominal speed
• CPC Class Codes: H02P 21/0089 using field weakening
• CPC Class Codes: H02P 21/05 specially adapted for damping motor oscillations, e.g. for reducing hunting
• CPC Class Codes: H02P 21/06 Rotor flux based control involving the use of rotor position or rotor speed sensors
• CPC Class Codes: H02P 21/14 Estimation or adaptation of machine parameters, e.g. flux, current or voltage
• CPC Class Codes: H02P 21/16 Estimation of constants, e.g. the rotor time constant
• CPC Class Codes: H02P 21/22 Current control, e.g. using a current control loop

Abstract

A control device 1 for an electric motor of the present invention includes: a current control unit 4 configured to calculate voltage command values v_d*, v_q* used to drive an electric motor 100, on the basis of a state quantity for voltage command value calculation and q and d-axis current detection values i_d, i_q, the state quantity calculated from a torque command value T*; and an over-modulation processing unit 16 configured to determine whether the electric motor 100 is stable or unstable in an over-modulation state, on the basis of the voltage command values v_d*, v_q*, current control constants, and electric motor constants, and to drive the electric motor 100 in the over-modulation state when determining that the electric motor 100 is stable.

Claims

1-21. -21. (canceled)

22. A control device for an electric motor configured to control an electric motor by vector control, comprising:

a current control unit configured to calculate a voltage command value used to drive the electric motor, on the basis of a state quantity for voltage command value calculation and a current detection value detected from the electric motor, the state quantity calculated from a torque command value used to drive the electric motor; and

an over-modulation processing unit configured to determine whether the electric motor is stable or unstable in an over-modulation state, on the basis of a phase of the voltage command value and a state quantity for control which is used to control the electric motor, and to drive the electric motor on the basis of a result of the determination, wherein

the over-modulation processing unit indentifies a stable phase region of the voltage command value in which the electric motor is stable in the over-modulation state, on the basis of quadrants on a coordinate system defined in a magnetic pole direction and a direction orthogonal to the magnetic pole direction, and determines whether the electric motor is stable or unstable in the over-modulation state, on the basis of whether the phase of the voltage command value is in the stable phase region or not.

23. The control device for an electric motor according to claim 22, wherein the over-modulation processing unit drives the electric motor in the over-modulation state when determining that the electric motor is stable in the over-modulation state.

24. The control device for an electric motor according to claim 22, wherein

the state quantity for control is an inductance value of the current control unit and an inductance value of the electric motor, and

the over-modulation processing unit includes:

an over-modulation characteristic determination unit configured to determine a characteristic related to stability of the electric motor in the over-modulation state, on the basis of the inductance value of the current control unit and the inductance value of the electric motor; and

a phase region determination unit configured to identify a stable phase region of the voltage command value in which the electric motor is stable in the over-modulation state, according to the characteristic, on a coordinate system defined in a magnetic pole direction and a direction orthogonal to the magnetic pole direction, and to determine whether the electric motor is stable or unstable in the over-modulation state, on the basis of whether the phase of the voltage command value is in the stable phase region or not.

25. The control device for an electric motor according to claim 24, wherein the over-modulation processing unit further includes a voltage phase limiting unit configured to change a current command value in such a way that the phase of the voltage command value is in the stable phase region, the current command value being the state quantity for voltage command value calculation.

26. The control device for an electric motor according to claim 22, wherein the over-modulation processing unit determines whether the electric motor is stable or unstable in the over-modulation state, by using such a characteristic that a state of the electric motor changes to a stable or unstable state every time the phase of the voltage command value moves to a different quadrant on a coordinate system defined in a magnetic pole direction and a direction orthogonal to the magnetic pole direction.

27. The control device for an electric motor according to claim 26, wherein

the state quantity for control is an inductance value of the current control unit and an inductance value of the electric motor, and

the inductance value of the current control unit and the inductance value of the electric motor are preset in such a way that a type of the characteristic related to stability of the electric motor in the over-modulation state is constant.

28. The control device for an electric motor according to claim 27, wherein

a current command value which is the state quantity for voltage command value calculation is calculated based on a preset current-voltage conversion map, and

the current-voltage conversion map is preset to enable calculation of such a current command value that the phase of the voltage command value does not move to a different quadrant.

29. The control device for an electric motor according to claim 25, wherein the current command value is a current in the magnetic pole direction.

30. The control device for an electric motor according to claim 22, wherein

the over-modulation processing unit further includes an over-modulation suppressing unit configured to suppress a modulation ratio when the electric motor is determined to be unstable in the over-modulation state, and

the over-modulation suppressing unit does not suppress the modulation ratio when the modulation ratio of the electric motor is within a preset threshold.

31. The control device for an electric motor according to claim 22, wherein the over-modulation processing unit stores an inductance value of the current control unit for each of a plurality of the characteristics related to stability of the electric motor in the over-modulation state, and selects one of the inductance values of the current control unit according to the phase of the voltage command value.

32. The control device for an electric motor according to claim 22, wherein

the electric motor is connected to a transmission, and

when the electric motor is unstable in the over-modulation state, the over-modulation processing unit moves the phase of the voltage command value to a phase region in which the electric motor is stable in the over-modulation state, by causing the transmission to perform gear-shift.

33. The control device for an electric motor according to claim 22, wherein

the electric motor is connected to a drive force transmission mechanism capable of switching a transmission direction of a drive force, and

when the electric motor is unstable in the over-modulation state, the over-modulation processing unit moves the phase of the voltage command value to a phase region in which the electric motor is stable in the over-modulation state, by switching the transmission direction of the drive force.

34. The control device for an electric motor according to claim 22, wherein

the electric motor is a power generator, and

when the power generator is unstable in the over-modulation state, the over-modulation processing unit moves the phase of the voltage command value to a phase region in which the electric motor is stable in the over-modulation state, by moving an operation point along an even output line of a relationship between a power generation amount and the number of revolutions of the power generator.

35. The control device for an electric motor according to claim 22, wherein

the state quantity for control is current control constants used by the current control unit to control the electric motor, and

the over-modulation processing unit stores the current control constants, selects the current control constant at which the electric motor is stable in the over-modulation state, on the basis of the phase of the voltage command value, and outputs the selected current control constant to the current control unit.

36. The control device for an electric motor according to claim 35, wherein the over-modulation processing unit stores the current control constant for each of a plurality of characteristics related to stability of the electric motor in the over-modulation state, determines that the electric motor is in the over-modulation state when a modulation ratio of the electric motor is equal to or larger than a predetermined value, and selects the current control constant of the characteristic at which the electric motor is stable, on the basis of the phase of the voltage command value.

37. The control device for an electric motor according to claim 36, wherein the over-modulation processing unit stores the current control constant corresponding to a position which is a boundary between the plurality of characteristics, and selects the current control constant corresponding to the position which is the boundary when the modulation ratio of the electric motor is smaller than the predetermined value.

38. The control device for an electric motor according to claim 35, wherein the over-modulation processing unit continuously changes the current control constants, according to the phase of the voltage command value.

39. The control device for an electric motor according to claim 35, wherein the over-modulation processing unit reduces the modulation ratio of the electric motor at a position where the phase of the voltage command value is near a boundary of quadrants.

40. The control device for an electric motor according to claim 35, wherein the current control constants are the inductance values of the current control unit.

41. A control method for an electric motor in which an electric motor is controlled by vector control, comprising:

calculating a voltage command value used to drive the electric motor, on the basis of a state quantity for voltage command value calculation and a current detection value detected from the electric motor, the state quantity calculated from a torque command value used to drive the electric motor; and

determining whether the electric motor is stable or unstable in an over-modulation state, on the basis of a phase of the voltage command value and a state quantity for control which is used to control the electric motor, and driving the electric motor on the basis of a result of the determination, wherein

the determining whether the electric motor is stable or unstable in the over-modulation state, on the basis of the phase of the voltage command value and the state quantity for control which is used to control the electric motor includes;

identifying a stable phase region of the voltage command value in which the electric motor is stable in the over-modulation state, on the basis of quadrants on a coordinate system defined in a magnetic pole direction and a direction orthogonal to the magnetic pole direction; and

determining whether the electric motor is stable or unstable in the over-modulation state, on the basis of whether the phase of the voltage command value is in the stable phase region or not.

42. A control device for an electric motor configured to control an electric motor by vector control, comprising:

current control means for calculating a voltage command value used to drive the electric motor, on the basis of a state quantity for voltage command value calculation and a current detection value detected from the electric motor, the state quantity calculated from a torque command value used to drive the electric motor; and

over-modulation processing means for determining whether the electric motor is stable or unstable in an over-modulation state, on the basis of a phase of the voltage command value and a state quantity for control which is used to control the electric motor, and driving the electric motor on the basis of a result of the determination, wherein

the over-modulation processing means indentifies a stable phase region of the voltage command value in which the electric motor is stable in the over-modulation state, on the basis of quadrants on a coordinate system defined in a magnetic pole direction and a direction orthogonal to the magnetic pole direction, and determines whether the electric motor is stable or unstable in the over-modulation state, on the basis of whether the phase of the voltage command value is in the stable phase region or not.