Digital implementation of a direct mean torque control for AC servo drives based on a hybrid DSP/FPGA controller system

This paper presents the digital implementation of a direct mean torque control (DMTC) for AC servo drives. DMTC combines the excellent dynamic performance of the direct torque control (DTC) with the advantages of inherently constant switching frequency and time equidistant control algorithms for suitable digital implementation. The basic idea is to predict the inevitable torque ripple in steady state and match it at the end of the cycle, so that, the mean torque is directly controlled. The criteria on how to preselect the appropriate voltage space phasor depend on the state of the machine and on the deviations of stator flux and electromagnetic torque at the end of the cycle. Experimental results using a hybrid digital system with a digital signal processor (DSP) and a field-programmable-gate-array (FPGA) and an AC servo machine verify the effectiveness of the proposed control scheme.