Environmental Engineering Reference
In-Depth Information
T
ref
U
d
,
U
q
U
s
Coordinate
transformation
Power
inverter
IM
l
ref
Sliding
mode
i
s
High gain
observer
w
w
ld
Rotor flux
estimator
e
j
q
Figure 7.12 Non-linear controller for sensorless induction machine drive
q
-axis current is implemented as a high gain observer. A functional diagram of this
technique is illustrated as Figure 7.12.
The controller shown in Figure 7.12 is able to estimate rotor speed and track
both flux and torque commands issued by a higher level vehicle controller. Dif-
ferentiator noise concerns are minimized by use of a high gain observer operating
on measured stator currents that have been transformed into the synchronous
reference frame. In Reference 7 experimental results are presented showing good
agreement with theory.
Sensorless control of permanent magnet machines is also very desirable for
hybrid propulsion systems because such machines are used not only as the main
driveline M/G but also for many of the ancillary electric drives [8,9]. Rotor position
sensing has been historically accomplished using shaft mounted encoders, resolvers
or Hall effect devices near the rotor or in the airgap. The overarching goal of
synchronous machine control is to use the machine itself as a sensor. Blaschke
et al.
[10] have proposed that the machine can indeed become its own position sensor by
capitalizing on the fact that the rotor flux vector induces areas of saturation into the
stator iron. It was discovered that the current transfer (stationary to synchronous
reference frames) in the direction parallel to the rotor flux vector occurs with
smaller gain than for current transfer orthogonal to the rotor flux vector when the
machine is saturated. From this asymmetry it is possible to determine the direction
of the rotor flux. During operation the stator current vector pulsates in parallel with
the rotor flux vector so that it has no effect on machine torque.
Position sensorless control of synchronous reluctance machines is similar to
that of permanent magnet machines [11,12]. All methods rely on accurate mea-
surements of the machine currents and voltages with due account of temperature
