Active Control of Transformer Noise by MIMO Algorithm

The Transformer Noise is called hum mainly constructed by harmonic waves of 100 Hz, 200 Hz, 300 Hz, ... , 1,400 Hz, 1,500 Hz. If each harmonic wave of a fixed frequency is stable to some extent measured at the position of error microphone, by producing the some amplitude wave with negative phase through the secondary source (the active control speaker), the noise at the position of error microphone will be greatly reduced. To reduce more than one position's noise, many active control speakers will be used, so the MIMO (Multi input Multi output) Frequency Response Function (FRF) matrix and MIMO algorithm are needed. In the paper, the relationship between preciseness of FRF and the stability of control system is discussed. The method to obtain the precise FRF matrix and the MIMO algorithm of ANC (Active Noise Control) are introduced. The algorithm is verified by field experiment with 2 speakers and 2 error microphones, the total noise in each microphone is reduced 6-10 dB at different time, the harmonic wave amplitude of fixed frequency can reduce 10-30 dB. The effect is prominent comparing to the results of other papers in active control of transformer noise.