Introduction
In V/f control, the speed of induction motor is controlled by fixing
the ratio of the stator voltages to stator frequency, usually defined by
the rated values. This will maintain the air gap flux at approximately
the desired value at steady-state. Sometimes this scheme is called the
scalar control because it focuses only on the steady state dynamic.
Objectives
The main objective of this lab is to operate the AC drive as a simple
constant ratio V/f source to supply the induction machine and see how
the induction machine performs under different speeds and load
levels.
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.
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 2. 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 lab.
- Read the Safety
Page to familarize yourself with the Laboratory Rules and
Dangers.
Pre-lab
Questions
- What is constant V/f operation for an Induction Machine Variable
Speed Drive?
- Which parameters effect the V/Hz operation of the drive for Open
Loop speed mode?
- At the low frequencies of the V/f curve? (4 parameters)
- At the high frequencies of the V/f curve? (4 parameters)
- using the name plate of the induction motor what should be the
torque at rated values? Show your calculations.
Experimental
Procedure
Setup
AC Drive/Motor
Setup
- Wire the AC Drive/Machine setup the same way you did in lab 1 as
shown in the diagram above.
- Use the shielded safety banana leads (available on the wall).
- 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.
- 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.
Circuit Check
At this point please get a lab instructor (LI) or teaching assistant
(TA) to double check your wiring.
- Go through the startup menu of the Powerflex 70 AC Drive
and configure it in a similar manner as Lab 1 as shown below.
- Apply power to the Powerflex 70 AC Drive by pressing
START on the 3 Phase Power Supply.
- Go through the the Start-Up on the Main Menu to configure
the Powerflex 70 AC Drive as shown below.
Main Menu:
Start-Up
- Input Voltage
- 208V 60Hz
- Reset the parameters to default
- Motor data/ramp
- PWR Units = HP
- NP Power = 2.00
- NP FLA (full load amp) = 5.8
- NP Volt = 230V (Can only put in a maximum of 208V)
- NP Hertz = 60
- NP RPM = 1730
- Stop Mode = Coast
- DC Resistor type = Internal
- Accel time = 10 Sec
- Decel time = 10 Sec
- S-curve = 0%
- Motor Test
- Direction test
- Hold Jog button to identify the motor direction.
- Do a static tune
- Speed Limits
- Prohibit reverse operation
- Maximum speed = 71
- Minimum speed = 0
- Speed Control
- Speed control = Local HIM port 1
- Start/Stop/IO input
- Digital Inputs – Custom Configuration = Digital Input (1-6) = 0 “Not
used”
- Done
Note
You won’t be able to run the motor to do the motor test section
without first going to step 6 to disable the digital inputs so you don’t
get a (Start Inhibit) error. So after step 2, first go to step 6 and
then return to do the direction test in step 3.
- Also change the following parameters on the Powerflex 70 AC
Drive to make it operate in constant voltage per hertz.
- 53 - Torque Perf Mode set to 2 “Custom V/Hz”
- 69 - Start/Acc Boost set to “0”
- 70 - Run Boost set to “0”
Quick Access to Parameters
You can use the menus to navigate to a parameter, however if you
don’t know which menu to find the parameter in it can be quicker to just
press ALT and then PARAM# on the HIM and then
punch in the known parameter number.
- The AC Drive/Machine should now be configured to run indicated by a
green blinking status light on the Powerflex 70 AC Drive.
Fluke 43B
Setup
- Setup the Fluke 43B the same way you did in Lab 1.
- plug it in using the supplied adaptor.
- connect the voltage test leads with 4mm test probes.
- connect the current probe configured with 10mV/A making sure it is
also zeroed.
- Connect the Fluke 43B to measure the DC component for the Baldor
PMDC Machines armature voltage leaving the current probe
disconnected for now.
DANGER
Check that the motors are free to rotate and are clear of any
wires/leads/fingers or anything else that could potentially touch them.
Especially the shaft as this rotates very fast and has a very
significant amount of power. The machine can also get fairly hot when
they are operating under load.
AC Drive and Fluke 43B Setup Check
At this point please get a lab instructor (LI) or teaching assistant
(TA) to double check your AC Drive and Fluke 43B setup.
Open Circuit Test of
Baldor PMDC Machine
- Using the AC Drive/Machine to rotate the shaft at the Command
Frequencies listed on the Results Sheet in the DC
Machine - Open Circuit Test table. Measure both the shaft speed and
the Baldor PMDC Machines DC component of the armature voltage
and record it in the appropriate spot on the results sheet.
- Once you have the results, press the red stop button on the
Powerflex 70 AC Drive to stop the AC Machine from rotating.
Turn off the 3 Phase Power Supply and leave the AC
Drive/Machine connected for the next part.
DC Drive/Motor
Setup
Warning
Make sure the 3 Phase Power Supply is off.
- Wire the DC Drive/Machine setup the same way you did in lab 1 as
shown in the diagram above.
- Use the shielded safety banana leads (available on the wall).
- 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)
- 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.
- 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.
Circuit Check
At this point please get a lab instructor (LI) or teaching assistant
(TA) to double check your wiring.
- Move the Fluke 43B’s current probe and voltage leads to the
output of the Baldor PMDC Machine as shown in Figure 3
so the DC Component of both the armature voltage and current can be
measured.
Warning
Check that the Machine Shaft is still clear of anything that can
interfere with it.
DC Drive and Fluke 43B Setup Check
At this point please get a lab instructor (LI) or teaching assistant
(TA) to double check your DC Drive and Fluke 43B setup.
Volts per Hertz
Operation of the Induction Machine
- 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 - Volts per Hertz table. Make the measurements in
Table 2 and record them in the appropriate spot on the results
sheet.
- 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.
- Use the Pocket-tach to measure the shaft speed.
- Use the Fluke 43B to measure both the DC Component of the
armature voltage and current.
- 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).
- 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).
- 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.
Warning
This is a reminder to make sure the speed/voltage and torque/current
knobs are fully counter-clockwise before you begin 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 load to much.
- Once you have the results to turn off the setup do the following:
- Return the torque/current knob on the PLX15 DC Drive to
minimum (counter clockwise).
- press the red stop button on the PLX15 DC Drive to discount
it from the circuit.
- press the red stop button on the Powerflex 70 AC Drive to
stop the AC Machine from rotating.
- 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 cleaing up you need to get another sign-off
from a LI or TA.
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 above. You need to obtain the signatures below after completing
the Laboratory exercises.
- Include the results sheet that you made all of your measurements
on.
- The calculation below showing your work for only one setpoint.
- The 4 graphs below.
- The answers to the post lab questions below.
Calculations
For the following calculations you need to show your work for only
one setpoint to show how you calculate the value.
- From the DC Machine - Open Circuit Test results calculate
\(k\phi\) for the Baldor PMDC
Machine for each command speed.
- Using the average of the \(k\phi\)
values above calculate the Torque on the shaft for all setpoints in the
AC Machine - Volts per Hertz table of the results.
- Calculate the slip speed values in rpm for all setpoints in the
AC Machine - Volts per Hertz table of the results.
Graphs
Create the following Graphs to hand in with your Results.
- Voltage vs. Speed for the DC Machine - Open Circuit
Test
- Voltage vs. Speed for the Induction Machine
- include 3 series (make sure the speeds are all in the same units)
- voltage vs. synchronous speed
- voltage vs. no-load speed
- voltage vs. full-load speed
- Torque vs. Speed * include a separate series for each command
frequency
- Torque vs. slip speed
- include a separate series for each command frequency
Questions
Answer the following questions to hand in with your Results.
- Is the assumption that \(\tau \propto
\Psi^2 sn_S\) reasonable for constant V/f operation? Explain your
answer.
- Did the AC drive with constant V/f control provide constant flux at
all speeds? If not, at what frequencies is it limited and why?
- what happens at low speeds
- what happens at high speeds (> 60 Hz)