Advanced Soft Switching for High Temperature Inverters Plenary Presentation at The 5th IEEE Vehicle Power and Propulsion Conference (VPPC'9) Jih-Sheng (Jason) Lai, Professor Virginia Polytechnic Institute and State University Future Energy Electronics Center 16 Plantation Road Blacksburg, VA 2461-356 1 Outline 1. Background DOE FreedomCAR Program 2. System Level Design Tradeoff 3. HEV Thermal Management System Design Considerations 4. Power Semiconductor Device Characteristics under Different Temperature Conditions 5. Efficiency and Loss Evaluation for Temperature Prediction 6. Summary 2
Background DOE FreedomCAR Program Inverter Target Goal: Electric Propulsion System with a 15-year life capable of delivering at least 55 kw for 18 seconds and 3 kw continuous at a system cost of $12/kW peak with a 15 C inlet coolant temperature by 215*. APEEM R&D Activities: 55-kW System at 15 C Electric Traction Drive 215 Electric Machines - Motors and Targets Camry Generators Cost ($) 66 374 858 Power Electronics - Inverter and Boost Converter (if needed) Weight (kg) 45.8 91.7 45.8 Thermal Control Key Enabling Volume (l) 157 33.3 12.5 Technology Vehicle Power Management Efficiency (%) 93 88 91 Source: DOE Vehicle Technology Program Bi-Directional Multi-Voltage DC-DC APEEM 29 Kickoff Meeting Converter R&D Pathways 3 System and Component Level Cost Trade-off with Consideration of Thermal Management System Dual cooling loops (7 C plus 15 C) Need dual thermal management systems, penalty on system level cost, size and weight Single cooling loop with 15 C coolant Need to beef up silicon or use wide bandgap devices, penalty on component level cost Need to use high temperature bulk capacitors, penalty on component level cost, size and weight Need to design circuit with high temperature rating, penalty on component level cost 4
Possible Solutions with Single 15 C Coolant Loop Loss reduction by reducing switching frequency will result in high motor current ripple and associated loss thus reducing the entire drive efficiency. Loss reduction by increasing device switching speed will result in high dv/dt, di/dt and associated EMI and common mode current issues. Emerging SiC and wide band-gap devices for high temperature operation is not cost effective today. Junction temperature reduction by reducing thermal impedance it helps but not enough. Advanced soft switching with silicon devices to achieve significant loss reduction a cost-effective way. 5 Proposed Approach Develop a variable timing controlled soft-switching inverter for loss reduction. A hybrid soft switch module for conduction loss reduction. Develop low thermal impedance module with integrated heat sink for high temperature operation. Develop a highly integrated soft-switch module for low cost inverter packaging. Modeling and simulation for design optimization. Test the soft-switching inverter with existing EV platform and dynamometer for EMI and efficiency performance verification. 6
Timing Diagram with a Variable Defined as Variable Timing Control t doff t doff V dc D x6 C dc S x1 D x1 S 1 D C 1 x3 n 1 1 L r2 Load S 2 S x2 S 1 S x1 I Lr I Load t dt S 2 S x2 S 1 S x1 I Lr I Load t dt S x2 D x2 D x5 n D x4 L r1 S 2 C 2 I D2 i C1 i C2 I D2 i C1 i C2 V CE2 V CE2 I S2 I S2 t t 1 t 2 t 3 t 4 t 5 t 6 t 7 t 8 V CE1 (a) light-load V CE1 t t 1 t 2 t 3 t 4 t 5 t 6 t 7 t 8 (b) heavy-load 7 Variable Timing Controlled Soft-Switching Verified with Simulation and Experiment V CE2 (325V) V CE2 (325V) i Lr (9Apk) 1 V ( X 2 : g a t e ) 2 V ( X 2 : d r a i n ) I Load (35A) t z ilr (9Apk) I Load (34.2A) VCE2 (325V) 1 V ( X 2 : g a t e ) 2 V ( X 2 : d r a i n ) I Load (22.A) t z i Lr (61Apk) V CE2 (325V) I Load (22.A) t z i Lr (62Apk) V CE2 (325V) 1 V ( X 2 : g a t e ) 2 V ( X 2 : d r a i n ) I Load (1.8A) i Lr (41Apk).5 1 1.5 2 2.5 3 3.5 4 4.5 5 Time (µs) t z V CE2 (325V) I Load (1.8A) t z t z i Lr (42Apk) Time (.5 µs/div) Turn-on delay controlled by zero-voltage crossing detection. Larger current, longer delay. Gating time after reaching zero voltage t z is fixed 8
Variable Timing Soft Switching over a Wide Load Current Range 5 4 3 2 1-1 5 4 3 2 1-1 I C V CE 5 4 I C at 2A 3 V CE 2 1-1 2 3 4 5 6 7 5 I C at 3A VCE 4 3 I C 2 1-1 1 2 3 4 5 6 2 13 24 35 64 57 1 21 32 43 54 56 Time (µs) Time (µs) (a) Turn-on (b) Turn-off During turn-on, current I C rises after voltage V CE drops to zero During turn-off, V CE slowly rises after I C drops to zero Variable timing achieves soft-switching at all current conditions Bonus slow dv/dt that will result in low EMI emission V CE 9 Conduction Loss Reduction with a New Hybrid Soft Switch Module Hybrid switch reduces conduction loss reduction over a wide range of current and temperature condition Integrated module with direct cooling to reduce thermal resistance Higher temperature, lower voltage drop ideal for high temperature operation Compared with commercial modules: 1.46V versus 1.67V drop @4A (13% reduction) Device Voltage Drop (V) 1.8 125 C commercial module 1.6 25 C 1.4 1.2 1..8 1 C.6.4 125 C.2. 5 1 15 2 25 3 35 4 Device Current (A) 1
Switching Loss Reduction Using LPT IGBT Switching energy (mj) 25 2 15 1 5 IGBT rating = 6 V, 4 A V dc = 3 V 5 1 15 2 25 3 35 4 Current (A) E off at 1 C E off at 25 C E on at 1 C E on at 25 C E off (1 C) E off (25 C) For hard switching, as compared to 25 C operating condition, Device switching loss is increased by 4% at 1 C Device switching loss is reduced by 8% under soft switching Losses in soft switching are due to layout parasitics with discrete components necessary to integrate the soft switch module E on Hard switching Soft switching 11 Direct Cooled Module Based Soft-Switching Inverter Assembly DC bus bar Coupled magnetics Interface board DC capacitor AC bus Water manifold Current sensor Water inlet Gate drive Soft switch module Direct cooled module no heat sink is required, but a custom-made water manifold is needed DC power bus bar and capacitors are placed on top of modules to reduce parasitic inductance Gate drive board snapped on top of the modules to avoid parasitic ringing 12
Power Meter Measured Peak Efficiency Exceeds 99% at Low Relatively Low Power Condition 99.5% 99.% 98.5% 98.% 97.5% 97.% 96.5% 96.% 95.5% 95.% Fixed PF=.83 Fixed RL 4.5 +4.5mH Fixed RL 9 +4.5mH Fixed RL 18 +4.5mH 1 2 3 4 5 6 7 8 9 1 Output power (kw) Test condition: V dc = 325 V, f sw = 1 khz (PWM), f 1 = 83.3 Hz, T a = 25 C Accuracy of Instrumentation: ±.2% Using well calibrated power meter, the measured peak efficiency of the inverter exceeded 99% at room temperature condition. 13 Projected Efficiency Using Loss Measurement with Inductor Load Test Efficiency 99.% 98.5% 98.% 97.5% 97.% 83.3Hz, 25 C 83.3Hz, 9 C 6Hz, 25 C 6Hz, 9 C 96.5% 5 1 15 2 25 3 35 4 45 Power Output (kw) Test condition: DC bus voltage: 325 V dc Switching frequency: 1 khz Load inductance: 2.4 mh per phase Modulation index:.2 to 1.15 14
Efficiency Measurement using Ratiometric Calorimeter Calorimeter Tested Efficiency Plots over a Long Period of Time Efficiency 1.% 99.5% 99.% 98.5% 98.% 97.5% 97.% 96.5% 96.% Motor speed: 265 rpm Motor torque: 33 Nm 6 12 18 24 3 Time (minutes) (a) Test results at 12.5 kw Efficiency 1.% 99.5% 99.% 98.5% 98.% 97.5% 97.% 96.5% 96.% Motor speed: 275 rpm Motor torque: 5 Nm 6 12 18 24 3 36 Time (minutes) (b) Test results at 18 kw Using integrated module with light-weight water manifold for the fullversion soft-switching inverter. Calorimeter chamber inlet and outlet temperatures stabilized after 6- hour testing. Chamber temperature differential was 1.6 C under.3 GPM flow rate. Efficiency exceeded 99% at full speed, 33% load torque condition. 16
Soft-Switching Inverter Testing with Motor Dynamometer The soft-switching inverter has been tested with the 55-kW motor dynamometer set Rigorous test with different torque commands and instant speed reversal speed reversal with negative torque commanded 2ms/div 17 Using FEA to Predict Temperature for Soft- Switching Inverter Boundary conditions: Ambient temperature: 45 C Heat sink temperature: 15 C 119.7 112.1 14.5 96.97 89.4 81.83 74.26 66.69 59.12 51.55 43.98 Simulated hot spot junction temperature consistent with theoretical calculation: 12 C or 15 C temperature rise Circuit components inside the chassis see temperature between 65 C and 85 C 1
Summary The advanced soft-switch module demonstrates 13% conduction loss reduction 8% switching loss reduction 6% thermal impedance reduction The advanced soft-switching inverter with variable timing control demonstrates high efficiency over a wide speed and torque range Soft switched inverter power losses are roughly a factor of 3 less than that of the hard switched inverter Calorimeter test verifies that peak efficiency exceeds 99% FEM analysis and projection indicate Less than 15 C junction temperature rise 15 C coolant operating at full load is possible 19? 2