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06.11.2012

Inverter Control-

Vacon driven by Profibus

Table of contents

1General information of the exercise

2Devices used in the exercise

3Profibus communication between the drive and the control system

3.1Fieldbuses and drives

3.2Profibus and drives

3.3Hardware Configuration - Making the PLC aware of the drive

3.4Profibus parameters in Vacon

3.5Testing the communication between the PLC and the drive

3.6Using analog input and output in PLC for frequency reference and actual value

3.7Dedicated Drive function block in the PLC

1General information of the exercise

The aim of this exercise isto give an idea,how inverters are controlled in systems.

The steps in the exercise are:

  1. Profibus communication between the drive and the control system
  2. How to apply the Profidrive-profile ja GSD-file
  3. Adding the frequency converter to PLC’s hardware configuration
  4. How to verify the communication with PLC’s programming tool
  5. Familiarize to profidrive state machine
  1. How the control system handles the frequency controller as a component
  2. A simple Drive-function block in the PLC
  3. A simplified drive control application in a PLC using Profibus communication

2The Preliminary Exercises

2.1Orientation

Read this document through and if necessary also the following: .

Your should get a general idea, what you are about to do in this exercise.

3Devices used in the exercise

The training arrangements for the exercisesare shown in fig. 1 and fig 2.

Fig.1.Training arrangements

Devices used in these exercises:

Frequency converter:Use cases number 8 and 9,

Vacon NXP , Software package NXP 2V170

Option BoardVacon OPTC5

MotorInternal motor in the demo case

PLC:Siemens S7-300, Use case number 9

Step 7 V5.4, Use laptop number 3.

Use the yellow cable between Laptop and Vacon. You should find the cable in EP2-area hanging at the cable tray.

Use the snipping-tool through the whole exercise to take the snapshots for documenting the exercise (foe ex. parametrization, programming and the testing results).

Use the following S7-application as the basis for this exercise.


4Profibus communication between the drive and the control system –

The laboratory Exercise

4.1Fieldbuses and drives

In industrial applications there is always a subordinate control system commanding the drives.

There are two interface possibilities between the drive and the control system – I/O and Fieldbus.

Today the fieldbus is the standard choice, because it has merely only advantages:

  • The control system has the fieldbus interface as a standard
  • No extra I/O cards (digital or analog) are needed at the control system or drive end – HW savings
  • No complicated wiring between the control system and the drive – Cabling and reliability savings
  • All control and supervisory information is accessible through the bus, but no through I/O – Operational and service savings

In these exercises we use Profibus as our example for fieldbus.

4.2Profibus and drives

Normal communication standards define strictly the communication. They enable data transfer between the devices, but do not say anything about the application. This means:

  • Bits and bytes are transferred but meaning of them is not defined.
  • Every drive is unique from controller’s point of view
  • The behaviour of the drive and meaning of the exchanged data has to be defined individually for each case.

This is why filed busses have an extra definition at application level called – Profile.

This profile targeted to drives applications is called Profidrive – When profibus is used

The Profibus communication works with Master – Slave principle.

  • The Controller issues a command with Control Data
  • The Slave responses immediately with Status Data

Fig.3.Master – Slave communication

The profile defines 5 different Control / Status –data pairs. Each pair carries a slightly different data.

The simplest of them is type number 3 called PPO3. It carries:

Command:

  • CW, Control Word – 2 bytes, 16 bits
  • REF, Reference –Frequency reference – 2 bytes, 16 bits

Response:

  • SW, Status Word – 2 bytes, 16 bits
  • ACT,Actual,– Actual Frequency – 2 bytes, 16 bits

Fig.4.Message structure in PPO3 mode

In the standard the Frequency Reference and Actual value are scaled:

  • -10000 – 10000=- FreqMaxLimit - FreqMaxLimit

The standard defines the meaning of the Control Word bits:

Fig.5.Control Word content

On the left side of the figure is presented the bits in the Control Word, when the drive is to be started. The bits form value 047F in Hex-form.

The standard defines the meaning of the Status Word bits:

Fig.6.Status Word content

On the left side of the figure is presented the bits in the Status Word, when the drive have started and reached the reference frequency. The bits form value 3337 in Hex-form.

The names of the Control Word bits describe themselves. In order to get the exact meaningof the Status Word bits the State Machine has to be investigated, but this is beyond of this exercise.

Fig.7. The State machine of the Profidrive frequency converter

There were altogether 5 different messaging types. They are presented below in the short form.

Fig.8. Profibus messaging types

  • Those two messages Control and Response are shown in the figure as one - The Message length to and from drive are equal, but with different content – see PPO3 for example. Each “box” represents one byte.
  • With parameter Field – Id, Ind, Value –an individual parameter can be changed or checked. This gives the same functionality as parameter setting from the panel.
  • Eight different Process Data values can be set and measured. The meanings of the PD-values areselected in the drive.

In these exercises we use type PPO3 messaging.

4.3Hardware Configuration - Making the PLC aware of the drive

Remark! take a screen snapshots during the exercise whenever reasonable!

The application in the PLC is a piece of software. In order to interact with the physical world it needs to know the interface with the surrounding hardware. This is done with the hardware configuration.

Below is shown a typical hardware configuration of the PLC -system used in this exercise. It may vary depending on the PLC unit which is in use.

Fig.9. HW-configuration

There is a CPU with a Profibus master capability. There is also I/O-cards: Digital Input , Digital Output, Analog Input and Analog Output. One of each type. Remark that there are defined the interface addresses, where the PLC program reads and writes. For example Analog Input bytes 288…291.

Check the default parameter values of the Profibus-master:

Network address:______

Transmission rate:______

Open the HW-catalogue to see the Vacon options: (If this option does not exist in the catalogue, ask your teacher to make it available)

How is it possible that in the Siemens HW-catalogue there exists Vacon NX?

______

Add the Vacon drive to be a node on the Profibus fieldbus – Drag the Vacon NX to the bus as shown below.

Give a node address for the Vacon drive – use number 3.

Define the messaging type to be used – here PPO3.

Drag the type to the row number 0 as shown below:

Save the configuration on the Hard disk and download to the PLC.

How the PLC application will reach the drive?

Incoming data packets: ______

Outgoing data packets: ______

Is there difference, how the PLC sees the drive data and the I/O-data? (Based on, what you see in the HW-configuration)

______(Yes/No)

Fill in the addresses on the lines below.

Fig.10. How the PLC application reaches the drive

4.4Profibus parameters in Vacon

Define the parameters for the Profibus option board, based on the previously done PLC-configuration.

Fig.11. Profibus parameters in Vacon

Slave Address:______

Baud Rate:______

PPO Type:______

Operate Mode:______

Do this part using the Panel:

Monitor the fieldbus communication from the Drive panel before and after setting the parameters you defined above.

Option Boards  OPTC5  Monitor  Profibus Status

Check the fieldbus status led on the PLC as well.

Please set the parameters on the Drive.

Option Boards  OPTC5  Parameters 

Now monitor the filedbus status from the panel and led on the PLC.

The result?

What is the actual meaning of the increasing bus monitor value on the panel?

______

______

From now on you use the NCDrive for parameterization and signal monitoring. You can ask a short introduction to NCDrive from your teacher if necessary.

Set the control place to Fieldbus.

4.5Testing the communication between the PLC and the drive

In this exercise we will test, how the PLC operates with the drive.

We make the PLC inputs and outputs to be our human interface:

  • Each input switch defines a bit in the Control Word
  • Each output led corresponds a status bit in the Status Word

Fig.12. The data content in the messages

The necessary PLC-program is shown below.Use M97.0 for “EN_BIT_MOVE”

Fig.13. I/O mapped directly to Vacon messages

Make and download the above shown testing program.

Open the Monitor window, where you can adjust the parameters in the PLC-program:

Activate the testing program by setting "EN_BIT_MOVE" = True.

Take the operating window in the NC Drive program to see the status of the drive (Stop / Running).

If the operating window is not available – use the panel on the freq. converter instead.

Define below: How you will set the input switches, in order to start the drive - 0 or 1.

7654321076543210

Try to start the drive.

The result:

Status of the drive

______(Run / Stop)

Status of the leds on the PLC

7654321076543210

Is the status what you expected it to be?

______

Now the drive should be running, but the frequency reference is zero.

What parameter in the PLC-monitor window defines the frequency reference?

What value at that parameter gives 25 Hz frequency reference?

Parameter:______

25 Hz value______

Set the drivefirst to 25 HZ and then 50 Hz at the reversing direction.

4.6Using analog input and output in PLC for frequency reference and actual value

We add to our human interface a feature:

  • Frequency Reference is read from the potentiometer on the PLC
  • Actual Frequency is shown on the mA meter on the PLC

The corresponding PLC program:

Fig.14. Reference from AI, Actual value from AO

Add the blocks above into the program. Do not forget to set the scaling in DB98 and DB99 at the proper values. Add M97.1 (EN_AI_AO ) to the pin named EN.

Activate this feature by setting "EN_AI_AO" = True at PLC monitoring window:

Adjust the Frequency Reference using the potentiometer on the PLC. Compare the frequency reference and actual values in PLC and Drive at monitoring window.

Comments:

______

4.7Dedicated Drive function block in the PLC

Now you have acquired knowledge about the technology, how Drives are interfaced to Control Systems.

In the previous exercise we were manipulating the direct HW-interface. Seen from application it is not very describing.

  • It is better to connect all addresses into one block (Control and Status words, Reference and Actual values).
  • At the same time the individual bits can be given meaningful names.
  • Also the unnecessary complexity can be hided.

This is why the Drive is shown as one function block in the application – see below.

Fig.15. “Drive” function block

Add the block into your program. Try now the Drive Function Block with Vacon NX:

Enable the feature in the PLC by setting:

  • M97.2, "EN_BIT_MOVE" = False
  • M97.1, "EN_AI_AO" = True
  • M97.2, "EN_DRIVE_BLOCK" = True
  • Set the inputs to proper values
  • Adjust the frequency reference using the potentiometer on the PLC

Comments:

______

Now you have knowledge, how industrial Drives are controlled.

Based on this knowledge, make another Drive by following these steps:

  • Connect the Fieldbus cable between the drive and PLC
  • Set the Profibus option board parameters in the Drive
  • Messaging type – PPO3
  • Define the node number on the Fieldbus
  • Set the Control Place to Fieldbus in the Drive
  • Add another drive to PLC HW-configuration
  • Drag and drop
  • Define the node number on the Fieldbus
  • Select messaging type – PPO3
  • Save and download
  • Add another drive to application program
  • Drag and drop a new Function Block
  • Give name Pump2
  • Connect I/O
  • Connect AI to Frequency Reference
  • Scale the reference in the AI Data Block
  • Save and download

When completed the steps above, test the Drive.

Comments:

______

Fig.16. How to make a Drive application

4.8Speed Profile

Make the speed profile, which is decribed below. Make the profile execution to start from input I1.6.

Set the maximum frequency in inverter to 100 Hz. Then the reference range -10000 - + 10000 corresponds frequency range -100 Hz - +100 Hz

5The Post Exercises

5.1Documenting

Document the made exercises in chapter 3:

  1. Present the answers to the questions in chapter 3
  2. Add the screen snapshots to your document presenting the results

5.2Answer the following questions

  • Answer with your own words, what good is in the Profidrive-profile.
  • How the communication bus cable should be grounded?
  • What is the output frequency, when the reference is set to be 10 via the bus

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