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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
First Claim
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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.

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