Increased bandwidth for plants with resonant modes using nonlinear notch filters

• US 5,929,700 A
• Filed: 06/26/1996
• Issued: 07/27/1999
• Est. Priority Date: 06/26/1996
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Rtx Corporation)
• Original Assignee: United Technologies Corporation (Rtx Corporation)
• Inventors: Fuller, James W., Nett, Carl N.
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): Luu, An T.
• Application Number:
  US08/669,729
• Time in Patent Office: 1,126 Days
• Field of Search: 327/551, 327/556
• US Class Current: 327/556
• CPC Class Codes: G05B 5/01 electric

Abstract

A control system includes a plant 56 having resonant modes and a controller 5 which receives plant input signals on lines 14,24 from the plant 56 and provides a controller output signal I, related to a filter output signal V, which controls the plant 6. The controller is provided with a non-linear notch filter 30 which receives a filter input signal x related to the plant input signals and provides the filter output signal V. The notch filter has at least one notch frequency near one of the resonant modes so as to attenuate one of the modes by a predetermined amount and has a phase lag a decade below the lowest notch frequency of said notch filter which is less than that of a corresponding linear notch filter, thereby allowing the control system 7 to exhibit faster time response and increased bandwidth than a system employing linear notch filters.

Claims

1. A control system comprising:

a plant having resonant modes; and

a controller which receives a plant output signal and a command signal and provides a controller output signal which controls said plant, said controller comprising;

a non-linear notch filter which provides a filter output signal and receives a filter input signal, said filter input signal being a function of said plant output signal and said command signal, said non-linear notch filter comprising;

linear notch filter logic responsive to said filter input signal and having a linear notch transfer function, which provides a linear notch filtered signal;

zero-cross logic responsive to said filter input signal and said linear notch filtered signal, which monitors said filter input signal and which provides a square wave signal which crosses zero at the same time and in the same direction as said filter input signal and has an amplitude proportional to the value of said linear notch filtered signal when said filter input signal crosses zero;

complementary notch filter logic responsive to said square wave signal and having a complementary transfer function which is complementary to said linear notch transfer function, which provides a complementary notch filtered signal; and

said complementary notch filtered signal and said linear notch filtered signal being added together to provide said filter output signal which exhibits less phase shift between said filter input signal and said filter output signal over certain frequency bands than that of said linear notch transfer function.

2. The control system of claim 1 wherein said complementary notch transfer function comprises a reduced-order transfer function which has a numerator polynomial of a lower order than said denominator polynomial.

3. The control system of claim 1 wherein said zero-cross logic comprises logic which sets said square wave signal amplitude proportional to the absolute value of said linear notch filtered signal when said filter input signal crosses zero from negative to positive and sets said square wave signal amplitude proportional to the negative of the absolute value of said linear notch filtered signal when said filter input signal crosses zero from positive to negative.

4. The control system of claim 1 wherein said amplitude of said square wave signal is equal to the value of said linear filtered signal when said filter input signal crosses zero.

5. The control system of claim 1 wherein said plant comprises an actuator.

6. The control system of claim 1 wherein said actuator comprises a bleed valve actuator.

7. The control system of claim 1 wherein said plant comprises a torque motor, a drive shaft connected to said torque motor, and an actuator connected to said drive shaft.

8. The control system of claim 1 wherein said controller comprises control logic which receives said plant output signal and provides said filter input signal.

9. The control system of claim 1 wherein said controller comprises control logic which receives a command input signal from an electronic engine controller and said plant comprises an actuator disposed on a gas turbine engine.

10. The control system of claim 1 wherein said phase lag of said non-linear notch filter allows for increased responsiveness of the control system.

11. A control system comprising:

plant means having resonant modes; and

controller means for receiving a plant output signal and a command signal and for providing a controller output signal which controls said plant, said controller means including non-linear notch filter means for providing a filter output signal and for receiving a filter input signal, said filter input signal being a function of said plant output signal and said command signal, said non-linear notch filter means comprising;

linear filter means responsive to a filter input signal and having a linear transfer function, for providing a linear filtered signal;

zero-cross means responsive to said filter input signal and said linear filtered signal, for monitoring said filter input signal, and for providing a square wave signal which crosses zero at the same time and in the same direction as said filter input signal and has an amplitude proportional to the value of said linear filtered signal when said filter input signal crosses zero;

complementary filter means responsive to said square wave signal and having a complementary transfer function which is complementary to said linear transfer function, for providing a complementary filtered signal; and

summing means responsive to said complementary filtered signal and said linear filtered signal for adding together said complementary filtered signal and said linear filtered signal and for providing a filter output signal which exhibits less phase shift between said filter input signal and said filter output signal over certain frequency bands than that of said linear transfer function.

12. The filter of claim 11 wherein said complementary transfer function comprises a reduced-order transfer function which has a numerator polynomial of a lower order than said denominator polynomial.

13. The filter of claim 11 wherein said zero-cross means comprises means for setting said square wave signal amplitude proportional to the absolute value of said linear filtered signal when said filter input signal crosses zero from negative to positive, and for setting said square wave signal amplitude proportional to the negative of the absolute value of said linear filtered signal when said filter input signal crosses zero from positive to negative.

14. The control system of claim 11 wherein said amplitude of said square wave signal is equal to the value of said linear filtered signal when said filter input signal crosses zero.

15. The control system of claim 11 wherein said plant means comprises an actuator.

16. The control system of claim 14 wherein said actuator comprises a bleed valve actuator.

17. The control system of claim 11 wherein said plant means comprises a torque motor, a drive shaft connected to said torque motor, and an actuator connected to said drive shaft.

18. The control system of claim 11 wherein said controller means comprises control logic which receives said plant output signal and provides said filter output signal.

19. The control system of claim 11 wherein said controller means comprises control logic which receives a command output signal from an electronic engine controller and said plant comprises an actuator disposed on a gas turbine engine.

20. The control system of claim 11 wherein said phase lag of said non-linear notch filter means allows for increased responsiveness of the control system.