1 Introduction

While V/f control is very good for many applications, it is not well suited to applications that require higher dynamic performance, applications where the motor runs at very low speeds, or applications that require direct control of motor torque rather than motor frequency. Sensorless Vector control was developed to improve these short comings in performance of V/f by improving speed regulation, low speed and starting torque, and dynamic performance.

1.1 Objectives

The main objective of this lab is to begin looking at ways to improve the speed and torque performance of an AC drive by making changes to the volts per hertz control of the AC drive. The 3 methods you will explore in the lab are the effects of adding a boost to improve the very low frequency performance, the effect of adding slip compensation which attempts to improve the speed regulation, and running the drive in Sensorless Vector mode to show how it compares to running the drive in Volts per Hertz mode from the last lab.

2 Prelab

Each student must complete a prelab to hand in at the beginning of your laboratory section. You must have completed all actions of the prelab before being allowed to participate in the Lab. The laboratory is usually completed in pairs, so please try and find a partner in the same lab section as you. See the laboratory schedule on eClass to make sure you show up to the correct time and place.

2.1 Prelab Reading

Review the safety information as well and equipment specifications for this laboratory by viewing the following information:

  • Look at equipment pages to familiarize yourself with the equipment listed below that is used in Lab 3. Note that there are links to the pdf user manuals available.
  • Read over the entire lab manual so you understand what you will be undertaking during the lab.
  • Make sure you print the Results Sheet to bring to the lab.
  • Read the Safety Page to familarize yourself with the laboratory rules and dangers.
  • Read AC Drive PWM Control Techniques to familiarize yourself with the different control techniques for induction motors.

2.2 Pre-lab Questions

  1. Which parameter do you modify so the AC Drive will operate with slip compensation enabled?
  2. What parameter monitors the slip RPM?
  3. How do you do a Rotate Tune? Which parameters are effected and in what Torque Performance Modes are these parameters used?
  4. From the AC Drive PWM Control Techniques handout, what are the four basic types of control for AC drives today?

3 Experimental Procedure

3.1 Setup

Figure 1: AC Drive/Machine Connections Diagram

  1. Wire the AC Drive/Machine setup the same way you did in lab 1 and 2 as shown in the diagram above.
    1. Use the shielded safety banana leads (available on the wall).
    2. Using the appropriate color banana leads, connect the supply terminals A, B, C and GND of the 3 Phase Power Supply to the input terminals R, S, T and GND of the Powerflex 70 AC Drive.
    3. Using the appropriate color banana leads, connect the output terminals U, V and W of the Powerflex 70 AC Drive to the input terminals X, Y and Z of the Allen-bradley Induction Machine. Also make sure you connect the Allen-bradley Induction Machine to earth ground.

Figure 2: DC Drive/Machine Connections Diagram

  1. Wire the DC Drive/Machine setup the same way you did in lab 1 and 2 as shown in the diagram above.
    1. Use the shielded safety banana leads (available on the wall).
    2. Plug in the PLX15 DC Drive control power supply available on the right side of the unit to a standard 120V recepticle. (this supply needs to be maintained at all times during drive operation)
    3. Using the appropriate color banana leads, connect the supply terminals A, B, C and GND of the 3 Phase Power Supply to input terminals L1, L2, L3 and GND of the PLX15 DC Drive, respectively.
    4. Using the appropriate color banana leads, connect the armature output terminals A+ and A- of the PLX15 DC Drive to the armature terminals +A1 and -A2 of the Baldor PMDC Machine, respectively. Also make sure you connect the Baldor PMDC Machine to earth ground.
  2. Setup the Fluke 43B the same way you did in Lab 1 and 2.
    1. Plug it in using the supplied adaptor.
    2. Connect the voltage test leads with 4mm test probes.
    3. Connect the current probe configured with 10mV/A making sure it is also zeroed.

Figure 3: Fluke 43B PMDC Armature Measurement

  1. Connect the Fluke 43B to measure armature voltage and current for the Baldor PMDC Machine as shown in the figure above. Use the Fluke 43B on Scope mode to measure only the DC Component of both the armature voltage and current.

Circuit Check

At this point please get a lab instructor (LI) or teaching assistant (TA) to double check your connections.

  1. Go through the Start-up menu of the Powerflex 70 AC Drive and configure it in a similar manner as Lab 1 and 2 as shown below.
    1. Apply power to the Powerflex 70 AC Drive by pressing START on the 3 Phase Power Supply.
    2. Go through the the Start-Up on the Main Menu to configure the Powerflex 70 AC Drive as shown below.

3.2 Run Boost

  1. Using the AC Drive/Machine to rotate the shaft at the Command Frequencies listed on the Results Sheet in the AC Machine - Run Boost table. Measure the Output Current, Output Voltage and Power Factor using the Powerflex 70’s monitor file and the shaft speed using the Pocket-tach. Record your measurements in the “Before” column on the results sheet.

  2. With the AC Drive/Machine stopped change the following parameters on the Powerflex 70 AC Drive to make it operate with a “Boost” voltage at low frequencies.

    • 69 - Start/Acc Boost set to “4.6”
    • 70 - Run Boost set to “4.6”

  3. Run the AC Drive/Machine again at the same Command Frequencies in the AC Machine - Run Boost table as “Before” with these new “After” parameters. Make the same measurements again and record them in the “After” column on the results sheet.

3.3 Slip Compensation

  1. Using the AC Drive/Machine to rotate the shaft and the DC Drive/Machine to create a torque/load on the shaft when required, run at the Command Frequencies listed on the Results Sheet in the AC Machine - Slip Compensaton table. Make the measurements in Table 1 and record your measurements in the “Before” column on the results sheet.
    1. Use the Monitor file of the Powerflex 70 AC Drive to measure the outputs of the AC Drive which is also the Inputs to the Allen-bradly Induction Machine.
    2. Use the Pocket-tach to measure the shaft speed.
    3. Use the Fluke 43B to measure the DC Component of the armature current.
    4. To obtain no-load for the Allen-bradley Induction Machine adjust the torque/current knob on the PLX15 DC Drive to minimum (fully counter clockwise).
    5. To obtain full-load for the Allen-bradley Induction Machine adjust the torque/current knob on the PLX15 DC Drive until the Powerflex 70 AC Drive displays the rated current of the Induction Machine (5.8 Amps).
    6. To obtain 1/2-load for the Allen-bradley Induction Machine take the PMDC machines armature current reading at full-load and divid it by 2. Take that new armature current value and adjust the torque/current knob of PLX15 DC Drive until this new value is obtained for the armature current.
  1. With the AC Drive/Machine stopped change the following parameter on the Powerflex 70 AC Drive to make it operate with a “Slip Compensation”.
    • 80 - Speed Mode set to “Slip Comp”
  2. Run the AC Drive/Machine again at the same Command Frequencies and torque/load in the AC Machine - Slip Compensation table as “Before” with these new “After” parameters. Make the same measurements again and record them in the “After” column on the results sheet.

3.4 Autotune

  1. Record the “Before Autotune” calculated values for the following parameters and record them in the AC Machines - Autotune table on the results sheet.
    • 62 - IR Voltage Drop
    • 63 - Flux Current Ref
    • 121 - Slip RPM @ Full Load

Warning

The Machine Shaft will rotate during the following test. It is important to run the following test with un-loaded or the automatic setting of the parameters will be wrong.

  1. Perform an Autotune on the AC Drive by doing the following:
    1. Make sure the DC Drive is stopped by pressing the red stop button.
    2. Change parameter 61 - Autotune to “Rotate Tune”.
    3. Press the Start green button on the AC Drive to start the test.
      • The AC Drive will first complete a Static Tune where the shaft doesn’t rotate.
      • The AC Drive will then do a Rotate Tune where the shaft rotates.
    4. Once completed the AC Drive will return to the Ready state after a successful Autotune calibration.
  2. Record the “After Autotune” values for the same parameters as before and record them in the AC Machines - Autotune table on the results sheet.

3.5 Sensorless Vector

  1. With the AC Drive/Machine stopped change the following parameter on the Powerflex 70 AC Drive to make it operate with a “Sensorless Vector” mode.
    • 53 - Torque Perf Mode set to “Sensrls Vector”

Warning

This is a reminder to make sure the speed/voltage and torque/current knobs on the DC Drive are fully counter-clockwise before you begin the procedure below so that you start in the unloaded condition.

Warning

During the experiment make sure that you don’t exceed the Allen-bradley Induction Machines rated current of 5.8 Amps which is fairly easy to do if you increase the torque/load too much.

  1. Use the AC Drive/Machine to rotate the shaft and the DC Drive/Machine to create a torque on the shaft when required at the Command Frequencies listed on the Results Sheet in the AC Machine - Sensorless Vector table. Make the measurements in Table 2 and record them in the appropriate spot on the results sheet.
    1. Use the Monitor file and/or the appropriate parameter numbers of the Powerflex 70 AC Drive to measure the outputs of the AC Drive which is also the Inputs to the Allen-bradly Induction Machine.
    2. Use the Pocket-tach to measure the shaft speed.
    3. Use the Fluke 43B to measure both the DC Component of the armature voltage and current.
    4. To obtain no-load for the Allen-bradley Induction Machine adjust the torque/current knob on the PLX15 DC Drive to minimum (fully counter clockwise).
    5. To obtain full-load for the Allen-bradley Induction Machine adjust the torque/current knob on the PLX15 DC Drive until the Powerflex 70 AC Drive displays the rated current of the Induction Machine (5.8 Amps).
    6. To obtain 1/2-load for the Allen-bradley Induction Machine take the PMDC machines armature current reading at full-load and divid it by 2. Take that new armature current value and adjust the torque/current knob of PLX15 DC Drive until this new value is obtained for the armature current.
  1. Once you have all of your results and want to turn everything off do the following:
    1. Return both the speed/voltage and torque/current knobs on the PLX15 DC Drive to minimum (counter clockwise).
    2. press the red stop button on the PLX15 DC Drive to discount it from the circuit.
    3. press the red stop button on the Powerflex 70 AC Drive to stop the AC Drive from controlling the AC Machine.
    4. Turn off the 3 Phase Power Supply.

Results Sign-off

Before you start to cleanup, if you are happy that you have completed all of the measurements required for the lab please get a LI or TA to double check results and sign-off on your results sheet.

Cleanup Sign-off

Please put everything back to where it was when you came into the lab.

  • Disconnect your circuit and leave all of the equipment neatly at your station.
  • Put the Fluke 43B back in the case and make sure the Current Probe is turned off.
  • Hang the Hookup Leads back on the wall neatly.
  • Please make sure you bring all your stuff with you.

Once you are finished cleaning up you need to get another sign-off from a LI or TA.

4 Lab Report

The following is what you are expected to hand-in one week (by 4:00pm) after completion of the lab. You only have to hand-in one copy per group. There is an assignment box in the ETLC atrium marked ECE432 Lab: H11, H31, H41. Please, staple everything together in the following order.

  • Use the first page of the results sheet as your cover page. Make sure your names, student ID’s, CCID’s and lab section are visible in the table. Make sure you have the required signatures from completing the Laboratory exercises and clean up.
  • Include the results sheet that you made all of your measurements on.
  • The the 4 graphs below.
  • The answers to the post lab questions below.

4.1 Graphs

Create the following Graphs to hand in with your Results.

  1. Output Current vs. Command Frequency for Run Boost.
    • include 2 separate series, 1 for before a Run Boost is applied and 1 for after.
  2. Output Voltage vs. Command Frequency for Run Boost.
    • include 2 separate series, 1 for before a Run Boost is applied and 1 for after.
  3. Torque vs. Speed for Slip Compensation * include 6 separate series for each command frequency, 3 for before a Slip Compensation is applied and 3 for after.
  4. Torque vs. Speed
    • include a separate series for each command frequency

4.2 Questions

Answer the following questions to hand in with your Results.

  1. What is the purpose of the Run Boost? Why does an induction machine produce low torque at low frequencies when operated under Volts per Hertz control?
  2. What is the purpose of Slip Compensation, how does the drive accomplish this? Explain
  3. Looking the AC Machine - Sensorless Vector results how are the following effected by increasing the load torque? Which of these are effected by the command frequency, load torque or both? Briefly explain for each of these why they behave the way they do.
    • Output Frequency
    • Output Current
    • Torque Current
    • Flux Current
    • Output Voltage
    • Output Power
    • Output Power Factor
    • Slip RPM Meter
    • Shaft Speed