A Comparison of Modulation Techniques for Three-Level Neutral-Point-Clamped Inverter Fed Motor Drives William Karls1, Ruirui Chen2, Dr Fred Wang2 1The University of Wisconsin-Platteville 2The University of Tennessee, Knoxville List schemes, include diagram INTRODUCTION Pulse width modulation (PWM) is the most popular method for driving inverter-fed motor drive. PWM also generates undesired harmonics in addition to the required sinusoidal voltage/current. Different modulation techniques will have a different impact on the common mode voltage, harmonic distortion, and switching loss of the motor drive system. Large common mode voltage and harmonic distortion may cause failure of motors. Large losses of the inverter may increase cost and degrade motor drive system performance. Fig. 1. A typical motor drive system in aircraft application. OPERATION AND IMPLEMENTATION OF MODULATION TECHNQUES OOO PPP NNN PNN PON OPN NPN NPO NPP NOP NNP ONP PNP PNO POO ONN OON PPO OPO NON NOO OPP OOP NNO ONO POP 1 2 3 4 5 6 Vreference Table 1. List of the modulation techniques that were implemented and examined. Carrier- Based Modulation Space Vector Modulation Phase Disposition Nearest Three Vector Modulation Phase Opposite Disposition & Alternative Phase Opposite Disposition Discontinuous Pulse Width Modulation Common Mode Reduction Modulation Common Mode Elimination Modulation Fig. 2. One phase leg of the three-level ANPC inverter (left) and its PWM sequences (right). Fig. 4. Space vectors for the Nearest Three Vector Modulation. ONN 4 t sub2 2 PNN sub5 PON POO sub4 Bigsector = 1 Subsector = 2 Fig. 3. Modulating wave (orange) and two carrier waves (green) for Phase Disposition carrier-based pulse width modulation. Fig. 5. Switching sequence of subsector 2 of sector I for Nearest Three Vector Modulation. Fig. 6. Simulink model utilized to implement each modulation technique. COMPARISON OF MODULATION TECHNIQUES Fig. 7. Peak common mode voltage for each pulse width modulation technique. Fig. 8. Switching losses for each pulse width modulation technique. Fig. 9. Line voltage total harmonic distortion for each pulse width modulation technique. Fig. 10. Line current total harmonic distortion for each pulse width modulation technique. CONCLUSION AND FUTURE GOALS 1 PON OPN NPO NOP ONP PNO OOO 2 3 4 5 6 Vreference Common mode reduction pulse width modulation is the best of the seven modulation techniques. Second lowest peak common mode voltage. Second lowest switching losses. Future goals: Modify the common mode elimination modulation to reduce switching loss. Fig. 11. Space vector diagram for common mode elimination modulation. This work was supported primarily by the ERC Program of the National Science Foundation and DOE under NSF Award Number EEC-1041877 and the CURENT Industry Partnership Program. Other US government and industrial sponsors of CURENT research are also gratefully acknowledged.