ECE 628 Experiment 8

ECE 628 Experiment 8 - Elferfmen‘t‘ 5 H-Bridge PWM...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Elferfmen‘t‘ 5 H-Bridge PWM Converter Switching of N—Channel Power MOSFETS BB 628 (Power Electronics Lab) Department of Electrical Engineering Ohio State University I. Introduction In this lab, we study the switching strategies of H~bridge PWM converter. Half—bridge and full-bridge operation with PWM bipolar and unipolar switching are examined. N-channel power MOSFETS H-bridge motor drive is used for the speed control of a DC motor. II. N-Channel Power MOSFET H-Bridge Description In the last lab, complementary P-channel and N-channel MOSFETs were used for a simplified gate drive circuit; however, P—channel MOSFETS have higher on resistance or are larger and more expen» sive. Motorola N-channel H-bridge motor drive used in this lab is well designed to minimize date drive complexity. Its features include: 0 User friendly isolated I CePAK TM package; 0 MOSFETS advantages (fast switching, large SOA, etc); 0 High input impedence; 0 Low on resistance; 0 Versatile and multi-purposes. The N-channel Power MOSFETS used can drive 24V to 48V voltage and 8A continuous current. RD5(°") < 40mg: Vbreakdown = Study the attached circuit schematics (Fig. 5). Design considerations: 0 Charge pump: drives upper N—channel MOSFETs above motor voltage (greater than 12V above motor rail at all speeds). 0 Gate drive impedeance optimization: to separate turn-on and turn-ofi‘ times, solving diode snap and shoot—through current. 0 Interface: use single voltage source (15V); closs~coupled NAND gates protection; NAND inputs compatible with 5V HCMOS'logic; half-bridge current sense (lOOch,) with low pass filtering; grounding for current sense, microcontroller and instrument). III. Switching Alternatives Fig. 1 shows the simplied H—bridge converter. It can be used as a. DGDC converter or a DC~AC converter. In DC—DC converter application, the following switching strategies will be studied: I. Single PWM: This is the gate drive scheme used in the last lab in the halfebridge operation. Only one of the bottom two MOSFETS is selected to be PWMed. 2. Bipolar PWM: Full-bridge operation. (TA+,TB-) and (TA._,TB+) are switched in pairs. 3. Unipolar PWM: Full-bridge operation. The two bridge legs are controlled independantly of each other. FIGURE Fuu~bridge dc—dc converter. For the specific design of the motor drive we use, Single PWM switching suites the best, since due to the limitations of their gate drives, the top MOSFETs turn-on speed is slower than that of the bottom ones, resulting in greater switching losses. In pratice, among the three strategies, the Unipolar PWM switching produces the best output voltage waveform with reduced ripples. IV. Procedures 1. Set the function generator to produce a square PWM signal with 0 to 5V peak-topeak, IkHz and a duty-cycle of about 50%. 2. Connect the circuit composing of the drive board, the DC motor, the function generator and the drive power supplies (see Fig. 2). Supply “A TOP” of the drive board with high (5V). 3. Double check the circuit connection carefully. Turn on the power of the breadboard. Check the direction of the motor. Observe and plot the output voltage and the output current. 4. Disconnect the “A TOP”. Supply “B TOP” with high. Check the direction of the motor. 5. Disconnect the circuit. Change the duty~cycle of the PWM signal to about 75%. Connect the circuit according to Fig. 3. The Hex Inverter is used to invert a logic signal. 6. firm on the power of the breadboard. Check the direction of the motor. Observe and plot the following output voltages: +M to GND; —M to GND. 2 7. Turn OK the power of the breadboard. Change the duty-cycle to 25%. Repeat the previous step 0 DCB. 8. Disconnect the circuit. Set the PWM signals from two function generators to 75% and 10% respec— tively. Connect the circuit according to Fig. 4. 9. Do Step 6 once. Does the motor run more quietly than before? 16. Turn off the power of the breadboard. Switch the connection of the two function generator signals. Do Step 6 once. References [1] N. Mohan, T. M. Undeland and W. P. Robbins, “ Power Electronics: Converters, Applications and Design”, John Wiley 81: Sons, 1989 [2] "Design Considerations for a Low Voltage N—Channel H—Bridge Motor Drive”, Motorola Semicon- ductor Application Note AN1319, Motorola Inc., 1992 — Isolation ’\I ——1 ’\.I Transf. — Function Generator A 301‘ 12" — A TOP #011: - .1 3 TOP out: B 301‘ GM) N—Channel MOSFET Motor Drive Laboratory Breadboard Fig. 2 Half—Bridge Operation Connection Diagram Oscillo- scope ~ — Isolation ’\I -——-. -— Function ’\./ A Generator ’\.I __i Transf. ’\/ 'lel Transf. L“ m N—Channel MOSFET Motor Drive Laboratory Breadboard Fig. 3 Full—Bridge Bipolar Switching Connection Diagram Isolation Function Generator Function Generator 12V 1301‘ A TOP +out: - 3 TOP -out: = F a now our: - w“! N—Channel MOSFET 0ND Motor Drive Laboratory Breadboard Fig. 4 Full—Bridge Unipolar Switching Connection Diagram Oscillo— scope Oscillo- scope ...
View Full Document

This note was uploaded on 04/03/2011 for the course ECE 628 taught by Professor Staff during the Spring '08 term at Ohio State.

Page1 / 4

ECE 628 Experiment 8 - Elferfmen‘t‘ 5 H-Bridge PWM...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online