# Status of Pure Electric Vehicle Power Train Technology and Future Prospects
## 4 Electric Propulsion
### Stator Permanent Magnet Motor  
Stator-PM motor deviates itself from conventional permanent magnet (PM) brushless motor drives, with an advantage of all PM materials being located in the stator while the rotor with salient poles offers higher robustness with better thermal stability for PM materials [100].  
For EV propulsion, there are three major stator motor types:  
* Doubly-salient permanent magnet (DSPM) machine
* Flux-reversal permanent magnet (FRPM) machine
* Flux-switching permanent magnet FSPM machine  
Above all, the mentioned three types of stator-PM machines are based on PM excitation, and are classified as a group as uncontrollable but with the inclusion of independent field winding or  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Factors** & **DC** & **Induction** & **SR** & **PMSM** & **PM BLDC** \\ \hline Power density & 2 & 3 & 3.5 & 4.5 & 5 \\ \hline Efficiency & 2 & 3 & 3.5 & 4.5 & 5 \\ \hline Controllability & 5 & 4 & 3 & 4 & 4 \\ \hline Reliability & 3 & 5 & 5 & 4 & 4 \\ \hline Maturity & 5 & 5 & 4 & 5 & 4 \\ \hline Cost level & 4 & 5 & 4 & 3 & 3 \\ \hline Noise level & 3 & 5 & 2 & 5 & 5 \\ \hline Maintenance & 1 & 5 & 5 & 5 & 5 \\ \hline Total & 25 & 35 & 30 & 35 & 35 \\ \hline \hline \end{tabular}  
1-worst; 5-best.  
\end{table}
Table 1: Evaluation of existing EV drives.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Drives Types** & **BEV Models** \\ \hline DC & \multicolumn{2}{c}{Panda Elettra from Flat, Citroen berlingo Electrique, reva G-Wiz DC,} \\  & \multicolumn{2}{c}{three-wheeled tempos} \\ \hline SR & Chloride Lucas, converted General Motor prototype, small pick-up prototype \\ \hline Induction & GM EV1, BMW Mini E, Tesla Roadster, Reva G-Wiz I, Mahindra Electric- E20 series, Verito, etc. \\ \hline PMSM &
\begin{tabular}{c} Nissan leaf, Mitsubishi i-MiEV Focus Electric, Citroen C-Zero, Peugeot iOn ED, \\ BY e6, Hyundai-Kona and Ioniq, KIA Soul EV and Niro, MG ZS EV, etc. \\ \end{tabular} \\ \hline PM BLDC & Smart fortwo ED, three-wheel electric tuk-tus, and some of Chinese electric cars. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Application of existing drives in BEV (car/three-wheeler).  
magnetizing winding in the stator for flux control, the stator-PM machines become flux controllable, which can be further classified as:  
* Hybrid-excited permanent magnet (HEPM)
* Flux-mnemonic permanent magnet (FMPM)  
These flux-controllable techniques can be applied to form various topologies, such as the hybrid-excited flux-switching permanent magnet (HE-FSPM) machine or flux-mnemonic doubly-salient permanent magnet (FM-DSPM) machine.  
The flux-controllable group, including the HE-DSPM (hybrid-excited doubly-salient permanent magnet), HE-FRPM (hybrid-excited flux-reversal permanent magnet), and HE-FSPM as well as the FM-DSPM, FM-FRPM (flux-mnemonic flux-reversal permanent magnet), and FM-FSPM (flux-mnemonic flux-switching permanent magnet) machines desire two external supplies, hence called the doubly-fed stator-PM machines.  
Potential Application in Electric Vehicle  
The stator-PM motor drives have high potentiality for EV application due to their capability of solving two fundamental problems of the existing PM motor drives:  
* Absence of PMs in the rotor, thus avoiding the problem of mounting them on the high-speed rotor and hence to withstand the high centrifugal force.
* All PMs are located in the stator, with cooling arrangement and proving the thermal instability.  
Concerning maturity for use in EV, the DSPM motor drive is the most favorable one because of its mature development for over two decades. Next, the FSPM and FRPM motor drives are decade-long mature technology. The HEPM and FMPM motor drives are immature technology as they are recently derived from the singly-fed stator-PM motor drives.