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EE 410 – Power Electronics Laboratory

Fall 2010

Dr. Dale Dolan

Experiment #1 – Diode Rectifier Circuits

Group #3

James Tuccillo, Scott Carey, Rene Canedo

10/15/2010

EE 410 – Power Electronics Laboratory Experiment 1 – Diode Rectifier Circuits

Diode Rectifier Circuits Laboratory – A Power Electronics Laboratory Experiment

Purpose: This lab seeks to illustrate the fundamental operation of uncontrolled rectifier circuits. The waveforms associated with these circuits are visualized using simulation and experimentation. The circuit operating values obtained using theoretical equations are challenged through simulation and experimentation.

1. LIST OF EQUIPMENT

PC Computer with ORCAD PSPICE Schematic Capture and Simulation Fluke 37 Digital Multimeter Fluke Power Scopemeter 97 GWinstek GPM 8212 AC Power Meter Power Diode Module Capacitor and Resistor Miscellaneous Connection Leads

2. CIRCUIT DIAGRAMS

Figure 1 - Single-Phase Full-wave Rectifier With Resistive Load

Figure 2 - Three-Phase Full-wave Rectifier with Resistive Load

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3. PROCEDURE

3.1 Computer Simulation Procedure

In all simulations, use an ac source voltage whose line to neutral voltage Vs = 100 Vac-rms at 60 Hz, a resistive load of R=150ohm, and for step g) a capacitor C = 4,700 uF.

a. Simulate the circuits shown in Figures 1 and 2 on one schematic page. Use the ideal diode Dbreak found in the “Breakout” library.

b. Set the simulation time to 500ms. Run the simulation.c. Obtain and include in your report plots of output voltage waveforms by copying and

pasting the plots into Word (instead of printing them out). Ask the instructor if you do not know how to do this.

d. For both circuits, use the AVG() and RMS() functions in the Probe Window to obtain the averages and RMS values of the outputs, and their ratios (AVG/Total RMS). Do not print out or include these plots in your report. Compare the results to those obtained in the calculation section.

e. For both circuits, determine the input power factor.f. For both circuits, obtain input current and input voltage waveforms. Include (copy and

paste) only the current waveforms in your report. g. Add a 7,400uF capacitor in parallel to the resistor in each circuit. Also, to help with the

convergence problem, insert a 10m resistor in series with the capacitor. h. Repeat part b) through f), but change the simulation time to 20 seconds.i. By comparing the input and output waveforms of Resistive Load with Resistive/Capacitor

load, what conclusion can you draw as to the effect of adding a capacitor at the load?

3.2 Hardware Simulation Procedure

Background:

In this part of the lab, you will build the rectifier circuits that you simulated in the previous part by using a Power Diode module shown in Figure 3. Since this experiment uses relatively high power circuits, make sure that you have the instructor check your circuit before turning on the power. Also, make sure to turn off the bench power before making any changes to your circuit.

Figure 3 - Power Diode Module

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Preliminaries

a. Check the Power Diode Module The Power Diode Module consists of three dual-diode packages. Each package has

two diodes whose internal connection diagram is shown on one side of each diode pack. Look for this diagram.

Find the datasheet for the diode on the Internet. From the datasheet, find the current and voltage ratings of the diode.

Perform a quick visual inspection on the 3A fuses located in front of each diode package. Let the instructor know if any of the fuses are missing.

b. Use either a scopemeter of a multimeter in conjunction with the variac (located underneath each bench) to obtain an AC input power of 100Vrms line to neutral of phase voltage.

Single-Phase Full-wave Rectifier

c. Build a single-phase full-wave rectifier with 150 resistive load with an AC power meter connected at the input side. On the output side, connect an ammeter (using a multimeter) and a voltmeter using a scopemeter.

d. Using the scopemeter with DC coupling, sketch the output voltage (include the scope settings, i.e. volts/div, sec/div).

How does the waveform compare to the simulated result? Count the number of pulses on the output voltage per one period of the input

voltage. Measure the peak to peak ripple voltage on the output voltage. Determine the ratio (Average/Total RMS) of output voltage. How does it compare

with calculation and simulation results?e. Using the Current Probe Amplifier + Oscilloscope, obtain the input current waveform and

include it in your lab report.f. Determine the efficiency of the circuit.g. While the power is off, turn the variac all the way down to zero volts and add a 7400uF

capacitor in parallel with the resistive load. Turn the power on and turn the variac gradually to 100Vrms.

h. Using the scopemeter with DC coupling, sketch the output voltage (including the scope settings, i.e. volts/div, sec/div). How does it compare to the results obtained in d)?

i. Using the Current Probe Amplifier + Oscilloscope, obtain the input current waveform and include it in your lab report. How does it compare to the results obtained in e) Explain how the input current waveform changes from what you observed in e).

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CAUTION: When using the scopemeter, do NOT connect one channel to output voltage and the other channel to the input voltage.


Three-Phase Full-Wave Rectifier

j. Build a three-phase full-wave rectifier with 150 resistive load. Connect the input side (which is the secondary side of the bench transformer) in an ungrounded ‘Y’ connection. On the output side, connect an ammeter (using the multimeter) and a voltmeter, using the scopemeter.

k. Using the scopemeter with DC coupling, sketch the output voltage (include the scope settings, i.e. volts/div, sec/div). How does the waveform compare to the simulated result? Count the number of pulses on the output voltage per one period of the input

voltage. Measure the peak to peak ripple voltage on the output voltage. Determine the ratio (Average/Total RMS) of output voltage. How does it compare

with calculation and simulation results?l. Using the Current Probe Amplifier + Oscilloscope, obtain the input current waveform and

include it in your lab report.

4. CALCULATIONS

4.1 Prelab Calculations

1.1 For the single-phase full-wave rectifier, calculate:a. The average and total rms values of the output voltage when the AC input is

100 Vrms.

b. The ratio of (Average/Total RMS)

c. The input power factor assuming ideal diodes, and Rload = 150

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4.1 Prelab Calculations (Cont.)

1.2 For the three-phase full-wave rectifier, calculate:

a. The average and total rms values of the output voltage when the phase voltage (line to neutral) AC input is 100 Vac-rms.

b. The ratio of (average/total rms).

c. The input power factor assuming ideal diodes, and Rload = 150 .

pf in=Pin=outS in

=~V out

~I out3~V LN

~I f=0 .956 √2√3V f3⋅√2

√3⋅V f

=0.956

1.3 Which rectifier circuit do you suggest has better dc output performance? Better AC input performance?

The 3- rectifier circuit has better DC output performance due to the increased ripple frequency. By increasing the ripple frequency, filtering becomes easier as well as the average DC value increases.

The 1- rectifier circuit has better AC input performance due to its processing of a single component of input current. Since the source is delivering power on both the positive and negative half cycles, the source has a zero distortion power factor. This is seen in the power factor calculation above in question 1.1.

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5. DATA AND OBSERVATIONS

Resistive Load With Capacitor

Theoretical Simulated Experimental Simulated Experimental

Single Phase

Vrms (V) 100 98.5 97.6 85.6 DNR

Vdc-rms (V) 90.03 88.4 86.9 69.5 DNR

pf 1 0.991 NA 0.072 NA

Three Phase

Vrms (V) 234.0 234.4 269.7 211.65 NA

Vdc-rms (V) 234.0 232.2 267.0 210.27 NA

pf 0.956 0.93 NA 0.298 NATable 1: Output Voltage Summary for Theoretical Calculations, Simulated, and Experimental Results

Resistive Load With Capacitor

Theoretical Simulated ExperimentalSimulated Experimental

Single Phase Vdc-rms/Vrms 0.903 0.897 .890 1.000 DNR

Three Phase Vdc-rms/Vrms 1.000 0.990 0.989 1.000 NATable 2: Calculated Efficiencies for Output Voltages of Table 1

Single-Phase Full Wave Rectifier

Three-Phase Full-Wave Rectifier

# of pulses 2 6

Peak-to-peak ripple

146 (1.7 w/cap) 38

Table 3: Experimental Results for Output Voltage Pulses Per Single Input Voltage Period

The efficiency of the single-phase rectifier as asked in procedure step f) is the following:

%Efficiency=PoutPin

=60.14W63. 40W

=94 .9%

DNR = Did Not Record Quantitatively

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NA = Non-Applicable or Not Procedurally Called for Measurement

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6. GRAPHS

6.1 Simulation Graphs

Time

20.0ms 30.0ms 40.0ms 50.0ms 60.0ms 70.0ms 80.0ms 90.0ms 100.0ms 109.2msV(V1:+,0)

-200V

0V

200V4

V(D1:2,D3:1)0V

50V

100V

150V

SEL>>

Graph 1: Simulate Voltage Waveforms for Single-phase Full-wave rectifier with resistive load.Green (Vout) Red (Vin)

Time

19.90s 19.91s 19.92s 19.93s 19.94s 19.95s 19.96s 19.97s 19.98s 19.99s 20.00sI(V1)

-1.0A

0A

1.0A

SEL>>

-I(R1)0A

0.5A

1.0A

Graph 2: Simulated Current Waveforms for Single-phase Full-wave rectifier with resistive load. Top Graph (Iout) Bottom (Iin)

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Time

150.0ms 160.0ms 170.0ms 180.0ms 190.0ms141.2ms 198.7msV(D8:2) V(D9:2) V(D7:1)

-100V

0V

100V

-150V

V(D6:2,R2:1)200V

225V

250V

SEL>>

Graph 3: Simulated Voltage Waveforms for 3- Full-wave rectifier with resistive load no cap.Top (Vout) Bottom (Vin)

Time

200ms 210ms 220ms 230ms 240ms 250ms 260ms 270ms 280ms 290ms 300msI(V2)

-2.0A

0A

2.0A

SEL>>

-I(R2)1.4A

1.5A

1.6A

1.7A

Graph 4: Simulated Current Waveforms for 3- Full-wave rectifier with resistive load no cap. Top Graph (Iout) Bottom (Iin)

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Time

19.90s 19.91s 19.92s 19.93s 19.94s 19.95s 19.96s 19.97s 19.98s 19.99s 20.00sV(V1:+,0)

-200V

0V

200VV(D1:2,R1:1) - I(C2)+139

140

150

160

135

165

SEL>>

Graph 5: Simulated Voltage Waveforms for 3- Full-wave rectifier with cap in parallel with resistor. Top (Green=Output Voltage Red=Icap) Bottom (Vin)

Time

19.90s 19.91s 19.92s 19.93s 19.94s 19.95s 19.96s 19.97s 19.98s 19.99s 20.00s-I(R1)

920mA

924mA

928mA

932mAI(V1)

-40A

0A

40A

SEL>>

Graph 6: Simulated Current Waveforms for 3- Full-wave rectifier with capacitor in parallel with resistor. Bottom (Iout) Top (Iin)

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Time

19.90s 19.91s 19.92s 19.93s 19.94s 19.95s 19.96s 19.97s 19.98s 19.99s 20.00sV(D8:2) V(D9:2) V(D7:1)

-200V

0V

200VV(D7:2,D8:1) - I(C1)+234

230

240

250

260

SEL>>

Graph 7: Simulated Voltage Waveforms for 3- Full-wave rectifier with cap in parallel with resistor. Top (Green=Output Voltage Red=Icap) Bottom (Vin)

Time

19.90s 19.91s 19.92s 19.93s 19.94s 19.95s 19.96s 19.97s 19.98s 19.99s 20.00sI(R2)

-1.622A

-1.620A

-1.618A

-1.616A

SEL>>

- I(V2)-40A

0A

40A

Graph 8: Simulated Current Waveforms for 3- Full-wave rectifier with capacitor in parallel with resistor. Bottom (Iout) Top (Iin)

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6.2 Experimental Graphs

Graph 9: Experimental Input Current for Single-Phase Full-wave rectifier with resistive load (0.5A/(10mV/div))

Graph 10: Experimental Input Current for Single-Phase Full-wave rectifier with parallel capacitor and resistor (2A/(10mV/div))

Graph 11: Experimental Input Current for Three-Phase Full-wave rectifier with resistive load (0.5A/(10mV/div)

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Graphs 12 & 13: Output Voltage of Single-Phase Full-Wave Rectifier Circuit. Without Capacitor (Left) With Capacitor (Right)

Graph 14: Output Voltage of Three-Phase Rectifier Circuit. Note that there are 6 pulses for each period of the output waveform signal.

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7. DISCUSSION

Single-Phase Full-Wave Rectifier The single-phase waveform with purely resistive load shown in Graph 9 looks very similar to the simulated result shown in Graph 1. Notice how there are two “pulses” for each input voltage period. Also, both of these current waveform graphs appear to have a pure sinusoidal form. This is due to the unity power factor operation of the single phase full-wave bridge rectifier circuit.

When the capacitor is added to the circuit as shown in Graph 10, the input current becomes more spiked and less sinusoidal. This is because the conduction time of the diode decreases the time where the diode current is following the voltage waveform as well as the effects of the capacitor. As the waveform becomes more peaked and less sinusoidal, the power factor begins to stray from unity. The output voltage waveform, Graph 13, shows how the output capacitor “holds” the output voltage during the off-cycles and linearly discharges during that period. During the positive half cycle, or “on” state, the capacitor is charged to the maximum value of the input voltage minus the diode forward conduction drop.

Three-Phase Full-Wave RectifierFor the three-phase full-wave rectifier circuit it can be seen that the input current waveform in Graph 11 looks very similar to the simulated result in Graph 4. The non-sinusoidal nature of this graph, as indicated by a small dip in the middle of the conducting period, shows that this circuit has contributed a harmonic to the input current signal. The creation of this harmonic is due to the switching of the input current from a conducting to an off state almost instantaneously. From the output voltage waveform shown in Graph 14, it is seen that the output voltage has 6 pulses per one period of input voltage. It is also shown that the output voltage following the three-phase line-to-line voltage of the transposition of the three voltage phasors.

8. CONCLUSION

Altogether, this lab illustrated the operation and behavior of uncontrolled diode rectifier circuits namely, the single-phase full wave rectifier and the 6-pulse three-phase full wave rectifier circuit. Through theoretical calculations the team was able to predict the circuit operating values and roughly sketch the types of expected waveforms. While this analytical method proved to be useful in establishing the mathematical principles, it was the simulation that truly gave the group the visual grasp of the circuit’s operational behavior. Finally, through experimentation the circuit was realized and implemented using real electronic circuit components. By implementing these circuits in laboratory, we were able to confirm the design and operation of the circuits from a high level understanding to a device performance level as seen in the non-ideal characteristics of the diodes (dead time and forward voltage drop).

This lab also let us accomplish prerequisite learning objectives such as reviewing our understanding of three-phase power concepts and the use of current and voltage probes for oscilloscope analysis. Another important understanding we gained was that of electrical safety. By working with capacitors and high AC voltage, we learned the proper attitudes and respect to have when dealing with >120V AC.

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9. SIGNATURES

_______________________ ________________________ ________________________Name Signature Date

_______________________ ________________________ ________________________Name Signature Date

_______________________ _______________________ _________________________Name Signature Date

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