Control apparatus for an inverter with self-adjustment function of control constants

A control apparatus for an inverter, which feeds an induction motor with output AC voltage of variable voltage magnitude and variable frequencies, which output voltage is obtained by converting AC voltage supplied by an AC voltage source on the basis of a vector control, comprising:

• current detecting means for detecting a primary current flowing through the induction motor;
• inverter gate control means responsive to an output voltage reference signal for producing gate signals for operating the inverter to control the output AC voltage thereof;
• for
• first coordinate transformation means producing the output voltage reference signal by converting an excitation voltage component reference and a torque voltage component reference by means of a coordinate transformation, in which there are used phase references depending on a frequency reference of said output AC voltage of the inverter;
• second coordinate transformation means for producing an excitation current component and a torque current component by converting a primary current detected by said current detecting means by means of a coordinate transformation, in which said phase references are used;
• instruction computing means for producing the references for the excitation voltage component and the torque voltage component and the phase references on the basis of at least one of the excitation current component and the torque current component of the detected primary current and instructions for the excitation current component and a speed of the induction motor, by using motor constants of the induction motor provided in advance therein;
• and
• constant determining means for calculating the motor constants on the basis of the primary current detected under the condition for a preliminary testing operation of the induction motor that the voltage reference for the excitation component and the torque component, the frequency of the output AC voltage of the inverter add the slip frequency of the induction motor are maintained at desired values necessary for calculating the respective motor constants and readjusting the motor constants provided in said instruction computing means on the basis of the calculation result.