Flux Braking

1 Flux Braking

0 5 f (Hz)

5 10 20 30 40 50 The drive monitors the motor status continuously, also during the 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 motor is efficient. The stator current of the motor increases during the Flux Braking, not the rotor current. The stator cools much more efficiently than the rotor.

Settings

Parameter 26.02 .

Flux Optimisation

Flux Optimisation reduces the total energy consumption and motor noise level when the drive operates below the nominal load. The total efficiency (motor and the drive) can be improved by 1% to 10%, depending on the load torque and speed.

Settings

Parameter 26.01 .

Acceleration and deceleration ramps

Two user-selectable acceleration and deceleration ramps are available. It is possible to adjust the acceleration/deceleration times and the ramp shape. Switching between the two ramps can be controlled via a digital input. Motor The available ramp shape alternatives are Linear speed

and S-curve. Linear: Suitable for drives requiring steady or slow

Linear acceleration/deceleration.

S-curve S-curve: Ideal for conveyors carrying fragile loads,

or other applications where a smooth transition is required when changing the speed.

Settings

2 t (s) Parameter group

22 ACCEL/DECEL .

Critical speeds

A Critical Speeds function is available for applications where it is necessary to avoid certain motor speeds or speed bands because of e.g. mechanical resonance problems.

Settings

Parameter group

25 CRITICAL SPEEDS .

Constant speeds

It is possible to predefine 15 constant speeds. Constant speeds are selected with digital inputs. Constant speed activation overrides the external speed reference.

This function operates on a 6 ms time level.

Settings

Parameter group

12 CONSTANT SPEEDS .

Speed controller tuning

During the motor identification, the speed controller is automatically tuned. It is, however, possible to manually adjust the controller gain, integration time and derivation time, or let the drive perform a separate speed controller Autotune Run. In Autotune Run, the speed controller is tuned based on the load and inertia of the motor and the machine. The figure below shows speed responses at a speed reference step (typically, 1 to 20%).

nn

A: Undercompensated

B: Normally tuned (autotuning)

C: Normally tuned (manually). Better dynamic performance than with B

D: Overcompensated speed controller

The figure below is a simplified block diagram of the speed controller. The controller output is the reference for the torque controller.

Derivative acceleration compensation

Proportional, integral

Derivative Actual speed

Settings

Parameter group

23 SPEED CTRL and

20 LIMITS .

Diagnostics

Actual signal 01.02 .

Speed control performance figures

The table below shows typical performance figures for speed control when Direct Torque Control is used.

T (%) T N

Speed Control

No Pulse

With Pulse

T load

Static speed error, + 0.1 to 0.5%

% of n N

(10% of nominal slip)

t (s) Dynamic speed

0.1 - 0.4 %sec n act error -n ref

0.4 %sec.*

0.1 %sec.*

*Dynamic speed error depends on speed controller tuning. T N = rated motor torque n N = rated motor speed n act = actual speed n ref = speed reference

Torque control performance figures

The drive can perform precise torque control without any speed feedback from the motor shaft. The table below shows typical performance figures for torque control, when Direct Torque Control is used.

T (%) T N

Torque Control

No Pulse

With Pulse

90 act Repeatability

T Linearity error

error Torque rise time

1 to 5 ms

1 to 5 ms

*When operated around zero frequency, the error may be greater.

< 5 ms t(s) T N = rated motor torque

T ref = torque reference T act = actual torque

Scalar control

It is possible to select Scalar Control as the motor control method instead of Direct Torque Control (DTC). In the Scalar Control mode, the drive is controlled with a frequency reference. The outstanding performance of the default motor control method, Direct Torque Control, is not achieved in Scalar Control.

It is recommended to activate the Scalar Control mode in the following special applications:

• In multimotor drives: 1) if the load is not equally shared between the motors, 2) if the motors are of different sizes, or 3) if the motors are going to be changed after the motor identification