GI/ITG KuVS Fachgespräch Energiebewußte Systeme und Methoden

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1 GI/ITG KuVS Fachgespräch Energiebewußte Systeme und Methoden RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems N. Lucas, C. Codrea, T. Hirth and J. Gutierrez {luc, codreacn, hirthts, F. Dressler dressler@informatik.uni-erlangen.de

2 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems Seite 2

3 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems What do I know about my battery? Seite 2

4 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems What do I know about my battery? What is Battery Management and Monitoring (BM 2 )? Seite 2

5 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems What do I know about my battery? What is Battery Management and Monitoring (BM 2 )? How can I implement a BM 2 system? Seite 2

6 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems What do I know about my battery? What is Battery Management and Monitoring (BM 2 )? How can I implement a BM 2 system? Is the effort worth it? Seite 2

What is Battery Management and Monitoring (BM 2 )?

7 What do I know about my battery? Battery technology Batterie- System Nennzellspannung [V] Energieinhalt [Wh/kg] Energiedichte [Wh/l] Mind. Zyklen- Lebensdauer [Zyklen] Memory Effekt Typische Anwendung Blei 2, Nein Batteriebetriebene Werkzeuge, Alarm- und Sicherheitssysteme NiCd 1, Ja Batteriebetriebene Werkzeuge, Modelle, Low- Cost-Produkte NiMH 1, Ja Laptop, Handy, Camcoder Li-Ion 3, Nein Laptop, Handy, Camcoder Seite 3

Zyklen- Lebensdauer [Zyklen] Memory Effekt Typische Anwendung Blei 2,0 25 36 70 110 250 500 Nein Batteriebetriebene Werkzeuge,

8 What do I know about my battery? Battery technology (2) Seite 4

9 What do I know about my battery? Battery models Characterisation of chargeand discharge cycles for a defined set of temperatures and loads Manufacturer s datasheets or field measurements EEPROM storage medium for Look-Up-Tables Seite 5

10 What do I know about my battery? Standard Battery vs. Smart Battery Common batteries seen as dummy power sources Smart batteries provide additional information Standard Battery + - Smart Charger Host Smart Battery + - Smart Battery System (SBS) Specification defines data and communication interface (a) (b) Seite 6

provide additional information Standard Battery + - Smart Charger Host Smart

11 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems What do I know about my battery? What is Battery Management and Monitoring (BM 2 )? Seite 7

12 What is Battery Management and Monitoring (BM 2 )? Battery Management Adjustment of charge voltage and current to the charge profile of the battery Battery Monitoring Calculation of remaining capacity under present operating conditions Battery supervision and generation of warnings and error alarms Seite 8

13 What is Battery Management and Monitoring (BM 2 )? Charge cycle: Li-Ion CC-CV profile: - Constant Current phase up to V - Constant Voltage charge phase until detection of threshold current Alternative: Pulse-charge with constant current and adjustable frequency and dutycycle Overcharge or undercharge: Integrated battery protection electronics Seite 9

2V - Constant Voltage charge phase until detection of threshold current Alternative:

14 What is Battery Management and Monitoring (BM 2 )? Charge cycle: VRLA Usually charged with moderate supply currents and no control hardware Slow procedure Alternative: multi-stage charge strategy - Conditioning phase - CC-CV profile - Trickle-current phase Seite 10

and no control hardware Slow procedure Alternative: multi-stage

15 What is Battery Management and Monitoring (BM 2 )? Remaining capacity Coulomb-Counter: Measurement of discharge current with shunt resistor and current-sense amplifier Registers for charge- and discharge currents Difference serves as a means to estimate remaining capacity Bat. NTC MUX ADC Temp. Reg. Voltage. Reg. Charge. Reg. Discharge. Reg. Remaining capacity = f (Ic, Id, T, Age) Accuracy depends on the quality of the battery models (Look-Up-Tables) and measurements R Control Logic Seite 11

Registers for charge- and discharge currents Difference serves as a means to estimate remaining capacity Bat.

16 What is Battery Management and Monitoring (BM 2 )? Battery Monitoring parameters SOC (State-Of-Charge) SOF (State-Of-Function) SOH (State-Of-Health) => Remaining capacity => Capability to fulfill the current demands => Lifetime estimation Seite 12

(State-Of-Function) SOH (State-Of-Health) => Remaining

17 What is Battery Management and Monitoring (BM 2 )? Battery Monitoring parameters SOC (State-Of-Charge) SOF (State-Of-Function) SOH (State-Of-Health) => Remaining capacity => Capability to fulfill the current demands => Lifetime estimation Battery Models + Measurements + Specification Seite 12

(State-Of-Function) SOH (State-Of-Health) => Remaining capacity =>

18 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems What do I know about my battery? What is Battery Management and Monitoring (BM 2 )? How can I implement a BM 2 system? Seite 13

19 How can I implement a BM 2 system? SBS Specification is a valuable reference model ( Smart Charger Host Smart Battery INTERFACE: I 2 C-based two-wire common interface. Describes protocols, addressing and electrical requirements DATA: Smart Battery Data (SBData) specification DEVICES: Specification of Smart Battery, Smart Battery Charger and Host Seite 14

org) Smart Charger Host Smart Battery INTERFACE: I 2 C-based two-wire common interface.

20 How can I implement a BM 2 system? Smart Batteries are rarely available Smart Charger Host Smart Battery Seite 15

21 How can I implement a BM 2 system? Smart Batteries are rarely available Host Standard Battery Smart Charger Host Smart Battery Smart Charger uc Sensors EEPROM Interface Interface Interface Seite 15

22 How can I implement a BM 2 system? RoBM 2 board RS232 Battery + - Smart Charger uc Sensors EEPROM Interface Interface Interface Seite 16

23 How can I implement a BM 2 system? RoBM 2 board RS232 Battery + - Smart Charger uc Sensors EEPROM Interface Interface Interface Seite 16

24 How can I implement a BM 2 system? RoBM 2 board RS232 Battery + - Smart Charger uc Sensors EEPROM Interface Interface Interface Seite 16

25 How can I implement a BM 2 system? RoBM 2 board RS232 Battery + - Smart Charger uc Sensors EEPROM Interface Interface Interface Seite 16

26 How can I implement a BM 2 system? RoBM 2 board RS232 Battery + - Smart Charger uc Sensors EEPROM Interface Interface Interface Seite 16

27 How can I implement a BM 2 system? RoBM 2 board: Features Level 2 Smart Battery Charger - chemistry independent, universal charger - Vext = 8-28V, Vbat = 19V max, Icharge = 8A max ATmega microcontroller - 16K Bytes ISP Flash, 512 Bytes EEPROM, 1K Byte SRAM, 8-channel 10-bit ADC - interface for SBS - RS232 interface to mobile robot system Seite 17

28 How can I implement a BM 2 system? RoBM 2 board: Performed measurements Total Battery voltage Battery-pack1 voltage External-supply voltage Open circuit voltage (OCV) Charge current Discharge current Ambient temperature, battery-pack1 and pack2 temperature (over connectors) Seite 18

29 How can I implement a BM 2 system? RoBM 2 board: Available data and Alarms over RS232 Remaining capacity in percent Measured voltages, currents and temperatures Charger s status register Battery models for consistency checks Presence of external supply Alarms on overtemperature, non-balanced battery pack, user-defined voltage thresholds Seite 19

30 How can I implement a BM 2 system? RoBM 2 board: Integration in the Robertino Robot System PC104 footprint (9cm x 10cm) for seamless replacement of the connector board RS232 interface between RoBM 2 and Robertino processor Plug-In manager in the processor enables dynamic power management (DPM) policies Seite 20

31 Discussion Topics RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems What do I know about my battery? What is Battery Management and Monitoring (BM 2 )? How can I implement a BM 2 system? Is the effort worth it? Seite 21

32 Is the effort worth it? Simple connector board vs. RoBM 2 RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems Seite 22

33 Is the effort worth it? Decision Aspects RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems Reliability System added value Total cost of ownership (TCO) Seite 23

34 Is the effort worth it? Decision: Reliability RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems Battery Management performs safe battery charge cycles : Overcharge and derivated damage to chemical equipment is avoided Abnormal operation can be detected and aborted: Alarms on non-balanced battery packs, overtemperature or user-defined events Battery Monitoring provides estimate of running time (Remaining Capacity) Seite 24

35 Is the effort worth it? Decision: System added value RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems Battery Management mature for Lead-Acid, Ni- and Li-based batteries Battery Monitoring enables battery-driven system design: - Device Level battery-aware task scheduling: reduce peak current consumption - Network Level battery-aware task scheduling: distributed execution depending on SOC of each device - Dynamic power management: service quality depends on SOC Seite 25

36 Is the effort worth it? Decision: Total Cost of Ownership RoBM 2 : Measurement of Battery Capacity in Mobile Robot Systems RoBM 2 board implies additional initial costs RoBM 2 board reduces maintenance costs - Battery lifetime is extended using battery management resources - Adoption of new battery technology (e.g. Li-Ion instead of VRLA) needs no hardware replacement Seite 26

37 Thank You! Seite 27

Battery Cell Balancing: What to Balance and How

Battery Cell Balancing: What to Balance and How Yevgen Barsukov, Texas Instruments ABSTRACT Different algorithms of cell balancing are often discussed when multiple serial cells are used in a battery pack