Delta Tau GEO BRICK LV User Manual

 

Direct-PWM Power-Block Amplifiers 

A direct-PWM power-block amplifier accepts phase voltage commands encoded as the actual pulse-
width-modulated on-off commands for the power transistors.  This type of amplifier expects the controller 
to calculate the commutation and current loop, using the torque/force command from the 
position/velocity-loop servo as the current-magnitude command into the commutation and current loop.  
The amplifier performs no control functions in this style. 

Turbo PMAC’s PID/feedforward/notch servo filter (PID filter for short) is by far the most commonly 
used servo filter.  It is easy to understand and tune, yet powerful enough to provide excellent control of 
the vast majority of systems. 

The PID filter is selected by default on the Turbo PMAC.  To use the PID filter on Motor xx, make sure 
that bit 0 of Ixx59 is set to 0, disabling any user-written servo algorithm, and Iyy00/50 (I3300 for Motor 
1, I3350 for Motor 2, etc.) is set to 0, disabling the Extended Servo Algorithm. 

-1

 1-z   

Ki

-1

-

1-z

Notch Filter

d

-

IM

: Proportional Gain (Ix30)
: Derivative Gain (Ix31)
: Velocity Feedforward Gain (Ix32)
: Integral Gain (Ix33)
: Integration Mode (Ix34)
: Acceleration Feedforward Gain (Ix35)

K

p

K

d

K

vff

K

i

K

aff

n

n

d

d

1

2

: Ix36

: Ix37

: Ix38

: Ix39

1

2

K

vff

(1-z    )

-1

K

aff

-1

(1-2z   +z   )

-2

Notch Coefficients

-1

-2

1

2

1+d   z   +d   z

-1

-2

1

2

1+n   z   +n   z

K

p

K

+

+

+

+

 

The PID feedback filter consists of proportional (P), integral (I), and derivative (D) terms, each with its 
own contribution to the control effort. 

Ixx30 Proportional Gain Term 

The proportional gain term set by Ixx30 provides the basic corrective action for position errors, providing 
a control effort proportional to the size of the error to try to reduce the error.  Proportional gain alone acts 
like a spring, and the magnitude of the proportional gain term is the spring constant; the higher this gain 
term, the stiffer the spring action. 

In Turbo PMAC, Ixx30 is an overall loop gain term, post-multiplying the other gain terms, and not just a 
proportional gain term.  This makes it possible to change Ixx30 alone if an external gain term (e.g. 
encoder resolution or amplifier gain) is changed; it also normalizes the derivative and integral gain terms 
into a time constant and inverse time constant, respectively.