Study on a Battery Thermal Management System Based on a Thermoelectric Effect

energies

Article Study on a Battery Thermal Management System Based on a Thermoelectric Effect

Chuan-Wei Zhang, Ke-Jun Xu *, Lin-Yang Li, Man-Zhi Yang, Huai-Bin Gao and Shang-Rui Chen College of Mechanical Engineering, Xi’an University of Science and Technology, Xi’an 710054, China; [email protected] (C.-W.Z.); [email protected] (L.-Y.L.); [email protected] (M.-Z.Y.); [email protected] (H.-B.G.); [email protected] (S.-R.C.) * Correspondence: [email protected]; Tel.: +86-159-9160-0997

Received: 27 December 2017; Accepted: 16 January 2018; Published: 24 January 2018

Abstract: As is known to all, a battery pack is significantly important for electric vehicles. However, its performance is easily affected by temperature. In order to address this problem, an enhanced battery thermal management system is proposed, which includes two parts: a modified cooling structure and a control unit. In this paper, more attention has been paid to the structure part. According to the heat generation mechanism of a battery and a thermoelectric chip, a simplified heat generation model for a single cell and a special cooling model were created in ANSYS 17.0. The effects of inlet velocity on the performance of different heat exchanger structures were studied. The results show that the U loop structure is more reasonable and the flow field distribution is the most uniform at the inlet velocity of 1.0 m/s. Then, on the basis of the above heat exchanger and the liquid flow velocity, the cooling effect of the improved battery temperature adjustment structure and the traditional liquid temperature regulating structure were analyzed. It can be seen that the liquid cooling structure combined with thermoelectric cooling demonstrates a better performance. With respect to the control system, the corresponding hardware and software were also developed. In general, the design process for this enhanced battery thermal management system can provide a wealth of guidelines for solving similar problems. The H commutation circuit, matrix switch circuit, temperature measurement circuit, and wireless communication modules were designed in the control system and the temperature control strategy was also developed.

Keywords: battery; thermal management system; Peltier effect; liquid cooling; thermoelectric cooler

1. Introduction Environmental pollution and the energy crisis are becoming more and more serious, so all countries are focusing on renewable energy. As a typical representative of the renewable energy industry, electric vehicles have attracted worldwide attention due to their cleanness. However, the function of an electric vehicle is restricted by its power battery [1–4]. It has been found that the battery life and work efficiency are the highest when the operating temperature of the lithium battery is in the range of 25–45 ◦C. Unfortunately, the temperature of the power battery often is not kept in the best range during actual operation. The internal resistance of the battery will rise sharply when the operating temperature is lower than 0 ◦C, which can greatly influence the performance of the battery. On the other hand, the speed of the battery’s side reaction will accelerate when the temperature is too high, and the capacity of the battery will be greatly reduced. A battery fire, explosion, or other safety incidents can also happen due to a high temperature [5–7]. In terms of the thermal mechanism of the battery, experts have studied the heat production model of the lithium-ion battery positively. The heat generation model of the battery can be divided into an electrochemical thermal coupling model and an electrothermal coupling model according to the principle of electrochemistry. Smith et al. [8] simulated the temperature field of the battery

Energies 2018, 11, 279; doi:10.3390/en11020279 www.mdpi.com/journal/energies Energies 2018, 11, 279 2 of 15 using a one-dimensional model and pointed out that the contact resistance heat, joule heat, and electrochemical reaction heat are the most important three parts of the heat production of the battery. However, the internal heat production during the charging and discharging process of battery charging is extremely complex. In order to establish accurate heat generation models, all kinds of reactive heat and Joule heat caused by different electrochemical reaction rates and an uneven distribution of internal electric current at different charging/discharging times and different battery temperatures should be studied. Gao et al. [9] proposed a coupled equivalent circuit and convective thermal model to determine the state-of-charge (SOC) and temperature of a LiFePO4 battery working in a real environment. Chiew et al. [10] studied the battery’s thermal wrap and analyzed the thermal effect of latent heat storage. Now, the widely recognized model for the heating effect is to treat a lithium ion battery as a uniform internal heat source. The transport equation of conservation and energy, reasonable boundary conditions, and initial conditions are established to obtain the internal and external temperature distribution of the battery [11]. The battery’s thermal management mainly has three methods: air adjustment, liquid adjustment, and phase change material adjustment. Chen et al. [12,13] studied the air condition of the battery’s thermal management system and optimized the angles of the plenums. The results showed that changing the angles of the plenums is one of the most effective approaches. Yu et al. [14] designed a battery thermal management system that contained both serial ventilation cooling and parallel ventilation cooling. The maximum temperature of the novel cooling system was reduced and the temperature uniformity was improved compared to the traditional system. The air conditioning method has advantages such as simple operation and a small cost, while the temperature regulating efficiency is low. Once the discharge current exceeds 30 A, the air cooling will not reach the heat dissipation requirement of the battery [15]. Therefore, the medium of the thermostat system is changed to improve the efficiency of the temperature adjustment. Yuan et al. [16] studied the liquid temperature control scheme and a uniform heating was obtained for the battery surface. Huo et al. [17] reviewed the research progress on the application of liquid medium to the thermal management of the battery, and pointed out that although the liquid temperature regulating efficiency is high, it needs a more complex structure and higher quality and is complicated to install. Lin et al. [15] studied phase change materials for the thermal management of batteries and found a better ratio of paraffin wax. Ramandi et al. [18] studied heat transfer in and thermal management of electric vehicle batteries with phase change materials. Wei et al. [19] used a phase change material and liquid cooling pipe combined scheme to study the effects of coolant flow rate on temperature rise in the battery. It shows that with the increase of coolant flow rate, the temperature rise and temperature difference of the battery gradually decrease. Ma et al. [20] reviewed phase change materials for battery heat management and pointed out the technical bottlenecks of phase change materials. In general, it is necessary to improve the traditional methods or find a new method to improve the efficiency of the battery’s temperature adjustment so as to overcome the shortcomings of the traditional methods. A battery thermal management program based on the theory of the second thermoelectric effect is presented in this paper, which is realized by the combination of semiconductor temperature and liquid temperature control. At the same time, the corresponding structure was designed and analyzed.

2. The Second Thermoelectric Effect The second thermoelectric effect is known as the Peltier effect [21]. When there is a current through the circuit composed of different conductors, in addition to producing irreversible Joule heat, the different conductors at the junction with the direction of the current will have different heat absorption, which is an exothermic phenomenon. Assuming that the number of free electrons in the A terminal is large, the number of free electrons at the B end is small, and if the current ﬂows from A to B, the temperature at the B end will increase; conversely, the temperature of the B side will be reduced. The schematic diagram is shown in Figure1. As early as 1834, Peltier found Energies 20182018,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 33 ofof 1515

A terminal is large, the number of free electrons at thethe BB endend isis small,small, andand ifif thethe currentcurrent flowsflows fromfrom AA Energies 2018, 11, 279 3 of 15 toto B,B, thethe temperaturetemperature atat thethe BB endend willwill increase;increase; conversely, the temperature of the B side will be reduced.reduced. TheThe schematicschematic diagramdiagram isis shownshown inin FigureFigure 1.1. AsAs earlyearly asas 1834,1834, PeltierPeltier foundfound thisthis thisphenomenon, phenomenon, but butbecause because the thetechnical technical conditions conditions were were not not allowed allowed at at that that time, time, it it was notnot popularized.popularized. Now, withwith thethe rapidrapid developmentdevelopment ofof semiconductorsemiconductorsemiconductor technology,technology, thermoelectricthermoelectricthermoelectric chipschipschips andand thermoelectricthermoelectric coolerscoolers werewere producedproduced [[22].22]. AA semiconductorsemiconductor thermoelectricthermoelectric chipchip isis mademade upup ofof severalseveral hundred pairs pairs of of thermocouples, thermocouples, and and the the temp temperatureerature control control can can be be realized realized at atboth both ends ends of ofthethe the coldcold cold andand and heat.heat. heat. ManojManoj Manoj etet et al.al. al. [23][23] [23 ]designeddesigned designed aa a vehiclevehicle vehicle refrigerationrefrigeration andand air air conditioningconditioningconditioning systemsystemsystem usingusing thermoelectricthermoelectric chipschips asas thethe corecore coolingcooling measures,measures, andand designeddesigned thethe correspondingcorresponding heatheat sinksink device.device. ThroughThrough comparison,comparison, the the effect effect of of this this air air conditioning conditioning system system is betteris better than than the the traditional traditional air conditioningair conditioning system. system. Kaushik Kaushik et et al. al. [24 [24]] gave gave the the number number of of thermocouples thermocouples in in the the ﬁrst first and and second second stagesstages ofof aa ThermoelectricThermoelectric ChipChip (TEC)(TEC) forfor maximummaximum coolingcooling powerpower energy,energy, andand thethe exergyexergy efﬁciencyefficiency conditionsconditions were were optimized. optimized. Meng Meng et et al. al. [25] [25 showed] showed the the effects effects of ofa th aermocouple’s thermocouple’s physical physical size size on the on theperformance performance of a ofthermoelectric a thermoelectric heat heatpump pump (TEH) (TEH) driven driven by a by thermoelectric a thermoelectric generator generator (TEG). (TEG). The Theschematic schematic diagram diagram of heat of transfer heat transfer for a ther formoelectric a thermoelectric chip is chipshown is shownin Figure in 2 Figure [26]. 2[26].

FigureFigure 1.1. PeltierPeltier effect.effect.

FigureFigure 2.2. HeatHeat transfertransfer ofof aa thermoelectricthermoelectric chip.chip.

AA thermoelectricthermoelectric chip chip has has the the characteristic characteristic of of absorbing absorbing heat heat at oneat one end end and and releasing releasing heat heat at the at the other end, and is also called a heat pump. Then, assuming that the temperature of the heat node otherthe other end, end, and and is also is also called called a heat a heat pump. pump. Then, Then assuming, assuming that thethat temperature the temperature of the of heat the nodeheat node is Th, is Th, the heat released to the environment is Qh. The cold junction temperature is Tc, and the heat theis T heath, the released heat released to the environmentto the environment is Qh. The is Q coldh. The junction cold junction temperature temperature is Tc, and is the Tc, heat and absorbed the heat absorbed from the outside (refrigerating capacity) is Q0. The input power of the thermocouple is W, fromabsorbed the outsidefrom the (refrigerating outside (refrigerating capacity) capacity) is Q0. The is input Q0. The power input of power the thermocouple of the thermocouple is W, and is theW, currentand the incurrent the loop in the is I .loop If all is possible II.. IfIf allall possible lossespossible are losseslosses not considered, areare notnot considered,considered, Equation EquationEquation (1) can be (1)(1) obtained cancan bebe obtained fromobtained the ﬁrstfromfrom law thethe of firstfirst thermodynamics. lawlaw ofof thermodynamics.thermodynamics. Q = Q + W (1) QQWh =+0 (1) QQWhh 00 (1) Perle absorption heat: Perle absorption heat: Qc = πI (2)

Energies 2018, 11, 279 4 of 15 where π is the coefﬁcient of peltier, which is determined by the beta coefﬁcient (α) and the cold end temperature (Tc). π = αTc (3) Joule heat: 2 Qj = I R (4) where R is the resistance of the thermoelectric element. If the couple arm length is L, ρ1 and ρ2 are the resistivity, and the cross section areas are S1 and S2, then: ρ ρ R = L( 1 + 2 ) (5) S1 S2

Due to the heat conduction of a semiconductor, a certain amount of heat is passed from the hot end to the cold end. Qk = k(Th − Tc) (6) where k represents the total thermal conductivity of a thermoelectric element with a length equal to L.

1 k = (λ s + λ s ) (7) L 1 1 2 2 where the coefﬁcient of thermal conductivity of the two electric couple arms is λ1 and λ2, respectively. Finally, we determine the heat absorbed by the cold end from the outside world.

Q0 = Qc − 0.5Qj − Qk (8)

2 Q0 = αITc − 0.5I R − k(Th − Tc) (9) Quantity of heat production:

2 Q1 = αITh + 0.5I R − k(Th − Tc). (10)

To make the thermoelectric thermostat module work properly, the applied voltage needs to be equal to the pressure drop plus the Seeback voltage. The corresponding input power is P.

P = I(α∆T + IR) (11)

Refrigeration coefﬁcient of thermoelectric refrigeration:

ECOP = Q0/P (12)

Merit coefﬁcient: α2r Z = (13) λ where r is the electrical conductivity of the thermoelectric components.

r = 1/ρ (14)

The maximum refrigerating capacity of the thermoelectric refrigeration module under certain conditions and the acquisition of the coefficient of refrigeration depend on the merit coefficient of the material. There is a positive correlation between the coefficient of merit and the effect of refrigeration. As long as the heat in the hot end can be taken out in time, the heat transfer efficiency of the thermoelectric chip will be greatly improved. Energies 2018, 11, 279 5 of 15

In this study, TEC-12708 thermoelectric chips (current 8 A, voltage 15.2 V, maximum cooling efﬁciency 76 W, produced by KJLP (SHENZHEN) ELECTCONICS Co., Ltd., Shenzhen, China) were Energies 2018, 11, x FOR PEER REVIEW 5 of 15 used. The corresponding parameters are shown in Table1. refrigeration.In order to As regulate long as the the temperature heat in the ofhot the end battery, can be a taken combined out in liquid time, and the thermoelectricheat transfer efficiency cooling systemof the wasthermoelectric adopted, especially chip will forbe whengreatly the improved. battery temperature is too high. The thermoelectric chips and waterIn this cooling study, system TEC-12708 were thermoelectric arranged on the chips surface (current of the 8 batteryA, voltage inthe 15.2 proper V, maximum order, and cooling the heatefficiency was transported 76 W, produced from the by battery KJLP to(SHENZ the waterHEN) cooling ELECTCONICS system by the CO., thermoelectric LTD, Shenzhen, cooler chips.China) Therefore,were used. the The adjustment corresponding of the battery’sparameters temperature are shown mayin Table be achieved. 1. In order to regulate the temperature of the battery, a combined liquid and thermoelectric Table 1. Parameters of the thermoelectric chip. cooling system was adopted, especially for when the battery temperature is too high. The

thermoelectricCharacteristic chips and water cooling Parameter system were Characteristicarranged on the surface of Parameter the battery in the proper order, Typeand the heat was transported TEC-12708 from the battery Size to the water 40 mm cooling× 40 mm system× 3.2 mm by the thermoelectricVoltage cooler chips. Therefore, 12 V the adjustment Maximum of current the battery’s temperature 8 A may be Maximum temperature difference 70 K maximum refrigeration power 76 W achieved.

3. Model Analysis and StructureTable Optimization 1. Parameters of the thermoelectric chip.

3.1. Three-DimensionalCharacteristic (3D) Model DesignParameter and Grid Partition Characteristic Parameter Type TEC-12708 Size 40 mm × 40 mm × 3.2 mm The L148F20 LiFePOVoltage 4 battery was selected 12 V in the Maximumpresent work, current which has a rated 8 voltageA of 3.2 V and a capacityMaximum of temperature 20 AH. The difference physical geometries 70 K maximum parameters refrigeration of the power battery and heat 76 W exchanger are shown in Table2. As shown in Figure3, based on the related geometries parameters, a single cell model,3. Model a water Analysis cooling and model, Structure and aOptimization thermoelectric cooling model were established in Solidworks 16.0 (Dassault Systemes S.A, Vélizy-Villacoublay, France). 3.1. Three-Dimensional (3D) Model Design and Grid Partition Table 2. Physical geometries parameters. The L148F20 LiFePO4 battery was selected in the present work, which has a rated voltage of 3.2 V and a capacity of 20 AH. The physical geometries parameters of the battery and heat exchanger Length (mm) Width (mm) Height (mm) are shown in Table 2. As shown in Figure 3, based on the related geometries parameters, a single cell Single battery 200 40 150 model, a water cooling model, and a thermoelectric cooling model were established in Solidworks Heat exchanger 200 20 150 16.0 (DassaultSimpliﬁed Systemes Thermoelectric S.A, Vélizy-Villacoublay, 200 France). 6 106

(a) (b) (c)

FigureFigure 3. Three-dimensional3. Three-dimensional model. model. (a) Single (a) batterySingle model;battery (b )model; Water cooling (b) Water model; cooling (c) Thermoelectric model; (c) coolingThermoelectric model. cooling model.

Table 2. Physical geometries parameters. Then, hexa-dormant structured mesh was drowned by ICEMCFD (ANSYS, Inc., Canonsburg, PA, USA) Hexa-dormant structured mesh has better Length orthogonality, (mm) Width ahigher (mm) calculation Height (mm) accuracy, and a fast computation speed.Single Because battery the complexity of 200 the geometric model 40 will increase 150 the computation resources required andHeat the exchanger complicated geometry200 model may easily20 create an error150 in the simulation, in this paper theSimplified model was Thermoel simpliﬁedectric to a heat200 source that was heated 6 with the 106 rate of 100 W from the inside. The mesh model is shown in Figure4. The number of cells, faces, and nodes of the single batteryThen, is 230,131, hexa-dormant 703,861, and structured 243,824, mesh respectively. was drowned The number by ICEMCFD of cells, faces, (ANSYS, and nodes Inc., ofCanonsburg, the water coolingPA, USA) model Hexa-dormant is 129,021, 399,860, structured and 141,792,mesh has respectively. better orthogonality, The number a ofhigher cells, calculation faces, and nodesaccuracy, of theand simpliﬁed a fast computation thermoelectric speed. model Because is 293,242, the 843,808,complexi andty of 266,435, the geometric respectively. model will increase the computation resources required and the complicated geometry model may easily create an error in the simulation, in this paper the model was simplified to a heat source that was heated with the rate of 100 W from the inside. The mesh model is shown in Figure 4. The number of cells, faces, and nodes of the single battery is 230,131, 703,861, and 243,824, respectively. The number of cells, faces, and nodes of the water cooling model is 129,021, 399,860, and 141,792, respectively. The number of

EnergiesEnergies 2018 2018, 11, 11, x, x FOR FOR PEER PEER REVIEW REVIEW 6 6of of 15 15 Energies 2018, 11, 279 6 of 15 cells,cells, faces,faces, andand nodesnodes ofof thethe simplifiedsimplified thermothermoelectricelectric modelmodel isis 293,242,293,242, 843,808,843,808, andand 266,435,266,435, respectively.respectively. TheThe model modelmodel was was simulated simulated simulated using using using Fluent Fluent Fluent 17.0 17.0 in in in the the the ANSYS ANSYS. ANSYS. 17.0. The The details Thedetails details of of the the ofparameters parameters the parameters are are shown shown are inshownin Table Table in 3; 3; Tableall all other other3; all parameters parameters other parameters used used the the used system system the default. default. system default.

(a(a) ) (b(b) ) (c()c ) Figure 4. Mesh model. (a) Single battery model; (b) Water cooling model; (c) Thermoelectric cooling Figure 4. Mesh model.model.( a(a)) Single Single battery battery model; model; (b) ( Waterb) Water cooling cooling model; model; (c) Thermoelectric (c) Thermoelectric cooling cooling model. model.model. Table 3. Simulation parameter details. TableTable 3. 3. Simulation Simulation parameter parameter details. details.

ItemItemItem FeaturesFeatures Features Item Item Item Features Features Features ViscousViscousViscous k-epsilonk-epsilon k-epsilon Solid Solid Solid Aluminum Aluminum Aluminum FluidFluidFluid Water-liquid Water-liquid Water-liquid Heating Heating Heating rate rate rate 100 100 100 WW W Velocity-inletVelocity-inletVelocity-inlet 1 1m/s 1m/s m/s Solution Solution Solution method method method Pressure–velocity Pressure–velocity Pressure–velocity coupling/SIMPLE coupling/SIMPLE coupling/SIMPLE TemperatureTemperatureTemperature 298.15 298.15 298.15 K K K Criteria Criteria Criteria for for for convergence convergence convergence Energy/1e-06 Energy/1e-06 Energy/1e-06

3.2.3.2. Heat HeatHeat Generation Generation Model Model of of Battery Battery InIn the the introduction introduction ofof of thisthis this paper,paper, paper, it it it is is is pointed pointed pointed out out out that that that many many many scholars scholars scholars have have have simplified simplified simplified the the the battery battery battery to tobeto be anbe an internalan internal internal homogeneous homogeneous homogeneous heating heating heating body. body. body. This This articleThis article article also followsalso also follows follows this method. this this method. method. Then, aThen,Then, battery a a battery battery model modelwasmodel built was was with built built a with heatingwith a a heating heating rate of rate 100rate of Wof 100 and100 W W an and and ambient an an ambient ambient temperature temperature temperature of 298.15 of of 298.15 298.15 K using K K using using ANSYS ANSYS ANSYS 17.0. 17.0.The17.0. temperature The The temperature temperature profiles profiles profiles of the batteryof of the the battery underbattery natural under under convectionnatural natural convection convection are shown are are in shown Figureshown5 in .in The Figure Figure maximum 5. 5. The The maximumtemperaturemaximum temperature temperature of the battery of of isthe the 383.8 battery battery K, and is is the383.8 383.8 battery’s K, K, and and center the the battery’s battery’s position cent iscent slightlyerer position position hotter is comparedis slightly slightly hotter tohotter the comparedbattery’scompared edge. to to the the This battery’s battery’s is in line edge. edge. with theThisThis mechanism is is in in line line wi ofwith theth the heatthe mechanism mechanism production of ofof the thethe battery.heat heat production production Then, the of aboveof the the battery.modelbattery. was Then, Then, regarded the the above above as amodel model reference was was andregarded regarded the following as as a a reference reference work wasand and basedthe the following following on this workmodel. work was was To based keepbased theon on thissimulationthis model.model. comparable, ToTo keepkeep thethe the simulationsimulation battery parameters comparable,comparable, are consistent thethe batterybattery with parametersparameters the heating areare power consistentconsistent of the battery withwith thethe in heatingtheheating temperature powerpower regulation.ofof thethe batterybattery The temperature inin thethe temperaturtemperatur regulationee isregulation.regulation. determined TheThe and temperature improvedtemperature by comparingregulationregulation the isis determinedsurfacedetermined temperature andand improvedimproved of water by coolingby comparingcomparing with that thethe of surfacsurfac thermoelectricee temperaturetemperature cooling, ofof and waterwater the cooling optimalcooling with temperaturewith thatthat ofof thermoelectricprofilethermoelectric of the battery cooling, cooling, was and and obtained. the the optimal optimal temp temperatureerature profile profile of of the the battery battery was was obtained. obtained.

Figure 5. Temperature proﬁles of the battery under natural convection. FigureFigure 5. 5. Temperature Temperature profiles profiles of of the the battery battery under under natural natural convection. convection.

Energies 2018, 11, 279 7 of 15 Energies 2018, 11, x FOR PEER REVIEW 7 of 15 Energies 2018, 11, x FOR PEER REVIEW 7 of 15 3.3.3.3. StructureStructure DesignDesign andand OptimizationOptimization ofof HeatHeat ExchangerExchanger 3.3. Structure Design and Optimization of Heat Exchanger AccordingAccording toto the the temperature temperature proﬁles profiles of of the the battery, battery, it canit can be be seen seen that that the the simpliﬁed simplified model model of the of According to the temperature profiles of the battery, it can be seen that the simplified model of thermoelectricthe thermoelectric chip chip should should be placed be placed in the in central the cent positionral position of the of positive the positive surface surface of the battery.of the battery. Based the thermoelectric chip should be placed in the central position of the positive surface of the battery. onBased the heatingon the heating mechanism mechanism of the battery of the and battery the structureand the ofstructure the thermoelectric of the thermoelectric chip, two structureschip, two Based on the heating mechanism of the battery and the structure of the thermoelectric chip, two ofstructures a heat exchanger of a heat forexchanger the cooling for the system cooling were syst designed.em were The designed. diameter The of diameter the inlet andof the the inlet outlet and is structures of a heat exchanger for the cooling system were designed. The diameter of the inlet and 18the mm. outlet As is shown 18 mm. in As Figure shown6, the in lowerFigure left 6, the is the lowe inletr left of is the the coolant inlet of and the the coolant upper and right the is upper the outlet. right the outlet is 18 mm. As shown in Figure 6, the lower left is the inlet of the coolant and the upper right Theis the other outlet. picture The isother the structurepicture is B, the in structure which the B, left in lowerwhich mouth the left is lower the inlet mouth of the iscoolant the inlet and of thethe is the outlet. The other picture is the structure B, in which the left lower mouth is the inlet of the uppercoolant left and is the outlet.upper left is the outlet. coolant and the upper left is the outlet.

(a) (b) (a) (b) Figure 6. Structures of liquid cooling method. (a) Structure A; (b) Structure B. FigureFigure 6.6. StructuresStructures ofof liquidliquid coolingcooling method.method. ((aa)) StructureStructure A; A; ( b(b)) Structure Structure B. B. Four different inlet velocities, v = 0.2 m/s, v = 0.5 m/s, v = 1.0 m/s, and v = 2.0 m/s, were adopted FourFour different different inlet inlet velocities, velocities,v =v = 0.2 0.2 m/s, m/s,v v= = 0.5 0.5 m/s, m/s,v v= =1.0 1.0 m/s, m/s, andandv v= = 2.02.0 m/s,m/s, were adoptedadopted in the simulation of structure A, and the corresponding velocity vectors were obtained as shown in inin thethe simulationsimulation ofof structurestructure A,A, andand the the corresponding corresponding velocityvelocity vectorsvectors werewere obtainedobtained asas shownshown inin Figure 7. The flow velocity distribution is Z-shaped, and the velocity is slow or even close to zero at FigureFigure7 .7. The The flow flow velocity velocity distribution distribution is Z-shaped,is Z-shaped, and and the the velocity velocity is slow is slow or even or even close close to zero to zero at the at the center of the channel. This phenomenon decreased with the increase of flow rate, but did not centerthe center of the of channel. the channel. This phenomenon This phenomenon decreased decre withased the with increase the increase of flow rate, of flow but did rate, not but disappear. did not disappear. Similarly, four different inlet velocities, v = 0.2 m/s, v = 0.5 m/s, v = 1.0 m/s, and v = 2.0 m/s, Similarly,disappear. four Similarly, different four inlet different velocities, inletv velocities,= 0.2 m/s, v v= =0.2 0.5 m/s, m/s, v =v 0.5= 1.0m/s, m/s, v = 1.0 and m/s,v = and 2.0 m/s,v = 2.0 were m/s, were adopted for structure B, and the corresponding velocity vectors were obtained as shown in adoptedwere adopted for structure for structure B, and theB, and corresponding the correspondi velocityng velocity vectors werevectors obtained were obtained as shown as in shown Figure 8in. Figure 8. The results show that the distribution of the liquid velocity is relatively uniform. However, TheFigure results 8. The show results that theshow distribution that the distribution of the liquid of velocity the liquid is relatively velocity is uniform. relatively However, uniform. the However, velocity the velocity of the central position of the flow channel is still relatively slow when the flow rate is 0.2 ofthe the velocity central of position the central of the position flow channelof the flow is still channel relatively is still slow relatively when slow the flow when rate the is flow 0.2m/s, rate is and 0.2 m/s, and even close to zero at some locations. It was found that increasing the flow velocity of the evenm/s, closeand even to zero close at someto zero locations. at some It locations. was found It thatwasincreasing found that the increasing flow velocity the flow of the velocity inlet coolant of the inlet coolant could alleviate this phenomenon. The vortex phenomenon at the central part of the flow couldinlet coolant alleviate could this alleviate phenomenon. this phenomenon. The vortex phenomenonThe vortex phenomenon at the central at the part central of the part flow of channelthe flow channel is further weakened when the flow velocity increases to 1.0 m/s, and the flow velocity is ischannel further is weakened further weakened when the when flow velocitythe flow increases velocity toincreases 1.0 m/s, to and1.0 them/s, flow and velocitythe flow is velocity basically is basically uniform within the whole flow channel. However, the phenomenon reappeared again uniformbasically within uniform the wholewithin flowthe channel.whole flow However, channel. the However, phenomenon the reappearedphenomenon again reappeared when the again flow when the flow velocity further increased. It is concluded that the stagnation of the liquid at the velocitywhen the further flow increased.velocity further It is concluded increased. that It theis co stagnationncluded ofthat the the liquid stagnation at the channel of the centerliquid firstlyat the channel center firstly decreased and then increased with the increase of the flow velocity. Therefore, decreasedchannel center and thenfirstly increased decreased with and the then increase increased of the with flow the velocity. increase Therefore, of the flow it isvelocity. maybe Therefore, the better it is maybe the better choice to have a flow velocity of 1.0 m/s. choiceit is maybe to have the a better flow velocitychoice to of have 1.0 m/s. a flow velocity of 1.0 m/s.

(a) (b) (a) (b)

Figure 7. Cont.

Energies 2018, 11, 279 8 of 15 Energies 2018, 11, x FOR PEER REVIEW 8 of 15 Energies 2018, 11, x FOR PEER REVIEW 8 of 15

(c) (d) (c) (d) Figure 7. Velocity vectors of structure A. (a) v = 0.2 m/s; (b) v = 0.5 m/s; (c) v = 1 m/s; (d) v = 2 m/s. FigureFigure 7. Velocity7. Velocity vectors vectors of structureof structure A. (A.a) v(a=) v 0.2 = 0.2 m/s; m/s; (b )(bv)= v 0.5= 0.5 m/s; m/s; (c ()cv) v= = 1 1 m/s; m/s; ((dd))v v= = 22 m/s.m/s.

(a) (b) (a) (b)

(c) (d) (c) (d) Figure 8. Velocity vectors of structure B. (a) v = 0.2 m/s; (b) v = 0.5 m/s; (c) v = 1.0 m/s; (d) v = 2.0 m/s. Figure 8. Velocity vectors of structure B. (a) v = 0.2 m/s; (b) v = 0.5 m/s; (c) v = 1.0 m/s; (d) v = 2.0 m/s. Figure 8. Velocity vectors of structure B. (a) v = 0.2 m/s; (b) v = 0.5 m/s; (c) v = 1.0 m/s; (d) v = 2.0 m/s. Generally, the cooling effects of the above two structures are different under the same Generally, the cooling effects of the above two structures are different under the same conditions, as shown in Figures 7 and 8. The fluid velocity in the flow channel is more uniform for conditions,Generally, as theshown cooling in Figures effects of7 and the above8. The twofluid structures velocity arein the different flow channel under the is more same conditions,uniform for the scheme B, which is a relatively better solution. Moreover, the flow velocity of v = 1.0 m/s is a asthe shown scheme in FiguresB, which7 and is 8a. relatively The fluid velocitybetter solution. in the flow Moreover, channel the is more flow uniformvelocity forof thev = scheme1.0 m/s B,is a better choice. v whichbetter is choice. a relatively better solution. Moreover, the flow velocity of = 1.0 m/s is a better choice. 3.4.3.4. CoolingCooling EffectEffect ofof thethe ModifiedModified CoolingCooling StructureStructure 3.4. Cooling Effect of the Modified Cooling Structure BasedBased onon thethe previousprevious meshmesh gridgrid model,model, thethe coolingcooling effectseffects ofof thethe modifiedmodified coolingcooling structurestructure Based on the previous mesh grid model, the cooling effects of the modified cooling structure werewere analyzed.analyzed. At At the the same same time, time, they they were were compared compar withed with the effectthe effect of liquid of liquid cooling. cooling. The inletThe flowinlet were analyzed. At the same time, they were compared with the effect of liquid cooling. The inlet velocityflow velocity of the of heat the exchanger heat exchanger is 1.0 m/s, is 1.0 and m/s, the and inlet the temperature inlet temperature of the liquid of the coolant liquid is coolant 298.15 K.is flow velocity of the heat exchanger is 1.0 m/s, and the inlet temperature of the liquid coolant is The298.15 corresponding K. The corresponding surface temperature surface temperature distributions distributions are shown are in Figureshown9 .in Figure 9. 298.15 K. The corresponding surface temperature distributions are shown in Figure 9. It can be seen that the temperature distribution of the combined thermoelectric cooling system is more uniform and the maximum temperature of the battery could be reduced to 291 K. In fact, if the power of the thermoelectric chip is further improved and the heat of heat end can be exported in time, the cooling effect will be better. Thus, the combination system of liquid and thermoelectric cooling is applied in the present paper.

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Energies 2018, 11, 279 9 of 15 Energies 2018, 11, x FOR PEER REVIEW 9 of 15

(a) (b)

Figure 9. Temperature profiles of liquid cooling and combined with thermoelectric cooling. (a) Liquid cooling; (b) combined liquid and thermoelectric cooling.

It can be seen that the temperature distribution of the combined thermoelectric cooling system is more uniform and the( amaximum) temperature of the battery could be reduced(b) to 291 K. In fact, if the power of the thermoelectric chip is further improved and the heat of heat end can be exported in time,FigureFigure the 9. cooling9.Temperature Temperature effect proﬁles will profiles be of better. liquid of liquid cooling Thus, cooling andthe combinedcombination and combined with system thermoelectric with thermoof liquidelectric cooling. and thermoelectriccooling. (a) Liquid (a) Liquid cooling; (b) combined liquid and thermoelectric cooling. coolingcooling; is applied (b) combined in the present liquid and paper. thermoelectric cooling. It can be seen that the temperature distribution of the combined thermoelectric cooling system 3.5.3.5. PackPack ModelModel DesignDesign is more uniform and the maximum temperature of the battery could be reduced to 291 K. In fact, if the AccordingpowerAccording of the toto thethermoelectricthe bestbest structurestructure chip determineddetermined is further improved above,above, wewe and designeddesigned the heat thethe of packpack heat modelmodel end can ofof thebethe exported batterybattery group.group.in time, TheThe the correspondingcorresponding cooling effect thermostatwill be better. structure Thus, andthe combinationthermoelectric system chip areof liquid added and at the thermoelectric same time, thethecooling schematicschematic is applied of of which which in the is is shownpresent shown in paper. Figurein Figure 10. 10. The The bottom bottom of theof the heat heat exchanger exchanger is connected is connected with with the liquidthe liquid inlet inlet of the of temperature the temperature regulating regulating pipeline, pipe andline, the and top the is top connected is connected with the with liquid the liquid outlet ofoutlet the temperatureof3.5. the Pack temperature Model regulating Design regulating pipeline. pipeline. The heat The exchanger heat exch hasanger a thermoelectric has a thermoelectric card slot card that canslot bethat plugged can be intoplugged six thermoelectric into six thermoelectric chips, which chips, is which equivalent is equivalent to twelve to thermoelectric twelve thermoelectric chips for chips each for battery. each According to the best structure determined above, we designed the pack model of the battery Thebattery. symmetrical The symmetrical structure designstructure can design ensure can full ensure contact full between contact the between battery andthe thebattery temperature and the group. The corresponding thermostat structure and thermoelectric chip are added at the same time, controltemperature module, control which module, is helpful which to improve is helpful the to temperature improve thecontrol temperature efﬁciency. control efficiency. the schematic of which is shown in Figure 10. The bottom of the heat exchanger is connected with the liquid inlet of the temperature regulating pipeline, and the top is connected with the liquid outlet of the temperature regulating pipeline. The heat exchanger has a thermoelectric card slot that can be plugged into six thermoelectric chips, which is equivalent to twelve thermoelectric chips for each battery. The symmetrical structure design can ensure full contact between the battery and the temperature control module, which is helpful to improve the temperature control efficiency.

1-Battery shell 2-Heat exchanger 3-Battery 4-Liquid storage tank 5-Conductive metal strip 6-Liquid outlet pipe 7-Thermoelectric chips 8-Liquid inlet pipe

FigureFigure 10.10. BatteryBattery packpack model.model.

4. Control System Design 4. Control System1-Battery Design shell 2-Heat exchanger 3-Battery According4-Liquid to the storage above tank analysis, 5-Conductive the correspo metalnding strip thermal control 6-Liquid system outlet pipewas designed and According to the above analysis, the corresponding thermal control system was designed and the the schematic7-Thermoelectric of the control chips procedure 8-Liquid is shown inlet in pipe Figure 11. The battery thermal management schematic of the control procedure is shown in Figure 11. The battery thermal management system system includes two parts: the battery pack and the control unit. The combination temperature includes two parts: the battery packFigure and the10. Battery control pack unit. model. The combination temperature control control system of thermoelectric and liquid cooling is adopted. The specific implementation process system of thermoelectric and liquid cooling is adopted. The speciﬁc implementation process is listed is4. listed Control as follows: System Design as follows: According to the above analysis, the corresponding thermal control system was designed and 1. The temperature sensor collects the temperature of each cell and feeds it back to the MCU (main the schematic of the control procedure is shown in Figure 11. The battery thermal management control chip); system includes two parts: the battery pack and the control unit. The combination temperature control system of thermoelectric and liquid cooling is adopted. The specific implementation process is listed as follows:

Energies 2018, 11, x FOR PEER REVIEW 10 of 15 Energies 2018, 11, 279 10 of 15 1. The temperature sensor collects the temperature of each cell and feeds it back to the MCU (main 2. controlThe main chip); control chip is used to determine whether there is a need to adjust the temperature

2. Theaccording main control to the datachip inis theused comparison to determine program. whether If necessary,there is a breakneed overto adjust the relativethe temperature single cell accordingbattery switch to the arraydata in module the comparison and the H program. commutation If necessary, circuit module; break over the relative single cell battery switch array module and the H commutation circuit module; 3. The ﬂow rate on the thermoelectric chip is controlled through the intelligent module of ﬂow 3. The flow rate on the thermoelectric chip is controlled through the intelligent module of flow control so as to control the temperature of the cold end and the hot end of thermoelectric chip, control so as to control the temperature of the cold end and the hot end of thermoelectric chip, to achieve the purpose of regulating the surface temperature of the battery. to achieve the purpose of regulating the surface temperature of the battery.

Figure 11. Schematic of the control procedure. Figure 11. Schematic of the control procedure.

The H commutation circuit is used to control the forward current when the temperature of the batteryThe is too H commutation high, and it can circuit control is used the reverse to control flow the of forward the current current when when the battery the temperature temperature of the is toobattery low. isThe too intelligent high, and hydraulic it can control control the unit reverse is controlled flow of the by currentthe main when controller, the battery and the temperature flow rate ofis the too internal low. The liquid intelligent is adjusted hydraulic in order control to regu unitlate is controlledthe temperature by the of main the controller,thermoelectric and chip. the flow In orderrate of to the effectively internal control liquid is the adjusted temperature in order of tothe regulate battery, the the temperature thermoelectric of thechip thermoelectric should be tightly chip. inIn contact order to with effectively the battery. control Additionally, the temperature a concave of the structure battery, thewas thermoelectric designed to ensure chip should that the be battery tightly wasin contact in effective with thecontact battery. with Additionally, the flow channel a concave and also structure as an wasauxiliary designed regulating to ensure module that the to batteryadjust thewas temperature in effective contactof the battery. with the flow channel and also as an auxiliary regulating module to adjust the temperature of the battery. 4.1. Hardware Design 4.1. Hardware Design In this study, TMS320LF2812 (a 32 bit chip produced by Texas Instruments Company, Dallas, In this study, TMS320LF2812 (a 32 bit chip produced by Texas Instruments Company, Dallas, TX, TX, USA) was used as the master chip and the corresponding peripheral circuit was designed. USA) was used as the master chip and the corresponding peripheral circuit was designed. Among Among them, the key circuit module includes the temperature acquisition module, the H them, the key circuit module includes the temperature acquisition module, the H commutation circuit commutation circuit module, the matrix switch circuit module, and the wireless communication module, the matrix switch circuit module, and the wireless communication module. module. 4.1.14.1.1. Temperature Temperature Acquisition Acquisition Circuit Circuit TheThe accurate accurate collection collection of of the the battery battery temperatur temperaturee is is the the premise premise of of the the thermal thermal management management of of thethe battery. battery. The The DS18B20, DS18B20, a a digital digital temperature temperature se sensornsor (produced (produced by by Dallas Dallas Semiconductor, Semiconductor, Dallas, Dallas, TX,TX, USA) USA) was was selected to realize the temperature ac acquisition.quisition. It It has has the the advantages advantages of of accurate accurate acquisition,acquisition, a a wide wide range, a wide application,application, andand so so on on [ 27[27].]. The The circuit circuit diagram diagram is is shown shown in in Figure Figure 12 . 12.The The temperature temperature information information collected collected by DS18B20 by DS will18B20 be passedwill be to passed the main to controlthe main chip control through chip two throughI/O interfaces two I/O of interfaces TMS320F2812, of TMS320F2812, PTD2 and PTD3.In PTD2 and order PTD3.In to fully order use to the fully characteristics use the characteristics of DS18B20, oftwelve DS18B20, units twelve were used, units which were wereused, divided which intowere two divided groups. into Each two one groups. is attached Each toone the is surfaceattached of to an theindividual surface cellof an so asindividual to accurately cell collectso as to the accurately temperature collect information the temperature of each battery. information of each battery.

Energies 2018, 11, 279 11 of 15 Energies 2018, 11, x FOR PEER REVIEW 11 of 15 Energies 2018, 11, x FOR PEER REVIEW 11 of 15

FigureFigure 12.12. TemperatureTemperature samplingsampling circuit.circuit. Figure 12. Temperature sampling circuit. 4.1.2. H Commutation Circuit Module 4.1.2.4.1.2. H H Commutation Commutation Circuit Circuit Module Module In order to realize the switch between the hot end and the cold end of the thermoelectric sheet, InIn order order to to realize realize the the switch switch between between the the hot hot en endd and and the the cold cold end end of of the the thermoelectric thermoelectric sheet, sheet, the H commutation circuit module was designed to change the direction of the current ﬂowing into thethe H H commutation commutation circuit circuit module module was was designed designed to to ch changeange the the direction direction of of the the current current flowing flowing into into the sheet. The circuit schematic is shown in Figure 13. thethe sheet. sheet. The The circuit circuit schematic schematic is is shown shown in in Figure Figure 13. 13.

Figure 13. H commutation circuit. Figure 13. H commutation circuit.

As shown in Figure 13, Q1 and Q3 are PNP triode; Q2 and Q4 are NPN triode. They are As shownshown inin Figure Figure 13 ,13, Q1 Q1 and and Q3 areQ3 PNPare triode;PNP triode; Q2 and Q2 Q4 and are NPNQ4 are triode. NPN They triode. are controlledThey are controlled by four GPIO driver ports of TMS320F2812. F1 and F2 are fuses to prevent the circuit from controlledby four GPIO by driverfour GPIO ports driver of TMS320F2812. ports of TMS320F2812. F1 and F2 are F1 fuses and F2 to preventare fuses the to circuitprevent from the shortcircuit circuit, from short circuit, and the middle of the block represents the thermoelectric sheets. The corresponding shortand the circuit, middle and of thethe blockmiddle represents of the block the thermoelectric represents the sheets. thermoelectric The corresponding sheets. The current corresponding direction current direction is displayed in Table 4. currentis displayed direction in Table is displayed4. in Table 4.

Table 4. Current direction. Table 4. Current direction. IO1IO1 IO2IO2 IO3 IO3 IO4 IO4 Result Result IO1 IO2 IO3 IO4 Result 11 00 00 11 Forward Forward current current 1 0 0 1 Forward current 00 11 11 00 Reverse Reverse current current 0 1 1 0 Reverse current

4.1.3.4.1.3. Matrix Matrix Switch Switch Circuit Circuit Module Module InIn orderorder toto realizerealize thethe controlcontrol ofof thethe thermoelecthermoelectrictric power,power, aa matrixmatrix switchswitch circuitcircuit modulemodule waswas addedadded toto thethe drivedrive circuitcircuit module.module. TheThe posipositioningtioning principleprinciple ofof thethe modulemodule isis thethe ijij positioningpositioning principle.principle. i i representsrepresents thethe numbernumber ofof thethe singsinglele batterybattery andand thethe valuevalue isis 1–12;1–12; j j representsrepresents thethe

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4.1.3. Matrix Switch Circuit Module

EnergiesIn order2018, 11 to, x realizeFOR PEER the REVIEW control of the thermoelectric power, a matrix switch circuit module12 was of 15 added to the drive circuit module. The positioning principle of the module is the ij positioning principle. i thermoelectricrepresents the numberchip group of the and single the value battery is and1–2.the The value corresponding is 1–12; j represents switch symbol the thermoelectric is represented chip by groupKij. and the value is 1–2. The corresponding switch symbol is represented by Kij.

4.1.4.4.1.4. Wireless Wireless Communication Communication Module Module InIn order order to to realize realize the the communication communication between between the hostthe host controller controller and theand host the computer,host computer, the SZ05 the wirelessSZ05 wireless communication communica moduletion wasmodule adopted was basedadopted on thebased ZigBee on the protocol, ZigBee which protocol, has the which advantages has the ofadvantages far communication of far communication distance, strong distance, anti-interference strong anti-interference ability, ﬂexible ability, networking, flexible andnetworking, reliable and and stablereliable performance. and stable The performance. interface circuit The ofinterface the wireless circuit communication of the wireless module communication is shown in Figuremodule 14 is. Theshown RX andin Figure TX ports 14. ofThe the RX wireless and TX communication ports of the wireless module communication are connected withmodule a TMS320F2812 are connected serial with connection;a TMS320F2812 TX is theserial interface connection; of sending TX is data,the interface and RX is of a datasending receiving data, interface.and RX is The a data main receiving control chipinterface. and the The wireless main control communication chip and the module wireless have communication RX and TX interface module tohave realize RX and the TX interaction interface ofto information. realize the interaction of information.

. Figure 14. Wireless communication modules. Figure 14. Wireless communication modules. 4.2. Design of Software 4.2. Design of Software The software of battery thermal management system is mainly based on the C language, and the masterThe software control chip of battery is carried thermal out under management the Code system Composer is mainly Studio based (CCS). on CCS the isC anlanguage, integrated and developmentthe master control environment chip is carried dedicated out to under the development the Code Composer of Digital Studio Signal (CCS). Processing CCS (DSP)is an integrated products produceddevelopment by TI environment companies. The dedicated procedures to forthe the deve implementationlopment of Digital of the process Signalare: Processing system power, (DSP) initialization,products produced and detection by TI companies. of system failure.The procedures After initialization, for the implementation the main program of the process is running. are: Thesystem temperature power, initialization, information ofand the detection battery isof collectedsystem failure. to judge After whether initialization, the temperature the main isprogram in the appropriateis running. range.The temperature If yes, the information temperature of information the battery directlyis collected transfers to judg toe thewhether host computer. the temperature If no, theis programin the appropriate judges whether range. the If temperature yes, the temper is tooature high information or too low. The directly refrigeration transfers subroutine to the host is performedcomputer. whenIf no, it isthe too program high; otherwise, judges whether the thermal the subroutinetemperature is performedis too high when or too it is low. too low.The Therefrigeration ﬂow chart subroutine of program is shownperformed in Figure when 15 it. is too high; otherwise, the thermal subroutine is performedWhen the when temperature it is too low. of theThe battery flow chart that of is detectedprogram byis shown the main in Figure controller 15. is too high, or even When the temperature of the battery that is detected by the main controller is too high, or even exceeds the safety limit TLimMax, the refrigeration control strategy is applied. The speciﬁc steps are asexceeds follows: the safety limit TLimMax, the refrigeration control strategy is applied. The specific steps are as follows: (1) Capture the coordinates of the battery and display them on the battery simulator according to (1) Capture the coordinates of the battery and display them on the battery simulator according to the temperature level; the temperature level; (2) The battery voltage Uij0, current I, and the estimated value of SOC are collected by the battery (2) The battery voltage Uij0, current I, and the estimated value of SOC are collected by the battery management system. The heating rate is determined to match the cloud database by the feedback management system. The heating rate is determined to match the cloud database by the information of the electronic label; feedback information of the electronic label; SOC (3)(3) AccordingAccording toto the corresponding relationship relationship between between the the SOC andand the the open open circuit circuit voltage, voltage, the theopen open circuit circuit voltage voltage of the of the battery battery is predicted; is predicted; (4) The heating efficiency of battery’s surface is calculated according to the collected battery information from the following formula:

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(4) The heating efﬁciency of battery’s surface is calculated according to the collected battery

Energiesinformation 2018, 11, x FOR from PEER the REVIEW following formula: 13 of 15

I dUOpen QB =I (∆U + TijdU0 ) (15) =Δ+VB OpendTij0 QUTBij()0 (15) VdTBij0 where I is the charge and discharge current of the battery, VB is the volume of the battery, UOpen iswhere the open I is the circuit charge voltage and discharge of the battery, current∆ Uof isthe the battery, difference VB is the between volume the of openthe battery, circuit U voltageOpen is the open circuit voltage of the battery, △U is the difference between the open circuit voltagedU andOpen and the terminal voltage of the battery, T 0 is the surface temperature of the battery, and is ij dTij0 dUOpen thethe temperature terminal voltage coefficient. of the battery, Tij0 is the surface temperature of the battery, and is dTij0 (5) Thethe required temperature cooling coefficient. efficiency is determined according to the heating rate of the battery. Using (5)the The fuzzy required control cooling strategy, efficiency the cold is determined end heat absorption according to rate theQ heatingm is equal rate toof KTtheij battery.0 multiplied Using by QBthe. Then, fuzzy wait control until strategy, the temperature the cold end sensor heat absorption detects the rate battery Qm is surfaceequal to temperatureKTij0 multiplied in theby Q bestB. operatingThen, wait temperature until the temperature range (Tm, T sensorn), and detect makesQ theB equal battery to Qsurfacem. At thetemperature same time, in the the hot best end ofoperating the thermoelectric temperature chip range is contacted (Tm, Tn), and with make the heat QB equal transfer to Q structurem. At the same so as time, to use the the hot flow end of of the heatthetransfer thermoelectric structure’s chip internalis contacted liquid with to takethe heat away transfer the excess structure heat. so The as flowto use rate theof flow the of cooling the systemheat transfer is regulated structure’s by adjusting internal liquid the regulating to take away valve the of excess the liquid heat. heating/coolingThe flow rate of the structure cooling so assystem to adjust is regulated the auxiliary by adjusting coolingefficiency. the regulating valve of the liquid heating/cooling structure so (6) Checkas to theadjust temperature the auxiliary of thecooling battery efficiency. again. The cooling circuit of the battery is cut off when the (6)temperature Check the temperature is OK, and thenof the the battery data again. are recorded The cooling and uploadedcircuit of the to thebattery on-board is cut off computer when the and cloudtemperature database. is OK, and then the data are recorded and uploaded to the on-board computer and cloud database.

FigureFigure 15. 15.Main Main schematicschematic of temperature regulation. regulation.

Similarly, when the temperature of the battery that is detected by the main controller is too low or Similarly,lower than when the safety the temperature limit TLimMin, of the the heating battery control that is strategy detected will by be the applied. main controller The difference is too is low orthat lower the than direction the safety of the limit cold TandLimMin hot, thedirection heating is changed control strategythrough willthe H be reversing applied. circuit The difference for the is thatthermoelectric the direction chips. of theAt the cold same and time, hot direction the interior is changed of the auxiliary through heat the transfer H reversing structure circuit will for be the thermoelectricfilled with a chips.higher Attemperature the same time,liquid. the interior of the auxiliary heat transfer structure will be ﬁlled with a higher temperature liquid. 5. Conclusions

Energies 2018, 11, 279 14 of 15

5. Conclusions In this paper, an enhanced battery thermal management system, based on the second thermoelectric effect, is proposed. The main contributions of this study are to introduce the structural design optimization and control method. Among them, the most special part is the use of thermoelectric chips, which increase the temperature regulation efficiency of the battery’s thermal management system in theory. By a finite element analysis of the flow field, the best liquid cooling structure and the inlet velocity are determined. The result shows that the enhanced cooling structure is more effective in cooling than the traditional one. In the meanwhile, the relative battery pack structure and the temperature control system are developed accordingly. The conclusions are drawn as follows: (1) A thermoelectric chip integrated into the liquid cooling unit is a better design for a battery’s thermal management system. (2) In the process of improving the heat exchanger structure, it is noted that the flow field distribution of the U-shape is more uniform than that of the Z-shape. (3) The vortex phenomenon at the center of the U-shape heat exchanger is initially weakened and then intensified as the inlet velocity of the pipe is increased. When the inlet velocity is 1 m/s, the distribution of the flow field is the most uniform. (4) The design process of this enhanced battery thermal management system can provide a wealth of guidelines for solving similar problems.

Acknowledgments: This work was supported by the Natural Science Foundation of Shaanxi Province of China (2016GY-007). Meanwhile, it was financially supported by the Xi’an University of Science and Technology. Author Contributions: Chuan-Wei Zhang conceived and designed the whole structure of the system and determined the optimal cooling structure model. Ke-Jun Xu analyzed the temperature modulation effect of the traditional structure and the improved structure. Lin-Yang Li and Man-Zhi Yang designed the hardware and software of the control system. Chuan-Wei Zhang and Ke-Jun Xu wrote the paper. Huai-Bin Gao and Shang-Rui Chen gave a general guide for the study and improved the language level of this paper. Conflicts of Interest: The authors declare no conflict of interest.

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