Delta Tau GEO BRICK LV User Manual

Turbo PMAC can perform commutation for a motor with or without closing the current loop for the 
motor phases.  If the current loops are closed in the Turbo PMAC, the outputs from Turbo PMAC are 
phase voltage commands, usually represented as pulse-width-modulated (PWM) digital outputs.  This 
technique is called direct PWM control.  If the current loops are not closed in the Turbo PMAC, the 
outputs from Turbo PMAC are phase current commands, usually represented as +/-10V analog voltage 
signals.  This technique is called sine-wave output control. 

Ixx82 controls which mode of operation is used.  If Ixx82 is greater than zero, Turbo PMAC will close 
the current loops for Motor xx, and Ixx82 specifies the address of the current feedback for the motor.  
Setup for this mode is covered in the next section, Setting Up for Direct PWM Control. 

If Ixx82 is set to 0, Turbo PMAC will not close the current loops for Motor xx.  Setup for this mode is 
covered in the following section, Setting Up for Sine-Wave Output Control. 

This section explains how to set up Turbo PMAC for direct PWM control of amplifiers.  In this mode, 
Turbo PMAC 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, Turbo PMAC 
outputs PWM voltage commands for each phase of the motor.  If not using Turbo PMAC to perform this 
task for any of the motors, skip this section.  Simply make sure that Ixx82 is set to 0 for all of the 
activated motors, so Turbo PMAC will not try to close the current loop for them. 

Direct PWM control can be performed only using PMAC2-style Servo ICs, either directly commanded 
from the CPU, or over the MACRO ring.  It is possible, but rare, to do this control through accessory 
boards when the base controller is a Turbo PMAC. 

In this mode, 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 auto-tuning are possible; gain values are easily 
stored for backup and copying onto other systems; and adaptive techniques are possible. 

When performing digital current loop closure on the Turbo PMAC, 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.  However, typically, these steps are 
automated through the use of the “Turbo Setup” program running on a PC and communicating with the 
Turbo PMAC. 

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 be taken from a list, and will not have to be tested, or 
tested as thoroughly as described in this section.  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. 

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.