Device for controlling an AC motor

A control device for an AC motor, comprising:

• inverter means provided with switching elements for converting DC voltage from a DC power source to AC voltage and for supplying the converted AC voltage to said AC motor;
• current detection means for detecting a current supplied from the inverter means to the AC motor and for generating a signal representative of the detected current that is determined from both of a detected current Ia occurring at a first time at least before a changeover of phase of an output of the inverter means and a detected current Ib occurring at a second time at least after the changeover of phase of the output of the inverter means;
• power calculation means for calculating a power passed to said AC motor from a command value and the detection signal of the current detection means;
• and
• control means for generating control signals and supplying the signals to the power calculation means and for supplying drive signals based on the signals from the power calculation means to the inverter means.

A control device for an AC motor, comprising:

• a source of DC power;
• inverter means for converting said DC power into AC power and for supplying a converted AC voltage to the AC motor;
• current detection means for detecting a current flowing from said DC power source to said inverter means and for generating a signal representative of the detected current flow that is determined from both of a detected current Ia occurring at a first time at least before a changeover of phase of an output of the inverter means and a detected current Ib occurring at a second time at least after the changeover of phase of the output of the inverter means;
• power factor calculation means connected to the current detection means for calculating the power factor of the AC motor from the detected current and for outputting a corresponding power factor signal;
• adder means for receiving the power factor signal and for adding to it a predetermined signal;
• proportional integrating means for proportionally integrating the output of the adder means;
• voltage frequency calculation means for receiving a predetermined reference signal and for generating a reference voltage signal;
• and
• control means for receiving the output of the proportional integrating means, the reference voltage signal, and the predetermined reference signal and for outputting a control signal to control the inverter means.