Backup Capacitor Discharge Circuit Thermal Management
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Solution Overview
Problem
In high-voltage battery systems, existing methods for discharging backup capacitors result in thermal overload of discharge resistors due to high voltage and power spikes, requiring long wait times before reconnecting the battery, and pose challenges in heat dissipation due to insulation constraints.
Innovation Solution
An electrical arrangement with a voltage converter that controls the discharge of the backup capacitor, allowing the resistor to be designed for a lower output voltage, and optionally isolating it from the high-voltage side, enabling better thermal coupling and reduced thermal load through a galvanically isolating or non-isolating configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the back-up capacitor is discharged by connecting it directly to a discharge resistor, then the discharge operation takes place in a relatively short space of time, but the resistor becomes thermally overloaded and requires long wait times before reconnecting the battery
Solution Approach 1:
The discharge process is divided into two distinct phases: a first discharge phase using the discharge resistor at reduced power, and a second discharge phase using a second capacitor for high-power discharge. This segmentation allows the resistor to avoid thermal overload while maintaining overall discharge effectiveness.
Solution Approach 2:
A control unit is activated upon opening the main switch to manage the discharge process. The control unit monitors capacitor voltage and selectively activates discharge paths, ensuring that the discharge resistor is only engaged when appropriate voltage levels are present, preventing thermal overload before it occurs.
2Reliability
If the discharge resistor is designed for maximum voltage and high power spikes, then it can handle the discharge requirements, but it becomes difficult to dissipate heat generated in the discharge resistor due to insulation constraints
Solution Approach 1:
A second capacitor is introduced as an intermediary energy storage element that handles the high-power discharge requirements. This mediator allows the discharge resistor to operate at lower, safer power levels while still achieving complete capacitor discharge through the two-phase process.
Solution Approach 2:
The system changes the power parameter during discharge by using two different capacitors with different capacitance values. The first capacitor (discharge capacitor) has lower capacitance and handles high-power discharge, while the second capacitor (backup capacitor) has higher capacitance and is discharged at lower power, optimizing both reliability and heat dissipation.
3Temperature
If a voltage converter is introduced to control the discharge, then the resistor can be designed for a lower output voltage with better thermal coupling, but the device complexity increases
Solution Approach 1:
The control unit serves multiple functions: it monitors capacitor voltage, determines when to activate discharge paths, controls the switching between different discharge phases, and manages the overall discharge process. This multi-functionality reduces the need for separate dedicated components for each function.
Solution Approach 2:
The discharge system uses the existing capacitor voltage as its own control signal. When the main switch opens and capacitor voltage rises above a threshold, the control unit automatically activates the appropriate discharge path without requiring external intervention or complex control circuits.
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 allows for efficient and controlled discharge of the backup capacitor, reducing thermal stress on the resistor, enabling faster reconnection of the high-voltage battery and improved heat dissipation, while maintaining safety and voltage tolerance.
Implementation Method 1
a voltage converter having an input side, connected to a high-voltage side of the back-up capacitor, and an output side connected to the discharge path
Implementation Method 2
the electrical energy stored in the back-up capacitor is converted into thermal energy by the discharge resistor
Data Source
AI summary
An electrical arrangement includes a high-voltage battery and a number of electrical utility arrangements connected to the battery via a main switch and a downstream back-up capacitor. A discharge circuit is connected to the capacitor and has a discharge path with an ohmic discharge resistor. In normal mode no current flows in the discharge resistor. Opening the main switch effects a transition from normal mode to special mode, while the discharge path is energized and electrical energy stored in the capacitor is converted into thermal energy by the discharge resistor. The discharge circuit has a voltage converter between the high-voltage side of the capacitor and the discharge path. The voltage converter has a first semiconductor switch for discharging the capacitor clock-controlled such that an electrical output voltage at the discharge path constantly has a rated value so long as a capacitor voltage at the capacitor is above the rated value.