Torque control system for AC motor

A torque control system for controlling the torque of an AC motor, comprising:

• driving means for converting a DC voltage from a DC power supply to generate a drive current to energize the AC motor based on a command amplitude value;
• first calculating means for calculating an input electric power supplied from the DC power supply based on a current and a voltage from the DC power supply;
• detecting means for detecting a rotational speed of the AC motor;
• second calculating means for calculating a target electric power based solely on both the rotational speed detected by said detecting means and a command torque value indicative of a desired torque to be produced by the AC motor, without detecting actual values of output torque of and input current to the AC motor;
• first control means for producing a control signal from the difference between the input electric power and the target electric power;
• and
• second control means for controlling said command amplitude value based on said control signal.