Method for operating a variable speed drive for driving an electric motor and variable speed drive for executing the method

Abstract

A method for operating a variable speed drive for driving an electric motor, in particular a synchronous motor, includes calculating a look-up table for a given motor, said look-up table having torque input values and flux input values referenced to current magnitude values and current angle values at the max torque per amp (MTPA) points and at increasing angular deviations from the MTPA points, wherein the current magnitude values and current angle values are out-put signals for controlling the motor; and outputting current magnitude values and current angle values as a function of torque input values and/or flux input values at the max torque per amp (MTPA) point to the motor as control variables, if the associated flux values are smaller than or equal to a flux limit; or outputting current magnitude values and current angle values as control variables, such that the associated flux values do not exceed a flux limit. The disclosure further discloses a variable speed drive for executing the method.