Figure 1. Typical laboratory setup for the single-phase diode rectifiers lab.

1 Introduction

The single-phase diode-rectifier is a widely used input stage for power supplies that connect to the utility mains supply. This laboratory observes the performance of a full-wave diode-rectifier using two different filter types: (1) a capacitor dc-filter that is widely used because if it’s low cost, light weight and high efficiency, (2) the same as 1 but adding an ac-supply-inductor at the input which is sometimes used to improve the rectifier input power quality by lowering the harmonic currents drawn from the ac-supply. You will obtain an understanding of the typical full-wave diode rectifier’s waveforms and characteristics in this Laboratory.

Below is a summary of what you will be working on during this first laboratory.

Equipment Familiarization:

  • Fluke 43B power quality analyser and its current probe.
  • Single-phase supply box.
  • Resistor load box.
  • Diode-bridge rectifier box.

Circuit 1: Measure Inductance

Measure the inductance of the AC-Supply Inductor used in circuit 3.

Circuit 2: Full-bridge with DC-link cap

Determine the performance of a full-bridge diode-Rectifier with a DC-link capacitor filter by loading it with a resistor load bank.

Circuit 3: With Added Supply Inductor

Compare the performance of the previous circuit to the same full-bridge diode-rectifier but now with an added supply inductor.

1.2 Safety

  • Please watch the Safety Video before attending your lab session.

  • Remember the voltages (300VDC and 208VAC) that you are working with can cause serious harm to you if not respected. Please be careful with your hands and fingers around the circuits to avoid electrocution. If you run into any problems during your experiment disconnect power immediately.

  • Do not leave banana leads connected at only one end of the circuit with the other end floating around. This free end of the cable can potentially have voltage on it and create a dangerous hazard.

  • While working with these voltages that can possibly be exposed it is a good idea to remove any metal watches, rings, bracelets etc…

  • Understand the ratings and limitations of the equipment you are operating. Monitor your circuits closely and try to operate the equipment within specifications at all times.

  • The capacitor in the Diode Rectifier Box has a resistor in series with it. The resistors purpose is to limit the destructive inrush current that is associated with the charging of a capacitor. Therefore the switch must be in an open state to allow the current to be limited by the resistor at start-up. After the capacitor is charged the resistor must be shorted via the switch because the resistor is unable to handle the continuous power flow. Leaving the resistor in will cause errors in your results because you’re limiting the current available to the capacitor. Failure to do either step will damage the equipment!!!

  • Do not make changes to the circuit while power is applied. This doesn’t include changing load switches or moving your voltage/current probes around to make different measurements.

  • Make sure that all large capacitors are discharged before making changes to your circuit. Mainly this is the DC-Link Capacitor that needs to have a significant load on it to make sure it discharges in a reasonable amount of time.

  • Please keep your work area tidy while working on experiments.

  • Always have an Instructor or TA check your circuit changes before you apply power.

2 Prelab

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

2.1 Prelab Reading

Familiarize yourself with the lab equipment, procedures, documents and results sheet.

  1. Take a look at the Fluke 43B getting started manual available on eClass to become familiar with the Power Quality Meter used in this laboratory.

  2. Look at the other equipment pages to familiarize yourself with the equipment that is used in Lab 1. Note that there are links to the lab equipment pages available.

  3. Read over the entire lab manual so you understand what you will be undertaking during the lab.

  4. Look at the provided ECE401 - Lab 1 - Results sheet to see what you will be recording as results during the laboratory.

  5. Print off a ECE401 - Lab 1 - Sign-off sheet . You only need one per group.

2.2 Pre-lab Questions

Figure 2. Prelab circuit - full-wave diode-rectifier with dc-link capacitor filter.

  1. For the full-wave diode-rectifier with a DC-side capacitor-filter and resistive load circuit above do the following calculations in the provided Prelab1: Calculation Worksheet to hand-in at the beginning of your scheduled laboratory session. (Show all your work).

    1. Use the iteration method template included on the following page to calculate θC, VR, VDC and IDC.

    2. Calculate the rms and peak of the output and capacitor currents (Im, IO,rms, IC, IC,pk)

    3. Calculate diode rectifier input power factor (PF).

    4. Calculate the remaining parameters.

  2. Copy your results from the previous question to the appropriate column in the ECE401 - Lab 1 - Results sheet .

3 Experimental Procedure

Danger!

The power used in this lab can cause severe electrocution that can lead to serious injury or even death. So please follow instruction carefully and be cautious with your experiments.

Have an Instructor or TA verify your circuit connections before you apply power!!!

3.1 Equipment Familiarization

It is good practice when working with equipment that has a danger associated with it that you familiarize yourself with the use, function and safety precautions necessary to operate the equipment in a manner which will keep the equipment in good working order and the user safe.

3.1.1 Fluke 43B and Current Probe

Figure 3. Current Probe, Fluke 43B Power Quality Analyser, Test Leads and the Power Adaptor for the Fluke 43B.

  1. Take the Fluke 43B out of the case and connect the following:

    1. The power supply to the device and an electrical outlet.

      Figure 4. Powering the Fluke 43B.

    2. The test leads with the 4mm probe tips to channel 1.

      Figure 5. Connecting the 4mm Test Probes to the Fluke 43B.

    3. The current probe to channel 2 using the supplied BNC adaptor.

      Figure 6. Current probe adaptor for the fluke 43B.

  2. Turn on the Fluke 43B and configure the current probe by:

    1. Turn on the current probe to 10mV/A and make sure the Fluke 43B is setup to use the same by going to ‘Instrument Setup/Probes’ in the ‘Main Menu’.

      Figure 7. Current probes scaling selection and the Fluke 43B probe setup menu.

    2. Zero the current probe using the dial on the current probe and also note the arrow on the current probe to specify the currents polarity.

      Figure 8. Current probes zero adjustment knob and the arrow which indicates the currents polarity.

  3. Set the function preferences as follows:

    1. Harmonics (%f) (DC .. 21).

    2. Power (Full).

      Figure 9. Fluke 43B’s function preferences.

  4. Go through all of the menus of the Fluke 43B to familiarize yourself with how to operate the meter and what it can measure. Volts/Amps/Hertz, Power, Harmonics and the Scope are the meter features that you will use most in this lab.

    Figure 10. Fluke 43B’s Main Menu screen.

3.1.2 1ph Supply Box

A fused 15A 120Vac single-phase supply is available on the banana plugs and standard NEMA receptacle. The output voltage can be turned on/off by the light switch. Notice the red light indicating when the power is on. Make sure you use the larger 14AWG cable to supply this box.

Figure 11. 15 Amp power cable for the 1ph supply box.

Figure 12. 1ph Supply Box.

  1. Use the Fluke 43B to measure the output voltage (120V) and the operation of the on/off switch.
    – Is the supply working properly? If not notify a lab instructor or TA –

3.1.3 3 Phase Resistor Load Box

The load box is configured into 3 groups of 5 parallel switched resistors per group. A single switch controls a Resistor in each group simultaneously. Each group is not electrically connected to each other in any way. Each resistor has a rating of 225 watt at 150 ohm. So as you increase the number of switches/resistors in the circuit you are decreasing the resistance which in turn increases the current, power and load. The maximum rms voltage that can be put on this load box is 183Vrms.

Figure 13. 3-Phase Resistor Load Box.

  1. Use the Fluke 43B on the ohmmeter setting and connect it to one of the groups on the Resistor Load Box. Turn the switches on 1 by 1 while observing how the resistance changes. Try the other groups and such until you understand how the 3 Phase Resistor Load Box operates.

Note

It is good practice to begin experiments under light load power (small currents using a large load resistance). This means having only one switch on initially and as you further load your circuit (higher power by switching in more load resistors in parallel in the load box) you should carefully watch your currents and voltages to make sure none of the circuit ratings are exceeded.

3.1.4 3-Phase Diode-Bridge Rectifier Box

The 3Ph Diode-Bridge Rectifier Box is made up of three main components that can easily be configured to make several common rectifier circuits. These components include the three-phase diode bridge, a DC-link capacitor with a simple current limiting circuit and an ac-supply inductor/reactor.

Figure 14. 3-Phase Diode-Bridge Rectifier Box.

3.1.4.1 3ph-bridge Rectifier Diodes

Figure 15. The 3Ph bridge diode rectifier used inside the box.

  1. Use the Fluke 43B on the diode setting to measure all of the forward biased voltage drops of the diodes.

3.1.4.3 AC-Supply Inductor

Figure 18. The 3-phase reactor used as the AC-supply inductor which is inside the 3Ph diode-bridge rectifier box.

3.2 Measure Inductance

  1. Connect the circuit as shown in Circuit 1. Make sure the power is off.

    1. Connect the ac-supply inductor to the hot and neutral of the 1ph Supply Box as shown.

    2. Connnect the other end of the ac-supply inductor to the 3 Phase Resistor Load Box as shown.

    3. Parallel 2 groups/phases of the 3 Phase Resistor Load Box to increase the available load power which is also dependant on the number of Load box switches that are turned on.

    4. Use two separate green safety banana leads to connect the Earth ground from the 1ph Supply Box to the chassis grounds of both the 3Ph Diode-Bridge Rectifier Box and the 3 Phase Resistor Load Box. This is so the enclosures are Earth grounded for safety and to prevent possible electricution in the case of equipment failure.

Warning

Get a lab instructor or TA to check your circuit before you energize.

Circuit 1. Inductance Test Circuit for the AC-supply Inductor.
Click here to see a simulation demo of this circuit.

  1. Energize the circuit and continue to increase the number of switches until the current through the inductor is approximately 5 amps.

  2. To determine the individual inductance of the red and blue winding’s measure the current through and the voltage across each winding and record them in table 1 of the results section.

3.4 With Added Supply Inductor

  1. Add the supply inductor to your circuit as shown in Circuit 3.

Circuit 3. Full-wave Diode Rectifier with a DC-link Capacitor and an added AC-supply-inductor.
Click here to see a simulation demo of this circuit.

Danger!

Do not make changes to the circuit while power is applied.

You can move the Fluke 43B probes and change the load box setting while power is applied but please be careful.

Warning

If you turn off the power use the resistor switch as required.

  1. When you think your circuit is ready get an instructor or TA to check your circuit and sign off on your results page.

  2. Make sure the capacitor current limit switch is in the proper position for start-up.

  3. Make sure your load box only has one switch turned on.

  4. If your circuit is correct apply power wait 2 seconds for the capacitor to fully charge and then use the switch to short out the resistor.

  5. Complete the remaining portion of table 2 on the results page.

  6. Complete the entire column for one load setting before moving on to the next one.

  7. When you finish all of the measurements required for this section, turn off the supply, then reset the capacitor current limit switch and turn off all of the load box switches except one.

  8. Before you clean up make sure that you have everything completed properly to complete the lab report. Verify your results with an Instructor or TA and get them to sign your results sheet.

3.5 Clean-Up

Figure 20. Return safety banana lead and the test leads to the wall, place the Fluke 43B back in the case as shown and return the 4mm test probes to the box.

Figure 21. Leave the remaining equipment tidy on the workbench.

  1. If you are finished make sure you put everything back to where you got it before you leave.

  2. Remember to log-off or shutdown the computer.

  3. Have a lab instructor or TA sign your results sheet to ensure that you have cleaned everything up properly before you leave.

4 Post-lab

The following is what you are expected to hand-in approximately one week after completion of the lab, check eClass for the exact time and date. All reports need to be submitted to the appropriate link on eClass. You only have to hand-in one copy per group. Please have your pages in a single pdf file in the following order:

  • Use a scanned/picture of your ECE401 - Lab 1 - Sign-off sheet as your cover sheet. Make sure that you have obtained the required lab sign-off signatures at the bottom of the page. Also make sure that all of your group members names, CCID’s and lab section are visible in the table at the top of the page.

  • The completed ECE401 - Lab 1 - Results sheet .

  • The answers to the post-lab questions.

4.1 Questions

  1. Explain in your own words, what purpose the switch and resistor have that are placed in series with the capacitor and why you needed to follow the powering up procedure described in the lab? (5 marks)

  2. For the case without an ac-inductor being present, how does the value of the capacitor (e.g. large versus small) affect the circuit performance (consider factors such as θc, Ipeak, rms of Is, THD of Is, capacitor voltage ripple VR)? Give quantitative arguments to justify your response. (5 marks)

  3. What effect does adding the ac-inductor have on the circuit performance (consider factors such as θc, Ipeak, rms of Is, THD of Is, capacitor voltage ripple VR)? Give quantitative arguments to justify your response. (5 marks)

  4. What affect does increasing the load power have on the circuit performance? Note that a higher load power is associated with a lower physical resistance value. (Consider factors such as θc, Ipeak, rms of Is, THD of Is, capacitor voltage ripple VR)? Give quantitative arguments to justify your response. (5 marks)

  5. For the case without an ac-inductor being present, when the rectifier is under high load the supply voltage becomes distorted. Give a brief explanation as to why this happens. (5 marks)

  6. List three assumptions that are made in order to predict theoretically the performance of the for the full-wave capacitor-filter rectifier when using a 25 ohm resistor load. (5 marks)

  7. Consider the case where the load is 25 Ω and there is no ac inductor present. Try to explain the reasons for the differences between your theoretical predictions and the actual circuit performance? (5 marks)