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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications Lab 3: Single-Phase Half-Wave Rectifier Jake Blair A01322231

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications Pre-Lab:

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications

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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications Objective The objectives of this lab are to:  learn how to use the power equipment, including voltage source converter (VSC), variac, load bank, capacitive filter, power analyzer, and digital multimeter (DMM).  observe the behavior of diodes.  learn the behavior of a half-wave rectifier. Safety Considerations and Rules You will be working with high voltages in this lab. The utmost professional behavior and attention to safety concerns are expected. Here are some points that you are expected to respect in the smart grid lab (SW3-2750):  Safety glasses are mandatory when working on live equipment (unless you have prescription glasses)  The default option for the circuit breaker in each station is to be off and locked.  You will be allowed to turn the circuit breaker on only after your circuit is checked by the lab instructor.  You are expected to attend the labs on time. Any delay will be penalized by mark deduction. You will not be allowed in the lab 20 minutes after the lab start time.  Prelabs are due before the lab start time.  For each lab, you will be working in a group of 2-3 (preferably 2). Each group member is expected to participate equally in the lab experiment.  Group members can use the same data for their lab reports, however separate individual reports are required. Any instance of plagiarism will be penalized based on BCIT’s code of ethics.  No foul play is tolerated in the lab. Equipment  Three-phase rectifier (External Rectifier) (used as a single-phase rectifier in this lab)  Capacitors: Filter Bank capacitors  Three-Phase Load Bank (used as DC load)  Variac (autotransformer)  Power Analyzer  Digital multimeter Pre-Lab (1 Mark)  Open the HW_Rectifier.slx SIMULINK file. Set the transformer’s winding ratio such that the secondary voltage is 30 V rms. Click on the scope input lines and add your two-letter initials. Change the R and C parameters according to the following table: V o,rms V o,dc No Capacitor (R=250/3 Ω) 20.76 13.16

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications 10 uF (R=250/3 Ω) 20.79 13.48 40 uF(R=250/3 Ω) 21.92 16.95 120 uF (R=250/3 Ω) 27.03 25.32 120 uF (R=250 Ω) 34.11 33.78  Capture the scope waveforms for all five cases. You will receive 0 marks if your initials do not appear on the waveform legends.  Deliverables: table and the waveforms in a file. (Waveforms should have your initials) Lab Performance (2 Marks)  Attendance: 0.5 mark  Participation: 0.5 mark  Safety: 0.5 mark  Cleaning: 0.5 mark Lab Report (10 Marks)

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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications Part A – Single-Phase Half-Wave Rectifier (3 Marks) The purpose of this section is to verify half-wave rectifier operation. 1. Perform a continuity check using DMM on fuses of the variac. Place the fuses back properly after checking. 2. (0.5 Mark) Using your multimeter, determine the forward voltage drop, 𝑉 ௙஽ , for each diode in the external rectifier. You will need to measure 𝐴 𝑡𝑜 + , 𝐵 𝑡𝑜 + , 𝐶 𝑡𝑜 + and − 𝑡𝑜 𝐴 , − 𝑡𝑜 𝐵 and − 𝑡𝑜 𝐶 to obtain these measurements. To do so, you use the diode option of DMM and connect the probes to the anode and cathode of each diode. D 1u D 1l D 2u D 2l D 3u D 3l V fd 0.529 0.529 0.528 0.528 0.528 0.529 3. We use the external rectifier in this part. a. Connect the D 1u diode of the external rectifier between the variac and the load. L 1 L 2 N D1u D1l D2u D2l D3u D3l A B C + - External Rectifier 4. We would like to measure the source and load voltages at the same time. To do so connect L 1 of power analyzer to the variac output and L 2 port of the power analyzer to the high end of load. N port of power analyzer is connected to the neutral. a. We need to change the electrical hookup setting of the power analyzer to a setting with L 1 L 2 N split-phase three wires). Press enter to save the setting. b. The current clamp of the power analyzer measures the load current. 5. Set the load resistance to 250/3 Ω. 6. Ask the lab instructor to check your circuit and then you may turn the power on. 7. (0.5 Mark) Change the variac knob to set the source voltage to 30 V rms. Check the rms voltage with the power analyzer. Now, we need to measure the output voltage. a. Measure the V rms and V dc of the output. If we assume ideal diode performance, Vrms of the output should be around V pk,in /2. Vdc should be equal to V pk,in /π. Are the experimental values close to the approximate theoretical values? Is this a good rectifier? Can we use the output voltage as a DC source? i. Vrms = 30.2 ii. 40/2 = 20, Vout = 20.5V iii. 40/pi = 12.7, Vdc = 12.9V

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications iv. The experimental values are close to the theoretical values, however the output is not purely dc therefore not a good rectifier. b. Please note that the power analyzer calculates THD values for an AC signal, assuming the desired component is the fundamental (1 st harmonic) component. In section 1 of the course, when we deal with AC to DC conversion; therefore, the desired component is the DC signal. The formulas that we have for THD for the rectifiers in the lecture notes are different from the values you see from the power analyzer. Use V rms and V dc readings to calculate THD of the rectifier output ( 𝑽 𝒂𝒄,𝒓𝒎𝒔 𝑽 𝒅𝒄 = ට𝑽 𝒓𝒎𝒔 𝟐 ି𝑽 𝒅𝒄 𝟐 𝑽 𝒅𝒄 ) . Is the calculated value close to the theoretical value (121%) seen in the lecture notes? THD = 45.5% measured. Sqrt(20.5^2 – 12.9^2)/12.9 * 100% = 123.5% Much better than power analyzer readings. 8. (0.5 Mark) Go through different output harmonics using the right and left buttons on the harmonic screen and find their relative value for the following harmonics: RMS value of the harmonics DC (zero harmonic) 13.7 Fundamental (1 st harmonic) 15.7 2 nd 6.6 3 rd 0.3 4 th 1.7 5 th 0.4 6 th 0.2

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications 7 th 0.3 9. (0.5 Mark) Use DMM to measure AC rms and DC voltage values. a. Compare the RMS and DC values read from the DMM and power analyzer. Note that DMM measures 𝑉 ௔௖,௥௠௦ , and power analyzer can measure 𝑉 ௥௠௦ . 𝑉 ௥௠௦ = ට𝑉 ௔௖,௥௠௦ ଶ + 𝑉 ௗ௖ ଶ . Measured ACrms and DCrms ACrms =30.41 DCrms = 16.27 10. Looking at the two voltage waveforms, make a comment on when the diode is forward or reverse biased. a. For what portion of a cycle, the diode is forward biased? Hint: On the signal display screen (RMS tab), U voltage is the voltage difference between L 1 and L 2 (in this case V 1 -V 2 ). In this case, V 1 is the anode voltage and V 2 is the cathode voltage. Therefore, U=V anode - V cathode is the voltage across the diode. i. The diode is forward biased whenever the input voltage is greater than 0.5V as that will make it greater than the cathode side accounting for the 0.5V drop. b. When the diode is forward biased, anode and cathode voltages are ideally the same. However, we know that there is a voltage drop between the two ends of the diode. You measured V fd in a previous section. Looking at U, determine if V 1 -V 2 is always equal to V fd when diode is forward biased or changes (Use the right and left button to move the cursor)? Is this voltage drop change related to the current value? Hint: in addition to V fd , diodes have a voltage drop due to R on . i. The Vfd is greater than measured at the beginning of the lab. Diodes have similar aspects to resistors, therefor increasing the current will increase the voltage drop.

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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications U = 21.8V Vout = 20.9 Vfd = 21.8 – 20.9 = 0.9 Diode Vdrop = 0.529 11. Turn the power off and put the current ports of the DMM in series with your resistor (instead of output of variac directly connecting to the load, the DMM ammeter should be between them). Ask your lab instructor to check your circuit before turning the power on. 12. (1 Mark) Compare the current measurements of the measurement devices in the lab: Current measurement DMM Power Analyzer (I ac,rms ) I ac,rms I dc R = 250/3 ~ 83 Ω 0.196 0.159 0.2 Note that the current clamp sensor cannot measure DC currents. That is why the current waveform is shifted down (resulting in zero average over one period). 13. Turn the power off and remove the DMM from your circuit and connect the DMM voltage probes back.

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications Part B – Single-Phase Half-Wave Rectifier with Capacitor (4 Marks) 2 marks for the waveforms and 2 marks for the tables 1. In this part, we want to see the impact of adding a capacitor filter. The load resistance is still 250/3 Ω. The voltage output of the variac is 30 V rms. 2. Fill out the first row of the table below based on your previous measurements from part A. Hint: You can find t d which is the time that diode is disconnected (reverse biased) by looking at U. V rms V dc t d (diode reverse biased) No Capacitor 20.5 13.3 8.5 10? uF 20.5 13.3 8.3 40? uF 20.8 13.3 8.1 120? uF 22.6 17.8 5.7 120? uF (R=250 Ω) 28.1 26.5 5.0 1/60 – 8.2e-3 No _ capacitor:

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications 120uf: 120uf _ & _ 250ohm: capture 3. Put the 10 uF capacitor of the filter box in parallel with the resistive load (Use port A of the capacitors as shown below).

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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications 4. To power up the filter box, take a connection of the 24 V voltage ports of the VSC box to the filter box. Make sure that the switch at the back of the VSC box is on. Measure the exact capacitance using the DMM (Ω option + the yellow button) to find the exact value. a. 10uF 5. Ask your instructor to check the circuit before turning the power on. 6. Complete the measurements in the table for this case. Capture the voltage and current waveforms of the power analyzer. 7. Turn the power off. 8. To increase the capacitance, we put the 30 uF and 10 uF capacitors in parallel (C eq =C 1 +C 2 ). To do so, we need to turn the S 1a and S 2a switches on. We can do that by connecting their contactors to 24 V as shown in the picture. Measure the exact capacitance using the DMM. a. 40uF 9. Ask your instructor to check the circuit before turning the power on. Complete the measurements in the table for this case. Capture the voltage and current waveforms of the power analyzer. 10. Turn the power off. 11. By making all three capacitor sets parallel (connecting the ends of the capacitor sets as shown in the picture) and turning all S 1* and S 2* (six switches in total) switches on, we can increase the capacitance to 120 uF (3*(30+10) uF). Measure the exact capacitance using the DMM.

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications a. 120uF 12. Ask your instructor to check the circuit before turning the power on. Complete the measurements in the table for this case. Capture the voltage and current waveforms of the power analyzer. 13. Now, change the resistor value to 250 Ω and complete the measurements in the table for this case. Capture the voltage and current waveforms of the power analyzer. Why do we get higher DC content for light loads (light load means lower current or higher R)? Hint: What is the time constant of an RC circuit? a. Increasing the resistance creates a larger time constant meaning the capacitor takes longer to de-energize making the voltage more like dc. Part C – Downloading the Data Here are the steps we used to successfully use the AEMC software within AppsAnywhere to detect the analyzer: 1. Do NOT connect the analyzer to the computer before starting the software. 2. Start AppsAnywhere and then launch the AEMC PowerPad III software. 3. Do NOT select yes when asked to upgrade the software to the latest version. 4. Once the software has started, wait for 5 minutes so the software can initialize. 5. Now connect the analyzer to the USB port of the computer. The ports on the computer itself are much more reliable than the ports on the display. 6. Within the software select Connect Instrument . The number of the model of the analyzer should be visible as an option, i.e., 8336 . If you don’t see the analyzer model number, restart the computer, and try the steps again from the beginning. 7. Proceed with your data upload. If you happen to connect the analyzer to the computer before you start the software, you will have to restart the computer, and then start over. Analysis Questions (3 Marks) 1. (0.5 Mark) Explain why the THD values read from the power analyzer cannot be used to determine the harmonic output of a rectifier. How can we measure the harmonic distortion of a rectifier output voltage based on V rms and V dc readings? a. The power analyzer only measures the AC component of the signal, this offsets the THD by a great amount. The way to measure THD with Vrms and Vdc is with the equation: ( 𝑽 𝒂𝒄,𝒓𝒎𝒔 𝑽 𝒅𝒄 = ට𝑽 𝒓𝒎𝒔 𝟐 ି𝑽 𝒅𝒄 𝟐 𝑽 𝒅𝒄 ) 2. (0.5 Mark) Draw the ideal and non-ideal voltage-current characteristic of a diode. Explain the importance of the following diode parameters V fd , R on , R off , leakage current, and reverse breakdown voltage.

BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications a. Vfd is how much voltage the diode drops or how much voltage is needed before the diode begins to allow current through. b. Ron is the diodes effective resistance when forward biased, as when a diode is forward biased it acts like a very small resistance, the smaller the better as there will be less voltage drop. c. Roff is the diodes effective resistance when reverse biased, as when a diode is reverse biased it acts like a very large resistor, the bigger the better as then there will be less current flowing when the diode is “off”. d. Leakage current is the very small amount of current that flows through the diode when it is reverse biased, an ideal diode does not have this so minimizing it is best. e. Reverse breakdown voltage is the voltage at which the diode starts conducting in reverse, if the voltage exceeds this it can cause permanent damage to the diode. f. 3. (0.25 Mark) Is the following equation true for any signal: V rms =V pk /√(2)? Explain. a. The equation is only true for a sinusoidal signal with no dc offset. 4. (0.25 Mark) As the value of a capacitor increases, what happens to its time constant? What is the impact of increasing C on t d ? a. Increasing the capacitance increases the time constant which increases td making the capacitor de-energize slower which is more like a dc signal. 5. (0.5 Mark) Compare the values of harmonics measured in Part A.8 with the simulation result you did for the prelab for the no capacitor case. Note that the Fourier block gives you the harmonic amplitudes (peaks), not the RMS. a. The Vdc was very similar, less than 0.6 off however the Vrms was off by quite a bit. 20Vrms to 15Vrms 6. (0.25 Mark) Time constant of an RC circuit is 𝜏 = 𝑅𝐶 . Does it make sense to increase the resistance instead of the capacitance to improve the power quality and lower the harmonic content? a. The resistance is the load, most rectifiers should work for varying loads which are typically quite small, this makes increasing the resistance not ideal.

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BCIT ELEX 4420 – Power Electronics and Renewable Energy Applications 7. (0.25 Mark) Explain how increasing the filter capacitance impacts V rms , V dc , t c , t d , and THD of a rectifier output. a. increasing filter capacitance in a rectifier circuit generally leads to a smoother DC output with reduced ripple, higher average DC voltage, longer charging and discharging time constants, and lower total harmonic distortion. 8. (0.5 Mark) Using the measurements from the power analyzer for part B, calculate the following values: ට𝑉 ௢,ோெௌ ଶ − 𝑉 ௢,஽஼ ଶ /𝑉 ௢,஽஼ 𝜃 ௗ = 2𝜋 𝑇 × 𝑡 ௗ No Capacitor 117 3.20 10? uF 117 3.12 40? uF 120 3.05 120? uF 78.2 2.15 120? uF (R=250 Ω) 35.2 1.88