EE152 Green Electronics

Transcription

1 EE152 Green Electronics Batteries 11/5/13 Prof. William Dally Computer Systems Laboratory Stanford University

2 Course Logistics Tutorial on Lab 6 during Thursday lecture Homework 5 due today Homework 6 out today Quiz 2 next Thursday 11/14

3 AC Input/Output Summary AC is just slowly changing DC But need to store energy during the nulls Power factor = P real /P apparent Want power factor very close to 1 Requires current proportional to voltage PF correcting input stage Controls input current sine x error Grid connected inverter Controls output current Independent inverter Control output voltage Use a full-bridge to generate a PWM Sine Wave Pulse width proportional to sin(x) LC Filter to reject high frequencies

4 Anti-Islanding Grid-connected inverters need to turn off when the grid goes down. Safety issue for firemen, linemen, etc How do you detect when the grid goes down?

5 Anti-Islanding Line monitoring Voltage limits, frequency limits. Rate of change of frequency Rapid phase shift Active detection Impedance measurement Forced phase shift/frequency shift

6 Batteries

7 Batteries Many Green Electronic systems require energy storage Batteries are widely used to store energy in chemical bonds Model as dependent voltage source Care required in charging and discharging

8 Energy Density Device Energy Density MJ/kg Gasoline 44 Lithium Ion Battery 1.7 Lead Acid Battery 0.15

9 Two Dimensions of Energy Storage igure 3. f o o of o

10 Energy Density vs Battery Chemistry 250 Lithium Polymer Prismatic 200 Lithium Phosphate WattHours/Kilogram Nickel Cadmium Lead Acid Cylindrical Prismatic Nickel Metal Hydride Cylindrical Prismatic Lithium Ion Cylindrical Aluminum Cans Prismatic WattHours/Litre

11 Photo of Pack

12 18650 Cell

13 Tesla Pack

14 Battery Model L B R B + V BS V B - V BS depends on state of charge and temperature

15 Panasonic Dimensions(Typ.) H 64.93mm of D 18.2mm Bare Cell d 7.9mm Discharged State after Assembling Rated Capacity (at 20 ) Nominal Capacity (at 25 ) Nominal Voltage Charging Method Charging Voltage Charging Current Charging Time Ambient Temperature Weight (Max.) Dimensions (Max.) Maximum size without tube Cell Type NCR18650B Volumetric Energy Density Gravimetric Energy Density Specifications Min.3200mAh Min.3250mAh 3350mAh 3.6V Constant Current -Constant Voltage 4.2V Std.1625mA 4.0hrs. Charge Discharge Storage g (D) (H) 18.25mm 65.10mm 676Wh/l 243Wh/kg 2G23X0KYKU

16 4.5 Discharge Temperature Rate Characteristics Characteristics for for NCR18650B NCR18650B1S cell-1 Charge:CC-CV:1.625A-4.2V Charge:CC-CV:1.625A-4.20V(65.0mA cut) cut) Temp: Discharge:CC:Variable Discharge:CC:3.25A(E.V.:2.50V) Current (E.V.:2.50V) 4.0 Cell Voltage / V CA 1.0CA 0.5CA 0.2CA Discharge Capacity / mah G23X0KYKU

17 Discharge Discharge Temperature Characteristics for for NCR18650B1S NCR18650B 4.5 cell Charge:CC-CV:1.625A-4.20V(65.0mA cut) Discharge:CC:3.25A(E.V.:2.50V) 4.0 Cell Voltage / V Discharge Capacity / mah

18 Charge Characteristics for for NCR18650B1S 4.5 No.1 Cell Voltage Charge:CC-CV:1.625A-4.20V(65.0mA cut) 5000 Cell Voltage / V Current Capacity Current / ma Capacity / mah Charge Time / min 0

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20 Lead-Acid Charge Cycle I B Battery Voltage Battery Current I C I T V C V F V T trickle bulk charge completion float t 0 t B t C t F Time

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22 High Charge Voltage Reduces Life

23 Deep Discharge Reduces Life

24 High Temperature Reduces Life Particularly at high SOC

25 Lead-Acid Charge Cycle I B Battery Voltage Battery Current I C I T V C V F V T trickle bulk charge completion float t 0 t B t C t F Time

26 Layered Control V bat State Machine State I bat V or I Control I max I M1 PWM Current Control G

27 Lead-Acid Charging States V Max >V V C Reset, V<0, V>V Max V B >V V T Off V T >V 0 Trick V V T Bulk V V C Comp I<I F Float Off I = I T I = I B V = V C V = V F

28 Charging Power Path CT F 1 D 1 V i 200:1 V ac input stage 400V C i 1mF G M 1 D 2 V x GND switched inductor L 1 50 H C o 1mF V o output filter R CS.005 V bat

29 Cells One Cell ~2.0V for lead-acid ~3.2V for LiFePO 4 ~3.7V for LiCo Capacity depends on volume 0.4Ah to 200Ah or more 1.28Wh to 640Wh

30 Series Connection Increases Voltage Ah remains the same 100 LiFePO4 cells is about 320V ( ) Capacity (in Ah) the same as one cell 128Wh (0.4Ah cells) to 64kWh (200Ah cells)

31 Series Parallel vs Parallel Series Which is preferred (assuming same Volts and Ah)?

32 Charge control CC, CV profile Battery Management Tasks Cell balancing Temperature monitoring/control SOC (state of charge) estimation Fuel gauge Integrate power Estimate from voltage, current, and temperature Lifetime extension Avoid deep discharge Avoid high-charge, high-temperature storage

33 Cell Balancing Maximum cell voltage must not be exceeded during charging Voltage of each cell must be monitored Current must be bled off of high-voltage cells before they exceed V max Simple resistive balancer or flyback to recycle energy

34 When Things go Wrong

35 Battery Summary Batteries store energy in chemical bonds Model as dependent voltage source with series R and L Terminal voltage is a function of charge state Q Also a function of temperature and charge rate Area of charge-discharge curve is loss in battery Cells connected in series and parallel to build large batteries (series connection of parallel cells) Cells must be balanced to avoid overcharge Battery management Charge control Fuel gauge Lifetime extension

36 Grounding

37 Ground Exactly one point in your circuit is GND An arbitrary point that we refer to as having 0 Volts potential All other voltages are referenced to this point Connections to GND should be made in a Spider not a Daisy Chain Good Bad

38 Avoid loops Ground Loops

39 Why Ground Loops are Bad

40 Consider The PV Lab Power Path

41 A Poor Way to Ground This Why?

42 Grounding Resistor Introduces a Loop

43 Single-point ground Avoid loops Grounding Summary

44 Debugging

45 Get one thing working at a time Work from input of circuit to output Work with simple stimulus, then more complex Form a hypothesis and test it Don t just randomly change things Debugging Work from the schematic Calculate voltage on each node and then verify it. If a chip isn t doing what it should Check every pin of the chip Vdd, GND, all inputs, all outputs For current monitor Check voltage across sense resistor Check bias voltage for op-amp (0.45V) Check that op-amp inputs have the expected voltage Verify output voltage Check with DC input first, then with operating MPPT Check AC common-mode input voltage Use a scope Signals that look good at DC (on a multimeter) may have big AC problems Signals that look good on a logic analyzer (digitized) may have big analog problems

46 Future Lectures Tutorial for Lab 6 Quiz 2 Review Guest Lectures Tesla, Renovo, Enphase Wrapup Project Presentations