TMS320F28379D: Delay in fast current loop

user5987527

Hello!

The figure below is a screenshot of the fast current loop in Ti training. When the comparison value is updated, it will take some time for the motor to obtain a new voltage, which can be equivalent to zero order delay in the digital control system, thus generating Zero point five Delay of sampling cycles. My question is, what is the time needed for the motor to obtain new voltage, and why it can be equivalent to zero order delay, so as to 0.5 Sampling periods?

thank you!

over 6 years ago

0 Ramesh Ramamoorthy over 6 years ago

TI__Mastermind 27240 points

user5987527 said:

My question is, what is the time needed for the motor to obtain new voltage

There is not a math behind this, ideally, it should to zero (continuous - analog)

user5987527 said:

why it can be equivalent to zero order delay, so as to 0.5 Sampling periods?

In digitial controls, ZOH is defined as half the sampling time.

0 user5987527 over 6 years ago in reply to Ramesh Ramamoorthy

Prodigy 60 points

Thank you for your reply.

I still don't understand why the delay from duty cycle update to motor voltage acquisition can be equivalent to zero order delay.

I think there are two possibilities: 1. The comparison value needs to be kept as a continuous value, and zero order delay 2 is introduced. In some papers, it is mentioned that the inverter can be simplified as zero order delay. Are these two statements right? Which one does it refer to here?

This is the address of the training video:https://training.ti.com/designdrive-fast-current-loop-technical-overview?context=1137615-1139618-1134685

Thank you

0 Ramesh Ramamoorthy over 6 years ago in reply to user5987527

TI__Mastermind 27240 points

If there should be no ZOH, then a Class A type of 3 phase generation should be used. But it is not practical. In an inverter, which is class D type, the dutycycle is updated periodically at a time of say Ts. Therefore, ZOH exists and can not be avoided.

If your concern is resolved, pls close the thread.

0 user5987527 over 6 years ago in reply to Ramesh Ramamoorthy

Prodigy 60 points

Thank you for your reply.

Would you please tell me about a class a type of 3 phase generation and class D type, or provide some related documents or links? I didn't search for relevant knowledge. Sorry for the inconvenience.

Thank you very much.

0 Ramesh Ramamoorthy over 6 years ago in reply to user5987527

TI__Mastermind 27240 points

Inverter is a type of amplifier, and, by type, I meant Class A / Class D type of amplifier. You can find more info on the net. I hope you already found it and so clicked resolved.

With this, am closing the thread.

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TMS320F28379D: Delay in fast current loop