EE467-567'10_lect14-Fnl

EE467-567'10_lect14-Fnl - EE 467/567 INTEGRATED POWER...

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EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] EE 467/567 -- INTEGRATED POWER EE 467/567 -- INTEGRATED POWER ELECTRONICS ELECTRONICS Dr. Douglas C. Hopkins Dept. of Electrical Engineering University at Buffalo [email protected] EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] See Special Lectures See Special Lectures on on PFCs PFCs
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EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] End End DCM Lecture DCM Lecture EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] Resonant Converters - Introduction Resonant Converters - Introduction
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EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] Introduction Introduction An ideal hard switched converter, i.e. zero transition time with no parasitic components, is the most dense configuration. ALL converter switching losses are due to parasitic components Mother nature forces us to live with parasitics If we can make the voltage across a capacitor, or current through an inductor of zero value during switching, then those switching losses can be eliminated. This is ZVS of ZCS switching. However, there can be losses introduced when extra components are introduced to accomplish ZVS or ZCS Diodes naturally have zero voltage turn on. The essence of ZVS and ZCS is to switch the device at the zero crossing. Either a source or special circuit situation needs to create the zero event for ZVS or ZCS to occur. EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] Simple Fully Resonant example Simple Fully Resonant example The SCRs are commutated off by the resonant current from L & C. Circuit must remain over damped, i.e. there must be more stored energy than energy supplied the load. The circuit requires excess voltages and currents Another way of viewing this is through the “Q” of the circuit. (Q>1/2) +V L +V C +V R +V S +V S
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EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] Schwartz Inverter Schwartz Inverter Here is a classic inverter for “fully resonant” power conversion +V L +V C +V R +V S EE467/567 Integrated Power © 2010, D. C. Hopkins [email protected] Zero Current Switched - Buck Converter Zero Current Switched - Buck Converter Assume diode is conducting and FET is off. When FET turns on, no current flows due to L r . Current builds until I in =I out and then diode begins turn off. Voltage in C r increases, but the current in L r continues past I out and starts to resonant with C r . The resonant charge from C r pumps back to L r through the FET Diode since it is an easier path than through L . During this time, the FET is switched OFF (with reverse current through it). The FET sees “zero current” and voltage during turn-off. When resonant current tries to swing positive, the FET blocks. Hence, no current is in L r .
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EE467-567'10_lect14-Fnl - EE 467/567 INTEGRATED POWER...

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