Design of a wavelet multiresolution controller for speed control of Travelling Wave Ultrasonic Motors

The design of a new multiresolution controller for speed control of a travelling wave ultrasonic motor is presented in this paper. The proposed controller, based on wavelet theory, takes advantage of the advanced filtering capabilities of the wavelet transform. The choice of the appropriate mother waveform for the wavelet analysis is made, considering optimal behavior for digital implementation and minimization of boundary problems. The waveform modulation in the power stage is based in the use of a synchronous unipolar voltage switching technique. The advantage of the unipolar modulation is the doubling of the output frequency, which leads to better harmonic content of the output waveforms. Proper operation of the proposed scheme is verified via simulation, while its advantages comparing with existing methods are discussed.