UCEM Tractive Accumulator System. ECE 4901 Senior Design I

Transcription

1 UCEM Tractive Accumulator System Final Report as of December 11, 2017 Submitted By Tejinder Jutla, Jason Clark and Sung-Lin Chen ECE 4901 Senior Design I Adviser: Sung Yeul Park Customer: UConn Electric Motorsports Club Department of Electrical Engineering University of Connecticut 1

2 Table of Contents Executive Summary... 3 Background 3 Accumulator Cell Selection...4 Battery Management System.6 Charging....8 Accumulator Container...9 Overcurrent Protection and Wiring.10 Accumulator Integration and Testing.10 Project Phases Project Budget...15 Appendix A...16 Relevant FSAE Rules...16 Appendix B Decision Matrices..20 Appendix C...24 Part and Component Datasheets Appendix D 27 Test Procedure Documents 27 Resources

3 Executive Summary This year, UConn has formed a club (UConn Electric Motorsports) which will build an electric racecar from the ground up and compete in a national level. The electric racecar will be powered by a tractive accumulator system (The term tractive refers to high voltage system), which includes a custom configured lithium ion battery pack, a battery management system, charger, and a cooling system. Since this is the first time the club is participating in this competition, most of this semester was used on researching concepts and components to meet the power requirements from the electric motor. Along with meeting the club s requirements, design also had to satisfy Formula Student Automotive Engineering (FSAE) rules. This was accomplished by creating decision matrices, comparing all options that meet requirements of rules and performance. As the semester progresses, the accumulator design was changed numerous of times, as this system impacts other subsystems on the car. By the end of this semester, the battery is selected and finalized, the battery management system is identified along with the charger. The accumulator container is designed, with accordance to FSAE rules and collaboration with the Chassis team, however it is bound to change due to chassis design alteration. Looking forward, the selected batteries will arrive, and construction of the accumulator will commence next semester. Thermal analysis and Computational Fluid Dynamic analysis will be carried out to determine cooling fans and design. Once the accumulator has been put together, testing will begin at component level and certified to go into the car, integrating the accumulator with other subsystems. Background There are significant FSAE rules to follow. The maximum allowed voltage is 300 V along with a maximum power from the accumulator of 80 kw. The accumulator must be separated into segments with each segment having maximum energy of 6 MJ and maximum voltage of 120 V. Each cell must be fuse protected. The maximum power required by the motor selected by the motor team is 80 kw. The team also requested a voltage above 200 V for the accumulator. This voltage is in direct relation to the torque and speed for the motor performance. Uconn Electric Motorsports (UCEM), the motor team, and the battery team came to a conclusion for the kwh of the accumulator. The FSAE 2017 results were analyzed from the endurance event to see how much energy the teams used, the completion time, and weights of the vehicles. The conclusion was made that the accumulator needed to be at least 4 kwh for this design. The accumulator must be designed to fit inside an accumulator container. The accumulator container must be removable from the vehicle, therefore must be placed in an accessible area. The accumulator needs to be transported on site to the charging station using a charging cart. A charger must be chosen to integrate into the system to meet the needs for the accumulator. A battery management system (BMS) is required. All cell voltages must be monitored and at least 30% of their temperatures need to be monitored as well. A cooling system needs to be implemented to keep the temperatures below 60 C as required by FSAE and the cell data sheets. The accumulator must also be monitored while charging. A BMS must be chosen to communicate with the components of the tractive system and accurately meet the monitoring requirements. 3

4 Accumulator Cell Selection Time and research was first spent on understanding the needs for the battery and making a proper selection of battery cells. It was discovered there were three realistic options to choose from: cylindrical cells, pouches, and modules. Batteries in the style of pouches offer a highpower output, and a simple way to connect them electrically. The problem arises with pressure. The pouches expand and must be pressurized by an outside component. Cylindrical cells are contained within the cylinder and are automatically pressurized by this design. This involves many connections because a single cell does not offer a high-power output. The third option is modules that contain cylindrical cells connected in parallel. This allows for easy electrical connections, but comes at an expensive price. The voltage and power requirements ultimately determine how the accumulator needs to be configured. Battery cell options were investigated comparing voltage, discharge current, capacity, weight, and cost. With these values, decision matrices were used to find the exact configuration to reach the desired power of 80 kw. Series connections add voltage, and parallel connections add current and capacity. The below equations were used for determining the configuration. Total Voltage (V) = Cell voltage (V) * series connections (1) Total Current (A) = Cell discharge current (A) * parallel connections (2) Total Capacity (Ah) = Cell capacity (Ah) * parallel connections (3) Discharge Time = Capacity (Ah) / discharge current (A) (4) C-rate = Current (A) / Capacity (Ah) (5) Power = voltage * current (A) P = VI (6) kwh = Accumulator voltage (V) * Accumulator capacity (Ah) (7) After these calculations, the number of batteries needed are known and calculations of total accumulator weight, volume, and price can be found. These are the ideal parameters to compare different cell types. A decision was made to use Samsung cells. These cells have a great discharge rate to capacity ratio, meaning they won t be drained fast. They are also less expensive than comparable cells, and weigh less. It was calculated roughly 600 cells were needed to meet the requirements given to us. There were many concerns in the battery team, along with the advisor Professor Park, and the club members of UCEM. The rules require temperature monitoring and fuse protection for each cell, so additional components were needed to assemble the accumulator. With hundreds of cells, all parties realized much time was needed to physically assemble the accumulator with individual cells. There were also concerns for error, because this is a delicate component to the vehicle. Not much time would be left for integrating a battery management system, charger, and a cooling system into the accumulator. 4

5 Nominal voltage Maximum Voltage Max. cont. discharge current Max. pulse current ( < 1 sec) Capacity Standard charge current Max. charge current 3.6 V 4.2 V 20 A 100A 2.5 Ah 1.25 A 4 A Weight 44 g Table 1: Samsung relevant cell data. After much consideration with UCEM, everyone came to an agreement on using prepackaged modules containing the cylindrical cells. The modules offer simple monitoring, and ease of assembly. Energus is a company that manufactures battery modules that many teams use for the FSAE competition. They even offer the Samsung cells we chose as a choice for the cells inside the modules. They have different module types and another decision matrix was used to compare modules and their configuration. A decision was made on the Energus Li8PT modules which have 8 Samsung cells in parallel. The modules contain temperature sensors for each cell and 2 fuses for each cell, satisfying the FSAE rules. The temperature sensors and assembly of modules can be seen in figure 1. The accumulator is designed to contain 62 Energus Li8PT modules in series. The modules have 8 cells in parallel already, and offer a maximum current of 360 A, so no further parallel connections are needed as this aligns with the motor requirements. This offers a nominal voltage of 223 V, a maximum voltage of 260 V, a peak discharge current of 360 A, and a capacity of 20 Ah. These values can obtain the maximum power of 80 kw, and give a 4.4 kwh accumulator. The configuration means the accumulator contains a total of 496 cells. Nominal voltage 3.6 V Maximum Voltage Peak Current Capacity Max. charge current w/ cooling 4.2 V 360 A 20 Ah 40 A Weight 427 g Table 2: Energus Li8PT relevant data. 5

6 The accumulator must be separated into segments with each segment having maximum energy of 6 MJ and maximum voltage of 120 V. We can find the total energy of the accumulator using equation [8]. If we separate the accumulator into four segments, two segments have 15 modules and the other two segments have 16 modules. Each 15-module segment has 4.5 MJ and 63 V. Each 16-module segment has 4.8 MJ and 67.2 V. Energy (J) = Voltage (V) * Capacity (Ah) *3600s (8) Figure 1: Energus Li8PT module (left) showing temperature sensors (top) and assembled (right). Battery Management System A battery management system (BMS) is essential to the design and functionality of the tractive accumulator. Many hours of research went into this portion of the design, in simple terms, a battery management system is capable of monitoring/protecting the battery, balancing cells, estimate state of charge, maximize performance and be able to report to users and/or external devices. These are only basic requirements, BMS functions depends on manufacturer as well as customization. The BMS was selected based on three categories: Analog versus Digital, Custom versus off-the-shelf and topology. Digital BMS is better, as it is capable of sensing each cell individually, this advantage allows the BMS to charge or discharge at cell level, as well as locate which cell might be at fault. A BMS off-the-shelf seemed like the only option, as the team does not possess the electrical experience one would need to carry out such an extensive task, several off-the-shelf BMS are available within budget. Lastly, there are several different BMS 6

7 topology. Centralized is compact, least expensive option and easy to replace. Modular BMS are divided into multiple identical modules, one acts as the master, higher cost and more tap wires required. Master-Slave BMS are similar to modular, with the exception to slave prices which are lower. Lastly, Distributed BMS have electronics contained on cell boards that are placed directly on the cells being measured, more points of error can occur which may be difficult to detect. The team decided on a centralized digital BMS, since all the voltage and thermistor tap wires are processed within a single BMS. This reduces error and eliminates the need to design individual circuit boards. Table 3: quick non-quantitative comparison of BMS topology As seen in the above table 3, a centralized BMS is the better candidate for the task at hand. A complete decision matrix can be found here comparing different BMS (BMS table). The BMS that was selected by our team and club was the Ewert Orion BMS the 72-cell configuration, since the battery packs are configured in a 62-series connection (BMS data sheet). Figure 2: Orion BMS input/output interface The Orion BMS operates at 12v 250Ma, capable of measuring state of charge, discharge current limit and charging current limit. This BMS has dual fully programmable CANBUS 2.0B, this is a high-speed Controller Area Network compared to many other options available. The CANBUS is a basic differential voltage, CAN-HI and CAN-LOW. The CANBUS is one of the requirements within the FSAE rulebook. This feature will be used to control the charger as well 7

8 as the DC load (motor, inverter, etc.). The Orion BMS is made for electric vehicle, this means that it is of very high quality in both performance and functionality. It is capable of reading cell voltages from 0.5 to 5 volts, EMI resistance and functions between -40 to 80 degrees Celsius. The maximum and minimum open circuit voltage can be set within the BMS, if the voltages reach these set limits the BMS will open the Accumulator Insulation Relays (AIR). The temperature can also be set, so the BMS is again capable of opening the AIR if limit is met. The BMS is also equipped with Onboard Diagnostic (OBD), this will allow the team to read any error codes given by the BMS. The Orion BMS comes with a current sensor with an amperage rating of choice, which is 500A for this design. A thermistor expansion module is needed alongside the BMS as the Orion is only capable of 4 thermistor inputs, and we need to be able to have 62 inputs for all modules. Therefore, a 60-thermistor expansion module will be purchased alongside the Orion BMS. Their company also offers a state of charge meter as a display module. It provides essential information on the accumulator as well as data logging for diagnostics. Charging The charger is also an important part to make accumulator run. The goal for our charging research is to find one that is compatible with the Battery Management System and has CAN communication protocol. Some of the chargers we found has a Battery Management System built in. However as more research was done, we found out that the BMS that build into the charger is not capable of handle our battery pack. Our battery pack contains 496 cells, therefore the voltage and current is very high. That s why a dedicated Battery Management System is required. As a result, the charger does not have to be smart. We just need to find a charger that just performs charging and have CAN protocol to communicate with Battery Management System. All the power management work could be processed by the Battery Management System. Also because the location of the race is in Canada which can only provide 120V AC voltage. So in the datasheet we can only view output current at 115V AC instead of 230V AC. So we cannot just look at the peak power because it output with 230V AC. In terms of the output power, higher output current gives us faster charging speed. But we also need to take into consideration that higher output power will generate more heat. If the charging environment is hot, it will reduce the performance of the charger. Initially we want to implement fast charger to reduce charging time so we choose Elcon PFC 5000 charger. However, charging time is not our priority since we have plenty of time during each event according to the club. So we don t need such high output current charger. There are several chargers we found that have very high charging power output but it s significantly more expensive. So, in terms of value, our final decision is the Elcon PFC 2500 charger which deliver sufficient amount of charging current at 6A at half of the price of Elcon PFC 5000 charger. Also Elcon charger is one of the few charger brand that is officially compatible with our Orion Battery Management System. As a result, it is easier to implement. Finally according to the FSAE rules, if the accumulator needs to charge, the accumulator is required to be taken out of the race car and transported with a hand cart equipped with a Deadman s braking system. This is for safety reasons. However this is not part of our project, other teams will handle this. 8

9 Charge time equation: (9) Accumulator Container The Tractive Accumulator design and function is specified in the FSAE rule handbook (EV3.3). There are a number of requirements, such as grounding to chassis, removable from the chassis frame to be taken to the charging station. This translates into an efficient design which is both lightweight and robust to handle the track debris. The handbook also states that the battery pack has to be broken into segments for safety purpose, along with galvanic insulation requirements. This is the first draft of design, as the chassis team has not yet finalized the design, the accumulator container is subject to change as time progresses. Figure 3: Accumulator Container design using Autodesk Fusion 360 The thickness requirement is as follows: floor must be 3.2mm thick, vertical and the segment separation walls must be 3.2mm thick, and the lid cover must be 2.3 mm thick. The material chosen for the container was aluminum, given its weight and strength properties. This material is also simple to construct out of and will save budget. Along with designing the Accumulator container, a cooling system will also be implemented within the accumulator system. Two fans will be used, in a push-pull configuration. This decision was made based on the observation that the cells will exceed their maximum operating temperature (60 degrees C) in certain events. The team will further test the battery packs when they arrive, with thermal analysis to determine the fan size, along with performing Computational Fluid Dynamics to ensure air flow is present where needed. The BMS also has to be cooled, this system is very important in keeping everything running at operating status. The two fans will be controlled directly by the BMS, as the Orion BMS has an option to run the fan, based on conditions and measurements taken from the cells. The team experimented with different outlets of cooling, such as running water jackets through the accumulator container and running coolant through. While this is the most effective method of dissipating unwanted heat, it 9

10 is very complex in this area, since the accumulator has to be able to come off the car. This option also creates many areas of failure such as leaks, which can cause total failure of the accumulator. Overcurrent Protection and Wiring Aside from the internal fuses of the Energus modules, there is one main fuse and two relays that protect the system. The relays are known as the Accumulator Isolation Relays (AIRs). According to the FSAE rules the main fuse must have a current rating that is lower than the continuous current of the component it is protecting, which in this case is the accumulator which has a constant current of 160 A. The fuse must also be rated for the maximum voltage of the system. Bussmann/Eaton FWH-150B is the decided fuse with a current rating of 150 A and maximum voltage of 500 VDC. The rules also state the relays must have a switch off current that is higher than the fuse rating. The relays must be of a normally open type and open both poles of the accumulator meaning one on each side. Kilovac Lev200A4NAA are the decided relays with a switch off current of 500 A and maximum voltage of 900 VDC. The relays must also be supplied with a 12v power supply. The accumulator segments must be connected by maintenance plugs or contactors. Some ideal connectors were found such as the Smiths Interconnect connectors. They offer an easy locking connection between the segments. It has also been discussed to use the same components used for the AIRs as the contactors to separate the accumulator segments. A final decision will be made in the future, as price quotes from Smiths Interconnect are received. The Orion BMS ships with the necessary wires needed for the voltage taps as well as temperature sensing. The main concern was finding wiring that was adequate for the high current path of the accumulator. A high current wire 2/0 AWG from evwest can handle up to 390A which meets our requirements. This wiring can be used to connect the main fuse, the AIRs, the segment connectors, and the high current path leading to the motor side of the vehicle. M8 ring terminals can be used to connect wires to the Energus modules because their electrical contacts are M8 bolt sockets. Accumulator Integration and Testing This is a new club to UConn and there was lack of funding in the beginning. Since there was no money at first, the team was not able to get any batteries to do any testing on. With a finalized battery decision, the club is in the process of obtaining the Energus modules, along with extra ones for the team to test and conduct experiments. Testing and experimentation begins in the Spring. The main testing aspects that will be carried out for the Energus modules are temperature changes due to different discharge rates, and charging time. The modules contain the Samsung cells and some temperature vs. discharge data was found. The maximum discharge rate in the graph shows 25 A, and we will be discharging the cells at 45 A for the acceleration event in order to reach the 80 kw. Figure 4 below shows the temperature increasing well beyond the 60 C required by the cells and by FSAE. The testing data directly leads to the design of the cooling system. 10

11 Figure 4: Samsung discharge and temperature characteristics. When batteries charge they start off with a fast current, and the current drops off to top off the charge on the battery. In the testing phase, the energus module will be drained to its shut off voltage of 2.5 V and then charged. From this charge time, it can be calculated how long the accumulator will need to charge once the whole system is operational. The Energus temperature sensors measure the voltage across the sensor or circuit. This voltage corresponds to a certain temperature as seen in table 4 and figure 5. The BMS can be programmed to report these temperatures for the voltages that are received. The BMS can also be tested in its accuracy of measuring the cell voltages before the whole accumulator is assembled. The actual integration is when the team will do more testing to confirm the tractive accumulator works as it should. The Orion BMS come with instructions on how to wire everything with the Energus modules. After integration is complete, the team will utilize the university s depot campus to test the accumulator. The ABC-150 will be used as the load, safety will be taken very seriously during these stages. The end goal of testing is to produce Acceptance Test Procedures (ATPs), this is a kind of documentation that will be passed onto the club and its members for future troubleshooting if needed. Table 4: Energus temperature sensors voltage to temperature conversions. 11

12 Figure 5: Energus voltage readings of sensors in relation to the temperature. Once the BMS is integrated into the accumulator and with the charger, the next step is the motor side of the vehicle. The first point of contact with the motor side to our accumulator system is the BMS and motor inverter. Through the CAN communication the motor side and accumulator side can communicate on the required power draw and in turn the current draw. These systems can be programmed to not draw over a certain current, offering extra protection alongside the fuses and accumulator isolation relays. Once the motor and accumulator sides of the vehicle are integrated and working, all components need to fit inside the designed chassis. After everything is assembled into the vehicle the real testing of the vehicle can begin. UCEM will be performing driving tests before the competition to make sure the vehicle meets the standards of the events at the competition. During these driving tests, our team will be monitoring the accumulator with the BMS to make sure again all systems are functioning as they should. All testing documents can be found in Appendix D, these documents are subject to change. Although testing procedures are valid, the university does not have the resources to test the accumulator since it requires a maximum current of 360A. Next step would be to complete the Accumulator and test with the motor, since it will be able to provide the load needed to dissipate the power. Project Phases The first phase of the project was understanding the requirements, and also the rules given by FSAE. Much time was spent into cell research and selection type. At first, cylindrical cells were decided on and the Samsung s were chosen. After consideration about having to assemble these cells and not having time to complete the other aspects of the project, it was agreed on that the Energus modules would be used. After analyzing the decision matrix the Li8PT modules were chosen, with a 62 series configuration to give optimal voltage and current. 12

13 The next milestone was researching battery management systems and finally selecting a model. The Orion BMS comes with multiple documents detailing how to use it and initialize the system. The unit also comes with software for monitoring the accumulator with a friendly user interface. This centralized unit is also less expensive and smaller than other units such at JTT electronics master/slave BMS. The accumulator container and charger have been undergoing research alongside one another. The dimensions have been received from the chassis team, and the container is being designed from these dimensions. The types of chargers have been researched, and the team is confident on the type and model needed for this design. The ElCon PFC 2500 offers a maximum charging current for the accumulator and can provide fast charging. In the coming weeks, thermal analysis will be done with theoretical calculations and a cooling system will be designed based upon this data. With these final steps taken, the accumulator system will be fully designed. The spring semester will be focused on testing components and integrating them into one another. With all integration and testing complete, there will be a full functioning accumulator system. 13

14 Table 5: Project timeline and phases 14

15 Figure 6: Gantt chart for project. Budget The main components have been selected for the accumulator system. These are the most expensive components and a budget can be given. The Energus modules are confirmed, the BMS is confirmed, and the charger is also confirmed. All other components are at relatively low costs compared to these three main components. UCEM did not give the team a definite budget for the accumulator system design. The club was waiting on responses from multiple teams working on the vehicle to determine a total price. As seen in the battery accumulator Bill of Material (BOM), in Appendix B as Table B.1, the total cost for the project is estimated at $9, This number is subject to change, next semester the club is anticipating more donations, which will directly impact the BOM for this build. 15

16 Appendix A: FSAE Relevant Rules EV2.2 Power and Voltage Limitation EV2.2.1 The maximum power drawn from the battery must not exceed 80kW. This will be checked by evaluating the Energy Meter data. EV1.1 High-Voltage (HV) and Low-Voltage (LV) EV1.1.1 Whenever a circuit has a potential difference where the nominal operation voltage is greater than 60V DC or 25V AC RMS it is defined as part of the High Voltage or tractive system. EV1.1.2 The maximum permitted voltage that may occur between any two electrical connections is different between the competitions allowing electric vehicles. The following table lists the respective values: Competition Formula SAE Electric Formula Student Voltage Level 300 VDC 600 VDC EV1.1.4 The tractive system accumulator is defined as all the battery cells or supercapacitors that store the electrical energy to be used by the tractive system. EV1.1.5 Accumulator segments are sub-divisions of the accumulator and must respect either a maximum voltage or energy limit. Splitting the accumulator into its segments is intended to reduce the risks associated with working on the accumulator. EV1.2 Grounded Low Voltage and Tractive System EV1.2.1 The tractive system of the car is defined as every part that is electrically connected to the motor(s) and tractive system accumulators. EV1.2.3 The tractive system must be completely isolated from the chassis and any other conductive parts of the car. EV1.2.4 The tractive-system is a high-voltage system by definition, see EV EV1.2.7 The entire tractive and GLV system must be completely galvanically separated. The border between tractive and GLV system is the galvanic isolation between both systems. Therefore, some components, such as the motor controller, may be part of both systems. EV1.2.8 All components in the tractive system must be rated for the maximum tractive system voltage. EV3.2 Tractive System Accumulator Container General Requirements EV3.2.1 All cells or super-capacitors which store the tractive system energy will be built into accumulator segments and must be enclosed in (an) accumulator container(s). EV3.3 Tractive System Accumulator Container - Electrical Configuration EV3.3.1 If the container is made from an electrically conductive material, then the poles of the accumulator segment(s) and/or cells must be isolated from the inner wall of the accumulator container with an insulating material that is rated for the maximum tractive system voltage. All conductive surfaces on the outside of the container must have a lowresistance connection to the GLV system ground, see EV4.3. Special care must be 16

17 taken to ensure that conductive penetrations, such as mounting hardware, are adequately protected against puncturing the insulating barrier. EV3.3.2 Every accumulator container must contain at least one fuse and at least two accumulator isolation relays, see EV3.5 and EV6.1. EV3.3.3 Maintenance plugs, additional contactors or similar measures have to be taken to allow electrical separation of the internal cell segments such that the separated cell segments contain a maximum static voltage of less than 120VDC and a maximum energy of 6MJ. The separation must affect both poles of the segment. EV3.3.4 Each segment must be electrically insulated by the use of suitable material between the segments in the container and on top of the segment to prevent arc flashes caused by inter segment contact or by parts/tools accidentally falling into the container during maintenance for example. Air is not considered to be a suitable insulation material in this case. EV3.3.5 The Accumulator Isolation Relays (AIRs) and the main fuse must be separated with an electrically insulated and fireproof material to UL94-V0 from the rest of the accumulator. Air is not considered to be a suitable insulation material in this case. EV3.3.7 Contacting / interconnecting the single cells by soldering in the high current path is prohibited. Soldering wires to cells for the voltage monitoring input of the AMS is allowed, since these wires are not part of the high current path. EV3.3.8 Every wire used in an accumulator container, no matter whether it is part of the GLV or tractive system, must be rated to the maximum tractive system voltage. EV3.3.9 Each accumulator container must have a prominent indicator, such as an LED that will illuminate whenever a voltage greater than 60V DC is present at the vehicle side of the AIRs. EV3.5 Accumulator Isolation Relay(s) (AIR) EV3.5.1 In every accumulator container at least two isolation relays must be installed. EV3.5.2 The accumulator isolation relays must open both (!) poles of the accumulator. If these relays are open, no HV may be present outside of the accumulator container. EV3.5.3 The isolation relays must be of a normally open type. EV3.5.4 The fuse protecting the accumulator tractive system circuit must have a rating lower than the maximum switch off current of the isolation relays. EV3.6 Accumulator Management System (AMS) EV3.6.1 Each accumulator must be monitored by an accumulator management system whenever the tractive system is active or the accumulator is connected to a charger. For battery systems this is generally referred to as a battery management system (BMS) however alternative electrical energy storage systems are allowed and therefore AMS will be the terminology used in this document. EV3.6.2 The AMS must continuously measure the cell voltage of every cell, in order to keep the cells inside the allowed minimum and maximum cell voltage levels stated in the cell data sheet. If single cells are directly connected in parallel, only one voltage measurement is needed. EV3.6.3 The AMS must continuously measure the temperatures of critical points of the accumulator to keep the cells below the allowed maximum cell temperature limit stated 17

18 in the cell data sheet or below 60 C, whichever is lower. Cell temperature must be measured at the negative terminal of the respective cell and the sensor used must be in direct contact with either the negative terminal or its busbar. If the sensor is on the busbar, it must be less than 10mm away from the cell terminal. EV3.6.4 For centralized AMS systems (two or more cells per AMS board), all voltage sense wires to the AMS must be protected by fusible link wires or fuses so that any the sense wiring cannot exceed its current carrying capacity in the event of a short circuit. The fusing must occur in the conductor, wire or pcb trace which is directly connected to the cell tab. EV3.6.5 Any GLV connection to the AMS must be galvanically isolated from the tractive system. EV3.6.6 For lithium based cells the temperature of at least 30% of the cells must be monitored by the AMS. The monitored cells have to be equally distributed within the accumulator container(s). EV3.6.7 The AMS must shutdown the tractive system by opening the AIRs, if critical voltage or temperature values according to the cell manufacturer s datasheet and taking into account the accuracy of the measurement system are detected. If the AMS does perform a shutdown, then a red LED marked AMS must light up in the cockpit to confirm this. EV6.1 Overcurrent Protection EV6.1.1 All electrical systems (both low and high voltage) must have appropriate overcurrent protection. EV6.1.4 If multiple parallel batteries, capacitors, strings of batteries or strings of capacitors are used then each string must have individual overcurrent protection to protect all the components on that string. Any conductors, for example wires, busbars, cells etc. conducting the entire pack current must be appropriately sized for the total current that the individual overcurrent protection devices could transmit or additional overcurrent protection must be used to protect the conductors. EV8.2 Charging EV8.2.1 There will be a separated charging area on the event site. Charging tractive system accumulators is only allowed inside this area. EV8.2.2 Accumulators must be removed from the car for charging within a removable accumulator container and placed on the accumulator container hand cart for charging. EV8.2.3 The accumulator containers must have a label with the following data during charging: Team name and Electrical System Officer phone number(s). EV8.3 Chargers EV8.3.1 Only chargers presented and sealed at Electrical Tech Inspection are allowed. All connections of the charger(s) must be isolated and covered. No open connections are allowed. EV8.3.2 All chargers must either be accredited to a recognized standard e.g. CE or where built by the team they must be built to high standards and conform with all electrical requirements for the vehicle tractive system, for example EV4.1, EV4.3 and EV4.6 as appropriate. 18

19 EV8.3.3 The charger connector must incorporate an interlock such that neither side of the connector become live unless it is correctly connected to the accumulator. EV8.3.4 HV charging leads must be orange EV8.3.5 When charging, the AMS must be live and must be able to turn off the charger in the event that a fault is detected. EV8.3.6 When charging the accumulator, the IMD must be active and must be able to shut down the charger. Either the charger must incorporate an active IMD or an active IMD must be within the accumulator. 19

20 Appendix B: Decision Matrices Table B.1 Accumulator BOM. 20

21 Table B.2: Energus modules comparison sheet. 21

22 Table B.3: Cylindrical cell comparison sheet Table B.4: BMS comparison sheet and selection. 22

23 Table B.5: Charger Comparison 23

24 Appendix C: Part and Component Datasheets Table C.1: Energus Li8PT data table. Full Energus data sheet here. 24

25 Table C.2: Samsung R data table. Full Samsung data sheet here. Orion BMS documents found here 25

26 ElCon PFC 2500 Battery Charger Technical Data Full Elcon PFC 2500 data sheet here 26

27 Appendix D: Test Procedure Documents 1. Purpose Charger Test Procedure The Charger is an important part of the accumulator system. The purpose to test a charger is to see whether it perform as expected so that it will not damage the battery pack. Also, to make sure it can charge our battery pack correctly. 2. Equipment Needed Part Name Elcon PFC V 20A charger Digital Multi Meter Timer Cable Input AC source Load Orion BMS Nomenclature High Frequency industry charger Test tool used to measure various value To measure time Cable that can handle up to 20A Need to have 120V AC to 240V AC Max Can draw up to 20A Battery Management System 3. Test Procedure 3.1: General test To test a charger, we need to first test the whether the actual output voltage and current of the charger is what it designed or programmed to be. Action Know the charger s programmed output voltage and current Prepare a Multi Meter switch Multi Meter to measure DC output voltage and current Results N/A DC output voltage should match expected value 27

28 3.1.3 Switch to DC output current DC output current should match expected value 3.2: Charging time Next, we need to test its charging time. The charging time equation is: where time h is in hours. Action Make sure the output voltage from the charger is larger than the overall voltage of the battery or battery pack. Otherwise it won t charge. Results N/A Calculate the expected charging time using the equation above. Get expected value to compare later Charge the battery and start a timer N/A to time the overall charge time When the battery is full, the charger N/A will shut down Stop the timer. Compare the expected charge time and actual charge time. Charge time may not be exactly the same so few minutes off is acceptable. 3.3: Thermal testing Next we test the thermal for the charger. Most charger come with over temperature protection. In our case, if the Elcon PFC 2500 charger s internal temperature of the charger exceeds 75, the charging current will reduce automatically. If exceeds 85, the charger will shut down protectively. When the internal temperature drops, it will resume charging automatically. To test this over temperature protection function: Action Results 28

29 3.3.1 Find a load, whether the battery or machine load that can drain high current or near max charger design current Plug in the charger into Orion BMS system to use it measure temperature of the charger Wait the charger s temperature to go up. Monitor charger s temperature using BMS. Measure the temperature Connect the output to a Multi meter and set it to DC current mode Observe the temperature and output current if temperature is over 75 degree C Observe the temperature and output current if temperature is over 85 degree C. Charge indicator should be on. Observe whether BMS pick up charger temperature Get charger temperature Get the output current from the charger Output current should reduce if temperature is over 75 degree C. Output current should be 0 if temperature of the charger is 85 degree C. 3.4: Short-circuit Protection Short-circuit Protection: When the charger encounters unexpected short circuit across the output, charging will automatically stop. When fault removes, the charger will re-start in 10 seconds. Action Results Grab a wire that can handle up to 20A. N/A Connect positive and negative terminal on the charger Short-circuit detected, charger will shut down for 10 seconds Disconnect positive and negative terminal Charger should restart To test this function, we can simply use a wire to connect the positive terminal and negative terminal together to simulate a short circuit. And the we can observe whether the charger stop charger or not. 3.5: Reverse Connection Protection: 29

30 When the battery is polarity reversed, the charger will disconnect the internal circuit and the battery, the charging will stop and avoid been damaged. To test this protection function, connect the positive terminal of the charger to negative terminal of the load and negative terminal of the charger to positive terminal of the load. Plug in the charger and if charger is not charging then this function works. 3.6: Input Low-voltage Protection When the input AC Voltage is lower than 85V, the charger will shut down protectively and automatically resume working after the voltage is normal again. Action Set the input AC voltage to 120V AC and plug it into the charger Connect the charger to a random load that it can charge Next lower the input AC voltage to the charger under 85V Crank up the AC input voltage to V, observe the charger. Results N/A N/A The charger should shut down and stop charging The charger should resume charging. 30

31 BMS TEST PROCEDURE UConn Electric Motorsports ACCEPTANCE TEST PROCEDURE NO. 01 DATE: 12/09/17 TITLE: BMS Pre-integration Test Procedure PREPARED BY: Tejinder Jutla CHECKED BY: 31

32 APPROVED BY: Table of Contents 1.0 Purpose Applicable Documents Drawings Test Equipment WARNING Test Procedure BMS SOC BMS Balance BMS Charging BMS Discharging Troubleshooting Grounding Wire Shielding Wire Routing 5 32

33 1.0 Purpose The Battery Management System basic functions will be tested in this Acceptance Test, main objective it to demonstrate satisfactory operation of the system installed on the FSAE racecar and compliance to the appropriate sections of the FSAE Rulebook This Acceptance Test will confirm operation of the BMS at a component level, before integration to any other systems. This will mitigate risks of failure, and promote safety of person working on the tractive accumulator. 2.0 Applicable Documents 1) Orion BMS Operational Manual 2) Orion BMS Troubleshooting Manual 3) Orion BMS Wiring Manual 4) Orion BMS Software Utility Manual 3.0 Drawings 1) Enclosure Assembly, Std. Capacity, Technical Outline 2) Orion BMS Quick-Start Guide 4.0 Test Equipment Part Number Nomenclature Orion BMS Standard Size Battery Management System 62 Li2x4PT Li-ion building block with temp sensor-3.6v/18c AeroVironment ABC-150 Testing of advanced batteries, fuel cells, capacitors, and other alternative energy technologies Digital Multi Meter test tool used to measure two or more electrical values PFC 2500 Battery Charger Constant current constant voltage charger 33

34 5.0 WARNING This Test Procedure requires the use of high current and high voltage equipment(s). Safety is the highest priority. The rules of the lab and instructor of the lab must be respected and in compliance with the university s safety rules. Verify all members of the team have the correct safety training to be working in such an environment. At this stage, the BMS is deemed unreliable unless proven otherwise by completing this Test Procedure. If the test procedure fails, identify, and correct the problem using other documentation if available. 6.0 Test Procedure 6.1 BMS SOC ACTION Assuming the battery pack is ideal, connect to ABC-150 at the negative terminal and discharge pack Connect battery pack to the BMS and note the reading Confirm the DMM reading with that of the BMS RESULTS Voltage across terminal should result in a decrease, confirm with DDM BMS should signal and give an indication of low voltage, charger should be activated at this point to bring voltage back up This will give you accuracy reading prediction from the BMS 6.2 BMS Balance ACTION RESULTS Take one pack from the 62 packs connected in module, using the ABC- 150, discharge this one pack and The one pack that was discharged will be out of balance compared to the rest of the packs. Confirm and note the voltage of this pack connect back to the battery Connect battery pack to the BMS and BMS should be able to read the pack that is out of 34

35 note any messages given At this point, allow BMS to balance the battery pack balance, and point out exactly which one is the culprit. Battery pack should be balanced out to original values 6.3 BMS Charging ACTION RESULTS Turn on power to the charger BMS should appear operational, since the BMS is digital, note the cell voltages, and current is now flowing into the pack N/A BMS is aware of the current flowing into the pack, the SOC value is increasing Verify cell temperature readings, making sure they are not excessive BMS should read correct values, if temp reaches beyond 60C then bms should shut off charging (60 degrees C) N/A Note that balancing starts occurring on the most charged cells when their voltages reach a certain threshold N/A As soon as any cell s voltage reaches the maximum threshold, charging is interrupted Turn off power to the charger Pack is fully charged 6.4 BMS Discharging ACTION RESULTS Turn on the load, in this case, the pack should be connected to the ABC-150 which will act as the motor BMS should appear operational, since the BMS is digital, note the cell voltages, and current is now flowing out of the pack N/A BMS is aware of the current flowing out of the pack, the SOC value is decreasing Verify cell temperature readings, BMS should read correct values making sure they are not excessive (60 degrees C) Discharge at 18C (360A) for five sec. Repeat step but at 8C (180A) constant As soon as any cell s voltage reaches the minimum threshold, batteries should be discharged current until voltage cutoff at 60C Turn off load N/A 35

36 7.0 Troubleshooting Normal BMS functions can be verified through the Test Procedure section. However, there can be many issues of failure, this section outlines some general pointers. 7.1 Grounding be sure to use a short, low-inductance conductor between the BMS case to the chassis of the car if needed. 7.2 Shielding Make sure that for communication/sense wires, shielded cables and/or twisted pairs are used instead. This will greatly mitigate errors. 7.3 Wire Routing High-voltage cables should be routed along the power conductor and away from the chassis ground. Low-voltage communication wires should be routed away from power conductors and close to chassis ground. 36

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40 Resources 1. Davide Andrea 2011, Battery Management Systems for Large Lithium Battery Packs. 2. September , SAE International Formula SAE Rules. Retrieved from pdf 3. Energus Power Solutions 4. Orion Battery Management System vwzneaayasaaegjxn_d_bwe 5. Elcon Charging Samsung Introduction of INR R retrieved from 7. Li-Ion BMS comparison 40