IEEE Electrification Magazine - June 2014 - 33

new scaling and commonality challenges but allows
for the optimization of each function. this architecture, shown in Figure 5, is the one used on the
letourneau technologies mining-class loader
l-1150 described later in this article.

Performance Requirements and
Attributes of electric Drive Vehicles
this section describes some of the attributes and requirements for the successful conception, design, development,
and implementation of electric drive vehicle systems.

show a great deal of promise in this area. significant
improvements may be realized by taking advantage of low
machine inertia and energy storage devices. Future electric
machine, inverter, and control algorithm developments,
along with careful system design, will likely also effect
improvements in vehicle productivity and traction control.
Dynamic electric braking can be an inherent feature of
this system, and it saves on mechanical brake wear and
simplifies vehicle control for the operator. if the system is
properly designed and implemented, the operator may
seldom/never need to use the mechanical brakes. the fast

Decreased Fuel Consumption
the electric drive has a higher efficiency than a standard
mechanical drive, which allows for reduced fuel consumption. electric drives can also automatically enable
energy recovery schemes. a prime example is a loader
application, where the vehicle has to move forward, stop,
push through a material pile to fill the bucket, reverse,
transport to destination, and unload. therefore, during a
work cycle, the vehicle may traverse through full speed
from one direction to another several times, pushing into
a stalled wheel condition and maintaining constant
intermediate speeds. each time braking or reversal of the
vehicle is demanded, this kinetic energy can theoretically be captured for later use. this allows for further fuel
efficiency gains.
at present, reliable and cost-effective high-voltage energy storage is not readily available for these rugged vehicle
applications. if a proper energy recovery system is desired,
it is imperative to deliver the maximum amount of recovered energy back to the vehicle for instantaneous use. an
example of this is to power the vehicle's other systems/
functions with this energy during the braking event. such a
solution will come through the smart power electronics
system, intelligent control of the electric motors, advanced
control algorithms, and ruggedized electronics with a powerful onboard signal processing/conditioning for decision
making. additional electrical/chemical energy storage
devices, such as superconducting magnetic energy storage,
new battery technologies, and super/ultracapacitors, are
becoming more prevalent as the technology evolves. Further research and development efforts in power electronics
systems will result in the increased viability of these technologies for increased fuel savings and energy recovery/
conservation. careful system design may also allow for the
increased use of mechanical energy storage systems such
as pressurized fluid storage (hydraulics or compressed air).

Diesel
Engine

Mechanical
Power Flow
(Shaft)
Traction
Motor

Generator

Gearbox/
Wheels

Figure 1. The electric drive system block diagram.

Induction
or
PM Machine

Figure 2. The induction or PM drive for vehicle applications.

Performance, Productivity, and Vehicle
Uptime/Maintenance Enhancements
electric drive vehicles are expected to perform the same
tasks as mechanical drive vehicles but with far superior
performance, productivity, and uptime. Fast dynamic
response and stable steady-state operation are very much
desired in vehicle control applications, and electric drives

Electrical
Power Flow
(HV dc Bus)

Mechanical
Power Flow
(Shaft)

Phase 1

Phase 2

Phase n

N-Phase Variable-Reluctance (VR) Machine

Figure 3. The multiphase variable-reluctance drive for vehicle applications.

IEEE Electrific ation Magazine / j une 2 0 1 4

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2014