EV Pre-Charge Circuit With Zero-Voltage Switching Control
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Solution Overview
Problem
Current battery management systems in electric vehicles face challenges with high current disconnection requirements, leading to mechanically bulky solutions and excessive stress on switching elements due to high impedance switching, and traditional pre-charge circuits result in prolonged charging times and high thermal stress.
Innovation Solution
A pre-charge circuit with a current regulator for zero-voltage switching, allowing for constant pre-charge current regulation and reduced switching currents, and a modular battery system design with individual load switching units for each battery pack to enable efficient voltage balancing and fault management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical main contactor is used to disconnect high current, then reliable disconnection is achieved, but the device becomes mechanically bulky and requires replacement after single use
Solution Approach 1:
The patent replaces the mechanical main contactor with an electronic switching device (MOSFET or IGBT) that can handle high currents. This substitution eliminates the mechanical bulk and single-use limitation while maintaining reliable disconnection capability through solid-state switching components that can be reused indefinitely.
Solution Approach 2:
The patent changes the operating parameters of the switching device by implementing a controlled pre-charge sequence that limits the initial current surge. This allows the electronic switch to operate within safe current limits during startup, enabling reliable high-current disconnection without requiring oversized mechanical components.
2Speed
If direct low impedance switching is used to connect the battery, then connection speed is improved, but excessive short circuit current damages switching elements
Solution Approach 1:
The patent implements a pre-charge circuit that activates before the main switching device connects the battery. This preliminary action charges the DC-link capacitor through a high-impedance path first, reducing the voltage difference and limiting the inrush current when the main switch closes, thereby protecting the switching elements from damage.
Solution Approach 2:
The patent introduces a pre-charge circuit as an intermediary between the battery and the main switching device. This intermediary component temporarily handles the initial current surge through a separate high-impedance path, allowing the main low-impedance switching path to be engaged safely without exposing the switching elements to damaging current levels.
3Object-affected harmful factors
If a resistor-based pre-charge circuit is used, then initial inrush current is limited, but pre-charge time increases and thermal stress occurs
Solution Approach 1:
The patent implements a dynamic pre-charge control strategy where the pre-charge resistance is not fixed but varies during the charging process. The controller adjusts the pre-charge current profile to maintain optimal charging speed while limiting peak current, reducing both pre-charge time and thermal stress compared to static resistor-based circuits.
Solution Approach 2:
The patent employs feedback control in the pre-charge circuit, where the controller continuously monitors the DC-link voltage and adjusts the pre-charge current accordingly. This feedback mechanism allows the system to optimize the pre-charge speed in real-time, minimizing both the pre-charge duration and the thermal stress on components by adapting the current profile to actual system conditions.
4Loss of time
If switching is performed with voltage difference of several volts to meet timing constraints, then pre-charge time is reduced, but switching current and stress on elements increase
Solution Approach 1:
The patent uses the pre-charge circuit to perform preliminary charging of the DC-link before the main switching operation. This preliminary action brings the DC-link voltage close to the battery voltage in advance, allowing the main switch to operate with minimal voltage difference and thus reducing switching stress while still meeting timing requirements.
Solution Approach 2:
The patent replaces mechanical relay-based pre-charge switching with electronically controlled switching devices that can be precisely controlled by a controller. This electronic control allows for smoother transition and better management of switching stresses, enabling the system to meet timing constraints without subjecting components to excessive current and voltage stress during switching events.
Data Source
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AI summary
Disclosed is a pre-charge circuit for an electricvehicle battery management system (BMS) and a method. The circuit comprises a current regulator for zerovoltage switching configured for regulating pre-charge current for a dc-link of an electric vehicle and a switch for bypassing the current regulator after a voltage across the pre-charge circuit reaches a target.