Dissipation Circuit for Electric Vehicle Load Dump Protection
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Solution Overview
Problem
In electric vehicles, the 'load dump' condition during regenerative mode can cause power to be dumped into a DC capacitor connected with the high-voltage bus, leading to rapid voltage rise, potentially exceeding the breakdown voltage of switching devices and capacitors without adequate protection, risking damage.
Innovation Solution
A dissipation circuit is implemented between the traction battery and DC bus, comprising discharge and sensing resistors in series, along with a switch that activates only when the voltage across the sensing resistor exceeds a threshold, allowing current flow through a dissipation resistor to safely discharge excess energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dissipation circuit is activated to protect against voltage overload, then component reliability is improved, but power loss increases due to continuous readiness of protective components
Solution Approach 1:
The dissipation circuit employs dynamic switching through a control switch that responds to voltage threshold conditions. The switch transitions between on and off states based on real-time voltage monitoring across the sensing resistor, allowing the circuit to adapt its protective function only when needed, thereby minimizing continuous power loss while maintaining component reliability.
Solution Approach 2:
The circuit incorporates a feedback mechanism where the voltage across the sensing resistor is continuously monitored and fed back to the control switch. When the voltage exceeds a predetermined threshold, the feedback signal activates the switch to engage the dissipation resistor, creating a closed-loop control system that automatically responds to voltage conditions and eliminates the need for continuous monitoring power consumption.
2Reliability
If a dissipation circuit with switch is used to protect against load dump, then component protection is improved, but device complexity increases due to additional components
Solution Approach 1:
The dissipation circuit is designed to perform multiple functions within a unified structure. The same circuit components (sensing resistor, control switch, and dissipation resistor) serve both normal operation and protective functions during load dump conditions. This multi-functionality reduces the need for separate protective circuits, thereby limiting the increase in device complexity while maintaining comprehensive component protection.
3Reliability
If dissipation resistor is always connected to discharge power, then voltage control is improved, but energy efficiency deteriorates due to continuous power dissipation
Solution Approach 1:
The dissipation resistor is dynamically connected or disconnected based on voltage threshold conditions. During normal operation, the control switch remains off, isolating the dissipation resistor from the circuit and eliminating continuous power dissipation. When voltage exceeds the threshold, the switch activates to connect the dissipation resistor, providing voltage control only when necessary, thus maintaining energy efficiency while ensuring voltage control reliability.
Solution Approach 2:
The dissipation circuit operates in periodic cycles rather than continuously. The control switch activates the dissipation resistor only during periodic voltage threshold exceedances, allowing the system to alternate between active protection and energy-efficient standby states. This periodic action pattern maintains voltage control capability while significantly reducing overall energy consumption compared to continuous dissipation.
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 effectively prevents voltage overload by activating the switch to discharge excess power when the voltage reaches a critical threshold, thereby protecting the high-voltage bus and associated components from damage during load dump conditions.
Implementation Method 1
responsive to a voltage across the sensing resistor being less than a threshold value
Implementation Method 2
permit current flow from the positive terminal to the negative terminal through the dissipation resistor
Data Source
AI summary
A method for dissipating power of an automotive electric drive system that includes a traction battery, and an inverter, wherein the inverter includes a DC bus between, and a dissipation circuit between the traction battery and DC bus, wherein the dissipation circuit includes a plurality of resistors connected in series between positive and negative terminals of the DC bus and a dissipation resistor and switch connected in series between the positive and negative terminals, the method includes responsive to a voltage across one of the plurality of resistors being less than a threshold value, deactivating the switch to prevent current flow from the positive terminal to the negative terminal through the dissipation resistor, and responsive to the voltage exceeding the threshold value, activating the switch to permit current flow from the positive terminal to the negative terminal through the dissipation resistor.