More Phases, Less Ripple: Modeling Multiphase PMSMs by Comparative Study

High-power, fault-tolerant drives push three-phase systems to their limits. We modeled and compared 3-, 5-, 3×5- and 5×3-phase PMSMs. The results show markedly smoother torque — especially for the 5×3-phase topology.

Why Multiphase?

• Less demand on power electronic devices
  For the same power requirement, the phase current and the phase voltage of multiphase machines can decrease, therefore less demanding of the power electronic devices. In high-power speed control systems such as pumps, and rolling mills, the reduce the required supply voltage by adopting a multiphase system avoids the voltage balancing issues associated with connecting power devices in series and avoids  the current sharing issues associated with paralleling power devices. 

• More creative SVPWM drive methods
  The increase of the phase number makes the number of the space vector of the inverter rise greatly, and the control methods are more diversified.  

What We Did

• Modeled & simulated: 3-, 5-, 3×5- and 5×3-phase PMSMs.

• Analyzed vector-space decomposition (VSD, see Figs. 1-2) vs. n-dq, deriving SVPWM strategies to suppress harmonic subspaces.

• For the 5-phase inverter, we used Nearest-Four-Vector (NFV) SVPWM, which cancels the third-harmonic in its α1-β1 subspace (Fig. 3).