Single sensor current control of AC servodrives using digital signal processors

Successful operation of AC servodrives requires precise control of the motor line currents. The emergence of fast digital signal processors (DSP) permits real-time digital current control. However, expensive current transducers are required to sense the instantaneous currents in at least two, and often the three, stator phases. A predictive current controller for the permanent magnet synchronous motor (PMSM) is presented which uses a space vector modulation (SVM) strategy to determine the switching instants of the voltage source inverter (VSI). Compensation of the inverter switching dead times is also incorporated. An innovative current feedback scheme using a single current sensor placed in the inverter DC link is proposed. This feedback mechanism employs a state observer to ensure reliable feedback signals under all operating conditions. The paper presents detailed algorithm development, describes the prototype DSP-based hardware system and includes experimental verification of the proposed control structure.