Design of a dedicated processor for AC motor control implemented in a low cost FPGA

Motor control for small series sometimes requires specialized control logic, requiring rewiring if new logic needs to be added. This paper describes a different approach to hardware and software co-design, namely designing a softcore processor with an instruction set to fit the purpose of control of drives. Furthermore the softcore processor is designed with a system for plug in of external logic. Doing so shortens development time, since functionality is simply added to or removed from the softcore. The designer can then choose between resource usage on the FPGA and execution speed in more degrees. The approach is tested for two different motor types, synchronous and hybrid switched reluctance motors, using a Spartan 3E FPGA. The impact of having ADC-communication in VHDL versus in assembler is also presented.