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This movie shows on the
oscilloscope the d-q axis circle diagram showing the state space
representation of the stator flux vector.
The challenge in induction
motor control is that both the stator flux and the torque
must be produced, and regulated. At zero speed, these challenges
become formidable because low frequency voltage signals on the motor
terminals become vanishingly small, and are buried in a sea of high
voltage, high frequency noise.
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(If this image is not moving, the
video is not compatible with your browser)
How does
CogniSim work?..... |
Since the torque command is zero, the ideal
performance consists of external shaft disturbances forcing the motor to
rotate unhindered with the application of external torque (the hand).
CogniSim detects the disturbance and complies with
it. Only two motor currents and the inverter DC bus voltage are required
for measurement. (as shown)
This is the essence of sensorless
torque control. |
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The Induction motor shown running CogniSim (on the
left) is a 600Vac, 10HP unit connected to a second identical motor that
is not used in this demo. The device mounted on the shaft is a torque
cell.
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Many vector control systems lose torque at low speed because of the
difficulty in measuring the terminal voltage of the motor, and
developing the stator flux signal. Because inverter chopping is
significant at zero speed, filters are typically required to extract the
stator voltage reliably. However these filters can compromise torque
response to step changes (when required) and maintaining torque into
irregular rotating loads is troublesome as a result. |
CogniSim torque control does not use filters and produces
torque in irregularly rotating loads, making it ideal for extruders,
crushers or other difficult to start mechanical loads.
The ability to control torque even during irregular rotation, and
at wide varying speeds, are attributes that offer unique capability to
generate power effectively in many wind, water and wave prime mover
applications. |
