Delta Tau PMAC2 PCI User Manual download pdf (Page 36)

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PMAC2 User Manual

28 Setting Up PMAC2 for Direct PWM Control

Current Loop Polarity Check

Observe the signs of the ADC register values in M105 and M106. These two values should be of

approximately the same magnitude and must be of the opposite sign from each other. (Again, remember

that these readings will appear noisy. Observe the base value underneath the noise.) If M105 is positive

and M106 is negative, the sign of the PWM commands matches the sign of the ADC feedback values. In

this case, the PMAC2 phase angle parameter I172 must be set to a value greater than 128 (171 for a 3-

phase motor, 192 for a 2- or 4-phase motor).

If M105 is negative and M106 is positive, the sign of the PWM commands is opposite that of the ADC

feedback values. In this case, I172 must be set to a value less than 128 (85 for a 3-phase motor, 171 for a

2- or 4-phase motor).

Make sure the I172 value is set properly before attempting to close the digital current loops on PMAC2.

Otherwise there will be positive feedback creating unstable current loops, which could damage the

amplifier and/or motor.

If M105 and M106 have the same sign, the polarities of the current sense circuitry for the two phases is

not properly matched. In this case, something has been miswired in the drive or between PMAC2 and the

drive to give the two-phase current readings opposite polarity. One of the phases will have to be fixed.

Do not attempt to close the digital current loops on PMAC2 until matched the polarities of the current

sense circuitry for the two phases have been matched properly. This will involve a hardware change in

the current sense wiring, the ADC circuitry or the connection between them. As an extra protection

against error, make sure that Ix57 and Ix58 is set properly for I

T protection that will quickly shut down

the axis if there is saturation due to improper feedback polarity.

Troubleshooting

If the current readings expected are not received, probe the motor phase currents on the motor cables with

a snap-on hall-effect current sensor. If current is not seen when commanding voltages, check for phase-

to-phase continuity and proper resistance when the motor is disconnected.

Voltage Six-Step Test

For a complete test of the motor/drive connection, try all six sign combinations for a 3-phase motor, or 8

for a 4-phase motor. It is best to command all phase values on a single command line to get simultaneous

changes.

For a synchronous motor, this test will step the motor through one commutation cycle. It can be used to

confirm the size of the commutation cycle in counts, the pole count of the motor, and the commutation

direction sense.

What To Look For

In performing this test, check the following:

• There should be a consistent relationship between M102 and M105 on Phase A, and between M104

and M106 on Phase B.

• For synchronous motors (and possibly for induction motors), the M101 position register should

change in approximately equal increments between each step.

• For synchronous motors (and possibly for induction motors), the total change in M101 between the

initial Step 1 and the return to Step 1 should be approximately equal to Ix71/Ix70.

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Delta Tau PMAC2 PCI User Manual Page 36

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