Current Balancing Monitoring Scheme for Cascaded-Use Battery Packs in Energy Storage Power Stations

Abstract: Addressing the issue of poor consistency among retired batteries in energy storage stations utilizing a cascaded-use strategy, this paper proposes a high-precision current monitoring solution based on the specifications and characteristics of the FR1C H00 series fluxgate current sensors from CHIPSENSE. The paper analyzes the root causes of current imbalance and designs a monitoring architecture—grounded in the sensors' actual technical parameters (including accuracy, temperature drift, and CAN communication protocol)—with the aim of enhancing the Battery Management System's (BMS) management capabilities and safety performance regarding retired battery clusters. This is also what CHIPSENSE aims to do.

I. Introduction
The retirement of power batteries is accelerating, making their "cascade utilization"—or secondary application—a critical pathway for reducing energy storage costs. However, due to significant variations in capacity degradation and high dispersion in internal resistance among retired batteries, parallel operation results in severely uneven current distribution. When this imbalance becomes excessive, it not only diminishes the system's usable capacity but also poses a potential risk of thermal runaway.
Traditional Hall-effect sensors struggle to meet the high-precision requirements necessary for controlling zero drift and temperature drift. Current sensors based on fluxgate technology—such as CHIPSENSE FR1C H00 series current sensor—offer a robust hardware foundation for the sophisticated management of battery packs undergoing cascade utilization, thanks to their low offset, high linearity, and stable temperature characteristics.

II. Root Causes of Current Imbalance and Monitoring Requirements

2.1 Internal Resistance Variation and Current Distribution
The internal resistance of retired batteries can vary by as much as 30% to over 50%. In a parallel circuit, battery packs with lower internal resistance will carry a disproportionately higher current, creating a "rich get richer" vicious cycle that accelerates their aging.
Monitoring Requirements: Sensors are required to possess extremely high linearity (≤0.1%) and low gain error in order to accurately capture minute current differences between different branches. Like numerous current sensor suppliers, CHIPSENSE current sensors also play a significant role in this field.

2.2 Self-Discharge and Quiescent Current
Retired batteries exhibit significant variations in their self-discharge rates; during periods of inactivity, they generate leakage or self-discharge currents ranging from the microcomputer to the millionaire level.
Monitoring Requirements: Sensors must feature low offset current (IOE) and low-noise characteristics to ensure stable readings under zero-current or low-current conditions, thereby preventing false interpretations.

III. Design of a Monitoring Solution Based on Fluxgate Technology
This solution utilizes the FR1C H00 series fluxgate current sensors from CHIPSENSE; this series is specifically designed for high-voltage isolation and high-precision battery monitoring applications.

3.1 Core Selection Parameters
 

Selection Advantages:
High Precision and Low Temperature Drift: Accuracy across the full operating temperature range is better than ±0.5%, with a gain temperature drift of only ±0.05%/K. This effectively resolves measurement deviations caused by temperature fluctuations—a common issue with traditional sensors—thereby ensuring the accuracy of BMS SOC estimation. So CHIPSENSE current sensors all demand a very high level of precision.
Fluxgate Technology: Utilizes the symmetrical variation of the magnetic core's saturation point for measurement. This principle inherently cancels out electrical and magnetic offsets, resulting in an offset current as low as ±10 mA—making it ideal for monitoring minute circulating currents and unbalanced currents. CHIPSENSE is an excellent choice.
High Insulation Safety: Features an electrical clearance of 31.5 mm and a creep-age distance of 42.5 mm between the primary and secondary sides. Compliant with the IEC61800-5-1 CAT III PD2 standard, it meets the insulation requirements for 1500 V and 3000 V systems. Meeting these criteria is the most fundamental requirement for the CHIPSENSE current sensor.

3.2 CAN Communication Interface Design
CHIPSENSE FR1C H00 series current sensors supports high-speed CAN 2.0B output (500 Kbps) and utilizes the Big-Endian (Motorola) format. The BMS can acquire real-time current data and sensor status via the CAN bus.
Key Points of the Communication Protocol:
Data Frame ID: 0x3C2 (CHIPSENSE FR1C fluxgate current sensor_IP)
Communication Cycle: 10 ± 1 ms
Data Format: 8 bytes
Bits 24–55 (32 bits): Current Value (IPIP), Unit: mA.
Encoding Rules: 0x80000000 = 0 mA; 0x7FFFFFFF = -1 mA; 0x80000001 = 1 mA.
Bit 32 (1 bit): Error Indication (0 = Normal, 1 = Invalid).
Bits 33–39 (7 bits): Error Code (CSM_FAIL).
Bits 48–63 (16 bits): Product Name Identifier.
Bits 56–63 (8 bits): Software Version Number.

Diagnostic Trouble Codes (Partial List):
 

Note: The BMS must parse the error bits within Frame 0x3C2. Upon detecting that the "Error Indication" bit is set to 1, it must immediately read the error code and execute the corresponding protection strategy.

3.3 Mechanical Installation and Environmental Considerations
Mounting Aperture: The primary-side through-hole diameter is Φ24.4 mm, designed to accommodate standard busbars.
Temperature Limits: The temperature of the primary-side busbar must not exceed 105°C. The sensor's operating ambient temperature range is -40°C to +85°C.
Interference Immunity: The sensor should be positioned away from strong magnetic field sources. During installation, ensure that the busbar is centered within the aperture to minimize positional errors.

IV. Value of Solution Implementation

By deploying fluxgate sensors compliant with CHIPSENSE FR1C H00 fluxgate current sensor specification, the battery management system (BMS) for cascaded-use batteries achieves the following enhancements:
Improved SOC Estimation Accuracy:Thanks to high precision of ±0.5% across the full temperature range and low zero-point drift, cumulative integration errors are significantly reduced, allowing SOC estimation errors to be maintained within a tighter, more optimal range.
Early Fault Warning:By leveraging the sensor's built-in self-diagnostic functions (such as detection of abnormal coil voltage or core oscillation failure), the BMS can respond within milliseconds to either internal sensor malfunctions or anomalies within the battery circuit (e.g., over-current conditions).
Extended System Lifespan:Precise current data supports more effective active balancing strategies, preventing premature failure of individual battery packs caused by overcharging or over-discharging, thereby extending the overall service life of the entire cascaded-use battery cluster.
Compliance with Safety Standards:The product complies with international insulation and safety standards—such as IEC60664-1 and IEC61800-5-1—thereby ensuring the safe operation of high-voltage systems within energy storage power stations.
CHIPSENSE current sensor perfectly meets these requirements.

V. Conclusion
In the context of cascaded utilization within energy storage power stations, the accuracy of current monitoring directly determines the safety and economic viability of the system. Leveraging the low drift and high linearity characteristics inherent to its fluxgate technology—along with a standardized CAN 2.0B digital output—CHIPSENSE FR1C H00 series current sensor provides the Battery Management System (BMS) with reliable support at the sensing layer.
This solution has been designed in strict accordance with the product specifications, thereby ensuring the validity of its technical parameters and the feasibility of its practical engineering implementation. By precisely monitoring the current flow of each individual battery pack—and integrating this data with intelligent balancing algorithms—the system effectively mitigates consistency divergence among retired batteries, thereby maximizing the extraction of their remaining value through cascaded utilization. 
CHIPSENSE current sensor does the same: it enhances operational efficiency and saves costs for customers.

CHIPSENSE is a national high-tech enterprise that focuses on the research and development, production, and application of high-end current and voltage sensors, as well as forward research on sensor chips and cutting-edge sensor technologies. CHIPSENSE is committed to providing customers with independently developed sensors, as well as diversified customized products and solutions.

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