An Integrated Approach to Digital Control of AC Motor Drives

The paper describes a high-performance microcomputer-based controller for inverter-fed ac motor drives. Both the implementation of high-level drive control policies and on-line computation of three-phase switching patterns for control of the inverter output frequency and voltage, are carried out by a single μP. The selection of a pulsewidth modulation (PWM) strategy with limited processing requirements, has made the integration of these features possible without devising a multiprocessor architecture, or relying upon dedicated hardware to support specific functions. Peculiar facilities, like on-line reconfigurability of control parameters, real-time tracing of system behavior and diagnostics, have also been implemented to enhance the overall controller performance and flexibility. The validity of the integrated solution has been thoroughly verified by extensive experimental tests carried out with a prototype system composed of an 8085-based microcomputer, a 30-kVA three-phase transistor inverter, and a 20-kW induction motor.