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# 1-ф to 1-ф Cycloconverter ppt

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Cyclo converters
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# 1-ф to 1-ф Cycloconverter ppt

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### 1-ф to 1-ф Cycloconverter ppt

1. 1. 1-ф Cycloconverter VGEC,Chandkheda
2. 2. Introduction to Converter Family • In industrial applications, two forms of electrical energy are used: direct current (dc) and alternating current (ac). • However, for different applications, different forms, magnitudes and/or frequencies are required. • There are four different conversions between dc and ac power sources. • These conversions are done by circuits called power converters
3. 3. Classification of Converters • The converters are classified as: • Rectifiers: from single-phase or three-phase ac to variable voltage dc • Choppers: from dc to variable voltage dc • Inverters: from dc to variable magnitude and variable frequency, single-phase or three phase ac • Cycloconverters : from single-phase or three-phase ac to variable magnitude and variable frequency, single-phase or three-phase ac
4. 4. Introduction to Cycloconverter • Traditionally, ac-ac conversion using semiconductor switches is done in two different ways: • 1- In two stages (ac-dc and then dc-ac) as in dc link converters. • 2- in one stage (ac-ac) cycloconverters. • Cycloconverters are used in high power applications driving induction and synchronous motors. They are usually phase- controlled and they traditionally use thyristors due to their ease of phase commutation.
5. 5. Operating principle for cycloconverter • Continuous modulation of the firing angle α of the individual converter. • The voltage produced by two converters have same magnitude, angle and phase.+ve and –ve converter produce respective half cycles.
6. 6. 1-ф to 1-ф Cycloconverter Mid-point configuration • Also known as centre tapped transformer cycloconerter • Assume purely resistive load • SCRs 1,2,3 & 4 connected antiparallel.
7. 7. Waveforms for fo =1/3fin • No. in waveform shows conducting SCR.
8. 8. Care to be taken • By mistake if from two pairs are turned on simultaneously(e.g. S1 and S4 or S2 and S3) then the secondary winding of transformer will be short circuited. • To avoid this, we should connect L at the other end of load. This will stop sudden change of current and will stop secondary from getting damaged. • In general, if o/p freq. is Nth part of i/p frequency than N positive and N negative half cycles should be produced across load by triggering SCRs in proper sequence. • o/p waveforms tends to be square waves. • For producing sine wave, the triggering of SCR should be delayed by varying degrees.
9. 9. Care to be taken • If inductive load is used than portion of –ve half cycle will appear in positive half cycle of load voltage waveform and vice versa. • The wave forms are as follows:
10. 10. Care to be taken • The o/p freq. should be always a sub multiple of i/p freq. Why?? • Yes, because if not, than incoming SCR would turn on before outgoing SCR and it will result in zero o/p voltage. • This condition continues for less than half cycle period and occurs at every half cycle. • This periodic short ckt will distort o/p voltage. • And due to asymmetrical waveforms the o/p transformer may get saturated.(if used.)
11. 11. Bridge type 1-ф Cycloconverter
12. 12. Operation of bridge configuration • 1.Non-Circulating Current mode: • In this mode,SCRs only from one side are triggered at any given instant. • The firing pulses to the SCRs from the other bridge are ‘’blocked’’.i.e. not given.
13. 13. 2.Circulating mode • Both bridges conduct simultaneously. • Inductor L can be placed at point L in figure. • Freewheeling diode can’t be connected across load as it wont allow one cycle of ac o/p appear across the load. • Semiconverters can’t be used in bridge because they do not allow load voltage to be negative due to internal freewheeling. • Therefore inverting mode cant be achieved, which is actually essential while feeding inductive loads.
14. 14. Notes • Cycloconverters are naturally commutated and the maximum output frequency is a fraction of the source frequency. • Therefore, cycloconverters are low speed ac motor drives in ranges up to 15 MW with frequencies from 0 to 20 Hz.
15. 15. Practical for 1-ф Cycloconverter
16. 16. Practical waveforms for 1-ф Cycloconverter
17. 17. Applications of Cycloconverters • There are other newer forms of cycloconversion such as ac-ac matrix converters and high frequency ac-ac (hfac-ac) converters and these use self-controlled switches. • Cement mill drives • Ship propulsion drives • Rolling mill drives • Scherbius drives • Ore grinding mills • Mine winders
18. 18. Advantages • No “DC LINK” required as in case of inverters to get sine waveforms • Bidirectional power flow possible. • Variable firing angle control possible so, we can obtain high quality Sine wave at low frequencies.So filters also gets eliminated and It will reduce losses and will increase efficiency. • Line commutated.Seperate circuit for commutation not required. • Why step down more used than step up?? • Due to addition of FORCED COMMUTATION circuit in step up cycloconverter.Also, inverter are more better than cyclo for high frequency operation than supply freq.
19. 19. Disadvantages • Smooth stepless control of o/p frequency is not possible. • More distortion at low frequencies. • Control circuit is difficult to design and complex. • i/p power factor is poor at large values of α.
20. 20. References • P.E.-2 by Dr.P.S.Bimbhra • P.E.-2 by J.S.Katre • Burak Ozpineci, Leon M. Tolbert Department of Electrical and Computer Engineering, University of Tennessee-Knoxville, Knoxville • Google Images • HITACHI Electronics division • Santosh Grampurohit,VGEC Electrical Student. • PANTECH Solutions
21. 21. THANK YOU