A Novel Proton Exchange Membrane Fuel Cell-Battery Partial Hybrid System Design for Unmanned Aerial Vehicle Application. Dr.

Transcription

1 A Novel Proton Exchange Membrane Fuel Cell-Battery Partial Hybrid System Design for Unmanned Aerial Vehicle Application Dr. Mebs Virji at Mānoa Hybrid SMALL FUEL CELLS Knowledge Foundation s 14 th Annual International Symposium July 18 th, 212

2 OUTLINE Objective & Approach Hybridization of Fuel Cell Systems Why? Rationale for Novel Partial Hybrid System Novel Partial Hybrid System Design Pros & Cons Design Considerations System Simulation Study & Results Hardware-in-the-Loop (HiL) Methodology & Setup Prototype Controller Design Real-Time HiL Test & Energy Balance Results Conclusions 2

3 OBJECTIVE AND APPROACH Improve the design of the most commonly used UAV hybrid system Comparison between three UAV Systems Novel Partial Hybrid (PH) System Non-Hybrid ( Following (LF)) and Full Hybrid (FH) Systems Methodology for Characterization and Performance Comparison System Simulation for 24+ hours Endurance Full tank of fuel Fully charged battery pack Repeated 2 minutes load profile Hardware-in-the-Loop (HiL) Testing System for Real Time Study Prove of concept test for the PH system with a prototype hardware controller, PEMFC stack, Battery Pack and balance of plant (BoP) components Comparison of Simulation Vs HiL Results System performance with different operational strategies UAV flight duration estimate using energy balance results under a 2 minutes load profile 3

4 Hybridization of Fuel Cell System Why? Hybridization Benefits: Fuel Cell does not meet power demand for several reasons 4

5 Rationale for Novel Partial Hybrid System PH Hybrid System resolves the main issues of the most commonly used Hybrid System - Full Hybrid Battery pack weight penalty Potential to reduce battery pack size and weight Large dc-dc converter Same power rating as the Fuel Cell Stack Weight penalty High power losses through converter Use smaller dc-dc converter and weight Minimizes power losses of the dc-dc converter Battery can be discharged quickly at continuous peak power Control the use of battery during peak power Optimize battery energy to minimizes the stack power and dynamics by sharing the load demand Fuel Cell Stack can t provide power to the system directly Flexibility to switch to different mode of operations 5

6 Novel Partial Hybrid (PH) System Design PEM Fuel Cell System 17 V BoP Fuel Cell System Switch 17 V DCDC Converter 5-1 W DCDC Converter Battery Switch Motor Controller Propulsion Motor 12 V Avionics 5 V Avionics 12 V DCDC Converter 5 V DCDC Converter Analog Current Controller Charging Switch Hybrid Battery Pack System Components: 5W PEMFC Stack 6Wh Battery Pack Size Propulsion Motor & Controller Smaller dc-dc converter (~1W) Three ancillary s (17V, 12V & 5V) Control Switches (2 x Zero-Volts Diode & 1 for Battery Charging) Flexible Modes of Operation: Parallel Battery and fuel cell supply power to the system Battery voltage regulates the stack power Charging Fuel cell supplies system and charging power when demand is < average system power Following when Battery State of Charge < 3% Fuel cell supplies all the power to the system including battery charging power Battery charging mode is controlled 6

7 UAV Systems Pros & Cons 5 W PEM Fuel Cell System Stack sees all dynamics & peak demand Following System (LF) No DC/DC Losses Motor Controller Propulsion Motor Power [W] Fuel Cell Following System (LF) Full Hybrid System (FH) W PEM Fuel Cell System 5 W DCDC Converter Hybrid Battery Pack Motor Controller Propulsion Motor 5 4 Fuel Cell Time [s] Full Hybrid System (FH) Discharging Charging Stack sees no dynamics & peak demand Large DC/DC Losses (~1% of Stack Power) Power [W] 3 2 Partial Hybrid System (PH) 1 5 W PEM Fuel Cell System Stack sees less dynamics & no peak demand 75-1 W DCDC Converter Small DC/DC Losses (~2% of stack power) * Ancillary loads not shown Hybrid Battery Pack Flexible modes of operation (Hybrid LF) Motor Controller Propulsion Motor Power [W] Fuel Cell Time [s] Partial Hybrid System (PH) 2 Parallel Mode (Stack & Battery share the load) 1 Charging Mode (Stack power only, Battery Charged) Time [s] 7

8 Partial Hybrid System Design Considerations DC-DC Converter Size Large enough to maintain battery state of charge (SoC) between 5-6% Small enough to minimize power losses and weight penalty Battery Pack Size Voltage optimized for parallel/charging mode ratio Voltage range in operating range of motor controller Pack size should be small to minimize weight penalty Controller Algorithm 12 Determines modes of operation as a function of system demand & SoC of battery Determines when battery is allowed to be charged Determines when the stack power is load leveled and utilizes excess fuel cell power to charge the battery pack (only in simulation study) Stack/Battery Volts / [V] Charging Mode Current Density / [A/cm 2 ] Parallel Mode Cells - Batt. Discharge SoC / [%] 7 Cells Stack Voltage 8 Cells Stack Power 9 Cells Cells - Batt. Discharge SoC / [%] Cells - Batt. Discharge SoC / [%] Stack Power / [W ] 8

9 Fuel Cell System Simulation Tool: UAV Simulation Simulation developed in Matlab & Simulink environment 5 W PEMFC Stack PEMFC System Model Propulsion & Ancillary UAV Demand Model UAV Controller & Operational Strategy Model 6 Wh Lithium Ion Battery Pack Battery Model 9

10 Fuel Cell System Simulation Tool Adaptable to any fuel cell and hybrid systems and components UAV, UUV, Auto-FCV, Stationary-CHP Following (LF), Partial Hybrid (PH) or Full Hybrid (FH) Fuel Cell, Batteries or Super capacitor Liquid and Gaseous Fuel tanks Characterization of overall system and components performance Mission profiles, drive cycles, dynamic load profiles Operating conditions (temperature, pressure, relative humidity, stoichiometry) Operating strategies (LF, PH, FH, dead-end, purge cycle, oxide clean-up) Control strategies (operating components at constant, average, dynamic modes) Easily converted to real time simulations for Hardware-in-the-Loop use System components under realistic dynamic conditions 1

11 Simulation Setup for 24+ Hrs Endurance Test Propulsion Profile & System Weight Penalty: 2 mins Profile: Repeated to calculate the final duration of the UAV Mission Repeated Until:.5 k of H 2 is consumed and SoC% Battery 1% Total weight penalty: Increase in propulsion power for hybrid systems System Ancillary s: Zero Avionics + BoP Nominal Avionics (cruise) + BoP Maximum Avionics (peak) + BoP ~ 2.5 X Nom. Avionics DC-DC Converter Efficiency 9-93% PEMFC System Nom. Power: 5 W Stack Temp : 5-55 o C Anode Stoich: 1.2 Cathode Stoich: ~ 2.5 Battery Pack: Lithium Ion Capacity: 2.3 Ah Nom. Voltage: 3.3 volts/cell Initial SoC: 1% Power / (w) Propulsion Profile Time / (sec) UAV SYSTEM TYPES LF FH PH No of Cells of Lithium Ion Increase in Battery Wt (g) (7g/cell) Increase in Electronics Wt (g) DC-DC Converter/MOSFET/Diodes Net Increase in System Weight (g) Net Increase in Propulsion Power (W)

12 Flight Endurance Results UAV Flight Duration / (h) Maximum Flight Duration with.5 kg of H and a fully charged Battery Pack % Loss LF UAV PH UAV FH UAV 1.4% 31.9 Loss 2% Loss % Loss 1.6% 25.8 Loss 1.4% Loss Zero Avionics Nominal Avionics Peak Avionics 12

13 HiL Test System Operational Concept Au xi liary Unit Pr o totype Co ntroller B attery P ack In divid ual Ce l mon ito ring Un i t Fuel Cel Sta ck Bo P Co m p one nt s 2 brake pos[1] 1 acpos[ 1] nm o tor [1/ mi n] Vs tac k [V] ac cp os [1 ] bra ke po s[ 1] bra ke fo rce [N ] Brake Asis tant motorand transmis sion Hot el s Vs tac k[ V] I_ fc _a ux [A] wh e lto rqu e[ Nm] Id riv e[ A] Sum b rak ef orc e[ N] Mwh e l[n m] -Knwheel [rad/ sec]-> nmotor [1/ min] Idr ive + I_v eh _au x[a ] ac cp os [1 ] vehicl ebody fuel celsystem n whel [r ad/ sec ] v eh [k m/h ] Vst ack [V ] Ist ack [A ] 1 v_veh[ km/h] 1 V_ sta ck [V] Vst ack [V ] I sta ck [A ] Result s Target Scope Id:2 Scope(xPC) 1 Embed Units Under Test Into Dynamic Fuel Cell & Stack Tester Control by Application Specific Simulation To mimic Complete System Hardware Auxi liary Unit Pr ot ot ype Controlle r Indiv idual Cell monitoring Uni t Fuel Cell Stack BoP Component s HiL FC Test station + = Ba tt ery Pac k Unit Under Test (Stack, Cell, Blower, Humidifier, Battery Pack, etc) Simulator (Valves, MFC, load unit, cooling system, etc) Simulation (Fuel Cell and Hybrid systems, control, load profile, etc) Application (Unmanned Aerial Vehicle, Fuel Cell Hybrid Vehicle, etc) 13

14 Prototype Hardware Controller PH system controller and control algorithm designed to: 14 Controller consists of: 2 Zero-Volts Diode Switches Measured Losses (.3-.5 W) 1 Charging Switch (MOSFET) 2 Schottky Diodes Measured Losses (1-2 W) DC-DC Converter Sized to ~ 1 W Input voltage range V Output voltage range 16-3 V Average Efficiency ~ 9% Isolated battery voltage & current measuring circuits Enable safe operation and switching between different modes of operations Parallel mode fuel cell and battery share the system load Following mode fuel cell supplies all the power to the system Charging mode fuel cell charges the battery via the DC-DC converter Enable safe supply of the ancillary load by the fuel cell and/or battery (no power back flow) Measure battery current and voltage for battery SoC estimate

15 Simulation Setup for 2 mins HiL Test Demand: 2 mins UAV Profile System Auxiliary : Nominal Avionics (cruise) + BoP PEMFC System Nom. Power: 5 W Stack Temp : 5-55 o C Anode Stoich: 1.2 Cathode Stoich: ~ 2.5 Battery Pack: Lithium Ion Capacity: 2.14 Ah (7% de-rated) Nom. Voltage: 3.3 volts/cell (8 Cells) Initial SoC: 1% Auxiliary Unit Battery SoC Estimation: SoC of battery is estimated by integrating the charge and discharge currents over time Future: Use of Resistance method Charging Algorithm: Charges battery at constant current Minimizes the current spike by voltage matching Prototype Controller Battery Pack Individual Cell monitoring Unit Fuel Cell Stack BoP Components 15

16 Demonstration of PH System with Prototype Controller on the HiL Station UAV Taking-off and Climbing UAV Cruising with Occasional Turbulence Fuel Cell & Battery Share Peak (Parallel Mode) Battery Charging Mode (FC power > Demand) Power/(W) SoC/(%) Total System (w) Battery Charging Stack Power (W) Batt Power (W) 1 Batt SoC (%) Time / (min) 2 16

17 Simulation Test Vs. HiL Test with Actual Hardware SoC/(%) Stack Power/(W) Battery Power/(W) SoC of Battery HiL Test with Prototype Hardware Controller Simulation Test with Software Control Algorithm PEMFC Stack Power Battery Power Time / (min) Simulation Results: Data based on new stack Stack provides more power during parallel mode of operation Less battery power is used therefore battery discharge is slower [1] Ideal Software Controller Better control of stack (load Leveled) and charging power [2] HiL Results: Measured stack and battery data Degraded stack performance (>15+ operating hours) Battery provides more power and therefore discharges faster [1] Hardware Prototype Controller Higher charging inrush current due to iterative control (to be replaced with analog current controller) [2] 17

18 PH System Operation with Different Initial Battery SoC Power/(W) Stack Power/(W) Battery Power/(W) Power & SoC of Battery Power 1%SoC 5% SoC 1 PEMFC Stack Power at Different SoC Battery Power at Different SoC Time / (min) SoC/(%) HiL Capability: Flexibility in changing system operating conditions/control strategy without hardware modification 1% SoC Test Run Higher battery power use Stack operates at lower power and higher efficiency [1] 5% SoC Test Run Stack provides more power [1] Battery starts charging at the beginning of the mission profile and maintains a battery SoC between 5-4% [2] PH Hybrid System Redundant power sources capable of supporting UAV power demand when one source degrades or fails

19 Partial Hybrid System Benefit 5 % Time spent at different power region Power / (W) 19 FCS Power for Partial Hybrid FCS Power for Non-Hybrid Average System (~ 355W) Non-Hybrid: The stack operates above the average power 4% of the time Partial Hybrid : The stack only operates above the average power 2% of the time No power demand > 475 W

20 Energy Balance Over a 2 mins Real Time HiL Test Surface Losses & Heat (cooling) BoP, Avionic s & DC-DC Converter Losses Propulsion (Prop) Motor & Controller Losses H 2 Energy PEMFC System Stack Power UAV Controller & 5,12,17 & 24 Volts DC-DC Converters Prop Power Motor Controller Propulsion Motor UAV Prop Energy Anode & Cathode Exhaust Losses Battery Pack Battery Energy Energy Balance 1 36 t t 2 1 t 2 t 2 PIN dt POUTdt PLOSS dt = t 1 t 1 Main assumptions: 1. Actual stack current, voltage, cooling and cathode exhaust temperatures are used to estimate the cathode losses & heat load 2. Stack energy balanced based on 98% H 2 utilization 2

21 UAV Systems Energy Balance & Flight Duration Summary 15% 14% 13% Estimation of UAV flight duration with.5 kg H 2 using 2 mins HiL energy balance Energy and duration normalized to non-hybrid (LF) results 12% 11% 1% 9% 8% 7% 6% 5% 4% 3% 2% 1% (Low stack Power due to stack degradation) Normalized Energy & Duration / (%) PEMFC Loss PEMFC Power Battery Power Power PEMFC Loss PEMFC Power Battery Power Power PEMFC Loss PEMFC Power Battery Power Power PEMFC Loss PEMFC Power Battery Power Power Duration Duration Duration Duration % Non-hybrid (LF) Partial Hybrid (SoC=1%) Partial Hybrid (SoC=5%) Full Hybrid 21

22 CONCLUSIONS A Novel Partial Hybrid (PH) System was Designed and Tested Flexible modes of operations (Parallel Following Charging) Uses smaller DC-DC Converter Lower power losses and weight penalty Maximizes the use of battery energy to minimize the stack power and dynamics during the peak demand by load sharing Redundant power sources capable of supporting UAV power demand when one source degrades or fails System Simulation Results PH UAV system has 2% loss in flight duration in comparison to LF UAV system (non-hybrid) PH UAV system has 9% gain in flight duration in comparison to FH UAV system HiL Results with Prototype Hardware Controller Reduced PEMFC stack power range by 5% above average system power PH has 1% and 3% higher flight duration than non-hybrid (LF) and full hybrid (FH) respectively Even with an initial SoC of 5%, the PH System has a similar performance as the non-hybrid (LF) Implementation of analog current controller to improve control of the charging current would further reduce stack operating power range and increase overall stack efficiency Potential increase in stack durability due to a narrow operating power range will be further characterized with life tests 22

23 Acknowledgments Project Supported by Office of Naval Research (ONR) Grants Grant # N Grant # N C8 Technical Support from Dr. Guenter Randolf of GRandalytics g.randolf@grandalytics.com Many Thanks For Your Attention 23