ABB MOTION CONTROL DRIVES ACSM1 Autophasing

In scalar control, some standard features are not available.

IR compensation for a scalar controlled drive IR stands for voltage.

I (current) × R (resistance) = U (voltage).

IR compensation is active only when the motor control mode is scalar.

When IR compensation is activated, the drive gives an extra voltage

boost to the motor at low speeds. IR compensation is useful in applications that

require a high break-away torque. In direct torque control (DTC) mode, IR

compensation is automatic and manual adjustment is not needed.

Autophasing

Autophasing is an automatic measurement routine to determine the angular position

of the magnetic flux of a permanent magnet synchronous motor or the magnetic axis

of a synchronous reluctance motor. The motor control requires the absolute position

of the rotor flux to control the motor torque accurately.

Sensors like absolute encoders and resolvers indicate the rotor position at all times

after the offset between the zero angle of rotor and that of the sensor has been

established. On the other hand, a standard pulse encoder determines the rotor

position when it rotates but the initial position is not known. However, a pulse

encoder can be used as an absolute encoder if it is equipped with Hall sensors,

albeit with coarse initial position accuracy. The Hall sensors generate so-called

commutation pulses that change their state six times during one revolution, so it is

only known within which 60° sector of a complete revolution the initial position is.

The drive monitors the motor status continuously, also during flux braking.

Therefore, flux braking can be used both for stopping the motor and for changing the

speed. The other benefits of flux braking are:

• The braking starts immediately after a stop command is given. The function does

not need to wait for the flux reduction before it can start the braking.

• The cooling of the induction motor is efficient. The stator current of the motor

increases during flux braking, not the rotor current. The stator cools much more

efficiently than the rotor.

• Flux braking can be used with induction motors and permanent magnet

synchronous motors.

Two braking power levels are available:

• Moderate braking provides faster deceleration compared to a situation where flux

braking is disabled. The flux level of the motor is limited to prevent excessive

heating of the motor.

• Full braking exploits almost all available current to convert the mechanical braking

energy to motor thermal energy. Braking time is shorter compared to moderate

braking. In cyclic use, motor heating may be significant.