SIMULATIONS WITH THE BOOST TOPOLOGY EE562: POWER ELECTRONICS I COLORADO STATE UNIVERSITY. Modified February 2006

Transcription

1 SIMULATIONS WITH THE BOOST TOPOLOGY EE562: POWER ELECTRONICS I COLORADO STATE UNIVERSITY Modified February 26 Page 1 of 24

2 PURPOSE: The purpose of this lab is to simulate the Boost converter using ORCAD to better familiarize the student with some of its operating characteristics. This lab will explore some of the following aspects of the boost converter: Discontinuous Conduction Mode Inductor sizing Differential voltage across the inductor Time it takes for the converter to reach steady state Output Ripple voltage and selection of the capacitor. Ripple current through the capacitor Equivalent Series Resistance (ESR) of the output capacitor. Effects of changing and removing load resistance Effects of the ON resistance of the switch Efficiency Effects of changing frequency NOTE: The simulations that follow are intended to be completed with ORCAD Capture CIS. It is assumed that the student has a fundamental understanding of the operation of ORCAD. ORCAD provides tutorials for users that are not experienced with its functions. PROCEDURE: Build the schematic shown in Figure 1. V1 is a DC voltage source (VDC) from the source library. It needs to be set for 24 volts. L1 is an ideal inductor from the Analog Library. Set for 1µH. R1 is an ideal resistor from the Analog Library. Set for 1kΩ. D1 is an ideal diode (Dbreak) and can be found in the Breakout library. C1 is an ideal capacitor from the Analog library. Change the value to 1µ F. Page 2 of 24

3 S2 is a voltage controlled switch and can be found in the Analog library. Change RON from 1Ω to 1mΩ. V2 is a pulsed voltage source and is intended to act as the output of a pulse width modulator. V2 needs the following parameters set: DC=, AC = 1, V1=, V2= 1, TR=1ns, TF=1ns, PW = 2µ, PER = 4µ. This results in a switching frequency of 25 khz. R2 Set to 1 kω. The purpose of R1 is to prevent any floating nodes. Two voltage markers need to be placed as shown in the schematic of figure 1. Figure 1 Boost schematic ORCAD. Once the above schematic is built simulations can be ran. First, the type of simulation will need to be specified. Most of these simulations are Transient simulations. The Transient simulation can be set by selecting PSpice on the menu then New Simulation Profile. The Run Time will need to be set to 1µsec. Page 3 of 24

4 Figure 2 Transient Analysis setup. Running the simulation will result in the following output. Figure 3 Page 4 of 24

5 Remove the voltage markers, and use a current marker to measure the inductor L1 current. Place the marker in series next to L1. Figure 4 QUESTION 1: What is the peak operating current, and what is the operating mode of the converter? Verify mathematically the mode and the peak current. 2L 2 Hint: K =, Kcrit D(1 D) RTs =, Vin = L Ipk DTs Figure 5 Page 5 of 24

6 QUESTION 2: What is the output voltage of the converter at steady state? Verify your results mathematically. Hint: 1+ Vout = Vin 4 D1 1+ K 2 2 Figure 6 Page 6 of 24

7 Now change L1 from 1µH to 1mH and rerun the simulation. Remember you can vary the Final Time in Transient Analysis. Keep the Print Step at. (Hint: Start this analysis with a Final Time = 1msec) QUESTION 3: What is the peak operating current now? What is the operating mode of the converter (remember that you can observe this by zooming in)? Also, verify the mode mathematically. Figure 7 Page 7 of 24

8 QUESTION 4: How long does it take for the converter to reach steady state? What is the peak inductor current during steady state? Verify peak current result mathematically. Hint: Vin = L Ipk DTs Figure 8 QUESTION 5: Calculate the size of the inductor required to put this converter in CCM. Hint: R Ts D(1 D) L 2 2 Page 8 of 24

9 Remove the current marker and add a differential voltage marker across L1. Change the Run to time to 18u and Start saving data after 15u. Figure 9 QUESTION 6: What can be said about the differential voltage measurement across L1? Figure 1 Page 9 of 24

10 Now change the Final Time to 25µ and remove any No Print Delay from the Transient Analysis setup. Remove the differential voltage markers across L1 and add a voltage marker to the top of C1. From this simulation we can see the output voltage stair step up to its final value. Figure 11 QUESTION 7: How long does it take for the output voltage to reach its peak? Figure 12 Page 1 of 24

11 QUESTION 8: How long does it take for the output voltage to reach its final value? What is the output voltage? Prove your simulation results mathematically (Vout). Hint: 1+ Vout = Vin 4 D1 1+ K 2 2 Figure 13 Now run the simulation for 1 µsec at a time greater than 2 µsec. QUESTION 9: What is the peak-to-peak ripple voltage? Figure 14 Page 11 of 24

12 QUESTION 1: With everything else left as is, what is the minimum output capacitance be to limit the output voltage ripple to 2 volts peak to peak? Figure 15 Now, place a current marker on one of the pins of the capacitor. Run the simulation for 2 µsec at a time greater than 1 msec. QUESTION 11: What can be said about the current through the capacitor? Figure 16 Page 12 of 24

13 QUESTION 12: If the ESR of the capacitor is modeled by a 1Ω resistor in series with the capacitor. What happens to the output voltage ripple and the capacitor current? Figure 17 Figure 18 Page 13 of 24

14 Figure 19 Page 14 of 24

15 Change the load resistance from 1kΩ to 1Ω with C=1µFand L=1mH. QUESTION 13: What happens to the inductor ripple current, capacitor ripple voltage, and capacitor current with respect to the original values? Figure 2 Figure 21 Page 15 of 24

16 QUESTIONS 14: What operating mode is the converter in now? QUESTION 15: What happens if the load resistance is removed? Figure 22 Figure 23 Replace the load resistance. QUESTION 16: What observations can be made from increasing the on resistance of the switch? Page 16 of 24

17 Figure 24 Figure 25 *Remember that your on resistance value of the switch will provide you a complete different output value from your classmates. QUESTION 17: What can be said about the efficiency of the converter? (Comment on the different configurations of the circuit used throughout this lab.) η = Pout Pin η = ( Vo Vg)*(1 D) Page 17 of 24

18 QUESTION 18: What can be observed by increasing the switching frequency to 1KHz? Hints: With everything else left as it is, change your PW and PER on PULSED voltage to 5u and 1u. Also change your Run to time in the simulation profile to 1 finaltime := 25 Switchfrequency. Figure 26 Page 18 of 24

19 Vg := 24 V L := H C := F R := Ω Duty cycle Switchfrequency := Hz 1 T := Switchfrequency PW := Duty cycle PW T = D f D := Switchfrequency PW D =.5 The output voltage Vo Vg 1 1 D 1 Vg 1 + D 1 Vo := 1 + Vg D Vo = 48 Inductor current Vin L il D T 1 il:= L Vg D T il = 48 Vo Io := R Io =.48 Page 19 of 24

20 IL := Io 1 D IL =.96 ILmin:= IL il ILmin = ILmax:= IL + il 2 ILmax= t := D T D T ( 1 D) T ( 1 D) T ( 1 D) T T T VL:= Vg Vg Vg Vg Vo Vg Vo Vg Vo Vg Vo Vg t1 := D T D T T IL1:= ILmin ILmax ILmax ILmin 4 Inductor voltage 4 inductor current inductor Voltage V VL 2 2 inductor current A IL1 2 2 ILmax is := id := t duty cycle ILmin ILmax ILmin t1 duty cycle ic := Io Io ILmax Io ILmax Io Page 2 of 24

21 capacitor current (A) ic Capacitor current t1 duty cycle Icmax:= ILmax Io Icmax = switch current diode current Vs. duty cycle 4 current A is 2 2 diode current (A) id t1 duty cycle Is := D IL Is = t1 ID duty := ( 1 cycle D) IL ID =.48 2 L K := K = R T Kcrit := D ( 1 D) 2 Kcrit =.125 D1 :=.1, DC gain for K>Kcrit V Vg 1 ( 1 D) M( D1) := 1 ( 1 D1) M1( t) := t 2 K Page 21 of 24

22 1 DC gain V/Vg M( D1) D1 Duty cycle 1 Vo := C Io D T Vo = for K<Kcrit DC gain vs. duty cycle 6 DC gain M1( D1) D1 duty cycle Page 22 of 24

23 Input and output Power Po := Io Vo Po = 2.34 W Ig := IL Pg := Ig Vg Pg = 2.34 W Efficiency η Pout pin Vo η := Vg ( 1 D) η = 1 DCM/CCM boundary Case 1: When inductor, switching frequency and other circuit parameters are constant, but R is varied ilmin:= ilmax:= il il il1:= 2 Io1 := ( 1 D) il1 il1 = 24 Io1 = 12 Vo R := R = 4 Io1 inductor current Vs. duty cycle 6 IL1:= ilmin ilmax ilmax ilmin inductor current IL t1 duty cycle Case 2: when R, switching frequency and other circuit parameters are constant, but L is varied ilmin:= ilmax:= 2 IL ilmax=.192 il:= ilmax Page 23 of 24

24 1 Lmin := il Vg D T Lmin = il2:= ilmin ilmax ilmax ilmin.2 il t1 R T D ( 1 D) 2 L1:= 2 L1 = Page 24 of 24