Bi-directional DC-DC converter with Soft Switching Cell EPE-PEMC 2006, Portoroz 31th Aug 2006 Bi-directional DC-DC converter with Soft Switching Cell Co-ordinators: Dr. Michael G. Egan Dr. John G. Hayes Student: Marek Ryłko

Topology basics Introduce Soft Switching Cell 5 extra elements 2 aux. Switches 2 aux. Diodes Autotransformer Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Hard Switching Soft Switching

Fundamentals of operation Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Continous conduction mode Fixed bus-voltages Operating frequency – above audible noise Maximum frequency limited by system topology and devices properties Efficiency 92-98% Hardware overcurrent protection Main switches operates as thyristor-dual Fully ZVCS switch-on main switches and snubber assisted switch-off ZCS switch-on and ZVCS turn-off of auxiliaries Main diodes reverse recovery limited by soft-switching cell inductance

Basic waveforms - BOOST Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Main inductor current Resonant ind. current Main switch current Flywheeling diode current Pole voltage Low voltage bus current Main inductor voltage

Basic waveforms - ZCCM Zero Current Crossing Mode Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Main inductor current Resonant ind. current Main switch current Flywheeling diode current Pole voltage Low voltage bus current

Basic waveforms - BUCK Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Main inductor current Resonant ind. current Main switch current Flywheeling diode current Pole voltage Low voltage bus current Main inductor voltage

Soft Switching boundary Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Pole voltage swing (boost): Minimum value is achieved for: Pole voltage must reach zero: Soft Switching boundary is:

Transformer turn ratio Presented boundary for soft switching refer to auxiliary voltage VS Damp resistance is present Rd and take part as voltage drop Initial conditions are significant factor when main current is large Diodes voltage drop affect soft switching Voltage swing must be overestimated to take into account main-switch turn-on time Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END

Duty factor Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Because bus voltages are fixed, the duty factor depends on main inductor current as derivative of average value of pole voltage Hard switching (square pole voltage) Soft switching rr = 0 (deformation of rising and falling edge)

System characteristic DvsI Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END

Damped Cell – non ideal case rr ≠ 0 Damped cell Duty factor Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END

System characteristic DvsI Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END

Difference between ideal and damped system Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END

Summary of soft switching system Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END EMI improvement Good efficiency Decreased switching losses Distributed heat radiation Silent operation (over audible frequencies) No significant volume improvement More complex system Gain affected due to cell operation

Further research plan Development of systems above 10kW Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Development of systems above 10kW Compare with other bi-directional topologies Interleaved, multiphase converters Comparison of high ripple current and low ripple current cases Investigation of IGBT operation in soft-switched regimes MOSFETs in interleaved systems for high power Inductor design Coupled inductor approaches Fully resonant approach Hardware, FPGA’s for control Conference papers

THE END Thank you for your attention! Topology Fundamentals BOOST ZCCM BUCK SS Boundary Turn ratio Duty – ideal Duty – damped Summary Further plans END Thank you for your attention!