Inverter DC Link Capacitor Discharge via Single Switch Activation
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Solution Overview
Problem
Existing electrical drive systems, particularly in electric and hybrid vehicles, face challenges in efficiently discharging intermediate circuit capacitors during freewheeling modes, which is essential for safety but often requires active short circuits that can lead to heating issues and large stator currents in asynchronous machines.
Innovation Solution
The solution involves briefly activating the second semiconductor switch in the primary bridge branch to allow energy from the intermediate circuit capacitor to be converted into heat, enabling efficient discharge without transitioning to an active short circuit, and using voltage sensors and rotor position evaluation to determine the primary bridge branch for efficient energy dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an active short circuit is used to discharge the intermediate circuit capacitor, then the discharge speed and reliability are improved, but heating of the inverter and electrical machine increases
Solution Approach 1:
The patent applies local quality by selectively activating only one semiconductor switch (either high-side or low-side) in a specific bridge arm rather than all switches. This localized approach creates a controlled discharge path through a single switch, distributing the discharge energy locally rather than requiring all switches to conduct simultaneously, thereby reducing overall heating in the inverter while maintaining reliable discharge.
2Speed
If an active short circuit is used to discharge the intermediate circuit capacitor, then the discharge speed is improved, but large stator currents occur in asynchronous machines
Solution Approach 1:
The patent segments the discharge process by selecting and activating only one specific semiconductor switch in one bridge arm, rather than engaging all switches simultaneously. This segmentation creates a controlled, localized discharge path that reduces the overall current magnitude flowing through the electrical machine, avoiding large stator currents while still achieving effective capacitor discharge.
3Reliability
If all switches are opened for freewheeling mode, then the electrical machine can operate safely, but the intermediate circuit capacitor cannot be discharged
Solution Approach 1:
The patent introduces dynamics by allowing the inverter to switch between different operational states: normal operation mode, freewheeling mode with all switches open, and a new intermediate mode where exactly one semiconductor switch is activated. This dynamic flexibility enables the system to maintain safe operating states while providing the capability to discharge the intermediate circuit capacitor when needed, resolving the contradiction between safe operation and discharge capability.
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 method allows for safe and efficient discharging of intermediate circuit capacitors in all operating states, including freewheeling, reducing heating and stator current issues, and enabling safe operation of asynchronous machines without active short circuits.
Implementation Method 1
energy can flow from the intermediate circuit capacitor through the semiconductor switch and be converted into heat
Data Source
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AI summary
The invention relates to the discharging of a DC link capacitor in an inverter arrangement, thereby allowing, for example, a DC link capacitor to be discharged while an electric machine that is connected to the inverters can operate in an idling mode as a safe mode. The DC link capacitor is discharged by very briefly triggering a semiconductor switch within the inverter. According to the invention, the inverter bridge arm with the smallest phase voltage is selected for the very brief triggering process.