Parallel Battery Power Supply with MOSFET Switching
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Solution Overview
Problem
Lead secondary batteries in vehicles with idle-stop functions experience early deterioration due to frequent charge and discharge cycles, and managing the state of charge between lead and high-performance secondary batteries is challenging, leading to potential overcharge or over-discharge issues.
Innovation Solution
A power supply unit is configured with a lead secondary battery and a high-performance secondary battery in parallel, using semiconductor switches with opposing parasitic diodes to prevent overcharge and over-discharge, and an energization maintaining mechanism to ensure power supply continuity when the control means is stopped.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the setting voltage Vreg is set to a high voltage to promote charge of the lead secondary battery, then charge of the lead secondary battery is promoted, but the generated power flows into the high-performance secondary battery even when its SOC is sufficiently high, causing overcharge concern
Solution Approach 1:
A switching means (semiconductor switch or relay) is introduced as an intermediary component between the power generator and the high-performance secondary battery. This switch is controlled by the control means to open or close the charging path to the high-performance battery based on its SOC level, preventing overcharge while allowing unrestricted charging of the lead secondary battery through voltage regulation.
Solution Approach 2:
The control means dynamically changes the electrical parameters (voltage and current) supplied to each battery type based on their respective SOC levels. By adjusting these parameters in real-time, the system optimizes charging efficiency for the lead battery while preventing overcharge of the high-performance battery, resolving the contradiction between charging speed and safety.
2Productivity
If the setting voltage Vreg is set to a low voltage to promote discharge from the lead secondary battery, then discharge from the lead secondary battery is promoted, but power is supplied from the high-performance secondary battery to electrical loads, causing over-discharge concern
Solution Approach 1:
The switching means acts as a protective intermediary that monitors the SOC of the high-performance secondary battery and prevents its discharge below a predetermined threshold. This allows the lead secondary battery to discharge freely at optimized voltage levels while the switch blocks excessive discharge from the high-performance battery, protecting it from over-discharge.
Solution Approach 2:
The control means continuously monitors the SOC of both batteries and uses this feedback information to dynamically adjust the setting voltage Vreg and control the switching means. This closed-loop control ensures that the lead battery discharges efficiently while the high-performance battery remains protected from over-discharge, resolving the contradiction between discharge speed and safety.
3Ease of manufacture
If both secondary batteries are connected in parallel, then cost is reduced by using inexpensive lead secondary battery for long-term power supply, but control complexity increases to prevent overcharge and over-discharge
Solution Approach 1:
The control means performs multiple functions: it regulates voltage for the lead secondary battery charging, monitors SOC of both batteries, controls the switching means to prevent overcharge/over-discharge of the high-performance battery, and optimizes power distribution. This multi-functional approach consolidates control complexity into a single unit while enabling cost-effective parallel battery operation.
Solution Approach 2:
The switching means serves as a simple intermediary component that adds minimal complexity to the system. By placing this single switch between the power generator and high-performance battery, the system achieves sophisticated charge/discharge control without requiring complex circuitry, maintaining ease of manufacture while preventing battery damage.
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
The solution effectively prevents overcharge and over-discharge of the high-performance battery, reducing its capacity requirements and maintaining power supply to electrical loads, thereby extending battery life and reducing costs.
Implementation Method 1
switching means configured by a plurality of semiconductor switches 50, 60 being connected in series such that respective parasitic diodes 51, 61 present in the semiconductor switches 50, 60 face opposite directions where current flows
Data Source
AI summary
The power supply unit includes a lead secondary battery (first battery) that is capable of being charged with power generated by an alternator (power generator); a lithium secondary battery (second battery) that is electrically connected in parallel to the lead secondary battery, capable of being charged with power generated by the alternator (power generator), and has higher output density or higher energy density than the lead secondary battery; and a switching means that is electrically connected between the alternator and the lead secondary battery, and the lithium secondary battery, and switches between conduction and blocking. The switching means is configured by a plurality of MOS-FETs (semiconductor switches) being connected in series such that respective parasitic diodes present in the semiconductor switches face opposite directions.