Delta Tau PMAC2 PCI Manual de usuario descargar pdf (Pagina 21)

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PMAC2 User Manual

Setting Up PMAC2 for Direct PWM Control 13

SETTING UP PMAC2 FOR DIRECT PWM CONTROL

One of PMAC2’s important new features is the ability to close motor current loops digitally. That is, the

current control loop is closed by using digital computation operating on numerical values in registers

rather than by using analog processing operating on voltage levels with op-amps. The digital techniques

bring many advantages:

• There is no need for pot tweaking or personality modules

• There is no drift over temperature or time

• Computer analysis and autotuning are possible

• Gain values are easily stored for backup and copying onto other systems

• Adaptive techniques are possible.

When performing digital current loop closure on the PMAC2, several hardware and software features

must be set up properly to utilize the digital current loop and direct PWM outputs correctly. The

following section details how to perform this setup manually. Delta Tau has new expert system PC

software running under Microsoft Windows to walk through this setup step-by-step, vastly simplifying

the process.

Note:

The instructions given in this section are for the first-time setup with an otherwise

unknown interface. For a given interface to the drive, motor and feedback device,

many parts of the setup will simply be taken from a list and will not have to be

tested, or tested as thorougly as described in this chapter. A list of configuration-

specific settings should come with the manual for each particular interface or

drive. Subsequent versions of the same setup should be even easier.

Direct PWM Control Of Amplifiers

This section explains how to set up PMAC2 for direct PWM control of amplifiers. In this mode, PMAC2

performs all of the control tasks for the motor, including commutation and digital current loop closure.

The amplifier performs only the power conversion task. In this mode, PMAC2 outputs PWM voltage

commands for each phase of the motor. If not using PMAC2 to perform this task for any of the motors,

skip this section. Make sure that Ix82 is set to 0 for all of the activated motors, so PMAC2 will not try to

close the current loop for them.

Digital Current Loop Principle of Operation

Traditionally, motor phase current loops have been closed in analog fashion, with op-amp circuits

creating phase voltage commands from the difference between commanded and actual phase current

signal levels. These analog phase voltage commands are converted to PWM format through analog

comparison to a saw tooth waveform.

PMAC2 permits digital closure of the motor current loops, mathematically creating phase voltage

commands from numerical registers representing commanded and actual current values. These numerical

phase voltage commands are converted to PWM format through digital comparison to an up/down

counter that creates a digital saw tooth waveform. The analog current measurements must be converted

to digital form with ADCs before the loop can be closed.

Frames of Reference

An important advantage of the digital current loop is its ability to close the current loops in the field

frame. To understand this advantage, some basic theoretical background is required.

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Delta Tau PMAC2 PCI Manual de usuario Pagina 21

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