Project review


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Two leg three-phase inverters (FSTPIs) have been proposed to be used in low-power; low-cost applications because of the reduced number of semiconductor devices, and space vector pulse width modulation (SVPWM) techniques have also been introduced to control FSTPIs. However, high-performance controllers are needed to implement complicated SVPWM algorithms, which limit their low-cost applications. To simplify algorithms and reduce the cost of implementation, an equivalent scalar method for SVPWM of FSTPIs is proposed. SVPWM for FSTPIs is actually a sine PWM by modulating two sine waves of 600 phase difference with a triangle wave, but in this method third harmonics doesn’t eliminated. So as to eliminate the third harmonics we have to compose a high frequency sine wave to on existing sine waves. So such a special sine PWM can be used to control FSTPIs. The Mathematical and simulation results demonstrate the validity of the proposed method.

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  • SVM treats the inverter as a single unit. Can be represented in a two dimensional space. There are 4 possible states for the inverter.
  • 4 active vectors occupy 4 vertices of the (Parallelogram)Rhombus If phase voltages are sinusoidal, the locus of Vs is a circular
  • Switching losses are increased Amplitude of higher order harmonics are increased The fundamental component of output voltage is less PWM method is unable to make full use of the inverters supply voltage and asymmetrical nature of switching characteristics , produce the high harmonic distortion in the supply.
  • Project review

    2. 2. INTRODUCTION <ul><li>Semiconductor switches mainly determine the overall price of power converters. </li></ul><ul><li>The main objective of this project is to prove 2leg inverters are the best option for low power applications for getting the good performance. </li></ul><ul><li>Two leg inverter produces the square wave or quasi-square wave. but low power applications allow the two leg inverter output. </li></ul><ul><li>In many industrial applications, it is often required to vary the output voltage of the inverter due to the following reasons </li></ul><ul><ul><li>To cope with the dc I/p voltage. </li></ul></ul><ul><ul><li>To regulate the voltage of inverters </li></ul></ul><ul><ul><li>To satisfy the constant voltage & frequency for control requirement. </li></ul></ul>
    3. 3. Pulse-Width Modulated For VSI <ul><li>Disadvantages of PWM </li></ul><ul><li>semiconductor devices must have low turn-on and turn-off times. so, they are very expansive </li></ul><ul><li>Reduction of available voltage </li></ul><ul><li>Increase of switching losses due to high PWM frequency </li></ul><ul><li>Control of inverter output voltage with out any additional components </li></ul><ul><li>Reduction of lower harmonics </li></ul><ul><li>The most common PWM approach is sinusoidal PWM . In this method a triangular wave is compared to a sinusoidal wave of the desired frequency and the relative levels of the two waves is used to control the switching of devices in each phase leg of the inverter. </li></ul><ul><li>Objective of PWM </li></ul>
    4. 4. <ul><li>Amplitude modulation ratio (m a ) </li></ul><ul><li>Frequency modulation ratio (m f ) </li></ul><ul><li>m f should be an odd integer </li></ul><ul><li>if m f is not an integer, there may exist sub harmonics at output voltage </li></ul><ul><li>if m f is not odd, DC component may exist and even harmonics are present at output voltage </li></ul><ul><li>m f should be a multiple of 3 for three-phase PWM inverter </li></ul><ul><li>An odd multiple of 3 and even harmonics are suppressed </li></ul>
    5. 5. Space vector modulation <ul><li>In sinusoidal PWM, the inverter can be thought of as three separate push-pull driver stages, which create each phase waveform independently. </li></ul><ul><li>SVM, however treats the inverter as a single unit </li></ul><ul><li>The space vector method is a d,q model PWM approach </li></ul><ul><ul><li>Modulation index is high </li></ul></ul><ul><ul><li>SVM produces 15% higher then the sinusoidal PWM in output voltages </li></ul></ul><ul><ul><li>Simple, inherently digital calculation of the switching times. </li></ul></ul><ul><ul><li>SVPWM has been gaining more attention in the industry. </li></ul></ul>
    6. 6. Block diagram of the project
    7. 7. Space Vector PWM for 3leg inverter Where, upper transistors: S 1 , S 3 , S 5 lower transistors: S 4 , S 6 , S 2 switching variable vector: a, b, c <ul><li>Eight possible combinations of on and off patterns for the three upper transistors (S 1 , S 3 , S 5 ) </li></ul>
    8. 8. <ul><li>The eight combinations, phase voltages and output line to line voltages </li></ul>
    9. 9. <ul><li>Basic switching vectors and Sectors </li></ul><ul><li>6 active vectors (V 1 ,V 2 , V 3 , V 4 , V 5 , V 6 ) </li></ul><ul><li>Axes of a hexagonal </li></ul><ul><li>DC link voltage is supplied to the load </li></ul><ul><li>Each sector (1 to 6): 60 degrees </li></ul><ul><li>2 zero vectors (V 0 , V 7 ) </li></ul><ul><li>At origin </li></ul><ul><li>No voltage is supplied to the load </li></ul>
    10. 10. Voltage Space Vector and its components in (d, q). <ul><li>Step 1. Determine V d , V q , V ref , and angle (  ) </li></ul><ul><li>Coordinate transformation </li></ul><ul><li>: abc to dq </li></ul>
    11. 11. <ul><li>Step 2. Determine time duration T 1 , T 2 , T 0 </li></ul>
    12. 12. <ul><li>Switching time duration at any Sector </li></ul>
    13. 13. Space Vector PWM switching patterns at each sector. Sector 1. Sector 2. <ul><li>Step 3. Determine the switching time of each transistor (S 1 to S 6 ) </li></ul>
    14. 14. Switching Time Table at Each Sector
    15. 15. Simulation Diagram of SVM 3leg inverter
    16. 16. Time durations T 1 , T 2 , T 0
    17. 17. Switching Times
    18. 18. Line voltages
    19. 19. <ul><li>Principle of Space Vector PWM </li></ul><ul><li>Treats the sinusoidal voltage as a constant amplitude vector rotating </li></ul><ul><li>at constant frequency </li></ul><ul><li>This PWM technique approximates the reference voltage V ref by a combination </li></ul><ul><li>of the Four switching patterns (V 1 to V 4 ) </li></ul><ul><li>Coordinate Transformation (abc reference frame to the stationary d-q frame) </li></ul><ul><li>: A three-phase voltage vector is transformed into a vector in the stationary d-q coordinate </li></ul><ul><li>frame which represents the spatial vector sum of the three-phase voltage </li></ul><ul><li>The vectors (V 1 to V 4 ) divide the plane into Four sectors (each sector: 90 degrees) </li></ul><ul><li>V ref is generated by two adjacent non-zero vectors and zero vectors </li></ul>
    20. 20. <ul><li>Comparison of Sine PWM and Space Vector PWM </li></ul><ul><li>Space Vector PWM generates less harmonic distortion </li></ul><ul><li>in the output voltage or currents in comparison with sine PWM </li></ul><ul><li>Space Vector PWM provides more efficient use of supply voltage </li></ul><ul><li>in comparison with sine PWM </li></ul><ul><li>Switching losses also reduced by space vector modulation </li></ul> Voltage Utilization: Space Vector PWM = 2/  3 times of Sine PWM <ul><li>Realization of Space Vector PWM </li></ul><ul><li>Step 1. Determine V d , V q , V ref , and angle (  ) </li></ul><ul><li>Step 2. Determine time duration T 1 , T 2 , T 0 </li></ul><ul><ul><li>Step 3. Determine the switching time of each transistor (S 1 to S 4 ) </li></ul></ul>
    22. 22. <ul><li>Space vectors representation </li></ul>
    23. 24. Determine the switching time of each transistor (S 1 to S 4 )
    24. 25. Switching Time for Each Sector of two-leg inverter
    25. 26. Simulation of 3phase to 2phase
    26. 27. Simulation for Sector Identification
    27. 28. Angle& Sectors Sector Angle Sector
    28. 29. Simulation circuit for 2 leg inverter by SVM
    29. 30. Switching time duration for two leg inverter
    30. 31. Connotative Modulation Functions for 2leg
    31. 32. Line Voltages
    32. 33. Third Harmonic Injection
    33. 34. Third Harmonic Injection to Switching Times
    34. 35. Third Harmonic Switching Times
    35. 36. Line voltages for 2 leg Inverter
    36. 37. Rotor & Stator currents
    37. 38. Speed& Torque Characteristics
    38. 39. SVPWM APPLIED TO THE 2-LEG INVERTER UNDER DC-LINK VOLTAGE RIPPLE CONDITIONS The phase-to zero voltages under balanced load conditions
    39. 40. phase-to-neutral voltages VAN, VBN andVCN The phase-to-neutral output voltages can be transformed into space vector
    40. 41. Phase-to-zero and phase-to-neutral output voltages Voltage vectors in αβ plane
    41. 42. Unbalanced dc-link voltages The Time Durations In sector 1: 0≤ α≤π
    42. 43. (a) Timing of gate pulse of space vector PWM (b) Timing of gate pulse of carrier–based PWM In sector 2: π≤α≤2π V t is the instantaneous carrier signal .
    43. 44. Simulation Circuit of proposed method
    44. 45. Reference signals V refb and V refc
    45. 46. Line voltages
    46. 47. Speed & Torque Characteristics
    47. 48. FFT analysis
    48. 49. Comparison of Different PWM techniques for FSTPIs Sine PWM SV PWM Scalar PWM Carrier PWM Calculation Burden Low Very High Medium Low THD 20.08% 1.86% 14.79% 4.07% Output Voltage Normal Normal Maximum Normal DC-link voltage ripple Resolved Switching loss high low low high
    49. 50. CONCLUSION <ul><li>In this work, it is shown that two-leg inverters are the best option for high performance low power applications. It can be resolved by comparing the no of semiconductor switches usage in 2-leg and 3-leg inverters and moreover two leg inverters allow the asymmetrical voltages </li></ul><ul><li>To enable this, space vector pulse width modulation (SVPWM) technique, Scalar PWM & Modified SVPWM of FSTPIs is presented. </li></ul>
    50. 51. BIBLIOGRAPHY Journals [1]. “Adaptive Carrier-based PWM for a Three-Phase Inverter under DC-link Voltage Ripple Conditions” Tuyen D. Nguyen*, Hong-Hee Lee† and Hoang M. Nguyen* Journal of Electrical Engineering & Technology Vol. 5, No. 2, pp. 290~298, 2010 [2]. Jae Hyeong Seo; Chang Ho Choi; Dong Seok Hyun, “A New Simplified space-Vector PWM Method for Three-Level Inverters”, IEEE Transactions on Power Electronics, Volume 16, Issue 4, Jul 2010, Pages 545 - 550 [3]. “the adaptive space vector pwm for four switch three phase inverter fed induction motor with dc – link voltage imbalance” by Hong Hee Lee*, Phan Quoc Dzung**, Le Dinh Khoa**, Le Minh Phuong**, Huynh Tan Thanh***School of Electrical Engineering, University of Ulsan Ulsan, Korea. [4]. Hind Djeghloud and Hocine Benalla, “Space Vector Pulse Width Modulation Applied to The Three-Level Voltage Inverter”, 5th International Conference on Technology and Automation ICTA’05, Thessaloniki, Greece, Oct 2010. Books [5]. P.S.Bimbhra, “Power Electronics”, Khanna publications. [6]. Muhammad H.Rashid “Power Electronics Circuits, devices, and Applications”, Prentice-Hall of India Private Limited, Third Edition, 2004. Thesis References [7]. Jin-woo Jung, “Space Vector PWM Inverter”, The Ohio State University, February, 2008. Website references [8].
    51. 52. THANK YOU