NANOTEC PD4-E, Техническое руководство

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Technical Manual PD4-E-M (EtherCAT)
5 General concepts
Clock-Direction operating mode
Change of the step resolution via objects 2057
h
(Clock Direction Multiplier) and 2058
h
(Clock Direction Divider). Optimize acceleration / deceleration ramps by adjusting the pulse
frequency to pass through the resonance range as quickly as possible.
5.1.3 Closed Loop
Introduction
The closed loop theory is based on the idea of a control loop. A disturbance acting on a system should
be compensated for quickly and without lasting deviation to adjust the control variable back to the set
point.
Closed loop using a speed control as an example:
Regulator
PI
I
, PI
V
Actuator
Current magnitude/current angle
Malfunction
Torque-
fluctuations
Control variable
Actual speed
I
actual
V
actual
Reference variable
Target speed
PI
I
= Proportional-integral current control loop
PI
V
= Proportional-integral velocity control loop
I
actual
= Actual current
V
actual
= Actual speed
The closed loop method is also referred to as "sine commutation via an encoder with field-oriented
control". At the heart of closed loop technology is the performance-adjusted current control as well
as the feedback of the actual values of the process. Using the encoder signals, the rotor orientation
is recorded and sinusoidal phase currents generated in the motor windings. Vector control of the
magnetic field ensures that the magnetic field of the stator is always perpendicular to that of the rotor
and that the field strength corresponds precisely to the desired torque. The current thereby controlled in
the windings provides a uniform motor force and results in an especially smooth-running motor that can
be precisely regulated.
The feedback of the control variables necessary for closed loop mode can be realized with various
technologies. In addition to the physical feedback with encoders or Hall sensors, it is also possible to
virtually record the motor parameters through software-based model calculation. Physical variables,
such as speed or back-EMF, can be reconstructed with the help of a so-called "observer" from the data
of the current controller. With this sensorless technology, one has a "virtual rotary encoder", which –
above a certain minimum speed – supplies the position and speed information with the same precision
as a real optical or magnetic encoder.
All controllers from Nanotec that support closed loop mode implement a field oriented control with sine
commutated current control. Thus, the stepper motors and BLDC motor are controlled in the same way
as a servo motor. With closed loop mode, step angle errors can be compensated for during travel and
load angle errors corrected within one full step.
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