For maximum efficiency we would like to excite only that portion of the winding that produces propulsive force. The “Locally Commutated LSM” has been proposed as a solution to this problem [8]. The idea is to have a separate electronic power module for exciting a small number of coils and only excite the coils when there is a magnet near it. Maglet has used this approach in small motors where electronic cost is not too high, but it becomes prohibitively expensive when each coil requires many kilowatts of power.
The most cost effective solution is to excite a “sub-block” which is typically less than three times the length of a vehicle. For LSM powered vehicles climbing very steep grades with heavy loads, the sub-block length could be a fraction of a vehicle length but for most people-carrying vehicles the best choice is usually 1.2 to three times the vehicle length.