Wesley BC-620-4CA - Manual (Page 126)

Curtis 1234/36/38 Manual,
OS
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to provide better control. The mathematical model of an induction motor
is complex. Using a series of reference frame transformations, vector control
simplifies the model to enable precise control of torque and flux, similar to a
SepEx motor controller.
Figure A-1 shows a typical diagram of indirect rotor flux orientation.
The instantaneous 3-phase currents are transformed to the rotor flux refer-
ence frame, using rotor speed and slip frequency—which means that the mo-
tor currents are now observed from the viewpoint of rotating with the rotor
flux. As a result of this transformation the currents, now in what is called the
d/q reference frame, lose their sinusoidal nature and look like DC signals. In the
d/q reference frame, q-axis current controls torque and d-axis current controls
flux. If properly oriented, the torque and flux remain independent of each other,
and the motor can achieve high efficiency and dynamic response.
Fig. A-1 Diagram of
Indirect Field Orientation
(IFO) technique.
The controller uses an advanced pulse width modulation technique to
maximize the utilization of battery voltage, minimize harmonic losses, and
increase system efficiency. This method achieves 15% greater linear utilization
of battery voltage, thereby effectively getting more usable motor power than
standard PWM at the same battery voltage.
Power Section
The power section efficiently generates high current 3-phase AC signals from
the DC battery voltage to drive the AC motor as requested by the motor con-
trol algorithms.
The power section is implemented as three high frequency MOSFET
half-bridge power stages controlled by three pulse width modulators, as shown
in Figure A-2. Each half-bridge power stage is a parallel array of high-side and
low-side power MOSFETs mounted to Insulated Metal Substrate (IMS) circuit
board. This technology provides a very low thermal resistance to the heatsink
and enables high power capability in a compact area.
APPENDIX A: THEORY OF OPERATION
A-2