Environmental Engineering Reference
In-Depth Information
Chapter 7
Drive system control
Use of the appropriate control technology cannot be overstated with regard to
hybrid propulsion systems. The traction and ancillary electric machines are pushed
to their absolute limits in terms of fundamental electric, magnetic, thermal,
mechanical and packaging constraints. Without the proper control techniques many
of the benefits gained through innovative design can be washed away. Asynchro-
nous machines, for example, work just fine under volts/hertz control, but this would
not be an appropriate strategy in a hybrid propulsion system because its torque/
ampere and transient performance would be far inferior to field oriented control
(FOC). All the scalar control methods noted fall short of the transient performance
afforded by vector control approaches.
This chapter gives an assessment of the most popular and relevant control
techniques for hybrid propulsion systems. Generally confined to the traction system
'outer-loop', the techniques to be described determine how torque is regulated and
speed controlled. Because of the presence of multiple torque sources in the hybrid
drivetrain, it is necessary to employ torque control of all the sources, including
engine, hybrid M/G(s) and any other source of motive power (flywheels).
Sensorless control is gaining more acceptance, especially for brushless dc and
induction machines. This chapter looks at some promising sensorless control
techniques and gives an assessment of where this technology is going.
Fault management, diagnostics and prognostics are important aspects of hybrid
powertrain development. How faults are sensed, what the consequences of a faulted
driveline component, particularly the electric M/G, are and how fault recovery is
managed are topics that face the hybrid propulsion control system designer.
Hybrid propulsion system M/G control is nearly universally implemented with
field orientation techniques, regardless of the electric machine type. It is the main
focus of this chapter to present FOC principles in an uncomplicated manner with
the essential principle of FOC as the enabler for any electric machine to deliver the
same performance and response as if it were a dc armature controlled machine.
Figure 7.1 illustrates this principle and the physics of field orientation in the case of
a brushed dc machine.
Armature current is delivered by brushes to the armature coils such that a total
armature mmf is developed as shown by the vector
I
a
. Field current is separately
supplied to the field winding (shunt wound dc machine), which establishes a
