TEMPERATURE COMPENSATOR CIRCUIT FOR AN INDUCTION MOTOR

The purpose of this invention is to provide secondary resistance low temperature compensation in vector speed control at values that are close to the actual secondary time constant even at startup of the motor wherein the secondary time constant operation is not carried out. The invention consists of vector speed control devices 1 to 5 of the induction motor IM, with secondary resistance low temperature compensation of the electric motor being carried out by installing a secondary time constant operator (6) which detects the secondary time constant of an electric motor; a comparator/register (7) which holds and outputs low temperature data .tau..sub.2 from a comparison of register data and the output .tau..sub.2 of the aforementioned operator (6); and a damping unit (8) which, during operation, carries out replacement of sequential data with the output .tau..sub.2 of the operator (6), and, during shutdown, which turns to the output values .tau..sub.2L of the comparator/register unit (7), is caused to hold the damping characteristics, and which outputs this data to a slip angular frequency operator (5) of the vector control circuit, and by output from the damping unit (8) a value that is close to the actual secondary time constant at the time of startup, and thereupon, output the sequential data .tau..sub.2 .