1. Diode Clamped Multilevel Inverter Fed Induction Motor BY K.Suresh (07091D4313) UNDER THE GUIDANCE OF Mr.NAGA BHASKAR REDDY, M.Tech Dept. of EEE RGMCET,NANDYAL

2. Abstract: The general function of the multilevel inverter is to synthesize a desired AC voltage from several levels of DC voltages. As the number of voltage levels increases the harmonic content decreases significantly. These multilevel inverters are used to increase inverter operating voltage. To minimize THD with low switching frequency, to reduce EMI due to lower voltage steps. The advantages of this multilevel approach include good power quality, good electromagnetic compatibility, low switching losses and high capability.

3.  This project proposes to study various multilevel inverter topologies.  To study and simulate various modulating techniques for diode clamped multi level inverter.  These modulation techniques include sinusoidal pulse width modulation, modified reference, modulation techniques.  The main objective of this project is the simulation of diode clamped multilevel inverter fed Induction motor using above techquies.

4. INTRODUCTION  Two level voltage source inverters produce an output voltage or a current with levels either 0 or ± Vdc  In high power and high voltage application these two level inverters, however, have some limitations in operating at high frequency mainly due to switching losses and constraints of device ratings.  Unique structure of ML-VSIs allow them to reach high voltages with low-harmonics without use of transformers.

5.  As the number of voltage levels increases, the harmonic content of output voltage waveform decreases significantly  MLIs have drawn tremendous interest in power industry.  It may be easier to produce high-power, high voltage inverter with multilevel structure because device voltage stresses are controlled in the structure.  Increasing number of voltage levels without requiring higher ratings of individual devices can increase the power rating.

6. Multi-level Concept  Three phase multilevel power processing system is considered.  Emc=Vdc / (m-1) where m is no. of levels.  The term “level” is referred as the no. of nodes to which inverter can be accessible.  m-level inverter needs (m-1) capacitors

7. Three-phase multilevel power processing system

8. Schematic of single pole of multilevel inverter by a switch

9. Typical output voltage of a five-level multilevel inverter

10. Features of MLI  Actual realization of the switch requires bidirectional switching devices for each node.  Topological structure of MLI must have  1. Less switching devices as for as possible  2. Be capable of withstanding very high input voltage for high power applications  3. Lower switching frequency for each switching devices.  MLI is to synthesize a near sinusoidal voltage from several levels of dc voltages obtained from capacitor voltage sources.

11. Types of MLI Classified into three types:  Diode – clamped multilevel inverter.  Flying – capacitors multilevel inverter.  Cascade multilevel inverter.

12. Comparison of Component requirements for Leg of three multilevel converters Converter TypeDiode ClampFlying capacitors Cascaded Inverters Main switching devices (m-1) x 2 Main diodes(m-1) x 2 Clamping diodes (m-1) x (m-2)00 DC bus capacitors (m-1) (m-1) / 2 Balancing capacitors 0(m-1) x (m-2) /20

13. Single phase five level DCMLI

14. Switch Combination Of Five Level Diode Clamped Inverter Output Voltage Va0 Switch State S a1 S a2 S a3 S a4 S’ a1 S’ a2 S’ a3 S’ a4 Vdc/211110000 Vdc/4 01111000 000111100 -Vdc/400011110 Vdc/200001111

18. Modeling of Induction Motor  The induction motor model can be developed in three reference frames and these are:  Stationary or stator reference frame  Rotor reference frame  Synchronously rotating reference frame.  Here the induction motor modeling is based on stationary or stator reference frame, which is also known as Stanley reference frame.

19.  The mathematical model of 3-phase induction motor expressed in stator reference frame is given by Where and

20.  The stator and rotor voltages of induction motor.  The stator and rotor flux linkages in the stator reference frame are defined as

21.  The electromagnetic torque of the induction motor in stator reference frame is given by  The electro-mechanical equation of the induction motor drive is given by

22. Specification of Induction Motor Stator Resistance R1=7.83 Rotor Resistance R2=7.55 Stator Inductance L1=0.4751 Rotor Resistance L2=0.4751 Mutual Inductance L m =0.4535 Motor Inertia Constant J=0.06 Friction Coefficient B=0 Number of Poles P=4 Power Rating = 1.5kw Rated Speed = 314rad/sec Rated Torque =9.5NM

23. GENERATION OF GATE PULSES FROM DIODE CLAMPED SINUSOIDAL PWM TO THREE-PHASE 3 LEVEL & 5 LEVEL INVERTER Amplitude

24. GENERATION OF GATE PULSES FROM DIODE CLAMPED TRAPIZOIDAL PWM TO THREE-PHASE 3 LEVEL & 5 LEVEL INVERTER Amplitude Time (sec)

25. GENERATION OF GATE PULSES FROM DIODE CLAMPED STAIRCASE PWM TO THREE-PHASE 3 LEVEL & 5 LEVEL INVERTER Amplitude Time (sec)

26. GENERATION OF GATE PULSES FROM DIODE CLAMPED STEPPED PWM TO THREE-PHASE 3 LEVEL & 5 LEVEL INVERTER Amplitude Time (sec)

27. GENERATION OF GATE PULSES FROM DIODE CLAMPED HARMONIC INJECTED PWM TO THREE-PHASE 3 LEVEL & 5 LEVEL INVERTER Amplitude Time (sec)

28. OFFSET VOLTAGE INJECTED SINE REFERENCE WITH TRIANGULAR CARRIER FOR 3 LEVEL & 5 LEVEL Amplitude Time (sec)

29. SIMULATION RESULTS

30. THD of DC3LI Fed I/M for Different Modulation Techniques

31. line voltage of SPWM

32. Stator Current of SPWM

33. Line Voltage of Trapezoidal Reference with triangular carrier

34. Stator Current of Trapezoidal Reference with triangular Carrier

35. line Voltage Stair Case Reference wave with triangular Carrier

36. Stator Current of Stair Case Reference wave with triangular carrier

37. Line voltage Stepped reference wave with triangular carrier

38. Stator Current of stepped reference wave with triangular carrier

39. line voltage of Third Harmonic Injected Reference with triangular Carrier

40. stator Current of Third Harmonic Injected Reference with Triangular Carrier

41. line Voltage of offset Voltage Injected Reference Wave with triangular Carrier

42. Stator Current of offset Voltage Injected Reference with Triangular Carrier

43. No-Load Speed & Torque of 3level MLI

44. Speed & Torque of 3 level with a load of 8N-M

45. THD of Five level Diode Clamped Multi level Inverter Fed Induction Motor for Different Modulation Techniques

46. TTHDt line voltage of SPWM

47. Stator Current of SPWM

48. Line Voltage of Trapezoidal Reference with triangular carrier

49. Stator Current of Trapezoidal Reference with Triangular Carrier

50. line Voltage of Stair Case Reference with Triangular Carrier

51. Stator Current of Stair Case Reference Wave with Triangular Carrier

52. Line Voltage of Stepped Reference with Triangular Carrier

53. Stator Current of Stepped reference with Triangular Carrier

54. Line Voltage of Third Harmonic Reference wave with Triangular Carrier

55. Stator Current of Third Harmonic injected reference with triangular Carrier

56. Line Voltage of offset Voltage Injected Reference wave with Triangular Carrier

57. Stator Current of offset Voltage Injected reference wave with triangular Carrier

58. Speed & Torque Characteristics of IM NO load

59. Speed & Torque Characteristics of IM with a load 8NM

60. Modulation Technique3-level(THD)5-level(THD) Line VoltageStator CurrentLine VoltageStator Current SPWM44.3%6.07%16.97%2.58% TRAPIZOIDAL With Triangular Carrier 40.08%5.3%18.39%1.72% STAIR with Triangular Carrier 44.53%4.88%17.13%1.58% STEP with Triangular Carrier 36.68%4.18%16.77%1.5% THIRD HARMONIC INJECTED SINE with Triangular Carrier 35.62%3.82%17.03%0.77% OFFSET VOLTAGE INJECTED SINE with Triangular Carrier 34.84%2.08%16.38%0.74% Comparison Table of THD

61. References Baiju, M.R., Gopakumar, K., Somasekhar, V.T., Mohapatra, K.K., and Umanand, L.: ‘A space vector based PWMmethod using only the instantaneous amplitudes of reference phase voltages inverters’, IEEE, Trans. Ind. Appl 2005, pp. 297–309. J. Rodriguez, J. Lai, F.Z. Peng: “Multilevel inverters: a survey of topologies,controls, and applications,” IEEE Trans. on Ind. Electronics, vol.49, issue 4, pp.724-738, 2002. B.P. McGrath and D.G. Holmes, “Multi-carrier PWM strategies for multilevel inverters”, IEEE Transactions on Industry Applications, vol.49, no.4, pp.858- 867,August 2002. L.M. Tolbert and T.G. Habetler, “Novel Multilevel inverter carrier-based PWM method,” IEEE Transactions on Industry Applications, vol.35, no.5, Sep/Oct., 1999. L. Tolbert, F.-Z. Peng, and T. Habetler, “Multilevel converters for large electric drives,” IEEE Trans. Ind. Applicat., vol. 35, pp. 36–44, Jan./Feb. 1999.

62. T.P.Chen, Y.S.Lai, and C.H.Liu, “New space vector modulation technique for inverter control,” IEEE Power Electronics Specialists Conference,Vol.2,1999,pp.777-782. P. Hammond, “A new approach to enhance power quality for medium voltage ac drives,” IEEE Trans. Ind. Applicat., vol. 33, pp. 202–208, Jan./Feb. 1997. J. S. Lai and F. Z. Peng, “Multilevel converters–A new breed of power converters,” IEEE Trans. Ind. Applicat., vol. 32, pp. 509–517, May/June 1996. C. Hochgraf, R. Lasseter, D. Divan, and T. A. Lipo, “Comparison of multilevel inverters for static var compensation,” in Conf. Rec. IEEE-IAS Annu. Meeting, Oct. 1994, pp. 921–928. T. A. Meynard and H. Foch, “Multi-level choppers for high voltage applications,” Eur. Power Electron. Drives J., vol. 2, no. 1, p. 41, Mar. 1992. References (Contd…)