Performance optimization controller and control method for doubly-fed machines

• US 5,798,631 A
• Filed: 10/02/1996
• Issued: 08/25/1998
• Est. Priority Date: 10/02/1995
• Status: Expired due to Fees

• Current Assignee: Oregon State University (Oregon University System)
• Original Assignee: Oregon State University (Oregon University System)
• Inventors: Bhowmik, Shibashis, Enslin, Johan H. R., Spee, Rene
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/725,187
• Time in Patent Office: 692 Days
• Field of Search: 322/25, 318/767, 290/52
• US Class Current: 322/25
• CPC Class Codes: F03D 7/0272 by measures acting on the electrical generator
• CPC Class Codes: F03D 7/046 with learning or adaptive control, e.g. self-tuning, fuzzy logic or neural network
• CPC Class Codes: F05B 2210/16 Air or water being indistinctly used as working fluid, i.e. the machine can work equally with air or water without any modification
• CPC Class Codes: F05B 2270/20 to optimise the performance of a machine
• CPC Class Codes: H02P 2101/15 for wind-driven turbines
• CPC Class Codes: H02P 2207/073 wherein only one converter is used, the other windings being supplied without converter, e.g. doubly-fed induction machines
• CPC Class Codes: H02P 9/007 Control circuits for doubly fed generators
• CPC Class Codes: H02P 9/42 to obtain desired frequency without varying speed of the generator
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction

Abstract

A variable speed, constant frequency (VSCF) system utilizes a doubly-fed machine (DFM) to maximize the output power of the system. The system includes a power converter that provides a frequency signal and a current signal to the DFM. The power converter is controlled by an adaptive controller. The controller signals the converter to vary its frequency signal and thereby the rotor speed of the DFM until a maximum power output is sensed. The controller also signals the converter to vary its current signal and thereby the portions of power carried by the respective windings until a maximum power output is sensed. The control can be augmented to not only maximize power and efficiency, but also provide for harmonic and reactive power compensation.

Claims

1. Apparatus for maximizing output power generated by a doubly-fed machine generator having a rotor, a stator and multiple windings including at least one control winding, the doubly-fed machine being responsive to changes in amplitude and frequency of a control winding excitation signal from a power converter coupled to said control winding, comprising:

a sensor for sensing the output power of the doubly-fed machine; and

a controller for controlling the power converter and responsive to the sensor, the controller adapted to maximize the output power by;

signaling the converter to adjust the frequency of its output signal so as to adjust the frequency of the control winding signal and thereby the rotor speed to maximize the output power; and

signaling the converter to adjust the amplitude of its output signal so as to adjust the amplitude of the control winding signal to maximize said output power,

whereby the maximum output power of the machine is determined as a function of both the frequency and amplitude of the output signal of the power converter.

2. The apparatus of claim 1 wherein the doubly-fed machine generator is operatively connected to a turbine driven by a variable energy resource.

3. The apparatus of claim 1 including an electrical connection to an electrical grid to supply the output power of the machine to the grid.

4. The apparatus of claim 3 including means for isolating current harmonics from the electrical grid.

5. The apparatus of claim 3 including means for regulating voltage at a point of connection to the grid.

6. The apparatus of claim 3 including means for maximizing the power factor at a grid interface.

7. The apparatus of claim 3 including means for filtering current harmonics at a grid interface.

8. A method for maximizing output power generated by a doubly-fed machine generator having a rotor, a stator and multiple windings including at least one control winding, the doubly-fed machine being responsive to changes in amplitude and frequency of a control winding excitation signal from a power converter coupled to said control winding, comprising:

sensing the output power of the doubly-fed machine; and

controlling the power converter in response to the sensed output power by;

adjusting the converter output signal frequency to adjust the frequency of the control winding signal and thereby the rotor speed to maximize the output power; and

adjusting the converter output signal amplitude to adjust the amplitude of the control winding signal to maximize the output power,

whereby the maximum output power of the machine is determined as a function of both the frequency and the amplitude of the output signal of the power converter.

9. Apparatus for minimizing input power consumed by a doubly-fed machine motor having a rotor, a stator and multiple windings including at least one control winding, the doubly-fed machine being responsive to changes in amplitude and frequency of a control winding excitation signal from a power converter coupled to said control winding, comprising:

a sensor for sensing the input power consumed by the doubly-fed machine; and

a controller for controlling the power converter and responsive to the sensor, the controller adapted to minimize the input power by signaling the converter to adjust the amplitude of its output signal so as to adjust the amplitude of the control winding signal to minimize said input power,

whereby the minimum input power consumed by the machine is determined as a function of the amplitude of the output signal of the power converter at any given frequency.

10. The apparatus of claim 9 including an electrical connection to an electrical grid to supply the power from the grid to the machine.

11. The apparatus of claim 10 including means for isolating current harmonics from the electrical grid.

12. The apparatus of claim 10 including means for regulating voltage at a point of connection to the grid.

13. The apparatus of claim 10 including means for maximizing the power factor at a grid interface.

14. The apparatus of claim 10 including means for filtering current harmonics at a grid interface.

15. A method for minimizing input power consumed by a doubly-fed machine motor having a rotor, a stator and multiple windings including at least one control winding, the doubly-fed machine being responsive to changes in amplitude and frequency of a control winding excitation signal from a power converter coupled to said control winding, comprising:

sensing the input power consumed by the doubly-fed machine; and

controlling the power converter in response to the sensed output power by adjusting the converter output signal so as to adjust the amplitude of the control winding signal to minimize said input power,

whereby the minimum input power consumed by the machine is determined as a function of the amplitude of output signal of the power converter at any given frequency.

16. Apparatus for controlling the output power generated by a doubly-fed machine, comprising:

a sensor for sensing the output power of the doubly-fed machine;

a power converter coupled to a control winding of the doubly-fed machine for controlling a generator through an excitation signal applied to the control winding;

a controller responsive to the sensor for controlling the power converter by;

signaling the converter through a control winding frequency reference signal to adjust the frequency of the control winding signal and thereby to control generator speed; and

signaling the converter through a control winding current amplitude reference signal to adjust the current amplitude of the control winding signal and thereby to control efficiency of the generator.

17. Method for controlling the output power generated by a doubly-fed machine system, the system including a power converter and a generator, the method comprising the following steps:

sensing the output power of the doubly-fed machine;

controlling the power converter in response to the sensed output power;

signaling the converter through a control winding frequency reference signal to adjust the frequency of the control winding signal and thereby to control generator speed; and

signaling the converter through a control winding current amplitude reference signal to adjust the current amplitude of the control winding signal and thereby to control efficiency of the generator.