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Department of Electrical and Computer Engineering Queens University

ELEC 431: Power Electronics

Fall, 2011 Group number: _______________________ Student names (ID): ____________________; ______________________; _________________ Lab date: _______________________

Lab #1: DC-to-DC Buck Converter Objectives: 1. Using PSIM to simulate the operation of DC-to-DC Buck converter 2. Testing the operation and performance of DC-to-DC Buck converter Instructions: There are two parts in this lab. The first part is computer simulation and the second part is circuit connecting and lab testing. The lab report is at the end. Please note, the first part (computer simulation) should be finished BEFORE the second part starts. Part 1: Computer Simulation Using schematic capture tool of PSIM, build a DC-to-DC Buck converter as shown in Fig.1. The input voltage is Vin = 140V. The input inductance value is Lin = 0.8H. The output inductor value is Lout = 0.8H. the load resistor value is R = 300. The output capacitor value is 15F. The following waveforms should be monitored: output voltage Vout, output inductor current Iind, current through MOSFET, Ids and voltage across MOSFET, Vds and the voltage across diode Vd, the gate drive signal for S1, Vpwm. The gate drive signal is obtained by a saw-tooth voltage source, a DC voltage source and a comparator, as show also in Fig.1. The switching frequency is set by the saw-tooth frequency at 1KHz. Please save the circuit as Lab1_Buck.sch. Please set the duty cycle of Vsw to 0.995. (do you know why?) (1) Set duty cycle at D = 50% by setting Vduty at 0.5V, simulate the steady state operation of the

circuit, plot the waveform of Vpwm, Vout, Vds, Vd, Iind. Please put no more than 3 screens in one graph. It is suggested that total time = 0.5(Second), print time = 0.49(Second) to get steady state waveform.

(a) Measure the average value and peak-to-peak value of Vout, (b) Measure the average value, peak-to-peak value and rms value of Iind (c) Measure the peak value and rms value of the MOSFET current (d) Measure the peak value and average value of the diode current

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(2) For D = 0.15, 0.3, 0.45, 0.6, 0.75, 0.9 simulate the steady state operation of the circuit, measure the following parameters and fill in the result to Table 2.

(a) Average value of Vd, average value of Vout, average value of Iind, peak-to-peak value of Iind and rms value of Iind

(b) Comment on the above simulation result (3) For load condition of R = 300, we want to maintain the average value of the steady state output

voltage equals to 90V, i.e., Vout(avg) = 90V. Determine the duty cycle value if Vin = 140V. Measure the peak-to-peak inductor current at this condition. If the input voltage change to Vin = 140V - 20% = 112V, what is the required D value? Measure the peak-to-peak inductor current at this condition. If the input voltage change to Vin = 140V + 20% = 168V, what is the required D value at this time? Measure the peak-to-peak inductor current at this condition. Fill in table 3. Please comment on the result in Table 3.

Fig.1 Buck converter

Part 2: Lab testing:

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Connect the Buck Converter according to Fig. 2. Use data acquisition system to monitor the following waveforms: Vin, Vd, Vout, Ids, Id and Iind. Use E1 to monitor Vin, E2 to monitor Vout, E3 to monitor Vd, I1 to monitor Ids, I2 to monitor Id, I3 to monitor Iind. Set ch1 to E1, ch2 to E2, ch3 to E3 and ch4 to I1, ch5 to I2 and ch8 to I3. Adjust the switching frequency to 1000Hz. Apply the max input voltage. (1) For D = 0.5, plot the following waveforms: Vd, Vout, Ids, Id, and Iind (2) Measure the average value of output voltage for D = 0.2, 0.4, 0.6 and 0.8 and fill in Table 4.

Fig.2 Test Circuit Connection

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Lab Report Part 1: Computer simulation results: 1. Print out the circuit schematic used to simulate the Buck converter 2. Print out the steady state waveforms of Vds, Vd, Ids, Id, Iind, Vpwm at D = 0.5

Fill in the following table for simulation task (1) Table 1:

Vout avg Vout pp Iind avg Iind pp Iind rms Ids pk Ids rms Id pk Id avg

3. Fill out the following table for simulation task (2) Table 2:

D 0.15 0.3 0.45 0.6 0.75 0.9 Vd avg

Vout avg Iind avg Iind pp Iind rms

Comment on the above simulation results: 4. Fill out the following table for simulation task (3) (Vo avg = 90V) Table 3:

Vin (avg) 112 140 168 D

Iind pp Comment on the above simulation results:

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Part 2: Lab testing results:

(1) Print out the waveform of Vout, Vds, Vd, Ids, Id and Iind at D = 0.5 (2) Record the measurement data at Table 4

Table 4: Measured average value of output voltage and rms value of the input current

D (target) 0.2 0.4 0.6 0.8 D (actual) Vout avg

ELEC 431: Power ElectronicsLab #1: DC-to-DC Buck ConverterPart 1: Computer Simulation