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Battery Packs, Stack, and Modules ... In this 3 part series, Nuvation Energy CEO Michael Worry and two of our Senior Hardware Designers share our experience in energy storage system design from the vantage point of the battery management system ... In part 1, Alex Ramji presents module and stack design approaches that can reduce system costs while meeting power and energy requirements. ... ... Click here to watch part 2..

Battery Management for Large-Scale Energy Storage (Part 4) ... Part 4 of 4: ... ... State of Charge (SoC) and Depth of Discharge (DoD) ... Lead Acid Batteries and Battery Management ... Optimizing for Cycle Count ... Conclusion ... To avoid battery damage, most battery manufacturers recommend that their batteries never be fully discharged or fully charged ... When setting SoC thresholds in the BMS to manage an energy storage system, system-level design considerations such as the PCS voltage requirements discussed earlier, and application-specific needs such as cycle count requirements are also factored in ... The terms “full” and “empty” are therefore inaccurate in this context of “never completely full” and “never completely empty.” That’s why battery industry professionals instead prefer to use the term State of Charge (SoC) to refer to the degree to which a battery has approached the lowest or highest recommended level of charge; 100% SoC is not \u2018full’ but is “as full as the system designers said we should go” and 0% SoC is not \u2018empty’ but is “as empty as the system designers said we should go.” These thresholds are programmed into the battery management system where they are accessed by the PCS and used to prevent overcharging and over-discharging. ... In Nuvation Energy’s battery management system, Depth of Discharge refers to how many amp-hours (Ah) of the total battery capacity have been used ... The highest Ah reading on the DoD gauge in the BMS Operator Interface is the maximum DoD available ... This enables a user to look at the Operator Interface to understand at a glance how much charge has been drawn from the battery and to determine how much is remaining. ... Nominal ranges for voltage, temperature, and current, with thresholds that trigger a BMS Warning (W) or Fault (F) ... H=High, L=Low ... Under the “Current” threshold: C=Charge Current, \u200bD=Discharge Current. ... How are SoC and DoD Measured by the BMS? ... When a cell is rated by the manufacturer to be x amount of Volts, that cell actually fluctuates in voltage as part of its normal operation ... The cell voltage is highest at 100% SoC and lowest at 0% SoC ... When a battery is at rest, i.e: there is no charge flowing through it, the BMS can determine the battery’s SoC based on its voltage alone ... When a battery is being charged or discharged, however, calculating SoC becomes more challenging. ... The voltage of a battery at rest is known as the “Open Circuit Voltage,” (OCV) because it represents the voltage of the battery when there is no circuit present carrying current ... One way of measuring the SoC of a battery at rest is to compare the OCV to a data set provided by the battery manufacturer that shows the OCV of their batteries at different SoCs ... This data set is known as the “open circuit voltage curve” or the “OCV curve.” Batteries do not deplete or retain energy in a uniform manner as they move from full to empty or vice versa, hence the “curve.” This curve varies from chemistry to chemistry, so it is provided by the battery manufacturer. ... When a battery cell is at rest, a BMS can determine the SoC of a battery be comparing the battery voltage to an Open Circuit Voltage (OCV) Curve provided by the battery manufacturer. ... Current flowing through the battery changes the voltage of the battery in a non-uniform manner ... When the battery is in use, this phenomenon makes it very difficult to accurately calculate SoC by using voltage alone ... Nuvation Energy’s battery management system adds a technique called coulomb counting to its approach to calculating SoC when a battery is in use ... Coulomb counting measures the current flowing in or out of the cell. ... The coulomb counting method integrates the measured current over time and factors in the battery capacity to update the SoC value ... This algorithm requires an initial SoC value, which can be determined by conducting a full charge/discharge cycle ... Unlike the OCV curve however, charge and discharge curves continually change as the battery is used, so charge-discharge cycle benchmarks are insufficient on their own to determine the SoC under current ... Nuvation Energy’s battery management system has solved this problem with proprietary algorithms that also include additional sensor data. ... Lead-acid batteries can become damaged if overcharged and over-discharged during regular use (and even when deliberately overcharged during equalization) ... In the case of vented lead-acid batteries, overcharging can expel poisonous and flammable gases ... Lead-acid cells as a whole tend to be less likely to catch fire than other chemistries, but some are still susceptible to thermal runaway ... Their reputation for resilience in the face of overcharging and over discharging, and their lack of a need for balancing has resulted in the misconception that lead-acid batteries do not need a BMS ... While \u2018need’ may be too strong word here, the lifespan of lead acid batteries can be dramatically reduced when the batteries are abused, and dramatically improved when managed by a BMS. ... In an application with a small number of lead-acid cells, replacing a lead-acid battery from time to time may cost less than integrating a battery management system into the ESS ... However, in a large-scale lead-acid energy storage system that outputs hundreds of kilowatt-hours or more of energy, the ROI of incorporating cell-level battery management becomes a simpler calculation, and developers of these systems tend to utilize a BMS. ... In a large-scale energy storage system that utilizes dozens of large-format lead-acid cells to output hundreds of kilowatt-hours or more of energy, the ROI of incorporating cell-level battery management becomes very simple math. ... There is also the use-case of battery backup systems and uninterrupted power supplies (UPS) where the battery is unused and in standby mode for 99% of its life and must be able to perform in the 1% use-case ... The BMS used in this system can also track the health of the lead-acid battery backup to determine when a replacement is required ... This enables pre-emptive maintenance or replacement before the next blackout occurs, and helps reduce routine maintenance visits. ... To meet the cycle count needs of their target customers, some battery manufacturers create charge/discharge ranges that are optimized to increase the total amount of cycles the battery can provide before being replaced ... For example, a battery may be specified to only be discharged to 50% despite the fact that there is no likelihood of the cell being damaged anywhere above 15% ... By defining such a partial cycle to the BMS as the nominal range of a full cycle, a battery manufacturer can provide a battery warrantied to support a higher cycle count. ... In an emergency situation, this can present an opportunity if you have a BMS that integrates with your other ESS control systems in a manner that provides you with the flexibility to make different decisions ... For example, during a protracted grid power failure you may wish to draw more charge from the battery at the expense of cycle count ... Nuvation’s battery management system provides users with the ability to log into the BMS user interface and change the maximum DoD threshold settings within minutes in order to derive more capacity from the battery. ... Alternately an emergency response function can be designed into the ESS control system by having SoC and DoD thresholds managed jointly by the BMS and the Energy Management System (EMS) or smart PCS ... The BMS can manage battery safety and system-level operational thresholds, and the EMS or smart PCS can manage the more flexible parameters that address battery warranty / cycle count/ lifespan objectives ... During typical ESS operation the EMS and / or smart PCS would respect the more flexible parameters while the BMS manages the safety limits ... In an emergency situation the PCS can be instructed to draw additional charge within the flexible parameters while the BMS continues to enforce safety and system thresholds ... This \u2018collaboration’ across control systems can be designed into an ESS that uses a MESA conformant BMS by leveraging MESA to expose the required BMS-derived data to the PCS and EMS over Modbus TCP/IP (Ethernet). ... We hope this exploration of battery management for large-scale energy storage provided you with some new knowledge and insights ... As with most electronic equipment, all battery management systems are not created equal, and some perform their role better than others ... When selecting a BMS important factors to consider include: ... How well does the BMS do its fundamental job of protecting batteries? A BMS uses a combination of sensor data and complex algorithms to derive the critical battery information used by numerous components in an energy storage system to prevent battery damage. ... How well does the BMS integrate with other components within and outside of the ESS that depend on receiving BMS data in real time to perform their functions effectively? ... How flexible is the BMS in terms of empowering users of the energy storage system to utilize the batteries in the manner they need and to respond to unexpected situations when they arise? ... Nuvation Energy battery management systems are designed from the ground up for use in large-scale high-power applications and critical energy infrastructure ... From initial ESS design, to systems integration, communications with internal and external control systems, and finally to being able to get what you need from your battery in any situation, Nuvation’s intelligent BMS has been designed with all of those tasks in mind ... We are confident that when you evaluate our battery management systems, you will be very impressed ... Contact Us today for a quote. ... Part 3.

Battery Management for Large-Scale Energy Storage (Part 3) ... Part 3 of 4: ... ... Warnings, Faults, & User-Defined Thresholds ... Protecting the Battery ... Power Conversion Systems (PCS) ... Energy Controllers ... Environmental Controls ... Communicating with Energy Controllers ... Cell Balancing ... Nuvation Energy’s battery management system provides two levels of response when a battery is moving out of its nominal operating parameters ... As cell temperature, current, and voltage drift outside of (i.e: above or below) nominal parameters, the battery management system will generate a \u2018Warning’ to the human user and/or to automated control systems in the battery pack, alerting them that although the battery is still operating within safe parameters, it is getting too close to the edges of those thresholds ... A Warning notification can trigger preventive actions that could potentially resolve the issue without requiring the battery to be taken offline ... In a situation where the safety thresholds have been passed, the BMS will trigger a \u2018Fault’ message and open the contactors to disconnect the battery from the power path. ... Nuvation Energy’s battery management system also enables the implementation of user-defined thresholds that can trigger responses from the PCS and other devices in the energy storage system ... User-defined thresholds reside within the safe operating ranges of the battery and can accommodate system-level performance requirements or trigger actions that ensure the battery never exceeds safety parameters ... For example, a user-defined temperature threshold can activate cooling fans in the battery rack before the batteries begin to overheat ... If the battery temperature continues to rise after the cooling fans have been activated, a slightly higher temperature threshold can initiate a reduction in current from the PCS ... All these actions can be initiated while the battery is well within nominal operating parameters, to ensure that it does not exceed them. ... Figure 1. Performance parameters can apply to battery safety, but there are also system level battery performance thresholds in an ESS ... This screenshot from Nuvation Energy’s battery management system is generating a Warning that the stack voltage has dropped below 720 Volts, the minimum required by the PCS used in this energy storage system being used at a municipal wastewater treatment plant. ... Figure 1 is a screen capture of Nuvation Energy’s battery management system managing a Nuvation-designed 2MW / 588 kWh energy storage system ... A user-defined threshold of a minimum stack voltage of 720 V has been programmed into the BMS, because the PCS requires this minimum stack voltage for proper operation ... To maintain the power levels required by the PCS, \u20180% SoC’ has been configured in the BMS to be 720 Volts, as opposed to the minimum SoC required to protect the battery ... In this screenshot taken during system testing before commissioning, we see that a Warning has been generated by the BMS due to the low stack voltage, and the SoC gauge reads 0% ... The cell voltage and temperature gauges, however, clearly show that the battery cells are within nominal operating parameters and not at risk ... If the Stack voltage drops further, the BMS will disconnect the stack from the DC bus in the ESS because the battery stack will no longer be generating the minimum voltage required by the PCS. ... User-defined thresholds can also initiate communications with system maintenance personnel ... An energy management system or PLC device can alert ESS management staff, trigger a service call, or initiate an emergency response via e-mail, text message, or through the control panel of a building management system. ... The BMS can provide data to “first response” environmental control systems such as fans that siphon heat away from the battery rack. ... The sharing of data between the PCS and BMS can be challenging when integrating proprietary communications protocols across the two products ... Fortunately the energy storage industry as a whole is moving towards the standardization of communications protocols ... If you are in the market for a battery management system for your ESS, it would be prudent to ask if it utilizes open or proprietary communications protocols, and to understand the level of effort that will be required for system integration ... Nuvation’s battery management system uses the open MESA protocol to enable the sharing of sensor data received by the BMS ... This enables the PCS to control with more precision the charge it is delivering to or drawing from the batteries, and improves the PCS’ effectiveness at regulating current for the purpose of thermal management. ... Control systems that manage energy storage applications such as PV smoothing, frequency regulation, and demand charge management are dependent on data from the battery management system regarding the level of charge available in the battery packs, as well as the amount of energy available in the ESS ... For example, if the BMS disconnects a battery stack for servicing or safety reasons, this reduces the amount of available energy that the ESS can provide ... If that energy reduction is not communicated to the controllers that are executing the energy storage application, those systems may erroneously assume that a higher amount of energy is available ... That omission in data reporting could result in a sudden and unexpected loss of power during ESS operation. ... The MESA protocol was designed for integration with other protocols used at successively higher levels in the energy storage system architecture, up to the utility-grid energy management level (i.e: DNP3) ... This greatly simplifies the sharing of battery data with higher-level energy controllers. ... Environmental controls protect battery cells from damage by regulating ambient temperature to prevent the batteries from getting too cold or too hot ... Where communications exist between the BMS and HVAC system, environmental controls can activate based on battery module temperature data provided by the BMS, as opposed to ambient room temperature readings, which would be received only after sufficient heat had built up inside the modules to impact the room temperature. ... In environmental control scenarios, real-time access to temperature data from the BMS can make the difference between the initiation of preventive actions and the management of a catastrophic event after the fact ... For this reason Nuvation’s Grid Battery Controller is designed to be able to communicate with up to 16 external devices at the same time ... These can include HVAC systems, PLCs, SCADA, energy management systems, control station interfaces, etc. ... Cell balancing refers to the process of maintaining an equivalent amount of charge in all series-connected cells ... Balancing ensures that all cells in each battery module get fully charged and none are overcharged in the process ... Many battery chemistries require cell balancing from the BMS during the charge cycle ... One exception is that some lead-acid batteries ensure that all cells reach full charge through a periodic calibration process called equalization, which involves overcharging the stronger cell while other cells catch up. ... Nuvation Energy’s battery management system performs cell balancing by diverting energy from the cells that are charging faster than others ... This enables all cells to charge at a fairly uniform rate until full ... Since battery cells in a module are usually very closely matched in terms of the rate at which they charge, very little energy is wasted in this process ... If one cell has a very different impedance from other cells (i.e: it is charging at a significantly slower or faster rate than the other cells), that battery module is generally considered to be damaged and is replaced as part of regular ESS maintenance. ... Up Next ... Part 4 of 4: ... How are SoC and DoD Measured by the BMS? ... State of Charge (SoC) and Depth of Discharge (DoD) ... Lead Acid Batteries and Battery Management ... Optimizing for Cycle Count ... Conclusion ... Part 2 ... Part 4 .

Understanding Contactors ... Nuvation Energy’s battery management system can provide power to the contactor coils directly, which strengthens its reliability as a safety system by enabling it to de-energize the contactors without assistance from any additional components ... Read more information about energizing and de-energizing the contactors here. ... .

Battery Management for Large-Scale Energy Storage (Part 2) ... Part 2 of 4: ... ... Open Wire Detection ... Energizing and De-Energizing the Contactors ... Thermal Runaway Mitigation ... The accuracy of battery data and the sharing of that data across BMS modules are of critical importance in ensuring precise battery management. ... There can be hundreds or even thousands of sense wires in a large-scale energy storage system, including sense connections between cells within a battery module ... A loose or unconnected sense wire between the cells in a module, between the batteries and BMS, or among the many wires that connect BMS modules to each other, could result in the BMS operating with incorrect data and sharing that faulty data with other ESS components ... This can lead to battery damage and safety issues ... For example: ... The PCS could overcharge or over-discharge cells. ... The PCS could provide or draw a damaging level of current during the charge or discharge process. ... Thermal management systems could fail to initiate in a timely fashion in response to overheating cells. ... The BMS may fail to disconnect the battery when safety thresholds have been exceeded. ... When designing energy storage systems, it is recommended to include a mechanism for ensuring that the BMS is receiving data from correctly connected sense wires, and a way of verifying that voltage, current, and temperature data from every cell are propagating correctly across all battery management modules. ... Nuvation Energy battery management systems include a feature called Open Wire Detection which detects damaged, loose, disconnected, or incorrectly torqued sense wires ... This includes identifying connection quality issues in sense wires between cells within the many battery modules in the energy storage system ... Nuvation’s BMS also includes a self-diagnostic function that auto-initiates during the BMS start-up sequence and: ... Verifies that all sensor data is propagating correctly across all battery management modules. ... Reports any errors by generating a system Fault through the BMS Operator Interface. ... Suspends the BMS startup sequence until any errors have been resolved. ... Automatically resumes the startup sequence from where it left off after issues have been resolved. ... Nuvation Energy battery management system modules \u200bundergoing electromagnetic interference susceptibility testing at TUV facilities. ... An incorrectly torqued sense wire can deliver incorrect readings to the battery management system. ... Since most safety situations arise and escalate while energy is flowing through batteries, disconnecting the batteries from the flow of energy is a quick and highly effective way to de-escalate an emerging safety issue ... If batteries begin to operate outside of safe performance parameters, the BMS will disconnect the batteries by de-energizing the contactors connecting the batteries to the power path ... Contactors are physical switches in the path of the energy flow ... The BMS is able to open and close a contactor by de-energizing (opens the contactor) and energizing (closes the contactor) magnetic coils inside the contactor unit ... Nuvation Energy’s battery management system can provide power to the contactor coils directly, which strengthens its reliability as a safety system by enabling it to de-energize the contactors without assistance from any additional components. ... Uni-directional contactors must be installed in a direction that is aligned with the direction the current is flowing, otherwise their power rating during connection and disconnection can be as much as 50% lower ... Bi-directional contactors have the same power rating for both directions of current flow during connection and disconnection. ... https://www.youtube.com/embed/ekOeQoiqpho ... When either type of contactor is energized it has the same power rating in both directions ... One design approach when designing Stack Switchgear is to put a separate contactor at each end of the power path (i.e: one on the side of the positive terminal and one on the side of the negative terminal), and to first disconnect the contactor that is aligned with the direction as the flow of current (i.e: charging or discharging) ... One can also choose to implement only a single bi-directional contactor, but Nuvation Energy has made the choice of creating the redundant safety feature of designing in two separate contactors so that if one fails, the other can sever the connection. ... Nuvation Energy’s battery management system allows the alignment of the contactor to be programmed into the BMS ... This enables the BMS to intelligently disconnect the battery from the flow of energy by first opening the contactor that is aligned with the direction in which the current is flowing ... It will then open the second contactor to completely disconnect the battery stack from all potential power sources, for added safety. ... Thermal runaway is a condition that can occur in several battery types, including lithium-ion and some lead-acid batteries ... It is a condition where a rapid rise in the temperature of one or more battery cells causes a reaction within the cell that triggers further increases in temperature ... Causes of thermal runaway include a short circuit within or outside of the battery, overcharging, and the excessive application of current during charging ... Once initiated, this reaction can continue and cascade to other cells in the pack and eventually become uncontrollable ... This can lead to battery fires and even explosions. ... There are multiple thermal management mechanisms in an energy storage system ... These include batteries themselves, which are designed to dissipate heat and contain thermal reactions ... However, the action most likely to prevent a thermal runaway event is to recognize when individual cells are approaching operational limits and to disconnect the batteries from the power path ... A thermal runaway event can take place within a short period of time, but thermal runaway reactions tend to begin only after cell temperatures have risen well beyond the battery manufacturer’s nominal operating temperature ranges. ... Batteries are designed to dissipate heat and contain thermal reactions ... In this image Warner ESS and Tactical Fire Productions is conducting battery fire containment testing by deliberately setting the batteries on fire and ensuring they burn in a manner that can be managed by emergency responders ... Image courtesy of Warner ESS and Fire Tactical Productions. ... Damaged batteries however, can go into thermal runaway while being operated within their nominal parameters. One way to damage batteries is by cycling them below their rated operating temperature ... At low temperatures, a number of chemical reactions can occur within the battery which can cause irreversible damage to the cells ... For example, the image below shows the nominal temperature range of a typical lithium-ion battery ... During testing at the University of Waterloo, an LFP cell was deliberately operated at -30\u00b0C for several hours ... This extended operation below nominal temperatures damaged the cell ... In subsequent operation under nominal conditions a short circuit developed in the battery, due the the damage caused during low-temperature testing ... The short circuit triggered a thermal runaway event within 5 seconds of occurring, while the battery was being operated within nominal operating parameters. ... This lab test illustrates the importance of ensuring the battery is kept within its operating limits throughout its entire lifetime ... Although a battery might appear to be functioning normally, any cycling outside the nominal operating range can damage the battery internally ... The role of a battery management system is to ensure that the battery never exceeds its nominal temperature, voltage and current limits ... This will help preserve battery life and prevent thermal runaway events from occurring. ... Up Next ... Part 3 of 4: ... Warnings, Faults, & User-Defined Thresholds ... Protecting the Battery ... Power Conversion Systems (PCS) ... Energy Controllers ... Environmental Controls ... Communicating with Energy Controllers ... Cell Balancing ... Part 1 ... Part 3 .