Patent ID: 7323700

Claim:
A method of controlling the waveform of a periodically varying magnetic field, produced by a periodic current in a magnet winding, so as to match an intended field waveform, comprising the steps of: a) sensing at least one period of the magnetic field and generating control input digital data representative of a control input waveform which is a predetermined function of said magnetic field waveform; b) performing a Fourier transform on said control input digital data to generate control input Fourier coefficients corresponding to said control input waveform; c) performing a Fourier transform on target digital data representative of a period of a target waveform which is said predetermined function of said intended field waveform, to generate target Fourier coefficients corresponding to said target waveform; d) comparing said control input Fourier coefficients and said target Fourier coefficients to generate a set of error coefficients; e) maintaining control output Fourier coefficients for use in generating a command current waveform for producing said periodic magnetic winding current; f) modifying said control output Fourier coefficients in accordance with said error coefficients to generate improved control output Fourier coefficients; g) performing an inverse Fourier transform on said improved control output coefficients to generate control output digital data representative of a control output waveform; h) periodically generating said command current waveform from said control output digital data, said control output waveform being an inverse of said predetermined function of said command current waveform; and i) amplifying said periodic command current waveform to produce said periodic magnetic winding current.