Intelligent Battery Management & Charging For Electric .

Intelligent batterymanagement and chargingfor electric vehiclesSang ChonC2000 MCU AutomotiveMarketing ManagerJon BeallMonitoring & Protection Battery Management SystemsMarketing ManagerTexas Instruments

IntroductionAs the green movement increases in popularity, more and more electric vehicles(EVs) of all kinds—from electric scooters to cars to buses and cargo trucks—willgrace the roads. Power designers will be challenged to provide systems that can beadapted to a wide variety of different types of batteries and vehicles with vastly diverseperformance requirements. This white paper examines the key considerations that arebest suited to meeting the challenges ofincluding battery performance, lifespanand, of course, safety while designingintelligent battery management andcharging systems.Pack Isolated 12VCell Module nEV battery packs are made up of multiplecell modules arranged in series and inBMS Module nCOMMbusFAULTbusparallel. Arranged around the batteryRemote TempInputs7BMS Module 2bq76PL455A-Q1 Monitor ProtectorVtopbattery management system (BMS)721IC Tempis comprised of several components,16including monitoring components1-one or more power-conversion stages1 UVDifferentialMUX16 16 -OVDaisyChainCommsVPRegulator OTclose to the battery cells themselves,ADCCell FaultDetectionCell Monitoring(Voltage)GPIODaisyChainCommsActive Cell Balancing(3x EMB1428Q EMB1499Q10SPI /- 5A (max) 7in the architecture to manage various3121 aspects of the power subsystem.-Intelligent Cell MonitoringDuring the charging and discharging of an EVCOMMbusCell Module 1battery, it is imperative that each cell within thebattery pack is closely and accurately monitoredbecause any number of out-of-spec conditionsSwitch Matrix9Switch Matrix-processors placed at strategic locations16-and intelligent controllers or embedded8 CellModule2Switch Matrixdictated by the needs of the vehicle,PowerSupplies12V12VFFAULTbusIsolated 12VBMS Module 1UART TX/RXWAKEUPFAULT NMicrocontrollerPack -can, at a minimum, quickly cause internal damageIntelligent battery management and charging for electric vehicles5.3VMUXpack and throughout the vehicle, theFigure 1: Multiple battery cell modules stack up to form a battery pack2

of the battery and vehicle or threaten the safety ofdetermine the charge remaining in the battery and,the vehicle’s occupants. EV batteries contain thein turn, the distance the vehicle can travel beforeenergy equivalent to a small explosive. Over-voltagethe battery will need to be recharged. Anotheror under-voltage conditions can lead to thermalcalculation, called state-of-health (SOH), providesrunaways that might cause a battery failure.important insight into the operating conditionsA battery monitoring integrated circuit (BMIC) orof the battery so that its remaining lifespan cancell-balancer device is typically assigned to monitorbe projected and the appropriate maintenancethe voltage of each battery cell in a module, theprocedures recommended.temperature of various points in the module andIntelligent Battery Managementother conditions. This data is reported to a cellmanagement controller (CMC) and, depending onDepending on the complexity of the vehicle, severalthe complexity of the system, on to higher-orderintelligent microcontrollers (MCUs) oversee andprocessing elements, such as one or more batterymanage various critical tasks with regards to themanagement controllers (BMC). The precision ofbattery and the power subsystem. Usually, thesethese measurements and the frequency of theMCUs contain multiple processing cores. Some maycommunications from the BMIC to the CMC andbe comprised solely of general-purpose reducedBMC is key to detecting a condition of concern earlyinstruction set computing (RISC) processors, suchon and taking corrective action before it becomesas ARM cores, while others, which are responsiblehazardous. For example, the BMC might stopfor tasks that are mathematically intense, usuallyregenerative charging or reduce the power drawfeature one or more digital signal processing (DSP)from a pack to return individual cell temperaturescore, like TI’s C28x DSP cores.to an acceptable range or the driver of the vehiclemight be alerted to such a condition through a“check engine” light on the dashboard. In anycase, the BMICs must be capable of very accuratemeasurements and robust communications with theCMCs so that a BMC can take the right correctiveaction in a timely fashion. An EV is indeed verychallenging in terms of designing an effectivecommunication network because of the abundanceof electrical noise in the environment.Often, the robustness of the BMIC’s and CMC’sFigure 2: BMS system overview with battery cell control and main controlcommunications depends on the overall designand routing of the network connecting the variousCMCs, working in concert with BMICs, play andevices in the BMS.important role in ensuring the performance of thebattery and its useful lifespan. For example, duringA BMC aggregates the voltage information froma charging cycle, the BMICs might detect that thethe CMC’s monitoring of the many cells in theeffects of heat have degraded one of the batterybattery pack. It also calculates the state-of-cells to the point where it is charging only to 4.1 V,charge (SOC) of the battery, which is used toIntelligent battery management and charging for electric vehicles3

while the rest of the cells are charging to 4.2 V.input current, intermediate DC bus voltage, batteryThe charging process could then be effectivelycharging current and battery terminal voltage.managed so that none of the cells are chargedThese control loops require the use of computation-above 4.1 V. This would reduce the stress placed onintensive algorithms such as a PID controller or two-all of the cells, extending the life of the battery packpole two-zero compensators. A MCU with a DSPas a whole and ensuring that the battery pack willcore(s) running special instruction sets supportingefficiently store energy and deliver as much powerspecial trigonometric math operations canneeded by the motor the instant it is needed.significantly reduce the number of processor cyclesOf course, real-time responsiveness is essential in aneeded for these algorithms. For example, whereasreal-time system, especially when the system is ana RISC core might need 60 cycles to complete aelectric vehicle traveling at 60 mph. A BMIC mustmath-intense sine or cosine operation, a DSP corebe able to frequently—in a matter of microsecondscould achieve the same result in two or three cycles.—report to the CMC the conditions it is monitoringSuch microcontrollers could also support drivingso that the CMC or higher-level controller canmultiple power topologies and multiple control loopsquickly take any needed corrective actions, suchfor voltage, current plus other system parametersas reducing the power drawn from the package towith such high performance that minimizesreduce overheating, before the situation worsens.“missing” changes in battery characteristics.Moreover, high-performance processing is requiredIntelligent Battery Chargingto support certain advanced operating modes inCharging and discharging the battery efficiently isEVs and Hybrid Electric Vehicle (HEV), such as stop/important as it avoids thermal runaways or otherstart mode and town and country mode.conditions that would either reduce the battery’s Stop/start mode allows the gas engine incapacity or its lifespan. To do this, requires a certainan HEV to be stopped to save fuel when theamount of intelligence in the controlling MCU sincevehicle is stopped at a traffic light or stuckthe parameters of the battery itself will change overin traffic.time. The MCU responsible for the actual charging Town and country mode lets an HEV switchof the battery must be able to quickly adjustback and forth between the gas engine andand adapt in real-time to the battery’s changingthe electric motor depending on which wouldproperties, like oxidation on the terminals, cellbe more efficient. For example, the gas enginevoltages and others. During charging in particular,would propel the vehicle on the highwaythe MCU must be able to respond quickly to over-at higher speeds while the electric motorvoltage conditions. Otherwise, it might cause thewould operate in slower city traffic with itsbattery to overheat and catch on fire.frequent stops.When designing battery charging modules such asEV and power supply manufacturers can also takean on-board charger, higher-order microcontrollersadvantage of the adaptability and versatility ofthat feature DSP cores and specialized co-digital power MCUs to leverage the same softwareprocessors or hardware-based accelerators canframework to control similar power topologiesbe deployed to meet specific real-time operationalwith different power ratings, different input/outputneeds for closed-loop control of on-board chargingvoltages and different PWM frequencies. In otherIntelligent battery management and charging for electric vehicles4

words, the same software developed for a specificinto a longer range per charge for the vehicle. Plus,topology (ex: totem pole PFC or resonant LLCthese new power-stage technologies have improvedfull bridge DC/DC) using a digital power MCU orpower efficiencies, so less power is lost duringa family of MCUs can be used from low power tocharging and charge times are reduced. Gallium-high power with appropriate changes only in digitalNitride (GaN) and Silicon Carbide (SiC) are twocontrol parameters and a few software parametersexamples of new wide bandgap technologies thatrelated to the new power stage. So, digital poweroffer higher switching capabilities and lower on-MCUs let manufacturers effectively re-use or re-resistance than the traditional silicon MOSFET.apply their investment in developing power-controlGaN power stages, such as LMG3410, provide asoftware over and over again in power supplieshigh power rating up to 600 V along with a GaNwith a wide range of power ratings that meetFET, an optimized driver and protection featureapplication requirements.for overcurrent and under-current conditions. SiCThis adaptability is particularly important todayis particularly well suited to switching devices inas innovations and new materials continue to bebattery charging applications for both AC-to-DCintroduced into power-stage components.and DC-to-DC power conversions (see Figure 3and Figure 4).Power Stage InnovationsIn particular, new wide bandgap technologies areSafetyemerging for EV onboard charging applications.Every design project involves tradeoffs amongThese technologies, which better accommodatedesign goals, such as cost, performance, durabilitydirect connection to AC outlets that tap into theand others. The only exception for an EV powerC2000MCUcontrollingpower grid,let EV manufacturersreduce the size 2 Phasesupply system is Interleavedsafety. Chief among the safetyand weight of the vehicle’s charger, which translatesconcerns are thermal runaways which could causeTotemPole PFC400VDCDriverDriverSi FETLMG3410UCC27714LMG3410ACDriverAMC1301TLV316Si FETDriverLMG3410LMG3410RTNISO7340FCZVSZVSIAC senseVAC senseReal-Time C2000 MCUFigure 3: C2000 MCU controlling 2-phase interleaved totem pole PFCIntelligent battery management and charging for electric vehiclesVBUS sense3.3 V5TLV70433TIDA-00708