01 introduction to multilevel inverters
- 1. INTRODUCTION TO MULTILEVEL INVERTERS Rijil Ramchand Associate Professor NIT Calicut
- 2. What is power electronics? Definition Conversion of electric power The interdisciplinary nature Position and significance in the human society PEGCRES 2015 2
- 3. What is power electronics? Power Electronics: – is the electronics applied to conversion and control of electric power. Range of power scale : milliwatts(mW) megawatts(MW) gigawatts(GW) A more exact explanation: The primary task of power electronics is to process and control the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads. PEGCRES 2015 3
- 4. Conversion of electric power Other names for electric power converter: -Power converter -Converter -Switching converter -Power electronic circuit -Power electronic converter Electric Power Converter Power output Power input Control input Frequency, magnitude, number of phases AC (Alternating Current) MagnitudeDC(Direct Current) Changeable properties in conversion Two types of electric power 4PEGCRES 2015
- 5. Classification of power converters DC AC AC AC to DC converter (Rectifier) AC to AC converter ( Fixed frequency : AC controller Variable frequency: Cycloconverter or frequency converter) DC DC to DC converter (Chopper) DC to AC converter (Inverter) Power output Power input 5PEGCRES 2015
- 6. Power electronic system Generic structure of a power electronic system Power Converter Power output Power input ControllerFeedforward/Feedback Feedback/Feedforward Reference (commanding) ( measurements of output signals )( measurements of input signals ) Control is invariably required. Power converter along with its controller including the corresponding measurement and interface circuits, is also called power electronic system. Control input 6PEGCRES 2015
- 7. Typical power sources and loads for a power electronic system The task of power electronics has been recently extended to also ensuring the currents and power consumed by power converters and loads to meet the requirement of electric energy sources. -Electric Motor -light -heating -power converter -other electric or electronic equipment Power Converter Source Power input Power output Load Controller Reference -Electric utility -battery -other electric energy source -power converter Vi ii io Vo Feedback/ Feed forward 7PEGCRES 2015
- 8. The interdisciplinary nature William E. Newell’s description Electronics Power Power Electronics Continuous, discrete Control Power electronics is the interface between electronics and power. 8PEGCRES 2015
- 9. Relation with multiple disciplines Power electronics is currently the most active discipline in electric power engineering worldwide. Power electronics Systems & Control theory Circuit theory Signal processing Simulation & computing Electronics Solid state physicsElectromagnetics Power systems Electric machines 9PEGCRES 2015
- 10. Position and significance in the human society Electric power is used in almost every aspect and everywhere of modern human society. Electric power is the major form of energy source used in modern human society. The objective of power electronics is exactly about how to use electric power, and how to use it effectively and efficiently, and how to improve the quality and utilization of electric power. Power electronics and information electronics make two poles of modern technology and human society—— information electronics is the brain, and power electronics is the muscle. 10PEGCRES 2015
- 11. The History The thread of the power electronics history precisely follows and matches the break-through and evolution of power electronic devices late 1980smid 1970s19571900 Mercury arc rectifier Vacuum-tube rectifier Thyratron Invention of Thyristor Power diode Thyristor Application of fast-switching fully-controlled semiconductor devices GTO GTR Power MOSFET Thyristor (microprocessor) IGBT Power MOSFET Thyristor (DSP) Pre-history 1st phase 2nd phase 3rd phase 11PEGCRES 2015
- 12. Applications Industrial Transportation Utility systems Power supplies for all kinds of electronic equipment Residential and home appliances Space technology Other applications 12PEGCRES 2015
- 13. Inverters - Introduction 2. Variable Frequency 3. Variable Phase 1. Variable Magnitude Static power converters that converts DC voltages and currents to AC waveforms are usually known as inverters Converts DC to AC with a fundamental component with adjustable phase, frequency, and amplitude to meet the needs of a particular application This conversion is achieved by the proper control, better known as modulation, of the static power switches that interconnect the DC source to the AC load using the different configurations or conduction states provided by the switches arrangement or topology. 13PEGCRES 2015
- 14. Inverters - Introduction Inverters convert DC voltage to variable magnitude, variable frequency AC voltage. Ideally, purely sinusoidal output voltage. Practically not possible. PWM Techniques makes the task of extracting sinusoidal voltage from output of inverters easier. 14PEGCRES 2015
- 15. Inverters - Introduction 15PEGCRES 2015
- 16. Inverters - Introduction The DC source is usually composed of a rectifier followed by an energy storage or filter stage known as DC link – Indirect Conversion CSI have been dominating in the medium-voltage high-power range with the pulse-width modulated CSI (PWM-CSI) and the load-commutated inverter (LCI) Single-phase and three-phase two-level VSIs are widely used in low- and medium-power applications. Recently, VSI have also become attractive in the medium-voltage high-power market with multilevel inverter topologies 16PEGCRES 2015
- 17. Two-level Voltage Source Inverter Three-phase Two-level VSI feeding Induction Motor 17PEGCRES 2015
- 18. Two-level Voltage Source Inverter VAN, VBN & VCN are known as pole voltages VAn, VBn & VCn are known as phase voltages VAB, VBC & VCA are known as line voltages 3 CNBNAN nN VVV V ,ANnAnN VVV &BNnBnN VVV CNnCnN VVV 3 nCnBnACNBNAN nN VVVVVV V 0 nCnBnA VVV 18PEGCRES 2015
- 19. Two-level Voltage Source Inverter 19PEGCRES 2015
- 20. Two-level Voltage Source Inverter A Phase B Phase C Phase α β V1(+--) V2(++-)V3(-+-) V4(-++) V5(--+) V6(+-+) V8(+++) V7(---) 1 2 3 4 5 6 Voltage space vector structure generated by a two-level VSI 20PEGCRES 2015
- 21. Multilevel Inverters - Introduction Power and Voltage ranges of the Medium Voltage drive Source: Rockwell Automation 21PEGCRES 2015
- 22. Multilevel Inverters - Introduction Drawbacks of two-level VSIs for MV Drives High dv/dt in the inverter output voltage – as high as 10,000V/µs Motor harmonic losses This can be solved by adding properly tuned LC filter. It has some disadvantages Increased manufacturing cost Fundamental voltage drop Circulating current between the filter and DC circuit 22PEGCRES 2015
- 23. Multilevel Inverters - Introduction Multilevel inverter output voltage: (a) two-level and (b) nine-level. 23PEGCRES 2015
- 24. Evolution of Multilevel Space vector structures Hexagonal space vectors. 2-level 3-level 5-level 24PEGCRES 2015
- 25. Multilevel Voltage Source Inverter One phase leg of general n-level inverter 25PEGCRES 2015
- 26. Multilevel Voltage Source Inverter Multi-level inverters are the preferred choice in industry for the application in High voltage and High power application Advantages of Multi-level inverters Higher voltage can be generated using the devices of lower rating. Increased number of voltage levels produce better voltage waveforms and reduced THD. Switching frequency can be reduced for the PWM operation. 26PEGCRES 2015
- 28. Diode Clamped (NPC) 3-level Inverter Three-phase three-level diode-clamped converter also called NPC converter 28PEGCRES 2015
- 29. Diode Clamped (NPC) 3-level Inverter On the dc side of the inverter, the dc bus capacitor is split into two, providing a neutral point Z. The diodes connected to the neutral point, DZ1 and DZ2, are the clamping diodes. When switches S2 and S3 are turned on, the inverter output terminal A is connected to the neutral point through one of the clamping diodes. The voltage across each of the dc capacitors is E, which is normally equal to half of the total dc voltage Vd. With a finite value for Cd1 and Cd2, the capacitors can be charged or discharged by neutral current iZ, causing neutral-point voltage deviation. 29PEGCRES 2015
- 30. Diode Clamped (NPC) 3-level Inverter 27 switching states ( n3 , where n is the number of levels in the inverter) invertertheinlevelsofnumbertheisnwhere1,m*6 1n 1m 19 space vector locations 30PEGCRES 2015
- 31. Diode Clamped (NPC) 3-level Inverter Switching State Device Switching Status (Phase A) Inverter Terminal Voltage VAZ S1 S2 S3 S4 P ON ON OFF OFF Vd/2 O OFF ON ON OFF 0 N OFF OFF ON ON -Vd/2 31PEGCRES 2015
- 32. Diode Clamped (NPC) 3-level Inverter No dynamic voltage sharing problem: Each of the switches in the NPC inverter withstands only half of the total dc voltage during commutation. Static voltage equalization without using additional components: The static voltage equalization can be achieved when the leakage current of the top and bottom switches in an inverter leg is selected to be lower than that of the inner switches. Low THD and dv/dt: The waveform of the line-to-line voltages is composed of five voltage levels, which leads to lower THD and dv/dt in comparison to the two-level inverter operating at the same voltage rating and device switching frequency. 32PEGCRES 2015
- 33. Diode Clamped (NPC) 4-level and 5- level Inverters 33PEGCRES 2015
- 34. Diode Clamped (NPC) 4-level and 5- level Inverters SWITCH STATUS VANFOUR-LEVEL INVERTER S1 S2 S3 S1’ S2’ S3’ 1 1 1 0 0 0 3E 0 1 1 1 0 0 2E 0 0 1 1 1 0 E 0 0 0 1 1 1 0 FIVE-LEVEL INVERTER VAN S1 S2 S3 S4 S1’ S2’ S3’ S4’ 1 1 1 1 0 0 0 0 4E 0 1 1 1 1 0 0 0 3E 0 0 1 1 1 1 0 0 2E 0 0 0 1 1 1 1 0 E 0 0 0 0 1 1 1 1 0 34PEGCRES 2015
- 35. Diode Clamped (NPC) 4-level and 5- level Inverters 5-level space vector structure 35PEGCRES 2015
- 36. Diode Clamped (NPC) multilevel Inverters Component Count of Diode-Clamped Multilevel Inverters Voltage Level m Active Switches 6(m-1) Clamping Diodesa 3(m-1)(m-2) DC Capacitors (m-1) 3 12 6 2 4 18 18 3 5 24 36 4 6 30 60 5 7 36 90 6 aAll diodes and active switches have the same voltage rating. 36PEGCRES 2015
- 37. Diode Clamped (NPC) multilevel Inverters Disadvantages Uneven loss distribution in the devices In a fundamental cycle, the conduction period of the inner devices is more than the outer devices. This causes unequal losses in devices in a leg. The fluctuation of the dc bus midpoint voltage Additional clamping diodes. Complicated PWM switching pattern design 37PEGCRES 2015
- 38. Flying Capacitor 3-level Inverter 38PEGCRES 2015
- 39. Flying Capacitor 3-level Inverter Sa1 Sa2 Sa3 Sa4 Pole voltage, VaO 1 1 0 0 Vdc/2 1 0 1 0 0 0 1 0 1 0 0 0 1 1 -Vdc/2 39PEGCRES 2015
- 40. Flying Capacitor 5-level Inverter 40PEGCRES 2015
- 41. Flying Capacitor 5-level Inverter Switching State Pole voltage, VANS1 S2 S3 S4 1 1 1 1 4E 1 1 1 0 3E 0 1 1 1 1 0 1 1 1 1 0 1 1 1 0 0 2E 0 0 1 1 1 0 0 1 0 1 1 0 1 0 1 0 0 1 0 1 1 0 0 0 E 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 41PEGCRES 2015
- 42. Flying Capacitor Multilevel Inverters Component Count of Flying Capacitor Multilevel Inverters Voltage Level m Active Switches 6(m-1) Clamping Diodes DC Capacitors 3 12 0 5 4 18 0 12 5 24 0 22 6 30 0 35 7 36 0 51 2m 1k k)(*31)(m 42PEGCRES 2015
- 43. Multilevel (3-level) Cascaded H- Bridge Inverters - with equal voltages 43PEGCRES 2015
- 44. Multilevel (3-level) Cascaded H- Bridge Inverters - with equal voltages Switching State Pole voltage, VANS1A S2A S3A S4A 1 0 0 1 E 1 0 1 0 0 0 1 0 1 0 1 1 0 -E 44PEGCRES 2015
- 45. Multilevel (5-level) Cascaded H-Bridge Inverters - with equal voltages 45PEGCRES 2015
- 46. Multilevel (5-level) Cascaded H-Bridge Inverters - with equal voltages Switching State VH1 VH2 Pole voltage, VANS11 S31 S12 S32 1 0 1 0 E E 2E 1 0 1 1 E 0 E 1 0 0 0 E 0 1 1 1 0 0 E 0 0 1 0 0 E 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 0 0 1 E -E 0 1 1 0 -E E 0 1 1 1 -E 0 -E 0 1 0 0 -E 0 1 1 0 1 0 -E 0 0 0 1 0 -E 0 1 0 1 -E -E -2E 46PEGCRES 2015
- 47. Multilevel Cascaded H-Bridge Inverters – with equal voltages The number of voltage levels in a CHB inverter can be found from m = (2H + 1) where H is the number of H-bridge cells per phase leg. The voltage level m is always an odd number for the CHB inverter while in other multilevel topologies such as diode-clamped inverters, it can be either an even or odd number. The total number of active switches (IGBTs) used in the CHB inverters can be calculated by Nsw = 6(m – 1) 47PEGCRES 2015
- 48. Multilevel Cascaded H-Bridge Inverters (7 and 9-level) – per phase diagram 48PEGCRES 2015
- 49. Multilevel Cascaded H-Bridge Inverters - with unequal voltages Per phase diagram 49PEGCRES 2015
- 50. Multilevel Cascaded H-Bridge Inverters - with unequal voltages Voltage Level and Switching State of the Two-Cell Seven-Level CHB Inverter with Unequal dc Voltages 50PEGCRES 2015
- 51. Cascaded H-Bridge Multilevel Inverters Component Count of Cascaded H-Bridge Multilevel Inverters Voltage Level m Active Switches 6(m-1) Clamping Diodes DC Sources 3 12 0 3 5 24 0 6 7 36 0 9 9 48 0 12 51PEGCRES 2015
- 52. References B. Wu, High-Power Converters and AC Drives, Wiley-IEEE Press, Piscataway, NJ, 2006. J. Rodriguez, J. S. Lai, and F. Z. Peng, Multilevel inverters: A survey of topologies, controls, and applications, IEEE Transactions on Industrial Electronics, 49(4), 724–738, August 2002. N. Mohan, T. M. Undeland, and W. P. Robbins, Power Electronics: Converters, Applications, and Design, 3 edn, Wiley, Hoboken, NJ, October 10, 2002. Rodriguez, S. Bernet, B. Wu, J. O. Pontt, and S. Kouro, Multilevel voltage-source-converter topologies for industrial medium-voltage drives, IEEE Transactions on Industrial Electronics, 54(6), 2930–2945, December 2007. 52PEGCRES 2015
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