Zero-Pole Cancellation Based Iterative Learning Control Method for Speed Ripple Suppression of Single Rolling Rotor Compressor

Owing to the severe load torque fluctuation, the speed ripple is a significant concern for the compressor drive system, especially within low frequency range. To address this issue, a zero-pole cancellation (ZPC) based iterative learning control (ILC) method is proposed for speed ripple suppression in this paper. The load torque characteristic is obtained based on the estimated speed harmonics. The essence of the speed ripple is investigated utilizing the compressor mechanical model, which attributes to the conjugate poles effect of the load torque term at the specific mechanical frequency. The zero point of the conventional ILC method is fixed at s=0, which can hardly reduce the dominant poles effect of the torque term. Afterwards, the poles’ matching function is analytically derived to cancel out the dominant poles of the torque term, and then the specific order harmonic can be effectively suppressed. Considering the non-periodic disturbance caused by the operating frequency and temperature variation, the error correction law is designed to avoid the error accumulation and ensure the performance of proposed ILC method. Finally, the effectiveness of the method is validated by experiments through a 750W compressor drive system. Experimental results indicate that the total speed ripples reduce by nearly 60% and each harmonic component of the speed ripple can be effectively suppressed according to the FFT results.