JPS57149931A - Measurement system for power of induction motor - Google Patents

Abstract

PURPOSE:To measure a load accurately under secure control by varying an energizing current according to the load, and making corrections so that a speed deviation is utilized as a torque command. CONSTITUTION:The rotational speed of an induction motor 101 is detected by a resolver 102 to generate pi/2 out-of-phase signals PA and PB, which are converted into pulse strings Pn and Pr at a part 103, and an actual speed voltage TSA processed by F/V conversion 104 is supplied to an arithmetic circuit 108 to calculate a difference voltage epsilonr from a command speed. It is supplied to a cubic root function generating circuit 111 through a proportional integrating circuit 109 and an absolute value circuit 110. The arithmetic result ER of a cubic root is processed by V/F conversion 112, and a current amplitude command I1' is generated by a CPU113, processed by D/A conversion, and multiplied by the ER at a part 115; and its output primary current amplitude I1 is multiplied by a sine wave signal from the CPU113 at parts 116 and 117 to be converted into an U-phase and a V-phase current command, or processed by addition arithmetic 118 to obtain a W-phase current command. Then, respective difference from an actual phase current are processed by PW modulation 123 and supplied to respective phases of the motor 101.