Computer-optimised smooth-torque current waveforms for switched-reluctance motors

The paper discusses the design of current waveforms for switched-reluctance motors, which give rise to a constant (ripple-free) torque. The waveforms are optimised by computer search techniques, to give the lowest RMS current per phase consistent with producing smooth torque. Furthermore, the waveforms are constrained to be within the converter’s VA rating. Current waveforms and the associated voltage waveforms are given for an example motor over a wide speed range. At low speeds it is demonstrated that the waveforms increase the thermally limited output of the drive compared with ‘conventional’ low-speed current waveforms, in addition to providing smooth torque. However, they give less output than waveforms optimised to give the most, thermally limited, mean torque irrespective of torque ripple.