Method and device for optimal torque control of a permanent magnet synchronous motor over an extended speed range

A method and device for controlling the torque of a permanent magnet (PM), synchronous, alternating-current (AC) motor, wherein the motor is powered by an inverter connected to a direct-current (DC) power source, is proposed. The method includes the steps of communicating a torque command signal from a user to a microcontroller, sensing the alternating-current phase currents of the motor and communicating electrical signals representing data concerning the phase currents to the microcontroller, sensing the position of the rotor of the motor and communicating electrical signals representing data concerning the position of the rotor to the microcontroller, and utilizing the microcontroller to implement a modulation technique to generate electrical switching signals for creating electrical sinusoidal waveforms. In addition, the method also includes the step of utilizing the microcontroller to implement a vector control technique to generate electrical control signals for adjusting the frequency and magnitude of the sinusoidal waveforms according to the phase current data, the rotor position data, the voltage supplied by the power source, and the torque command signal. In this particular step, generating the control signals includes the step of referring to look-up tables in an electronic memory only when operating the motor in a constant torque mode. Lastly, the method also includes the step of utilizing the microcontroller to communicate the switching signals for creating sinusoidal waveforms to the inverter. In this way, the inverter is able to generate and transmit sinusoidal waveforms, as dictated by the switching signals, to the motor for optimal torque control.