Datasheet

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FAST Provides Sensorless FOC Performance

• Eliminates or reduces motor parameter variation effects.

• Automatically designs a stable and functional control system for most motors in under two minutes.

6.2 Rotor Angle Accuracy Critical for Performance

Why has the need for a precise estimation of the rotor flux angle driven many to use mechanical sensors?

For efficient control of three-phase motors, the objective is to create a rotating flux vector on the stator

aligned to an ideal orientation with respect to the rotor in such a way that the rotor field follows the stator

field while creating necessary torque and using the minimum amount of current.

• Stator: stationary portion of the motor connected to the microprocessor-controlled inverter.

• Ideal Orientation: 90 degrees for non-salient synchronous; slightly more for salient machines, and

slightly less in asynchronous machines since part of the current vector is also used to produce rotor

flux.

• Rotor: rotating portion of the motor, produces torque on the shaft to do work.

To achieve this, you need to extract the following information from the motor:

• Current being consumed by each phase.

• Precise relative angle of the rotor flux magnetic field (usually within ± 3 electrical degrees), so you can

orient your stator field correctly.

• For speed loops, you also need to know rotor speed.

6.3 Phase Currents Key to Estimator Accuracy

Resistor shunt current measurement is a very reasonable technique for measuring phase current in a

motor control inverter. There are three widely used examples, the 1-, 2-, and 3-shunt resistor

measurements. While at first the 1- and 2-shunt techniques seem to reduce cost, they require much faster

and more expensive amplifier circuits. These 1- and 2-shunt current measurements also limit the capability

of the current feedback which will limit the ability of the drive to use the full voltage that is provided to the

inverter. The 3-shunt technique is superior and not much different in cost due to the advantage of using

cheap slow current amplifier circuits. For best performance and cost with the FAST and InstaSPIN-FOC,

the 3-shunt technique is recommended.

For more details, see the TMS320F2806xF, TMS320F2802xF InstaSPIN-FOC/TMS320F2806xM

InstaSPIN-MOTION User's Guide (literature number SPRUHJ1).

SPRUHP4–August 2013 TMS320F28026F, TMS320F28027F InstaSPIN™-FOC Software

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