The design of a power battery system is a critical step in the development of electric vehicles (EVs) and other electric-powered applications. Key parameters such as capacity, voltage, and battery type play a significant role in the selection and configuration of batteries. In this article, we will explore the basic principles of power battery system design using a real-world case study.
Battery Pack Design Input
The following input parameters were considered in the design of the battery pack:
Range: 100 km
Energy Consumption Factor: 0.15 kWh/km
Drive Voltage: DC 350 V (drive motor and controller DC side voltage)
Continuous Current: 1C output
P/E Value: 5
Battery Type: Soft package ternary lithium battery
Battery Specification: 20Ah / 3.6V
Battery Pack Design Output
Based on the input parameters, the following design output was calculated:
Total Capacity of Battery Pack System: ≥ 15 kWh (Design Mileage * Energy Consumption Coefficient)
Total Available Capacity of Battery Pack System: ≥ 12 kWh (Total capacity * SOC operating range)
Battery Pack System SOC Operating Range: ≥ 80% (10%SOC~90%SOC)
Nominal Voltage of Battery System: DC 350V (Driving voltage)
Working Voltage Range of Battery System: DC 287V408V (3V4.2V)
Continuous Charging/Discharging Power of Battery System: 15 kW (1C continuous output capacity)
Peak Charge/Discharge Power of Battery System: 60 kW @ 10s (P/E)
Operating Temperature Range of Battery System: 0°C~60°C
Battery System Cooling Mode: Not specified
Battery System Service Life: 8 years or 100,000 km
Self-Discharge Rate of Battery System: 5% per month
Total Weight of Battery System: ≤ 150 kg
Module Design Output
In module design, the following parameters were determined:
Number of Module Strings: 98 strings
Module Parallels: 2 parallel
Concatenation Method: First merge and then string
Module Voltage Range: 294V~411.6V
Module Rated Voltage: 352.8V
Module Pressure: 800N~1000N
Battery Design Output
The battery design output includes parameters for the individual battery modules:
Type of Battery: Soft package ternary lithium battery
Single Battery Voltage Range: 3.0V~4.2V
Single Battery Capacity: 20Ah @1C
Nominal Voltage of Monomer Battery: 3.6V
Cycling Life: ≥3000 times @1C
Operating Temperature: -20°C~60°C
Safety Specification
In battery module design, it’s crucial to ensure that safety specifications exceed those of the battery pack to enhance overall reliability. Specific safety-related requirements for the module include:
Module Open Circuit Voltage (OCV): ΔV ≤ 5mV~10mV between total positive and negative.
Module Monomer Battery Voltage: ΔV ≤ 5mV~10mV between series batteries.
DC Internal Resistance of Module: Measured at 3C magnification of 10s.
Module Communication Internal Resistance: ACR test at 1kHz.
Module Insulation Impedance: Insulation resistance between metal and the total positive and negative terminals.
Degree of Pressure Resistance of Module: Electrical gap between the total positive and negative terminals and the shell.
Conclusion
Designing a power battery system for electric vehicles involves meticulous consideration of various parameters, ensuring that the system meets performance, safety, and reliability requirements. In this case study, we’ve highlighted the critical design inputs and outputs, as well as safety specifications that are essential for the successful development of power battery systems. It’s worth noting that Battery Management System (BMS) design is a separate but crucial aspect of the overall battery system design process.
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