Page - 149 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 1503 Figure5.Diagramof thedigitaldiagnosisandprotectionschemeforexternal-faultdiagnosis. 2.3.2. FaultDiagnosisofBatteryCells Theover-charged,over-discharged,over-currentandover-temperatureconditionsare thefour different fault conditions of the battery cells. They can cause permanent damage to the battery cells. As these fault conditions are related to the parameters of the battery, they are included in thefaultdiagnosis. Batterychargeanddischarge involvecomplexchemicalandphysicalprocesses. However, theover-charged,over-dischargedandover-current states canalso lead tofiredue to the explosionof thecells. Tocircumventtheseproblems, thebattery-chargingordischargingvoltageneeds tobemonitoredcontinuously inreal-time. If theupperor lowercut-offvoltageor thecurrent reaches themaximumvalue, thesystemcontrollerwilluse theover-charged/over-discharged/over-current protectiontostopthechargingordischargingof thebatterycells. Similarly, over-temperature is another fault to be avoided. In the 12S system prototype, six thermistors are attached to the gaps between every twobattery cells tomonitor the inner-cell temperatures.Atwo-level reportingandprotectionscheme,aswellas theself-recoveryschemewith a temperaturewindow,areproposed. If the temperaturereaches50 ◦C, thecontrollerwill trigger the first-levelprotectionactiontoalerttheuserswithoutinterruptingthechargingordischargingprocesses. However, if thecell’s temperaturereaches60 ◦C(i.e.,quitehighforacell), thecontrollerwill trigger the second-level protection to stop the charging/dischargingprocess immediately. The controller will trigger the self-recoveryprocess automaticallywhenall the cell’s temperaturesdrop to40 ◦C. Theflowchartof the faultdiagnosisandprotectionschemeofover-temperature is showninFigure6. Thesystemwilldetect the faultsmentionedabovetoallowprotectionto takeplace immediately. Figure6.Flowchartof the faultdiagnosisandprotectionschemeforhightemperature. 149