The majority of battery management systems available in the present market employ lithium-ion battery modules connected in a series. However, to enhance capacity and operational voltage, a large portion of these BMS for lithium-ion battery modules have been modified to utilize either series or parallel configurations. Nevertheless, the existing battery management system still encounters challenges in effectively performing its designated tasks. To this end, MOKOEnergy has proposed a modular battery management system that is suitable for serving larger scale and higher power application scenarios, and it can also handle many different package types and sizes while still providing basic BMS services. Through this blog, let’s take a closer look at this leading modular battery management system, take a look at its principles of design of modular BMS and architecture, and the convenience it brings us.
How does MOKOEnergy Modular BMS Work?
An optimal modular BMS monitors, controls, and protects the battery to address internal inconsistencies that lead to inconsistent performance, such as early aging effects or battery degradation. BMS can be divided into three categories: centralized, distributed, and modular. Among these options, the modular BMS demonstrated superior efficacy. MOKOEnergy has developed a modular battery management system that employs a signal processor as its central controller and incorporates a versatile battery monitoring chip capable of swift balancing and protective functions for multiple batteries. This BMS system can handle series and parallel configurations, as well as oversee numerous autonomous BMS battery modules through a centralized control mechanism. The BMS accurately gauges battery voltage, charging and discharging currents, along with temperature, before transmitting this information to a mixed-signal processor responsible for monitoring, balancing, and safeguarding battery modules.
MOKOEnergy Modular BMS Design Consideration
When designing modular BMS, MOKOEnergy focuses on the design requirements of its important components, such as LMU, CMU, etc. The selection of these components is very important to ensure the performance of the battery management system. Here’s a look at which components we designed and how we thought about them.
(1) Local management unit
In a modular battery management system, the local management unit is designed to be coordinated by the central management unit via CAN communication.
To be able to act as a comprehensive centralized battery management system, the local management unit is designed to have the following functions:
- Real-time data acquisition, including current, voltage, and temperature.
- Precise timing control.
- Charge and discharge connection control.
- Data and command communications with the centralized management unit.
- Provide battery balancing and thermal management interfaces.
- Provides on-chip programming.
The local management unit is developed under modular technology. It consists of several modules, each of which can be developed and debugged separately. These modules include a central processor module, a protection module, a power supply module, a clock module, a reset module, a data acquisition module, a charge/discharge control module, a communication module, and cell balancing and thermal management interfaces. The detailed design of some of these modules is described below:
Central processor module
The main requirement of the central processor of the local management unit is to fulfill the various functional requirements of each module. Therefore, the central processor requires a relatively fast computational speed, resources including analog-to-digital converters for data sampling, self-reset resources, real-time clock resources, serial communication resources, online programming resources, and multiple general-purpose input and output ports. The modular BMS architecture consists of multiple local management units and therefore constitutes its main cost. Therefore, functionality beyond what is needed should be avoided to achieve cost-effectiveness. To achieve a compromise between functionality and cost, we have chosen the AT90CAN128 microcontroller. The AT90CAN128 chip is based on a high-level Reduced Instruction Set Computer (RISC) architecture, and its most important feature is that it integrates a CAN controller, which avoids the requirement of developing additional CAN controller circuits.
The main purpose of the power supply module is to provide power to the entire local management unit hardware, including the central processor, reset circuitry, data acquisition module drive circuitry, balancing module drive circuitry, signal drive circuitry for the power load control module, and communication module drive circuitry. The power supply for the Local Management Unit is taken directly from both ends of the battery pack, a feature that further contributes to the independence of the Local Management Unit. The power supply module supports any voltage from 9V ~ 100V and outputs a constant 5V voltage to the entire local management unit. Voltage conversion is power-based, so the current in the power circuit can be reduced by increasing the input voltage.
To adapt to temperature changes, temperature detection needs to be very flexible within individual cells as well as within battery packs. However, the limited space in a battery pack requires that the temperature sensors be as small as possible.MOKOEnergy used an array of Negative Temperature Coefficient (NTC) thermistors for temperature measurement.NTC thermistors are resistors whose resistance decreases as the temperature increases.NTC thermistors can be placed anywhere in a single cell or a battery pack.
Measurement of current is carried out by active Hall effect sensors which generate a voltage based on the magnetic field generated by the flowing current. Large variations in current are offset by the accuracy of the dual-range Hall effect sensor, which has two complete ranges of 25 A and 200 A. Compared to a reference voltage, the Hall effect sensor can also indicate the direction of current flow, which indicates whether the battery is charging or discharging. A single current measurement consists of two current samples, one for the 25A channel and one for the 200A channel. Thus, a single current measurement costs O.68ms and produces two current values. To distinguish the real current values, two thresholds, 20A and -20A, are predefined. If the current value of the 25A channel is greater than the 20A threshold or less than the -20A threshold, the current value of the 200A channel is used as the true current value. Otherwise, the 25A channel value is used.
Charge/discharge control module
The charge/discharge control module controls the electrical connections during the charge/discharge process. The charge/discharge control module uses a small signal to generate a mA current from the central processor to control the high current flow of 100A. In the charge/discharge control module, there are two levels of isolation circuits. Level 1 uses an optocoupler to provide isolation between the central processor signals and the drive signals for the level 2 isolation BMS circuit, which requires a large amount of drive power that cannot be provided directly by the central processor. The second stage isolation element may consist of a relay or an insulated gate bipolar transistor (IGBT). If the applied BEV current is less than 30 A, the on-board IGBT is applied. otherwise, an external IGBT or relay is applied. The local management unit can switch between charging, discharging, or both. The main control strategy for electrical load control is based on voltage. When the battery reaches the charge/discharge voltage limit, the charge/discharge control module cuts off the current flow. The optimized control strategy is based on the battery state.
The reset emus BMS module consists of the software reset and the hardware reset.
- The software reset prevents the software from runaway through the actions of a watchdog. A watchdog is a circuit repeatedly fed within a given time interval. Feeding a watchdog is equivalent to toggling the voltage level of the input pin of the watchdog circuit. The feeding period in the LMU is 1s, which is provided by a dedicated clock resource independent of the processor clock. If software runaway occurs, the watchdog is not fed and instead generates a signal to reset the processor and subsequently the local management unit as well.
- The hardware reset is straightforward. By pressing a reset button, a reset signal is generated to reset the processor.
The communication module includes two different types of communication: CAN (controller area network) communication and TIA-485-a communication. The CAN communication of the Local Management Unit (LMU) is used to communicate with the Central Management Unit under the BMS communication protocol. Typically, the LMU transmits and receives data, status, commands, and acknowledgments over the CAN bus.TIA-485-A communication, also known as RS485, where RS stands for Recommended Standard, is used for serial communication and for updating the firmware of the LMU.TIA-485-A communication is a half-duplex communication.
(2) Central management unit
As an up-layer part of the modular battery management system, the central management unit is designed as both a coordinator for the local management units and an interface to the other vehicle components.
The functions of the central management unit include:
- Data and command communication with local management units.
- Configuration of the whole BMS network.
- Storage of important battery information.
- Provision of the graphic user interface.
The functions of the central management unit are primarily realized by software. Therefore the central management unit mainly requires a central processor, with limited use of various other BMS cell modules. Modules in the central management unit consist of a central processor, power module, clock module, reset module, communication module, storage module, and graphic user interface. The detailed design of some of these modules is described below:
Because the central management unit coordinates with multiple local management units, its central processor requires powerful computation ability. Meanwhile, the central processor needs to manage processes such as computation, communication, and display. The central management unit adopts an ARM chip as its central processor, giving the central processor the ability to multitask. Since the central management unit has no dedicated hardware module requirement, its hardware does not require specific development and can be realized by a generalized ARM platform.
Graphic user interface
A graphic user interface provides a clear interpretation of the battery information to the users. Currently, the graphic user interface is displayed on a PC monitor but will be transplanted to a dedicated display in the future. The communication between the central management unit and the display is based on the Ethernet and user data is entered from a keyboard on the PC. The graphic user interface has a series of display windows, including the modular BMS dashboard window, the overall information window, the local management unit information window, and the configuration window. The modular BMS dashboard displays an intuitive graphic view of the whole battery and modular BMS status, including the SOC, current, SOH, and cycle life dashboard, the vehicle operation, BMS status, and error indicator, the power and menu button, and finally the clock.
Where MOKOEnergy Modular BMS Applies?
MOKOEnergy’s modular BMS is designed for use in a variety of industries and applications, especially some of the larger power and scale application scenarios. Here are some of the main areas where MOKOEnergy’s modular BMS is already in use:
Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs): MOKOEnergy’s Modular BMS can be integrated into electric and hybrid vehicle battery packs. Its ability to accommodate different battery chemistries, pack sizes, and power requirements makes it a suitable choice for optimizing the performance, range, and safety of EVs and HEVs.
Renewable Energy Storage: The modular BMS can be employed in energy storage systems that harness renewable energy sources such as solar and wind. Its scalability allows it to manage large battery arrays used to store excess energy for later use, enhancing grid stability and promoting sustainable energy practices.
Uninterruptible Power Supply (UPS) Systems: MOKOEnergy’s BMS can be utilized in UPS systems that provide backup power during grid outages. Its adaptive design ensures reliable energy storage and release, contributing to an uninterrupted power supply for critical infrastructure and facilities.
Industrial Equipment and Robotics: Battery-powered industrial equipment and robots can benefit from MOKOEnergy’s modular BMS. Its ability to handle various power demands and battery configurations ensures efficient and reliable operation in manufacturing and automation settings.
Aerospace and Aviation: Battery-powered aerospace applications, such as electric aircraft and drones, can leverage the modular BMS for efficient energy management solutions, weight optimization, and improved safety.
Medical Devices: Medical equipment relying on battery power, such as portable medical devices and patient monitors, can benefit from the modular BMS’s advanced management capabilities, ensuring consistent and safe operation.
MOKOEnergy has innovated a modular battery management system consisting of multiple local management units and a central management unit. Moreover, the application of the developed modular battery management system to high-power and large-scale electric vehicles and energy storage industries is also significant, which lays a good foundation for the further development of the MOKOEnergy modular battery management system in the future. If you are interested in this area or need help, please feel free to contact us, we can provide you with efficient modular BMS solutions.
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