Battery Parallel Balancing Circuit with FET Current Regulation
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Solution Overview
Problem
The connection of multiple battery packs in parallel for post-vehicle-life applications is complicated by variations in state of health, leading to uneven charging and discharging rates, which can cause excessive charging or discharging and damage to cells if current is not regulated.
Innovation Solution
A current balancing circuit using two field effect transistors (FETs) in series, with a current sensor and proportional-integral control, regulates charging and discharging current through each battery pack to ensure balanced operation, eliminating the need for mechanical switches or relays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple battery packs with varying states of health are connected in parallel, then the system can store more energy and provide backup power, but the battery packs will charge and discharge at different rates causing excessive charging or discharging
Solution Approach 1:
The patent divides the current regulation function into separate charging and discharging control paths, with dedicated FETs for each direction. This segmentation allows independent optimization of charging and discharging current regulation, preventing excessive current in either direction while maintaining high energy storage capacity
Solution Approach 2:
The patent implements feedback control by monitoring the actual current through the battery pack and comparing it with the target current. The control circuit adjusts the FET gate voltages based on this feedback to maintain current balance, ensuring reliable operation even with varying battery health states
2Device complexity
If a single FET is used to control current, then the device complexity is reduced, but the transistor cannot control current effectively when reverse biased
Solution Approach 1:
The patent uses asymmetric configuration with two FETs oriented in opposite directions, where each FET is optimized for controlling current in its forward bias direction. This asymmetric design ensures that each transistor operates in its optimal conduction mode, providing excellent current control capability for both charging and discharging
Solution Approach 2:
The patent creates a universal current control circuit that handles both charging and discharging functions through the coordinated action of two FETs. This multi-functional design provides effective current control for all operating conditions without requiring separate control circuits
3Ease of operation
If a DPDT switch is used to keep the transistor forward biased, then the current control capability is improved, but mechanical switches and relays are required increasing device complexity
Solution Approach 1:
The patent replaces the mechanical DPDT switch with solid-state FETs controlled by electronic control circuits. The FETs are driven by gate voltages generated from current error signals, eliminating all mechanical moving parts while maintaining effective current control capability for both charging and discharging operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for seamless regulation of current, preventing excessive charging or discharging and enabling the productive use of battery packs with varying energy storage capacities in parallel-connected systems, such as Community Energy Storage systems.
Implementation Method 1
The current balancing circuit includes two field effect transistors (FETs) arranged in series and in opposite directions, such that one FET controls charging current and the other controls discharging current
Implementation Method 2
The balancing circuit also includes a current sensor, and uses proportional-integral control to provide a signal to the gates of the FETs
Implementation Method 3
uses proportional-integral control to provide a signal to the gates of the FETs such that the actual current flowing through the circuit is regulated to a target current value
Data Source
AI summary
A method and device for regulating charging and discharging current through a battery pack. Two or more battery packs are connected in parallel to an inverter, such that the inverter can use grid power to charge the battery packs or the battery packs can provide AC power through the inverter. A current balancing circuit device is placed in series with each battery pack and is used to regulate the current through the battery pack so that none of the battery packs is excessively charged or discharged. The current balancing circuit includes two field effect transistors (FETs) arranged in series and in opposite directions, where one FET controls charging current and the other controls discharging current. The balancing circuit also includes a current sensor, and uses proportional-integral control to provide a signal to the FETs such that the actual current flowing through the circuit is regulated to a target current value.