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Harmonic reduction


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Harmonic reduction

  1. 1. A PRESENTATION ON Harmonic reduction in inverter output voltage By RAJ KUMAR TIWARI M.E
  2. 2. What are Harmonics? Definition: Harmonics are integral multiples of some fundamental frequency that, when added together, result in a distorted waveform.
  3. 3. What are Harmonics? f(x) = sin(x) f(x) = sin(5x) 5 + The resulting wave shows a strong departure from the smooth waves comprising it: f(x) = sin(x) + sin(5x) 5=
  4. 4. What are Harmonics? In fact, any function may be constructed from a sine wave and some number of its harmonics:
  5. 5. Where do they come from? The power company typically supplies a reasonably smooth sinusoidal waveform:
  6. 6. Harmonic Distortion • DC Drives, UPSs, DC power supplies (computers, duplicators, fax’s) will cause current (and voltage) harmonics • Single phase – 3rd , 6th , etc (triplens) can cause transformer neutral conductor overheating • Three phase – 5th , 7th , 11th , 13th , etc can cause equipment malfunctions • Big questions – “How much?” and “How much is too much?”
  7. 7. Common sources of Harmonics Lighting ballasts UPS systems M AC and DC drives
  8. 8. AC drives and Harmonics Converter DC bus & smoothing Inverter Determine the line-side harmonics Determines load-side harmonics
  9. 9. AC drives and Harmonics Inverter Determines load-side harmonics EFFECTS OF LOAD-SIDE HARMONICS: Have implications for the motor insulation and windings. Essentially have zero effect on other equipment on the power system.
  10. 10. AC drives and Harmonics Converter DC bus & smoothing Determine the line-side harmonics LINE-SIDE HARMONICS CAN HAVE FAR-REACHING EFFECTS ON THE POWER SYSTEM: Distribution transformers Standby generators Communications equipment Switchgear and relays Computers, computer systems Diagnostic equipment
  11. 11. AC drives and Harmonics Typical 6-step converter waveform: Harmonic Content I5 = 22.5% I7 = 9.38% I11 = 6.10% I13 = 4.06% I17 = 2.26% I19 = 1.77% I23 = 1.12% I25 = 0.86%
  12. 12. Recommended limits - IEEE 519 The Institute of Electrical and Electronics Engineers (IEEE) has set recommended limits on both current and voltage distortion in IEEE 519-1992. Voltage distortion limits (@ low-voltage bus): Application class THD (voltage) Special system 3 % General system 5 % Dedicated system 10 %
  13. 13. Recommended limits - IEEE 519 MAXIMUM HARMONIC CURRENT DISTORTION in percent of IL Individual harmonic number (odd harmonics) Isc/IL <11 11<h<17 17<h<23 23<h<35 TDD <20 4.0 2.0 1.5 0.6 5.0 20-50 7.0 3.5 2.5 1.0 8.0 50-100 10.0 4.5 4.0 1.5 12.0 100-1000 12.0 5.5 5.0 2.0 15.0 >1000 15.0 7.0 6.0 2.5 20.0 Isc: Maximum short-circuit current at the Point of Common Coupling (PCC). IL: Maximum demand load current (fundamental) at the PCC.
  14. 14. Attenuation of Harmonics Inductive Reactance Method: Add a line reactor or isolation transformer to attenuate harmonics. Benefits: Low cost. Technically simple. Concerns: Tends to offer reductions in only higher order harmonics. Has little effect on the 5th and 7th harmonics. Because of the associated voltage drop, there are limits to the amount of reactance that may be added.
  15. 15. Attenuation of Harmonics Passive Filters Method: Provide a low-impedance path to ground for the harmonic frequencies. Benefits: May be tuned to a frequency between two prevalent harmonics so as to help attenuate both. Concerns: Tuning the filters may be a labor-intensive process. Filters are difficult to size, because they offer a path for harmonics from any source. Quite sensitive to any future system changes.
  16. 16. Attenuation of Harmonics Active Filters Method: Inject equal and opposite harmonics onto the power system to cancel those generated by other equipment. Benefits: Have proven very effective in reducing harmonics well below required levels. Concerns: The high performance inverter required for the harmonic injection is costly. Power transistors are exposed to conditions of the line, so reliability may be a problem.
  17. 17. Attenuation of Harmonics 12-pulse Rectifiers Method: Two separate rectifier bridges supply a single DC bus. The two bridges are fed from phase- shifted supplies. Benefits: Very effective in the elimination of 5th and 7th harmonics. Stops harmonics at the source. Insensitive to future system changes. Concerns: May not meet the IEEE standards in every case. Does little to attenuate the 11th and 13th harmonics.
  18. 18. Attenuation of Harmonics 18-pulse Rectifier Method: An integral phase-shift transformer and rectifier Input which draws an almost purely sinusoidal waveform from the source. Benefits: Meets the IEEE standards in every case! Attenuates all harmonics up to the 35th. Stops harmonics at the source. Insensitive to future system changes. Concerns: Can be expensive at smaller HP’s
  19. 19. Comparison of waveforms 6-pulse converter 12-pulse converter 18-pulse converter note the level of distortion and steep current rise. the waveform appears more sinusoidal, but still not very smooth. virtually indistinguishable from the source current waveform.
  20. 20. HARMONIC REDUCTION BY PWM (pulse width modulation)
  21. 21. • Amplitude of fundamental component for values of α1 and α2 b1= 4Vs/π{ 1-2cos 23.62+ 2cos 33.304} =1.0684 Vs • Amplitude of the fundamental component of unmodulated output voltage is: b1=4Vs/ π=1.27324 Vs • Un modulated voltage wave ,the amplitude of the 7th ,9th ,11th harmonics are 24.78%,40.86%,30.39 % • 3rd and 5th harmonics are been eliminated • Amp of fundamental output voltage =83.91% i.e. .8391 amp of fundamental unmodulated voltage wave. Harmonics reduction =16.09%
  22. 22. Harmonics reduction by Transformer connections • Two or more inverters can be combined by means of transformers to get a net output voltage with reduced harmonic content . • Output voltage waveforms from the inverters must be similar but phase-shifted from each other.
  23. 23. By stepped wave inverters • Pulses of different widths and heights are superimposed to produce a resultant stepped wave with reduced harmonic content . • two transformers are used have different turn ratio from primary to secondary . • Turns ratio from primary to secondary is assumed 3 for transformer 1and 1 for transformer 2. • Inverter 1 is gated that its output voltage is vo1 • During first half cycle output voltage woud be zero or negative.
  24. 24. • This output voltage waveform is named as TWO –LEVEL MODULATION . • When inverter2 is triggered output voltage is v02 • level of this voltage is positive, negative or zero for first half cycle. • For this the inverter has THREE LEVEL MODULATION • By superimposing both the waveforms the output voltage is 4Vs and wave for four steps. • 3rd ,5th ,and 7th harmonics are eliminated .
  25. 25. • A Novel Approach of Harmonic Reduction with TransformerConnected 3-Phase Multilevel Inverter • By:Vipul Rastogi,Sudhanshu Tripathi (Iss.7| July. 2014 ) • This paper proposes a multilevel inverter arrangement employing a series connectedtransformer to suppress 5th,7th,11th &13th order harmonics. • eliminates the need of output filter
  26. 26. Harmonics reduction in three phase multilevel inverters using space vector modulation Published in: 19-20 March 2015 • Harmonic reduction in three phase multilevel inverter is an imperative factor to obtain the quality of output voltage and current. • This paper proposes the switching strategy of space vector pulse width modulation uniquely to minimize THD. Publisher:IEEE INSPEC Accession Number:15380959 • To reduce the total harmonic distortion and study the harmonic analysis of five-level inverter in diode clamped inverter, flying capacitor inverter and cascaded H-bridge multilevel inverters are simulated in MATLAB
  27. 27. International Journal of Engineering Technology, Management and Applied Sciences June 2015, Volume 3, Issue 6, ISSN 2349-4476 • New Approach for Harmonics Reduction in Inverters
  28. 28. • This paper primarily compares and analyzes the two DC- AC power conversion approaches. These two approaches are • 1. Cascaded H Bridge inverter • 2. Multilevel scheme with H-Bridge and level modules. • The primary advantage of cascaded topology is that it uses multi-level DC voltage to accurately synthesize an expected AC voltage .The level of output voltage shape can be calculated by using appropriate level module. MATLAB Simulink is used to design the above mentioned two approaches. Comparatively, the THD produced in the second approach is more efficient and productive than the first approach.
  29. 29. Multilevel approach
  30. 30. THANK YOU