Ok - that's interesting - thanks!
I looked closer at the ORNL Prius test motor, and there is an exposed neutral wire. Also, the diagram of the testing apparatus shows the inverter directly feeding the motor - no isolation transformer. From the inverter to the motor, 4 lines are shown, indicating either 3 phases and a neutral or 3 phases and ground.
Unfortunately, my motor doesn't have an
easily accessable neutral. I cannot find one on the exposed side of the stator windings. Perhaps there is one on the other side; right now that's hidden by the case. I can probably take it apart further to investigate this - it would be nice to have access to the neutral for testing.
Here is some interesting stuff regarding their test apperatus:
Quote:
ORNL’s dynamometer test cell and Opal-RT-based speed and current feedback controller were adapted to provide the torque needed at each reference speed. Thus, as the applied torque from the dynamometer was varied manually, the controller regulated the torque producing current appropriately. The current controller consists of two standard proportional-integral (PI) controllers for the direct and quadrature currents, id and iq , respectively. These d-q components are obtained by applying the d-q transformation to the three-phase currents which have a fixed reference for steady state operation. The transformation converts the three-phase currents into two-phase vectors, which have a reference that rotates with the rotor. Therefore, precise rotor position feedback is used during this transformation.
The steady state torque equation for the salient PM machine is expressed by:
Tl = np * ( Ld - Lq ) * i d * i q + np * K * iq , (1)
where
np is the number of pole pairs,
Ld is the d-axis inductance,
Lq is the q-axis inductance, and
K is the back-emf and torque-current factor.
The total torque given by Eq. (1) consists of two torque terms which are reluctance torque and PM torque, respectively. PM torque is produced only by the current component along the q-axis. If current is applied which results with a negative component along the d-axis, positive reluctance torque is developed since the difference, Ld -Lq , in the first term is negative and all remaining variables and constants are positive in the motoring region. In theory, there is an infinite amount of d-q current combinations that will satisfy a particular operation condition. There is an optimal d-q current combination in which the motor efficiency is maximized for each particular torque. It is difficult to determine the optimal current trajectories for the entire torque-speed range, as complex factors such as effects of saturation and harmonics must be considered. Therefore, the DAQ was used to monitor the system efficiency to ensure that the controller is operating optimally.
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