Active DC Link Capacitor Discharge via Step-Down Converter
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Solution Overview
Problem
In electric vehicles, the DC link capacitor retains a charge after disconnection from the battery, necessitating safe and timely discharge to meet regulatory requirements, which existing systems struggle to achieve efficiently.
Innovation Solution
A power converter in the high voltage domain is used to actively discharge the DC link capacitor by converting high voltage to lower voltage, utilizing a step-down power converter and discharge circuitry that operates in the low voltage domain, allowing for safe and efficient discharge without requiring high-voltage rated components and minimizing the risk of cascading failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a discharge switch and resistor are used to discharge the DC link capacitor, then the capacitor can be discharged to meet safety requirements, but the system requires additional high-voltage rated components that increase complexity and risk of cascading failures
Solution Approach 1:
The patent introduces a step-down power converter as an intermediary device between the high-voltage DC link capacitor and the low-voltage discharge circuitry. The converter includes a high-voltage switch and transformer that isolate the low-voltage discharge components from high voltage, allowing safe discharge operation without requiring high-voltage rated discharge switches and resistors. This mediator enables the discharge function while reducing overall system complexity and eliminating cascading failure risks associated with high-voltage discharge components
2Reliability
If high-voltage rated discharge components are used, then safe discharge can be achieved, but the cost and complexity of the system increase
Solution Approach 1:
The step-down power converter acts as an intermediary that transforms the high-voltage discharge requirement into a low-voltage operation. The high-voltage switch and transformer isolate the discharge circuitry from high voltage, allowing the use of inexpensive, low-voltage rated discharge components while maintaining discharge safety. This approach significantly reduces manufacturing costs and simplifies the overall system compared to using high-voltage rated discharge components
3Reliability
If the discharge switch is switched into conduction after battery disconnection, then the DC link capacitor discharges through the resistor, but the process may not meet the 2-second discharge requirement to below 60 volts
Solution Approach 1:
The patent employs dynamic control of the high-voltage switch in the step-down power converter to achieve rapid discharge. The switch operates in pulse-width modulation (PWM) mode, dynamically adjusting the duty cycle to control the amount of energy transferred from the DC link capacitor through the transformer to the discharge circuitry. This dynamic switching enables the system to meet the 2-second discharge requirement to below 60 volts, which would be difficult to achieve with a simple resistive discharge circuit
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 ensures rapid and safe discharge of the DC link capacitor to meet regulatory requirements, reducing the risk of electrical hazards and maintaining system integrity by leveraging the backup power supply capabilities of the power converter, even in the event of low voltage domain failures.
Implementation Method 1
A power converter in the high voltage domain is used to actively discharge the DC link capacitor by converting high voltage to lower voltage
Data Source
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AI summary
Discharge systems for electric vehicles and electric vehicles having discharge systems. In one implementation, a discharge system for an electric vehicle includes a step-down power converter configured to step down an input voltage to an output voltage; discharge circuitry coupled to the output of the step-down power converter, wherein the discharge circuitry is reversibly driveable to load the step-down power converter; an input component configured to receive input that originated from a human user or a sensor of the electric vehicle, wherein the input indicates that the electric vehicle is to shutdown; and discharge drive circuitry configured to drive the discharge circuitry to load the step-down power converter in response to the indication that the electric vehicle is to shutdown.