Constant-Current Pre-Charge Circuit for Arc-Free HV Bus Capacitors
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Solution Overview
Problem
Conventional pre-charge circuits for electric vehicle energy storage capacitors suffer from reliability issues, power losses, and potential damage due to arcing, especially when using current limit resistors and mechanical relays.
Innovation Solution
A pre-charge apparatus utilizing a power converter, isolation interface, and constant current control unit to provide a constant current charge to the capacitor, replacing mechanical relays with semiconductor switches and employing a peak current mode control scheme.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a current limit resistor is used in the pre-charge circuit, then the surge current is reduced, but power losses increase and the circuit size becomes bulky
Solution Approach 1:
The patent replaces the passive mechanical current limit resistor with an active electronic pre-charge circuit comprising a pre-charge switch, control circuit, and current sensing mechanism. This substitution enables dynamic control of pre-charge current, reducing energy losses while maintaining surge current limitation functionality.
Solution Approach 2:
The patent dynamically adjusts the pre-charge current parameter through control circuitry that monitors capacitor voltage and modulates the pre-charge switch duty cycle. This allows the system to optimize current levels during different charging stages, minimizing power losses in the pre-charge path while ensuring safe charging of the capacitor.
2Object-generated harmful factors
If a current limit resistor is used in the pre-charge circuit, then the surge current is reduced, but the circuit size becomes bulky
Solution Approach 1:
The patent replaces the bulky passive current limit resistor with a compact active electronic pre-charge circuit using semiconductor switches and integrated control logic. This significantly reduces the physical footprint and weight of the pre-charge circuitry while maintaining effective surge current limitation.
Solution Approach 2:
The pre-charge circuit is designed to perform multiple functions: limiting surge current, charging the capacitor, and providing control signals for coordination with the main power relay. This multi-functionality eliminates the need for separate dedicated components, reducing overall circuit size.
3Duration of action of moving object
If a mechanical relay is used for pre-charging, then the capacitor can be charged before power relay closure, but arcing can occur and damage the relay contacts
Solution Approach 1:
The patent replaces the mechanical pre-charge relay with an electronic pre-charge switch (such as a MOSFET or IGBT) controlled by a microcontroller or dedicated control circuit. This eliminates mechanical contacts and arcs, significantly improving reliability while maintaining precise timing control for capacitor pre-charging before main power relay closure.
Solution Approach 2:
The patent incorporates voltage sensing across the capacitor and feedback control logic that monitors the pre-charge voltage level. When the capacitor voltage reaches a predetermined threshold, the control circuit automatically disables the pre-charge switch and triggers the main power relay closure, ensuring optimal timing without mechanical contact wear.
4Speed
If the power relay closes immediately after battery connection, then the system responds quickly, but a huge surge current damages the power relay
Solution Approach 1:
The patent implements a preliminary pre-charge phase that activates automatically when the battery is connected. The control circuit detects battery voltage and immediately begins charging the capacitor through the pre-charge switch before the main power relay is commanded to close. This preliminary action ensures the capacitor is pre-charged to an appropriate voltage level, eliminating surge current when the main relay closes while maintaining fast system response.
Solution Approach 2:
The patent uses voltage feedback sensing across the capacitor to monitor pre-charge progress. The control circuit continuously compares the capacitor voltage against a target threshold and adjusts the pre-charge switch duty cycle accordingly. When the threshold is reached, the feedback signal automatically triggers main relay closure, achieving optimal response time without surge current 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
Improves reliability, reduces circuit size, and prevents arcing while efficiently charging the capacitor to the required voltage level, minimizing power consumption and preventing circuit damage.
Implementation Method 1
a power converter configured to provide a constant current charge to a capacitor coupled to a high voltage bus
Implementation Method 2
an isolation interface configured to receive a pre-charge signal on a primary side of the isolation interface, and convert the pre-charge signal into a bias voltage signal and a control command signal on a secondary side of the isolation interface
Data Source
AI summary
An apparatus includes a power converter configured to provide a constant current charge to a capacitor coupled to a high voltage bus through a mechanical contact, an isolation interface configured to receive a pre-charge signal on a primary side of the isolation interface, and convert the pre-charge signal into a bias voltage signal and a control command signal on a secondary side of the isolation interface, and based on the bias voltage signal and the control command signal, a constant current control unit configured to generate a gate drive signal for the power converter.