ECEN5817, ECEE Department, University of Colorado at BoulderDC TransformerUltimate switched-mode power converter:• Minimum possible voltage and current stresses on all components• Zero-voltage switching of all semiconductor devicesIt 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” conceptDCX 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 ratioSi lti t b d iECEN 58171•Single-ratio converters by designOutline:• Introduction to DCX, dual-active-bridge DCX realization example• Application examplesDCX derivation: basic idea+Vg V+–_ECEN 58172ECEN5817, ECEE Department, University of Colorado at BoulderDCX derivation: insert DC-to-AC and AC-to-DCQ1Q3Q5Q7+Vg V+–v2Q2 Q4v4v6Q6 Q8v8_ECEN 58173DCX derivation: dual-active-bridge converter*Q1v2Q3v4Q5v6Q7v8+1:nVgV+–2Q2Q446Q6Q88_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.ECEN5817, ECEE Department, University of Colorado at BoulderZVS via magnetizing inductanceQ1v2Q3v4Q5v6Q7v8+1:nVgV+–2Q2Q446Q6Q88_ECEN 58175State-plane analysisECEN 58176ECEN5817, ECEE Department, University of Colorado at BoulderExampleECEN 58177Operating waveforms: zero loadECEN 58178ECEN5817, ECEE Department, University of Colorado at BoulderSame example: 1 kW loadECEN 58179Operating waveforms: 1 kW loadECEN 581710ECEN5817, ECEE Department, University of Colorado at BoulderEffects of leakage inductance?ECEN 581711V = 280 VOperating waveforms with 1% leakage inductance at 1 kW loadECEN 581712ECEN5817, ECEE Department, University of Colorado at BoulderDual-active-bridge with series inductance and phase shift between primary and secondary bridgesQ1v2Q3v4Q5v6Q7v8+1:nVgV+–2Q2Q446Q6Q88_ECEN 581713DCX (V/nVg= 1) waveforms neglecting resonant transitionsVgV+–Q1v2Q3Q2 Q4v4Q5v6Q7Q6 Q8v8+_1:nvpvp/niECEN 581714irioECEN5817, ECEE Department, University of Colorado at BoulderExampleECEN 581715Operating waveforms at 1 kW loadECEN 581716Phase shift: 0.69 usECEN5817, ECEE Department, University of Colorado at BoulderDetails of negative-to-positive iltransition at 1 kWECEN 581717Details of positive-to-negative iltransition at 1 kWECEN 581718ECEN5817, ECEE Department, University of Colorado at BoulderState plane analysis of ZVS condition at V/nVg= 1ECEN 581719State-plane analysis of ZVS condition at V/nVg= 1ECEN 581720ECEN5817, ECEE Department, University of Colorado at BoulderOperation at 360 W, close to ZVS boundaryECEN 581721Waveforms at 360 WECEN 581722Phase shift: 0.2 usECEN5817, ECEE Department, University of Colorado at BoulderDetails of negative-to-positive iltransition: operation at 360 WECEN 581723Details of positive-to-negative iltransition: operation at 360 WECEN 581724ECEN5817, ECEE Department, University of Colorado at BoulderDual 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)Hlfbid d hll i ti il blECEN 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 2003ECEN5817, ECEE Department, University of Colorado at BoulderIntermediate bus architectureECEN 581727*Bob White, Emerging On-Board Power Architectures, IEEE APEC 2003Approaches to generating the 2nd-level distribution bus voltageECEN 581728ECEN5817, ECEE Department, University of Colorado at BoulderEfficiency comparisonECEN 581729Application 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 2010ECEN5817, ECEE Department, University of Colorado at BoulderEfficiency resultsECEN 581731Power 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 2007qy ,g ,MVA unit, each transformer weights around 4,000 kgECEN5817, ECEE Department, University of Colorado at BoulderSolution based on modular DCX• Each cell can be switched as +E, -E, or 0ECEN 581733• With N = 9 cells, a total 19 levels are available to synthesize high-quality sine-wave Converter realizationECEN