1/10/2014 Power Electronic Circuits Prof. Daniel Costinett ECE 482 Lecture 2 January 10, 2014 Power Electronics in EVs 12V battery High voltage storage system (~300V) Conventional low power loads DC/DC converter LV Battery HV Battery Battery charge/ discharge unit Propulsion system Electric machine PE converter Battery charge/ discharge unit 14V DC bus DC/AC inverter Air‐conditioning system PE converter Power steering PE converter Electric motors 1 1/10/2014 PHEV/EV Drivetrain Battery Management System SOCmax SOCmin + Vpack – • BMS monitors batteries to ensure operation within safe limits of • Charge/discharge current • State‐of‐Charge (SOC) • (Temperature, SOH, … ) 2 1/10/2014 Battery Mismatch SOCmax SOCmin + Vpack – • EV battery consists of many (100’s) series battery cells (LFP, Li‐ion, NiMH) • Cells share a charging and discharging current, but may have mismatches in series resistance, capacity, operating temperature, health, or dynamics • Cells binned by manufacturer to limit mismatch at beginning‐of‐life Battery Management System SOCmax SOCmin + Vpack – • Discharge is limited by the first cell to reach the minimum allowable State‐of‐ Charge (SOC). 3 1/10/2014 Battery Management System SOCmax Inaccessible Capacity SOCmin + Vpack – • Discharge is limited by the first cell to reach the minimum allowable State‐of‐ Charge (SOC). • Effective pack capacity limited to the capacity of the lowest cell (in Amp‐hours) Battery Management System SOCmax Uncharged Capacity SOCmin + Vpack – • When recharged, charging is stopped when the first cell reaches maximum capacity, leading to incomplete charging of some cells and lower total pack capacity 4 1/10/2014 Battery Management System SOCmax SOCmin + Vpack – • Option 1: Dissipate, then recharge • Repeat a number of cycles to balance all cells at full charge Battery Management System SOCmax SOCmin + Vpack – • Option 2: Redistribute • Requires more advanced circuits • Can be run continuously, during runtime 5 1/10/2014 (Optional) Bidirectional DC‐DC Converter • A DC‐DC converter to boost battery voltage is included in many EVs • Allows higher η operation of ED • Wider operating range • Lower pack voltage Reference: Oak Ridge National Lab, “Benchmarking of Competitive Technologies” DC‐AC Motor Drive • Motor drive generates three, 120° out of phase signals to drive motor windings • Individually operate as three individual electronic power converters 6 1/10/2014 Growing Popularity of E‐bikes Electric Bicycles Worldwide • E‐bikes accounted for $6.9 billion in revenue in 2012 • By utilizing sealed lead‐acid (SLA) batteries, the cost of e‐ bicycles in China averages about $167 (compared to $815 in North America and $1,546 in Western Europe) • China accounts for 90% of world market • Western Europe accounts for majority of remaining 10% despite $1,546 average cost • North America: 89,000 bicycles sold in 2012 7 1/10/2014 Electric Bicycle Platform Power Conversion and Control Battery Electric Motor Electric Bicycle System 8 1/10/2014 System Structure Battery BMS 3‐φ Inverter / Driver Boost DC‐DC Converter D Vout g1‐6 Throttle Brake Filtering and Control Iabc 3‐φ PWM Controller PWM Controller Motor θabc Vref fref Experiment 1 Battery Motor BMS θabc • • • • Identification and characterization of motor Modeling of system using simulink Derivation of model parameters from experimental data Specification of performance for power electronics 9 1/10/2014 Experiment 2 Battery BMS Boost DC‐DC Converter D Motor Vout θabc • • • • Open‐loop operation of Boost converter Inductor design Converter construction and efficiency analysis Bidirectional operation using voltage source / resistive load Experiment 3 Battery BMS Boost DC‐DC Converter D Motor Vout PWM Controller θabc Vref • Closed loop operation of boost converter • Feedback loop design and stability analysis • Analog control of PWM converters 10 1/10/2014 Experiment 4/5 Battery BMS 3‐φ Inverter / Driver Boost DC‐DC Converter D Vout Motor g1‐6 3‐φ PWM Controller PWM Controller θabc Vref • Circuit layout and PCB design • Device selection and implementation according to loss analysis • Basic control of BLDC motors Experiment 6 Battery BMS 3‐φ Inverter / Driver Boost DC‐DC Converter D Vout g1‐6 Throttle Brake Filtering and Control Iabc 3‐φ PWM Controller PWM Controller Motor θabc Vref fref • System‐level control techniques 11 1/10/2014 Example System Implementation Experiment 7 Battery Charger and BMS ZVS Conv. Battery BMS D Solar Cell 3‐φ Inverter / Driver LED Driver Throttle Brake Pedal Torque Filtering and Control Vout g1‐6 Iabc Vector Controller PWM Controller Motor θabc Vref fref • System improvements 12 Characterize 1/10/2014 Test Design Expo • No final exam • Demo operational electric bicycles with system improvements • Competition to determine the most efficient and well‐controlled system 13 1/10/2014 Electric Bicycle Safety and Law • Traffic Law: • Electric motor with power output not more than 1000 W • Not capable of propelling or assisting at greater than 20 mph • No helmet laws for riders over age 16; you may request one at any time • Read Tennessee bicycle safety laws on website General Safety • Lab will work with high voltages (Up to 100 V) • Will use various machinery with high power moving parts • Use caution at all times 14 1/10/2014 Introduction to Vehicle Dynamics Vehicle as a Feedback Sytem 15 1/10/2014 Basic Vehicle Dynamics Angle of inclination H tan 1 L Slope or “grade” H Z L g 9.81 m/s2 Air density 1.204 kg/m3 Rolling resistance coefficient Cr Aerodynamic drag coefficient Cd 16 1/10/2014 Rolling resistance coefficient Cr Aerodynamic drag coefficient Cd Reference: Mehrdad Ehsani, Yimin Gao, Sebastien E .Gay, and Ali Emadi, Modern Electric, Hybrid Electric, and Fuel Cell Vehicles, CRC Press 2004. Chapter 2 Typical Performance Specifications •Cruising (v = const) specs –Top cruising speed on a flat road: vmax –Gradeability: ability to ascend a road of grade Z (in %) at a cruising speed vzmax •Acceleration specs –Time ta it takes to accelerate from vs to vf Typical: vs = 0 mph to vf = 60 mph (100 km/h) in ta seconds 17 1/10/2014 Cruising on a flat road Pv Fv v 1 dv Cd Av v 3 Cr M v gv M v v 2 dt Engine Traction Characteristics 18 1/10/2014 Acceleration Spec Mv dv 1 Fv Cd Av v 2 Cr M v g 2 dt Engine Power Rating Pv 1 Mv 2 1 2 3 vb v f Cd Av v f Cr M v gv f 2 ta 2 19