1. 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

2. 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

3. 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 %
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

4. 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

5. 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

6. 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

7. 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:

8. 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

9. 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)

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

11. 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

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

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

14. 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

15. 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

16. 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!