DEVELOPMENT OF COMPACT VARIABLE- VOLTAGE, BI-DIRECTIONAL 100KW DC-DC CONVERTER Leonid Fursin 1, Maurice Weiner 1 Jason Lai 2, Wensong Yu 2, Junhong Zhang 2, Hao Qian 2 Kuang Sheng 3, Jian H. Zhao 3, Terence Burke 4, and Ghassan Khalil 4 1 United Silicon Carbide, Inc., New Brunswick Technology Center, Building A, New Brunswick, NJ 08901, USA 2 FEEC, ECE Department, Virginia Tech, Blacksburg, VA24060, USA 3 SiCLAB, ECE Dept., Rutgers University, 94 Brett Road, Piscataway, NJ 08854, USA 4 U.S. Army TARDEC, Warren, MI 48397-5000, USA for AECV-2007
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Outline Project goals Power Stage Design DSP controller, interface circuit and gate driver implementation Power stage layout and packaging Converter testing Summary and Conclusions
Project Goals Bidirectional dc-dc converter targets: Input voltage range: 200-300 VDC (battery pack voltage) Output voltage range: 300-600 VDC Bidirectional power flow Continuous Power: 100 kw, Peak: 150kW Power density: 4 to 8 kw/liter Specific power density: 4 to 6 kw/kg Total efficiency: 95% SVM frequency: ~20kHz Coolant Temperature: 90 o C
Innovations A novel yet simple zero-voltage soft-switching scheme without adding any extra switch making a 25KHz switching frequency possible High-end digital signal processor controller allow fast and smooth mode transition An interleaving 3-phase design substantially reducing the ripple current and filter capacitor size Nano-inductor design High permeability, high saturation flux density lead to small inductor size SiC Schottky diode-si IGBT power modules Minimized thermal resistance Robust diodes, zero-recovery charge
POWER STAGE DESIGN
Proposed Soft-switching Bi-directional DC/DC Converter with Lossless Snubbers S 1u S 2u S 3u L d1 200-300 V L d2 L d3 S 1d S 2d S 3d High freq. cap. C 300-800 V Load/ Source A special switching scheme that utilizes unused switches to perform soft switching: The basic idea is to have the unused switch turned on while the active switch is turned off. This will allow current continuously flow in opposite direction, thus avoiding the discontinuous current and parasitic ringing. Now to reduce the turn-off loss, we can put the lossless snubber across the device to slow down the rate of switching.
Overall hardware system structure: power stage, gate driver and DSP controller Power Stage in Bidirectional Soft-switched DC/DC Converter SIGNAL CONDITIONING CLOCK SYSTEM INTERRUPT SYSTEM EPWM GATE DRIVER V-high V-low TMS2808 I inductor1 I inductor2 I inductor3 ADC GPIO A0 A1 A2 A0 1 0 0 A1 x 1 1 A2 x 1 0 Mode Stop Buck-I Buck-V DSP Controller 0 0 0 0 1 0 Boost-I Boost-V
Summary of Testing Results of IGBT Loss 60 Turn-off energy (mj) V DC =700V, C snub = 0.14μF 50 40 30 20 10 0 w/o capacitor with 0.14μF 0 50 100 150 200 250 300 350 Current (A) 3 loss reduction Achieved without extra switches/inductors
Inductor Design A superior core, FINEMET, is used High permeability, high flux density
Inductor Design Verification L=14.5μH, I SAT =456A, 20% design margin v CE1 (100V/div) v GE1 (10V/div) i L (100A/div) Saturation Point=456A i C (100A/div) t (5µs/div) Each inductor core: 3.35kg, 0.47 liter
Liquid cooled heatsink design Liquid-cooled θ th <0.01 C/W
Physical Layout Dimensions of IGBTs
DSP controller, interface circuit and gate driver implementation
Auxiliary Gate Drive Power Supply 15.24 2.54 1 2 5 6 7 CTC 100mA/ 100mA MSVH-241505 19.65 1 2 5 6 7 Pin no Function 1 +Vin 2 Vin 5 Vout 6 COM 7 +Vout 10.20 4.10 7.05 0.50 The gate driver power supply module provides isolated outputs of +15V and 5V at 90 C.
DSP TMS320F2808 function blocks
Simulation results for the efficiency of boost mode and buck mode Efficiency 0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.9 V in = 300V V in = 200V Boost Mode 400 450 500 550 600 650 700 Output Voltage (V) Boost mode efficiency Efficiency 0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.9 V o = 200V Buck Mode V o = 300V 400 450 500 550 600 650 700 Input Voltage (V) Buck mode efficiency
Power stage layout and packaging
Inductors Converter module Fiber-optical cables Gate driver board IGBT modules
DSP controller with interface board The DSP controller includes signal conditioning circuit and TMS320F2808 digital signal processor.
The IGBT driver circuit Provides electrical isolation by optocouplers, fiber optics, and by transformers With overcurrent detection and pulse-by-pulse overcurrent protection function
The Power Stage Layout With minimized size of the inductors for 100kW output power Zero-voltage switching on and zero-voltage switching off with capacitor Compact bus capacitor size with Interleaving ripple cancellation
Converter testing with Coolant at 90 o C
Measured Current Waveforms i Lall (100A/div) i L (100A/div) v o (100V/div) t(10µs/div) Inductor current ripple is greatly reduced by interleaving three phases
Detailed Measured Waveforms in 100kW Load v CE (200V/div) i L (100A/div) v GE (10V/div) Turn-on t(2µs/div) Turn-off Test condition : Vin=450V, Vout=280V, P=100KW Note that Inductor current negated. Switch is turned on under ZVS condition.
Start-up Voltage and Current Waveforms at 108-kW Operation in Boost Mode
Transient response of the converter under boost mode operation with a step load change from no load to 80-kW v o (200V/div) 400V i a (100A/div) 200A i o (100A/div)
Experimental efficiencies in Buck Mode (450V input and 280V output) 100 Test condition : Vin=450V, Vout=280V, buck mode Efficiency (%) 90 80 70 60 Analytical Results Experimental Results 50 0 10 20 30 40 50 60 70 80 90 100 Output Power (kw) Maximum efficiency is around 97%
Efficiency (%) 100 95 90 85 80 75 70 65 60 55 50 Experimental efficiencies in Boost Mode (240V input and 360V output) Experimental Results Analytical Results 0 10 20 30 40 50 60 70 80 90 100 Output Power (kw) Maximum efficiency is around 98%
Summary Si-based soft-switching bidirectional DC-DC converter has been successfully demonstrated Novel soft-switching circuit without extra switch/inductor DSP (TI-TMS320F2808), inductor, gate driver, optical fiber interface designed Successfully tested at 90 C temperature for 30-kW continuous and 108-kW. Efficiency of 97-98% achieved in both buck and boost modes Compact size (less than 25 liters) demonstrated SiC/Si hybrid power modules being packaged for DC-DC converter operating at high coolant temperature >90 o C Six phase interleaved design will reduce stress to inductors for robust long-term reliable DC-DC converter for FCS