Drive system control - Propulsion Systems for Hybrid Vehicles - page 386

of leakage inductance s L s and the torque producing current I qsm , all multiplied by
the electrical speed w e . The voltage command for torque is then modified by the
stator resistance times q -axis current command I qsm , resulting in the maximum
value that the M/G back-emf may take on, namely, E qs-limit . Since the machine
back-emf is speed times flux linkage, a simple calculation results in a command for
how the next level of flux should be adjusted, and that is in response to dl s as
shown. When added to the flux command and processed through the appropriate
machine inductance and scaling factors, the flux change command results in mod-
ifications to the M/G d - and q -axis current commands as illustrated in Figure 7.14.
The overall result is that flux is programmed according to M/G speed and
adjusted so that it conforms to the usage dependent capability of the vehicle's
power supply. Because the machine flux has been adjusted to optimize effi-
ciency, the torque component of stator current, I qs , is similarly adjusted by a
modification to the torque command so that M/G torque is unaffected by the
optimization for efficiency. This entire process is constrained to small changes in
d - and q -axis commands since trading core loss for copper loss can be a delicate
balance. The significant benefit of the procedure illustrated in Figure 7.14 is to
optimize the utilization of available bus voltage and to optimize the M/G per-
formance for those conditions.
Another very useful efficiency optimization technique that has been applied is
to monitor the dc link voltage and current and from this to calculate the electrical
power input to the inverter [21-23]. Figure 7.15 is a functional block diagram of the
fuzzy efficiency optimizer when the hybrid M/G is operating in the generating
mode, an operating state that occurs for the majority of its operating time. In this
experimental setup, a drive motor controlled by the host computer establishes the
torque and speed operating point of the M/G and also coordinates with the digital
signal process that is controlling the M/G inverter.

dc load
bank

Power
electronics

Drive motor
controller

M/G BDCM

Sensor
system
and
observer

Velocity
controller

Control
computer

Vector
current
controller

*

I qs

*

I ds

w e

Fuzzy logic
controller

Graphical
user
interface

U dc , I dc , P e

T , w , P m

Figure 7.15 Fuzzy logic efficiency optimization of hybrid M/G