Active Discharge Circuit Timing Control for EV Inverter DC Link
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional active discharge resistor circuits in electric vehicle drive systems require high power and heat dissipation capabilities to handle continuous current discharge scenarios, leading to increased costs and space requirements due to the need for continuous operation during shutdowns, especially in situations where ongoing voltage is applied to the DC link capacitor.
Innovation Solution
A timing circuit powered by the DC link capacitor is introduced to limit the operation of the active discharge circuit to a short, fixed duration, automatically turning off the discharge switch when the voltage source continues to energize the capacitor, thereby reducing the power and cooling requirements of the discharge resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If an active discharge resistor is used to quickly discharge the DC link capacitor, then the discharge time is reduced, but the power rating and heat dissipation requirements increase
Solution Approach 1:
The patent applies periodic action by using a timing circuit to activate the discharge resistor only for a predetermined time interval after shutdown is detected. This allows the system to achieve rapid discharge during the initial phase when capacitor voltage is highest, then deactivate the discharge resistor to avoid continuous power dissipation. The discharge switch transitions from continuous operation to periodic/pulsed operation, resolving the contradiction between fast discharge and power rating requirements.
2Reliability
If an active discharge resistor is used to discharge the capacitor in continuous operation mode, then safety is ensured, but the cost and space requirements increase due to cooling systems
Solution Approach 1:
The timing circuit creates periodic action by limiting discharge resistor operation to a predetermined time interval after shutdown detection. This eliminates the need for continuous cooling systems while maintaining safety, as the discharge resistor only operates when needed (during the initial discharge phase) rather than continuously. The cooling system complexity is reduced because the discharge resistor operates intermittently rather than continuously.
Solution Approach 2:
The patent effectively treats the discharge resistor operation as a short-lived, temporary function rather than a continuous requirement. By using the discharge resistor only for the brief period needed to safely reduce capacitor voltage after shutdown, the system avoids the need for expensive, complex continuous cooling infrastructure. The discharge resistor serves its safety function temporarily, then is deactivated.
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 decreases the power rating and cooling needs of the active discharge resistor, lowering costs and space requirements by ensuring the discharge resistor only operates for the necessary time to safely discharge the capacitor, while maintaining safety during shutdowns.
Implementation Method 1
The simplest conventional methods for discharging the link capacitor dissipate the charge through a resistance placed across the capacitor
Data Source
AI summary
A DC link capacitor coupled to positive and negative DC busses between a high voltage DC source and an electric vehicle inverter is quickly discharged during a shutdown. An active discharge circuit connected across the link capacitor has a discharge resistor in series with a discharge switch. The discharge switch has a control terminal for selectably turning the discharge switch on and off. A disable circuit is coupled to the control terminal and is responsive to a disable command signal to turn off the discharge switch. The disable circuit turns on the discharge switch upon cessation of the disable command signal. A timing circuit powered by a voltage from the link capacitor initiates a predetermined time interval upon cessation of the disable command signal, and continuously turns off the discharge switch after the predetermined time interval while the voltage from the link capacitor remains above a threshold.