Increased bandwidth for plants with resonant modes using nonlinear notch filters

Claim 2

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.

Claim 3

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.

Claim 4

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.

Claim 5

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.

Claim 6

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

Claim 7

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

Claim 8

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.

Claim 9

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

Claim 10

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.

Claim 11

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

Claim 12

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.

Claim 13

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.

Claim 14

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.

Claim 15

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.

Claim 16

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.

Claim 17

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

Claim 18

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

Claim 19

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.

Claim 20

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.

Claim 21

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.

Claim 22

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.