DC Link Capacitor Active Discharge With Controlled Switch Current
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Solution Overview
Problem
Regulatory agencies require the discharge of DC link capacitors in electric drive systems to below 60 volts within 2 seconds after shutdown, but existing methods can lead to high current and potential damage to components.
Innovation Solution
Utilize power switches in the electric motor drive system to actively discharge the DC link capacitor by controlling the voltage difference between the control and reference terminals, reducing the transconductance to manage current flow and avoid damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a discharge switch and resistor are used to discharge the DC link capacitor, then the capacitor can be discharged within regulatory time requirements, but high current may flow causing potential damage to components
Solution Approach 1:
The patent applies dynamics by making the discharge process adaptive rather than static. The controller dynamically adjusts the discharge current based on real-time voltage measurements across the DC link capacitor. The system transitions from a fixed resistor discharge approach to a controlled, variable current discharge that adapts to the capacitor's instantaneous state, thereby achieving regulatory compliance while preventing component damage.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the voltage across the DC link capacitor during discharge and using this information to adjust the discharge current. The controller receives voltage feedback signals and modifies the discharge rate accordingly, ensuring the voltage remains within safe limits while achieving the required discharge time. This closed-loop control prevents excessive current that could damage components.
2Productivity
If the discharge current is increased to meet the 2-second regulatory requirement, then discharge time is reduced, but component damage risk increases
Solution Approach 1:
The system transitions from a static discharge approach to a dynamic one where the discharge current is continuously adjusted based on real-time voltage conditions. The controller modulates the discharge current to be high when voltage is high (accelerating discharge) and reduces current when voltage approaches safe levels (protecting components), thereby simultaneously achieving fast discharge and component safety.
Solution Approach 2:
The patent changes the discharge current parameter dynamically during the discharge process. Instead of maintaining a constant high current, the system varies the current magnitude based on the capacitor's instantaneous voltage state. This parameter adjustment allows the system to achieve rapid initial discharge while preventing excessive current that would compromise component reliability.
3Device complexity
If a fixed resistor is used for discharge, then the circuit is simple, but the discharge current cannot be controlled to prevent damage
Solution Approach 1:
The patent introduces a controller as an intermediary between the DC link capacitor and the discharge resistor. This intermediary component monitors the capacitor voltage and regulates the discharge current flowing through the resistor, transforming the simple but dangerous fixed-resistor approach into a controlled system. The controller acts as a mediator that maintains circuit simplicity while adding necessary current control to prevent component 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
Effectively discharges the DC link capacitor without damaging components, ensuring compliance with regulatory requirements and safety standards.
Implementation Method 1
controlling the voltage difference between the control and reference terminals, reducing the transconductance to manage current flow
Data Source
AI summary
A method for discharging a dc link capacitor coupled between a positive rail and a negative rail of an electric drive system. The method comprises generating an internal supply voltage with a relatively high value with respect to the negative rail, driving a control terminal of a power switch based on the internal supply voltage with the relatively high value, detecting a discharge command in the electric drive system, reducing the internal supply voltage from the relatively high value to a relatively lower value in response to the detected discharge command; and driving the control terminal of the power switch based on the internal supply voltage with the relatively lower value, and discharging the dc link capacitor through the power switch when the power switch is driven based on the relatively lower voltage value.