DC Link Capacitor Discharge Circuit Using Series Nonlinear Transistors
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Solution Overview
Problem
Existing systems face challenges in efficiently and stress-free discharge of direct current (DC) link capacitors, particularly in high-voltage applications, which are crucial for protecting electrical components from voltage spikes and ensuring safe operation.
Innovation Solution
A circuit utilizing two power transistors connected in series, operated in non-linear mode, with a controller managing sequential switching cycles to discharge the DC link capacitor through a discharge current pathway, leveraging parasitic capacitances when overlap is minimal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single power transistor is used to discharge the DC link capacitor, then the discharge path is simple, but the transistor experiences excessive stress and cannot achieve rapid discharge
Solution Approach 1:
The discharge function is segmented across two power transistors connected in series. Each transistor handles a portion of the discharge current, dividing the stress burden. The controller manages sequential switching cycles where each transistor operates in non-linear mode during specific phases, enabling rapid discharge while distributing thermal and electrical stress, thus improving reliability without sacrificing discharge speed.
2Productivity
If power transistors operate in linear mode, then precise current control is achieved, but the discharge process is slow and inefficient
Solution Approach 1:
The operating parameters of the power transistors are changed from linear mode to non-linear mode. In non-linear mode, the transistors operate with gate-source voltages that exceed threshold values, enabling faster switching and more rapid discharge current flow. The controller manages the switching cycles to achieve both speed and adequate control by leveraging the non-linear characteristics during brief overlap periods.
3Productivity
If overlapping activation phases are applied to both power transistors, then rapid discharge current is achieved, but excessive stress is placed on the transistors
Solution Approach 1:
The controller implements periodic switching cycles with controlled overlap periods. During each cycle, transistors are activated in a periodic pattern where brief overlapping activation phases create discharge current bursts for rapid capacitor discharge. The periodic nature allows stress to be distributed across multiple cycles rather than concentrated in continuous operation, maintaining both speed and reliability.
4Reliability
If the DC link capacitor is charged to high voltage for protection, then component safety is improved, but the discharge process becomes more challenging and time-consuming
Solution Approach 1:
The high-voltage discharge process is segmented into managed phases using two transistors in series. Each transistor handles specific voltage and current portions during sequential switching cycles, enabling the system to safely discharge high-voltage capacitors more rapidly. The segmentation allows controlled energy dissipation that maintains safety while reducing the time required to discharge the capacitor to safe levels.
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 allows for rapid and stress-reduced discharge of DC link capacitors, ensuring safe voltage levels and protecting electrical components by evenly distributing stress across the transistors, thereby enhancing system reliability and safety.
Implementation Method 1
electrical current may flow from the capacitor through the discharge current pathway via parasitic capacitances of the first power transistor and the second power transistor
Data Source
AI summary
A circuit includes a first power transistor and a second power transistor. The circuit also includes a controller configured to control the first power transistor to perform a sequence of first switching cycles by applying, for each switching cycle of the sequence of first switching cycles, a first gate voltage exceeding a threshold gate voltage so that the first power transistor operates according to a non-linear transfer function. The controller is also configured to control the second power transistor to perform a sequence of second switching cycles by applying, for each switching cycle of the sequence of second switching cycles, a second gate voltage exceeding the threshold gate voltage so that the second power transistor operates according to the non-linear transfer function. The controller is configured to cause the capacitor to discharge according to a sequence of discharge phases.