FPGA-based design and implementation of direct torque control for induction machines

We present a field programmable gate array (FPGA) based implementation for direct torque control (DTC) of induction motor drives. The proposed design utilizes several improvements to execute the functional blocks in DTC that reduce the execution time and improve the sampling frequency. The FPGA system is implemented on a Xilinx Virtex-5 board using VHDL code assembled from scratch and the DSP based solution is implemented using dSPACE DS 1104. Both systems are validated experimentally with hardware-in-the-loop, on a small 200 W, 3 phase induction machine. Experimental results indicate that the proposed design enables a far higher sampling frequency (up to 800 kHz), compared to typical digital signal processors (DSP) based solutions which are limited to 20kHz. The higher sampling frequency helps mitigate torque ripple which is a well known limitation of DTC. Additionally, the short execution times suggest the possibility of extending the use of such FPGA implementations to serve auxiliary motor diagnostic functions.