Vector control system for induction motor

Claim 1

A vector control system for an induction motor which is driven by an inverter controlled by a pulse width modulation circuit, the system carrying out compensation for variation of a secondary resistance, comprising: a first means for calculating target values I₁d* and I₁q* of d- and q-axis components of a primary current of the induction motor on d-q coordinates having a secondary magnetic flux set as a reference axis, said d-q coordinates being rotational coordinates which rotate in synchronism with a power source angular frequency of the induction motor; a first coordinate transformation part arranged to calculate in accordance with said target values I₁d* and I₁q* of said d- and q-axis components a target value I₁γ* (= I₁) of a γ-axis component of the primary current and a phase difference ψ on γ-δ coordinates having said phase difference ψ with respect to d-q axes and having said primary current I₁ set as a reference axis; a slip angular frequency operation part arranged to input and calculate said ratio λ 2d */M* and said target value I₁q* of said q-axis component so as to output a target value ω S * of a slip angular frequency; a second means for calculating target values V₁γ* and V₁δ* of γ- and δ-axis components of a primary voltage in accordance with a ratio λ 2d */M* of a target value λ 2d * of said secondary magnetic flux to a target value M* of an exciting inductance, calculation results of said first coordinate transformation part and a command value ω₀ of said power source angular frequency; a second coordinate transformation part arranged to transform a detection value of said primary current into actual γ- and δ-axis components I₁γ and I₁δ on said γ-δ coordinates; a third means for calculating a variation ΔV₁δ with respect to said V₁δ* of said δ-axis component of said primary voltage in accordance with said target values I₁γ* and I₁δ* of said γ- and δ-axis components of said primary current and said actual γ- and δ-axis components I₁γ and I₁δ derived from said second coordinate transformation part; a polar coordinate transformation part arranged to add said target values V₁γ* and V₁δ* derived from said second means to said variation ΔV₁δ derived from said third means so as to output a magnitude |V₁| of a vector of said primary voltage and a phase angle φ thereof with respect to a γ axis; and a fourth means for minimizing an error with regard to compensation for variation of the secondary resistance.