Variable speed drive with a synchronous electric motor

• US 6,975,082 B2
• Filed: 03/03/2004
• Issued: 12/13/2005
• Est. Priority Date: 03/03/2003
• Status: Expired due to Fees

• Current Assignee: Nugen Mobility
• Original Assignee: New Generation Motors Corporation (NuGen Holdings, Inc.)
• Inventors: Crain, Stephen G., Jermakian, Joel B.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US10/792,680
• Publication Number:
  US 20050012486A1
• Time in Patent Office: 650 Days
• Field of Search: 318/138, 318/139, 318/254, 318/268, 318430-434, 318720-724
• US Class Current: 318/400.09
• CPC Class Codes: B60K 1/00 Arrangement or mounting of electrical propulsion units B60K7/00 takes precedence; arrangement or mounting of plural diverse prime-movers for mutual or common propulsion B60K6/00; electric transmission arrangements B60K17/12; electric equipment or propulsion of electrically-propelled vehicles per se B60L; current-collectors for power supply lines of electrically-propelled vehicles B60L5/00
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 25/0925 wherein the converter comprises only one switch per phase
• CPC Class Codes: H02P 25/098 Arrangements for reducing torque ripple
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position
• CPC Class Codes: H02P 6/181 using different methods depending on the speed
• CPC Class Codes: H02P 6/34 Modelling or simulation for control purposes

Abstract

This invention relates to a variable speed drive with synchronous AC motor. In the disclosed embodiment, a variable speed drive operates in three modes: a first predetermined mode, in which a function (e.g., trapezoidal current waveform) controls operation at low motor speeds; a transitional mode, in which a transition function is applied to anticipate transitions of the first function, thus causing a smoothing of transitions at higher speeds; and a second predetermined (e.g., sinusoidal or smoothly-varying current) waveform at high speeds. This allows for the reduction in required rotor position sensor resolution as compared to conventional synchronous variable speed drives, resulting in cost savings in the sensor device and associated wiring. Additionally, it is quieter and more efficient operation at high speed as compared to conventional trapezoidal-current/DC-brushless motor drives.

Claims

1. A variable speed drive system, comprising:

a synchronous electric motor, operably coupled to an output shaft, and operable for applying a varying force to the output shaft in response to a varying input AC electric signal;

a control unit, operably coupled to a battery, plural rotor sensors, and a drive unit, and operable, in response to signaling indicative of the position of one or more sensors, to generate the input signal according to a first mode for low speed operation, a second mode for high speed operation, and a transitional mode between first and second thresholds, wherein the control unit comprises a polyphase inverter coupled to the drive unit, a controller coupled to the inverter, and a position estimator coupled to the controller and operably coupled to the sensors, wherein the position estimator comprises a phase locked loop operable to control the drive unit in the second mode according to a continuous waveform function, and an angular position interpolator operable to control the drive unit in the first mode according to a step waveform function.

2. The drive of claim 1, wherein the position estimator is operable to initialize the first mode based on a midpoint of an angular range between detected immediately prior and next sensor positions, and after initialization the controller is operable to change settings of inverter switches based on an input control angle, the control angle derived from detected sensor position information;

wherein the position estimator and controller together comprise a processor configured to execute a polyphase AC control program; and

wherein the processor, when executing said program, is operably configured to perform an operation having plural instructions comprising first instructions for controlling the drive unit in the first mode according to a step waveform function, second instructions for controlling the drive unit in the second mode according to a continuous waveform function, and third instructions for controlling the drive unit in the transition mode according to a transition waveform function.

3. The drive of claim 2, wherein the processor, when executing said program, is operable to execute mode change instructions to apply the first instructions when operating at less than a first angular speed, the second instructions when operating at a second angular speed greater than the first angular speed, and the third instructions when operating at an angular speed between the first and second angular speeds.

4. The drive of claim 1, wherein the control unit is configured for changing the input control angle based on the position output of the phase locked loop, θ

_PLL, such that a control angle θ

_ctrl is held constant until θ

_PLL>

(θ

_max−

Δ

*F(ω

)), where θ

_max is the angular position of a next sensor transition and F is a non-decreasing function equal to zero below the first threshold ω

₁ and 0.5 above the second threshold ω

₂, and Δ

is the width of a current interval between the detected immediately prior and next sensor positions.

5. The drive of claim 4, wherein the control unit is configured such that, when θ

_PLL>

(θ

_max−

Δ

*F(ω

)),θ

_ctrl is raised at a fixed rate ω

_ctrl, which is greater than ω

_PLL, to θ

_max−

6. The drive of claim 5, wherein the control unit is configured such that, when θ

_ctrl is equal to θ

_max, θ

_ctrl is held constant until a next sensor transition is detected.

7. The drive of claim 3, wherein the position estimator is operable to initialize the first mode based on a midpoint of an angular range between detected immediately prior and next sensor positions, and after initialization the controller is operable to change settings of inverter switches based on an input control angle, the control angle derived from detected sensor position information;

wherein the position estimator and controller together comprise a processor configured to execute a polyphase AC control program; and

wherein the processor, when executing said program, is operably configured to perform an operation having plural instructions comprising first instructions for controlling the drive unit in the first mode according to a continuous waveform function, second instructions for controlling the drive unit in the second mode according to the step waveform function, and third instructions for controlling the drive unit in the transition mode according to a transition waveform function.

8. The drive of claim 7, wherein the processor, when executing said program, is operable to execute mode change instructions to apply the first instructions when operating at less than a first angular speed, the second instructions when operating at a second angular speed greater than the first angular speed, and the third instructions when operating at an angular speed between the first and second angular speeds.

9. An electric vehicle, comprising:

a multi-wheel drive system coupled to a drive shaft;

a battery; and

a variable speed drive system, comprising;

a synchronous electric motor, operably coupled to the drive shaft, and operable for applying a varying force to the drive shaft in response to a varying input AC electric signal;

a control unit, operably coupled to a battery, plural rotor sensors, and the motor, and operable, in response to signaling indicative of the position of one or more sensors, to generate the input signal according to a first mode for low speed operation, a second mode for high speed operation, and a transitional mode between first and second thresholds,

wherein the control unit comprises a polyphase inverter coupled to the motor, a controller coupled to the inverter, and a position estimator coupled to the controller and operably coupled to the sensors, and wherein the position estimator is operable to control the motor in the second mode according to a continuous waveform function, and an angular position interpolator operable to control the motor in the first mode according to a step waveform function.

10. The vehicle of claim 9, wherein the position estimator is operable to initialize the first mode based on a midpoint of an angular range between detected immediately prior and next sensor positions, and after initialization the controller is operable to change settings of inverter switches based on an input control angle, the control angle derived from detected sensor position information.

11. The vehicle of claim 10:

wherein the position estimator and controller together comprise a processor configured to execute a polyphase AC control program;

wherein the processor, when executing said program, is operably configured to perform an operation having plural instructions comprising first instructions for controlling the motor in the first mode according to a continuous waveform function, second instructions for controlling the motor in the second mode according to the step waveform function, and third instructions for controlling the motor in the transition mode according to a transition waveform function;

wherein the processor, when executing said program, is operable to execute mode change instructions to apply the first instructions when operating at less than the first threshold, the second instructions when operating at a second angular speed greater than the second threshold, and the third instructions when operating at an angular speed between the first and second thresholds.

12. The vehicle of claim 10, wherein the control unit is configured so the input control angle is changed based on the position output, θ

_PLL, of the position estimator, which position estimator comprises a phase locked loop, such that a control angle θ

_ctrl is held constant until θ

_PLL>

(θ

_max−

Δ

*F(ω

)), where θ

_max is the angular position of a next sensor transition and F is a non-decreasing function equal to zero below the first threshold ω

₁ and 0.5 above the second threshold ω

₂, and Δ

is the width of a current interval between the detected immediately prior and next sensor positions.

13. The vehicle of claim 12, wherein the control unit is configured such that:

wherein when θ

_PLL>

(θ

_max−

Δ

*F(ω

)),θ

_ctrl is raised at a fixed rate ω

_ctrl, which is greater than ω

_PLL, to θ

_max; and

wherein when θ

_ctrl is equal to θ

_max, θ

_ctrl is held constant until a next sensor transition is detected.

14. The vehicle of claim 10, wherein the sensors comprise one of the group consisting of Hall effect sensors and optical encoders.

15. A method of operating an electric vehicle, comprising:

providing a varying force to a drive shaft of a multi-wheel drive system by a synchronous electric motor, operably coupled to the drive shaft, the varying force being applied in response to a varying input AC electric signal generating the input signal by a control unit, operably coupled plural rotor sensors and the motor, in response to signaling indicative of the position of one or more sensors, the input signal being generated according to a first mode for low speed operation, a second mode for high speed operation, and a transitional mode between first and second thresholds, wherein the control unit comprises a polyphase inverter coupled to the motor, a controller coupled to the inverter, and a position estimator coupled to the controller and operably coupled to the sensors, further comprising controlling the motor in the second mode according to a continuous waveform function, and controlling the motor in the first mode according to a step waveform function.

16. The method of claim 15, further comprising initializing the first mode based on a midpoint of an angular range between detected immediately prior and next sensor positions, and after initialization changing settings of inverter switches based on an input control angle, the control angle derived from detected sensor position information.

17. The method of claim 16, wherein the position estimator and controller together comprise a processor configured to execute a polyphase AC control program operably configured to perform an operation having plural instructions, further comprising:

controlling the motor in the first mode according to a continuous waveform function when operating at less than the first threshold;

controlling the motor in the second mode according to the step waveform function when operating at a second angular speed greater than the second threshold; and

controlling the motor in the transition mode according to a transition waveform function when operating at an angular speed between the first and second thresholds.

18. The method of claim 16, wherein the input control angle is changed based on the position output, θ

_PLL, of the position estimator, the position estimator comprising a phase locked loop, such that a control angle θ

_ctrl is held constant until θ

_PLL>

(θ

_max−

Δ

*F(ω

)), where θ

_max is the angular position of a next sensor transition and F is a non-decreasing function equal to zero below the first threshold ω

₁ and 0.5 above the second threshold ω

₂, and Δ

is the width of a current interval between the detected immediately prior and next sensor positions.

19. The method of claim 18:

wherein when θ

_PLL>

(θ

_max−

Δ

*F(ω

)),θ

_ctrl is raised at a fixed rate ω

_ctrl, which is greater than ω

_PLL, to θ

_max; and

wherein when θ

_ctrl is equal to θ

_max, θ

_ctrl is held constant until a next sensor transition is detected.

20. A method of operating a variable speed drive unit, comprising:

providing a varying force to a drive shaft by a synchronous electric motor of the drive unit, operably coupled to the drive shaft, the varying force being applied in response to a varying input AC electric signal;

generating the input signal by a control unit, operably coupled plural rotor sensors and the motor, in response to signaling indicative of the position of one or more sensors, the input signal being generated according to a first mode for low speed operation, a second mode for high speed operation, and a transitional mode between first and second thresholds wherein the control unit comprises a polyphase inverter coupled to the motor, a controller coupled to the inverter, and a position estimator coupled to the controller and operably coupled to the sensors, further comprising controlling the motor in the second mode according to a continuous waveform function, and controlling the motor in the first mode according to a step waveform function, further comprising initializing the first mode based on a midpoint of an angular range between detected immediately prior and next sensor positions, and after initialization changing settings of inverter switches based on an input control angle, the control angle derived from detected sensor position information.

21. The method of claim 20, wherein the position estimator and controller together comprise a processor configured to execute a polyphase AC control program operably configured to perform an operation having plural instructions, further comprising:

controlling the motor in the first mode according to a continuous waveform function when operating at less than the first threshold;

controlling the motor in the second mode according to the step waveform function when operating at a second angular speed greater than the second threshold; and

controlling the motor in the transition mode according to a transition waveform function when operating at an angular speed between the first and second thresholds.

22. The method of claim 21, wherein the input control angle is changed based on the position output of the position estimator, θ

_PLL, the position estimator comprising a phase locked loop, such that a control angle θ

_crtl is held constant until θ

_PLL>

(θ

_max−

Δ

*F(ω

)), where θ

_max is the angular position of a next sensor transition and F is a non-decreasing function equal to zero below the first threshold ω

₁ and 0.5 above the second threshold ω

₂, and Δ

is the width of a current interval between the detected immediately prior and next sensor positions;

wherein when θ

_PLL>

(θ

_max−

Δ

*F(ω

),θ

_ctrl is raised at a fixed rate ω

_ctrl, which is greater than θ

_PLL, to θ

_max; and

wherein when θ

_ctrl is equal to θ

_max, θ

_crtl is held constant until a next sensor transition is detected.