The backup battery platform is an important feature of power management systems in an OCP ORV3 architecture and data center application, especially in the field of uninterruptible power supplies (UPS). These platforms, with their precise design focused on housing and organizing backup batteries, act as key sentinels, ensuring the proper functioning of critical equipment during power outages and voltage fluctuations.
The critical importance of reliable backup power systems is undeniable in our modern era, characterized by technological sophistication. The stability of data centers, telecommunications nodes, and server rooms is essential for business operations, making a robust backup power system indispensable. In this context, backup battery platforms play a key role as the foundation of these systems. Acting as a central hub for efficient BBU storage, these platforms create a link that enhances the availability of critical power reserves. Their primary purpose is to house and manage up to six BBU modules, each precisely aligned to accommodate lithium-ion batteries paired with power converters. The architecture of these platforms has been meticulously tuned, seamlessly blending space efficiency with accessibility, streamlining maintenance and simplifying replacement operations.
One of the key advantages of these backup battery platforms is the centralized and organized inventory of BBU modules. The availability of a defined storage system allows for easy tracking, labeling, and maintenance of BBU modules, reducing the risk of loss or confusion, especially in critical situations. Furthermore, this centralized system has proven to be a real advantage for monitoring battery health. This structure facilitates routine inspections, testing, and replacements.
The diverse range of sizes and configurations of BBU platforms has been tailored to the individual requirements of various industries and institutions. The modular design of some platforms provides flexibility, allowing for future development to meet evolving power demands. In addition, these platforms contain integrated monitoring systems that provide real-time information on battery health. Details such as voltage levels, temperature, module activity, and remaining capacity are displayed at a glance, enabling preventative maintenance and ensuring that the batteries are always ready to deliver power during critical moments.
BBU Platform Overview:
As defined by OCP for its new architecture for ORV3, the open rack power architecture consists of a centralized, scalable power rack and a BBU rack that distributes power via a common bus bar to the payload devices (IT equipment). This specification will define the BBU platforms that fit within the open rack. The BBU platform will contain six BBU modules with 5+1 redundancy to provide DC power to all payloads within the rack. When an AC power outage occurs, the BBU platform can provide backup power up to the platform's maximum rated power for a specified backup time. The BBU platform's backup time allows the rack to be moved between power sources without interrupting IT operations and enables applications to be drained or moved before power is lost.
Figure 1. BBU platform configuration in an OCP ORV3.1 architecture
Platform Microcontroller Firmware
The platform microcontroller used in the BBU application is the MAX32625, an ultra-low-power Arm® Cortex®-M4 microcontroller. The microcontroller is responsible for multiple processes:
1. Communicating with the host computer via the Modbus protocol
2. Communicating with the modules via the Modbus protocol
3. Managing the periodic charging of the modules
4. System control modes
Figure 2. (a) Module-to-platform communication diagram and (b) Platform-to-PC communication block diagram.
Communication with the host computer via the Modbus protocol.
In Figure 2, the platform's microcontroller plays a fundamental role in establishing seamless communication with the host computer through the robust RS-485 interface, acting as an expert Modbus server. Its primary function is to collect data from numerous modules in real time, which it does tirelessly. This accumulated data is sent to the host computer, where it is used to populate a dynamic GUI application, providing an enhanced visual representation. When communications are received from the host computer, the platform's microcontroller acts as a gatekeeper, methodically authenticating the validity and integrity of each message. Once the microcontroller is convinced of the message's authenticity, it quickly formulates its response, based on the amount of information stored in the hold registers. This carefully crafted response contains the answers the host computer needs, presented in a structured manner.
However, the platform's microcontroller doesn't fail when the incoming message is contaminated by anomalies. It quickly assumes the role of an effective communicator, responding with an error message based on the Modbus protocol. This error notification alerts the host computer to the anomaly, allowing it to take appropriate corrective action.
Essentially, the importance of the platform's microcontroller lies in its multifaceted role as a data conduit, guardian of data integrity, and responsive informant. All of this contributes to orchestrating a robust and reliable communication framework within the Modbus-powered interactions.
Communication with Modules via the Modbus Protocol.
In Figure 2, the key role of the platform microcontroller becomes clear, as it seamlessly switches between the functions of a Modbus client and a Modbus server, coordinating a complex and efficient communication ecosystem. When interacting with multiple BBU modules, the platform microcontroller acts as the Modbus client, initiating and maintaining communication with each module. These BBU modules act as Modbus servers, continuously updating their registers with the latest information. The platform microcontroller undertakes a cyclical journey while operating in sync. It traverses the environment of the BBU modules, capturing telemetry data from each module on a cyclical cadence. This data, which provides useful information, is carefully stored in the microcontroller's memory, ready to respond should a query arise from the host computer.
However, the purpose of the platform microcontroller is not limited to client-server interactions within the BBU system. It transforms into a Modbus server, delivering the collected data to the host computer upon request, creating a crucial bridge between the host computer and the numerous BBU modules. Simultaneously, it continues its function as a Modbus client, organizing interactions with the BBU modules and ensuring that the information is up-to-date and accurate.
Essentially, the platform's microcontroller embodies versatility and adaptability, skillfully working as both client and server, fostering interaction between the host computer and the BBU modules. This interconnection demonstrates its ability to maintain a robust communication structure, increasing the overall efficiency and reliability of the system.
Periodic Module Charging Management:
In accordance with OCP requirements, a BBU module must be charged periodically because the battery pack loses current while in standby. Since a BBU module can only be charged once every 10 days, the platform microcontroller must monitor and manage which BBU modules will be charged. As a result, periodic charging is initiated by the platform microcontroller, which uses a unique Modbus protocol command to determine which BBU modules require periodic charging. A fundamental requirement for BBU modules within the system architecture stems from the precisely developed standards of the OCP. These modules, which are key components of the configuration, must be charged periodically. This requirement arises from the current leakage experienced by the battery pack during standby periods. Consequently, periodic charging is necessary to maintain optimal performance and operational reliability.
System control modes
Finally, the OCP suggests adding a user control to override BBU module operations. Using Modbus, the user can configure the operation of a single BBU to determine whether it requires charging or unloading.
BBU shelving graphical user interface
Figure 3. A BBU module. A BBU module.
The BBU module's graphical user interface is divided into several sections that provide important information to the user. These components and functions are detailed below. See Figure 3.
1. Module operating status indicator
2. Module internal temperature readings
3. Module fault indicator table
4. Fan speed indicator (in rpm)
5. Power converter metric information
6. Cell information (voltage and temperature)
Module operating status indicator.
In the graphical user interface, there are at least four LED indicators:
► The blue LED indicates that the BBU module is operating in charging mode.
► The first amber LED indicates that the BBU module is in discharging mode and providing backup power to the data center backplane.
► The second amber LED indicates that the BBU module needs to be replaced and is at the end of its useful life (EOL).
► The red LED informs the user that the BBU module is experiencing a failure.
Internal temperature readings of the module
In addition to the BBU's operating status, the module's internal temperature is also displayed on the graphical user interface. At least nine temperature sensors are located on the battery stack and power board. The LTC2991 provides digital temperature readings to the main MCU, while the ADBMS6948 provides analog readings of the battery stack temperature.
Module Fault Indicator Table
The GUI has a fault table that indicates the different types of faults that occur during module operation. The module faults are as follows:
► Overvoltage Protection (OVP)
► Overcurrent Protection (OCP)
► Overtemperature Protection (OTP)
► Overcharge and Discharge Protection
► Fan Shutdown
Power Converter Metrics:
While the module is operating, the GUI is an important resource, providing vital metrics for both the battery stack and the backplane. These metrics are comprehensive, encompassing crucial data such as input and output voltages, as well as currents. This dynamic interaction between the module's operation and the GUI provides users with complete, real-time insight into the system's performance and power dynamics.
Cell Information:
The graphical user interface displays the voltage and temperature level of the battery stack cells. This data is fundamental for determining the state of health (SOH) and state of charge (SOC) of the battery stack.
Figure 4. BBU module summary GUI.
The BBU module's graphical user interface includes a window with a brief overview and user controls. This specific tab of the graphical user interface allows monitoring of all six BBU modules, while also providing individual control over a specific BBU, including the ability to implement operational decisions.
See Figure 4 for a visual representation.
► Direction selector
► Platform system control
Platform system parameters
► Platform fault and current sharing
Address Selector:
Users can seamlessly access specified BBU modules by strategically selecting the precise BBU slot address. This strategic assignment is not random; it is a precautionary step designed to avoid Modbus communication conflicts, achieved by predefining a fixed BBU platform slot address.
Platform System Control:
Giving users the authority to modify BBU operations. They can request a specific BBU module to charge or discharge during its operating period. If forced discharge mode is selected, the boost voltage is increased from 48 V to 51 V, facilitating backplane power while maintaining uninterrupted operation of the power supply unit (PSU) within the data center. This nuanced control ensures an optimized balance between BBU functionality and the uninterrupted operation of the broader infrastructure.
Platform and Power Sharing Failure:
The summary table displays any detected failures across the six BBU modules and notifies the user. This is the fastest way to locate any faults in the BBU platform. Additionally, during parallel or redundant operation of the BBU modules, the power sharing bus indicator shows a bus voltage of 7 V when the motherboard load is at its maximum and 10.5 V when operating under maximum load.
Summary:
The BBU platform serves as a crucial component in a reliable power management system. These platforms are securely interconnected to create a stable environment for a battery backup system, acting as a central hub for efficient management. The result is uninterrupted operation where critical systems remain powered and protected from power outages and voltage fluctuations. The BBU platform provides significant protection in data centers, telecommunications networks, or any environment where a UPS is essential. Its primary mission is to ensure business continuity, improve reliability, and maintain a robust electrical infrastructure. A subsequent article in this series will explain how to select components for the BBU's auxiliary circuitry. This will serve as a criterion and advantage when selecting parts to power critical devices and reduce design inconsistencies.
Reference
David Sun. "Open Compute Project Open Rack V3 BBU Shelf Rev 1.1". Open Compute Project, September 2022.
About the author:
Christian Cruz is an application development engineer at Analog Devices, Inc. in the Philippines. He holds a degree in electronic engineering from the University of the East in Manila, Philippines. He has over 12 years of engineering experience in analog and digital design, firmware design, and power electronics, including the development of power management integrated circuits, as well as AC-to-DC and DC-to-DC power conversion. He joined ADI in 2020 and is currently supporting power management requirements for cloud-based computing and system communications applications.
About the author:
Marvin Neil Solis Cabueñas holds a Bachelor of Science in Electronic Engineering from De La Salle University in Manila, Philippines. Before joining Analog Devices in 2021, Marvin worked as a Systems Engineer for Azeus Systems Philippines, Inc., as a Network Engineer for Technistock, Philippines, Inc. from 2014 to 2017, and as a Research and Development Engineer for Nokia Technology Center Philippines from 2017 to 2020. He has over 10 years of work experience in fields such as embedded systems programming, digital signal processing, and simulation modeling, among others. He currently works as a Senior Software Systems Engineer on various energy-related technology projects. He is currently pursuing a Master of Science in Electrical Engineering at the University of the Philippines.
