Comparison of five-phase, six-phase and seven-phase fault tolerant electric drives

Automotive industry is evolving towards more fault-tolerant actuators to fulfill future autonomous vehicles requirements. Critical applications such as steering or braking have to resist to fault occurrences while being low cost due to mass production market. Considering these two criteria, multiphase electric drives offer a good tradeoff between increasing the degrees of freedom and limiting system oversizing. This paper proposes to compare three multiphase electric drives for electro-hydraulic power steering for trucks: a five-phase machine and a six-phase machine both fed by a full bridge inverter (FBI), and a seven-phase machine fed by a standard half-bridge inverter (HBI). Several comparison criteria are considered in the meantime: motor, electronics, control and manufacturing parameters. Some of criteria are obtained from finite-element analysis (FEA), while others are derived from analytic formula or dynamic simulations. criteria are evaluated for each drive and then results are discussed In the given low-voltage high-current application, H-bridge inverter topology seems to be a promising solution. Both five-phase and six-phase present similar results. However, six-phase drive could be more interesting, as it could be brought close to standard three-phase solutions and adapted to dual-lane supply.