Encoderless Velocity Control User Function

Introduction

Encoderless Velocity Control is a specific user function that is supported by the device variants “Standard Plus”, “Advanced Plus”, and “Application defined” of the Lexium LXM62 Drive.

The user function allows you to control the speed of a PMSM (Permanent Magnet Synchronous Motor). Encoderless means that the motor can be run without a position sensor (any kind of encoder).

If set to Encoderless Velocity Control mode, the motor moves in two different submodes:

At low speeds defined parametrically, the motor operates in encoderless open-loop control mode such that the speed and position control-loop is not closed.

The motor is driven like a stepper motor; that is, a constant motor current is applied and the motor phase current frequency is directly driven by the motion profile. The required motor torque is indirectly created by the angle between rotor magnetic flux and stator flux produced by the stator current.

The pre-defined current is shown in the StartingRefCurrent parameter. You can adjust this current with the UserStartingRefCurrent parameter.

When driven at low speeds, the motor can become warm because of the constant high stator current. Therefore, ensure that the maximum motor torque, which depends on the adjustable reference current, is not exceeded (possible overload).
At high speeds, the motor runs in closed-loop control: the speed and position control-loops are closed.

The motor moves like a servo motor. The position loop is closed via the P-control structure and the speed control is closed via the PI-control structure. The required torque is produced by the amplitude of the stator applied current.

The control switches from open-loop control mode to closed-loop control mode and vice versa automatically at a defined, motor dependent speed (indicated by the MinimalOperatingVelocity parameter). The switching mechanism is parametrized internally via motor parameters, taken from the motor type plate (no user action required).

Enabling the Encoderless Velocity Control

To enable the encoderless velocity control, proceed as follows:

Step	Action
1	Double-click the device in the Devices tree.
2	In the Feature Configuration tab of the device editor, select Application defined / 0, Standard Plus / 2, or Advanced Plus / 3 in the Device Variant list.
3	Select the Encoderless Velocity Control check box.
4	On the Parameters tab of the device editor, the ControlMode parameter under Control loop is set automatically to the value encoderless velocity closed-loop control / 2.