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1-phase AC/AC Cycloconverter PowerPoint Presentation
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1-phase AC/AC Cycloconverter

1-phase AC/AC Cycloconverter

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1-phase AC/AC Cycloconverter

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  1. 1-phase AC/AC Cycloconverter 180- Isolation trafo B2 B1  Sign Iload Enable B1 Enable B2 http://hermes.eee.nott.ac.uk/teaching/h5cpe2/ where 2 << 1  cycloconvertor If Input voltage (50 Hz) Load voltage (10 Hz) Load current (10 Hz) B1 B2 Input current = distorted (has also sub-harmonics)

  2. Classification of PWM Converters http://hermes.eee.nott.ac.uk/teaching/h5cpe2/ Voltage Source Inverter Current Source Inverter Inductive load Capacitive (voltage Source) dc-link Inductive (Current Source) dc-link Capacitive load Voltage Source Converter (rectifier+inverter) Cdc Vdc=unipolar Current Source Converter (rectifier+inverter) Ldc Idc=unipolar

  3. DC-link Voltage Comp. in PWM-VSI 6 V http://hermes.eee.nott.ac.uk/teaching/h5cpe2/ Ldc/2 3-ph Voltage Supply 3-ph R-L Load Cdc 3-ph Diode Rectifier Ldc/2 3-ph PWM Voltage Source Inverter L-C smoothing=based on energy storage components • Small dc-link voltage ripple still present (no filter is perfect!!) • The 6 V ripple compared to 550 V mean value (1%) causes no visible impact on output voltage& current waveform • What would be the effect of reducing the filter size (cost)?

  4. DC-link Voltage Comp. in PWM-VSI http://hermes.eee.nott.ac.uk/teaching/h5cpe2/ Reduced dc-link capacitor size Vdc = 70 V 70 V No dc-link capacitor Vdc = 80 V 80 V No dc-link capacitor  still able to operate !!

  5. DC-link Voltage Comp. in PWM-VSI Modulating fnc Vout dutycycle = * Vpk-carrier Vdc No dc-link capacitor Vdc = 80 V 80 V http://hermes.eee.nott.ac.uk/teaching/h5cpe2/ H-bridge output voltage = Vdc*(2*dutycycle - 1) Vdc&Vout = linear dependency: Vdc ripple  Vout distortion compensation Vdc ripple  no visible distortion in output waveforms 120 Input current=typical diode rectifier with Id=const (current source rectifier)

  6. Direct Power Converters http://hermes.eee.nott.ac.uk/teaching/h5cpe2/ Bidirectional switches on input side give the possibility to commutate the dc-link current to the input line of choice: increase conduction angle from 120 to 180 degrees and shape the average input currentsinus It is possible to combine the functionality of rectifier stage switches and inverter stage switches MATRIX CONVERTER Virtual Single Stage AC/AC converter with no dc-link storage, sine wave input current sine wave output voltage capability Problems: many semiconductor devices, Vout = 86% Vin, sensitive to input voltage disturbances

  7. Matrix Converter: Bidirectional switch Diode embedded switch: - 4 FRD and 1 IGBT - higher conduction losses (2 FRD and 1 IGBT) - higher switching losses (hard-switching) Overlap comm. Dead time comm. Ideal comm. a) SA SB Anti-paralleled switch: - 2 FRD and 2 IGBT - lower conduction losses (1 FRD and 1 IGBT) - lower switching losses (semi-soft switching) - Common Emitter (CE) connected (b) - Common Collector (CC) connected (c) - Anti-paralleled Reverse Blocking IGBTs b) SA A VA ~ c) out VAB SB Bidirectional Switch Commutation: VB ~ Iout Zload B on on on off off off on on on off off off http://hermes.eee.nott.ac.uk/teaching/h5cpe2/

  8. Matrix Converter: Bidirectional switch State diagram of IGBTs A(+) B(-) 11 - 00 Iout >0 Iout <0 Gate Driver 01 - 00 10 - 00 01 - 01 10 - 10 00 - 01 00 - 10 IL >0 ULine >0 00 - 11 SAp SAn Switch format symbol: ON ON SA - SB SBp SBn ApAn–BpBn OFF OFF http://hermes.eee.nott.ac.uk/teaching/h5cpe2/ Load current sign controlled commutation • Better measure currents than voltages • Suitable for 3/1 phase modular approach • Inductive currents give a more stable sign signal • Failure in detecting the correct sign causes dead-time commutation (Li2 = small if offset)

  9. Performance of a Matrix Converter Uin Iin Imot Umot Uin Iin Imot Uin Iin here the DC-machine starts motoring IDCgen http://hermes.eee.nott.ac.uk/teaching/h5cpe2/