Conventional field oriented control suffers from increased harmonics and losses under the low switching frequency of large-capacity inverters in urban transit. To address this issue, this paper proposes a multistep predictive flux control (PFC) for three-level inverter-fed LIM drive system adapted to urban transit. Firstly, the cost function and reference voltage vector (VV) sequence with switching frequency constraint for multistep PFC are derived. Based on the reference VV sequence, a region division is developed to reduce the complexity in VV optimization. Secondly, weighting factor tunning due to multi-dimensional objectives in the multistep PFC are eliminated by the sequential optimization scheme and switching frequency adaptive adjustment. Finally, experiments have been carried out, showing that the proposed method can effectively achieve lower current harmonics and less machine losses under low switching frequency.

Linear induction machine, three-level inverter, predictive flux control, low switching frequency