Controller design for active noise control of compressor by using the time window POCS technique

To design an active noise controller, the transfer function between the reference signal and the error signal should be measured and defined. When the noise source operates at specific frequencies, the transfer function can only be measured at the operating frequency and its harmonics. This transfer function has reliable values only at the operating frequency and its harmonic frequencies. The frequency domain controller is implemented as an FIR filter, and the coefficients are calculated using the inverse Fourier transform. At this time, the second half part of the coefficient values of the FIR filter is high due to the insufficient frequency resolution and the unreliable transfer function. As a result, the magnitude and phase response of the filter do not follow the design values. To overcome this problem in filter design, the time window projection onto convex sets (POCS) technique is proposed. POCS technique is utilized repeatedly to make the response of the filter to converge by setting the second half part of the filter to 0, and to reassign the response in the control frequency band. The response of the converged filter was verified by comparing it with that of a time-shifting filter and Wiener filter. As a result, the FIR filter designed using POCS showed high performance, regardless of the magnitude of the disturbance and the reference signal.