L42 ECEN5817 Notes
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Transcript of L42 ECEN5817 Notes
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ECEN5817, ECEE Department, University of Colorado at Boulder
DC Transformer
Ultimate switched-mode power converter:
• Minimum possible voltage and current stresses on all components
• Zero-voltage switching of all semiconductor devices
It is possible to approach the above by restricting the conversion ratio to a single value, V/Vg = const., which leads to the “DC transformer” or “DCX” or “unregulated DC-DC” concept
DCX realizations
• Any hard-switched or soft-switched converter (e.g. ZVT) operated at constant control (duty ratio or phase shift), optimized for a single conversion ratio
Si l ti t b d i
ECEN 58171
• Single-ratio converters by design
Outline:
• Introduction to DCX, dual-active-bridge DCX realization example
• Application examples
DCX derivation: basic idea
+
Vg V+–
_
ECEN 58172
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ECEN5817, ECEE Department, University of Colorado at Boulder
DCX derivation: insert DC-to-AC and AC-to-DC
Q1 Q3 Q5 Q7 +
Vg V+–
v2
Q2 Q4
v4 v6
Q6 Q8
v8
_
ECEN 58173
DCX derivation: dual-active-bridge converter*
Q1
v2
Q3
v4
Q5
v6
Q7
v8
+
1:n
Vg V+–
2
Q2 Q4
4 6
Q6 Q8
8
_
ECEN 58174
* R.W.A.A. De Doncker, D.M. Divan, M.H. Kheraluwala, "A Three-phase Soft-Switched High-Power-Density DC-DC Converter for High-Power Applications," IEEE Tran. on Industry Applications, Jan/Feb 1991, Vol. 27, No. 1, pp. 63-73.
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ECEN5817, ECEE Department, University of Colorado at Boulder
ZVS via magnetizing inductance
Q1
v2
Q3
v4
Q5
v6
Q7
v8
+
1:n
Vg V+–
2
Q2 Q4
4 6
Q6 Q8
8
_
ECEN 58175
State-plane analysis
ECEN 58176
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ECEN5817, ECEE Department, University of Colorado at Boulder
Example
ECEN 58177
Operating waveforms: zero load
ECEN 58178
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ECEN5817, ECEE Department, University of Colorado at Boulder
Same example: 1 kW load
ECEN 58179
Operating waveforms: 1 kW load
ECEN 581710
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ECEN5817, ECEE Department, University of Colorado at Boulder
Effects of leakage inductance?
ECEN 581711
V = 280 V
Operating waveforms with 1% leakage inductance at 1 kW load
ECEN 581712
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ECEN5817, ECEE Department, University of Colorado at Boulder
Dual-active-bridge with series inductance and phase shift between primary and secondary bridges
Q1
v2
Q3
v4
Q5
v6
Q7
v8
+
1:n
Vg V+–
2
Q2 Q4
4 6
Q6 Q8
8
_
ECEN 581713
DCX (V/nVg = 1) waveforms neglecting resonant transitions
Vg V+–
Q1
v2
Q3
Q2 Q4
v4
Q5
v6
Q7
Q6 Q8
v8
+
_
1:n
vp
vp/n
i
ECEN 581714
ir
io
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ECEN5817, ECEE Department, University of Colorado at Boulder
Example
ECEN 581715
Operating waveforms at 1 kW load
ECEN 581716
Phase shift: 0.69 us
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ECEN5817, ECEE Department, University of Colorado at Boulder
Details of negative-to-positive il transition at 1 kW
ECEN 581717
Details of positive-to-negative il transition at 1 kW
ECEN 581718
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ECEN5817, ECEE Department, University of Colorado at Boulder
State plane analysis of ZVS condition at V/nVg = 1
ECEN 581719
State-plane analysis of ZVS condition at V/nVg = 1
ECEN 581720
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ECEN5817, ECEE Department, University of Colorado at Boulder
Operation at 360 W, close to ZVS boundary
ECEN 581721
Waveforms at 360 W
ECEN 581722
Phase shift: 0.2 us
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ECEN5817, ECEE Department, University of Colorado at Boulder
Details of negative-to-positive il transition: operation at 360 W
ECEN 581723
Details of positive-to-negative il transition: operation at 360 W
ECEN 581724
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ECEN5817, ECEE Department, University of Colorado at Boulder
Dual active bridge DC-DC converter summary
• At V/nVg = 1 (DCX), waveforms are close to ideal if F << 1
• ZVS of all semiconductors for loads greater than a minimum
• ZVS can be extended to lighter loads by reducing magnetizing inductance
• Phase shift can be used to control the conversion ratio (non-DCX operation), but with efficiency penalties
• High step-down, or high step-up conversion ratios feasible at high efficiencies (well above 90%)
• Dual active bridge: bidirectional power flow is possible
• For standard unidirectional applications, the secondary-side bridge can be just diodes (operation is similar, but not the same)
H lf b id d h ll i ti il bl
ECEN 581725
• Half-bridge and push-pull variations are available
• Some issues: • Transformer saturation (may require a series blocking capacitor)
• Series inductance (leakage + discrete) value is very important
• Switching frequency limited (F << 1; transformer and inductor core and proximity losses)
Application example:Computing and Telecom Server Power Distribution Systems*
ECEN 581726
*Bob White, Emerging On-Board Power Architectures, IEEE APEC 2003
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ECEN5817, ECEE Department, University of Colorado at Boulder
Intermediate bus architecture
ECEN 581727
*Bob White, Emerging On-Board Power Architectures, IEEE APEC 2003
Approaches to generating the 2nd-level distribution bus voltage
ECEN 581728
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ECEN5817, ECEE Department, University of Colorado at Boulder
Efficiency comparison
ECEN 581729
Application example:Automotive battery power management in a fuel-cell vehicle*
ECEN 581730
*F. Krismer, J.W.Kolar, “Accurate Power Loss Model Derivation of a High-Current Dual Active Bridge Converter for an Automotive Application, IEEE Trans. On Industrial Electronics, March 2010
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ECEN5817, ECEE Department, University of Colorado at Boulder
Efficiency results
ECEN 581731
Power flow control in 3-phase AC power distribution*
• Purpose: control active and reactive power flow; increasingly important function in AC power distribution systems with distributed resources
• Solution above requires bulky 50/60 Hz transformers, e.g. for a 6.6 kV, 1
ECEN 581732
* A. Inoue, H. Akagi, “A Bidirectional Isolated DC–DC Converter as a Core Circuit of the Next-Generation Medium-Voltage Power Conversion System,” IEEE Trans. on Power Elect., March 2007
q y , g ,MVA unit, each transformer weights around 4,000 kg
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ECEN5817, ECEE Department, University of Colorado at Boulder
Solution based on modular DCX
• Each cell can be switched as +E, -E, or 0
ECEN 581733
• With N = 9 cells, a total 19 levels are available to synthesize high-quality sine-wave
Converter realization
ECEN 581734