DC-Link-Fluctuation-Resistant Predictive Torque Control for Railway Traction Permanent Magnet Synchronous Motor in the Six-Step Operation

In railway traction applications, the six-step operation of traction inverters is frequently applied at high speed due to the limitation of switching frequency of the converter which is installed in very limited space on the train. Meanwhile, without hardware filters installed, fluctuation components of dc-link voltage will emerge due to the input power ripple introduced by the single-phase rectifier, and can cause significant current and torque ripple in the motor. In this article, a direct torque control scheme for permanent magnet synchronous motor in a six-step operation is proposed to suppress the dc-link voltage fluctuation-induced current and torque ripple without extra hardware. It adjusts the duration of voltage space vectors according to the predicted dc-link voltage waveform six times per fundamental cycle, and minimizes the error between output torque and reference torque at the end of each time. Experimental results on an interior permanent magnet synchronous motor demonstrate that the proposed control can more effectively suppress current and torque ripple than state-of-the-art controls and achieve torque control with high dynamics and accuracy.