Tacho-less vector control adaptive system for motor drive

Claim 1

Apparatus for the determination of the rotor speed r of an induction motor having a squirrel cage rotor of stator resistance R r , of stator reactance L r , of rotor resistance R r , of rotor reactance L r , of mutual inductance M, a rotor flux represented by orthogonal components λ dr and λ qr in a stationary reference frame, the motor being supplied under three terminal voltages (v a , v b , v c ) and three line currents (i a , i b , i c ) derived from three AC phase lines without neutral connection, comprising: means responsive to the terminal voltages and line currents for deriving signals representative of the direct and quadrature components (v ds , v qs ) of the stator voltage vector and signals representative of the direct and quadrature components (i ds , i qs ) of the current vector in accordance with the matrices: ##EQU7## with i a +i b +i c =0; v a +v b +v c =0; and v ab and v bc being line to line voltages; reference model means responsive to said voltage vector and current vector direct and quadrature components representative signals in relation to the first rows of the following model matrix expressed in a stationary reference frame: ##EQU8## where: R r is the resistance of the rotor; R s is the resistance of the stator; L r is the inductance of the rotor; L s is the inductance of the stator; λ dr =(Mi ds +L r i dr ); λ qr =(Mi qs +L r i qr ); σ=(1-M 2 /L s L r ) namely the motor leakage coefficient; whereby said reference model means is generating first and second signals representative of the direct and quadrature components of the rotor flux vector, λ dr and λ qr respectively; adjustable model means responsive on the one hand to said current vector direct and quadrature components signals, and on the other hand to an estimated signal ω r characteristic of rotor speed, and operative in relation to the two last rows of said model matrix, for generating respective third and fourth signals representative of the direct and quadrature components of a speed related rotor flux vector, λ dr and λ qr ; means responsive to a deviation between the pair of said first and second signals, on the one hand, and the pair of said third and fourth signals on the other hand, for generating said estimated signal ω r ; whereby said deviation, through said estimated signal, causes said speed related flux representative vector to be aligned with said flux representative vector and said estimated signal ω r to be equal to said rotor speed ω r .