MMC Submodule Capacitor Discharge via Dynamic Resistance Switching
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Solution Overview
Problem
Conventional capacitor discharge methods in modular multi-level converters are inefficient and unsafe, requiring external discharge devices that are costly and pose safety risks due to the need for manual handling and slow discharge processes.
Innovation Solution
A capacitor discharge device within the sub-module of an MMC converter uses a switched-mode power supply to operate a switch, connecting a capacitor to a first resistor for slow discharge and a second resistor with lower resistance and higher heat capacity for rapid discharge, controlled by a switching unit and control unit to manage voltage and ensure safe and quick discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a discharge resistor is connected to the capacitor for discharge, then the capacitor can be discharged, but it takes a long time to discharge causing increased loss during operation
Solution Approach 1:
The patent applies a dynamic switching mechanism that changes the discharge resistance value based on the capacitor's voltage state. During normal operation, a high resistance prevents discharge. When discharge is needed, a low resistance is switched in to enable rapid discharge, thus reducing energy loss while maintaining discharge capability.
Solution Approach 2:
The invention changes the resistance parameter dynamically during the discharge process. By switching between different resistance values (high resistance during operation, low resistance during discharge), the system optimizes both the discharge capability and energy efficiency, resolving the contradiction between reliable discharge and minimal energy loss.
2Reliability
If an external discharge device is used to forcibly discharge the capacitor, then the capacitor can be discharged, but it is tremendously dangerous for workers and requires separate provision of discharge device resulting in cost increase
Solution Approach 1:
The patent merges the discharge function with the existing sub-module structure by integrating the discharge resistor and switching mechanism directly into the converter bridge. This eliminates the need for separate external discharge devices, reducing safety hazards and costs while maintaining effective discharge capability.
Solution Approach 2:
The system performs self-discharge through integrated components within the sub-module. The switching mechanism automatically connects the capacitor to the discharge resistor when needed, eliminating the need for external manual intervention and associated safety risks to workers.
3Speed
If a discharge resistor with lower resistance value and larger heat capacity is used for rapid discharge, then the discharge speed increases, but the device complexity increases
Solution Approach 1:
The patent uses a dynamic switching mechanism to activate the low-resistance discharge path only when rapid discharge is needed. During normal operation, the high-resistance path is used, keeping the system simple. The switching element adds minimal complexity while enabling rapid discharge capability when required.
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 enables quick and safe discharge of capacitors, reducing maintenance time and costs while suppressing overvoltages, and is more cost-effective and safer than traditional methods.
Implementation Method 1
a capacitor storing a direct current (DC) voltage inside a sub-module of an MMC converter
Implementation Method 2
a second resistor having a lower resistance value and a larger heat capacity than the first resistor so as to rapidly discharge the capacitor storing the voltage therein
Data Source
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AI summary
The present invention relates to a capacitor discharge device that quickly and safely discharges a capacitor charged with energy inside a sub-module of an MMC converter. According to the present invention, the capacitor discharge device includes: a capacitor storing a direction current (DC) voltage inside a sub-module of an MMC converter; a power supply unit supplying operating power required in the sub-module by using the voltage stored in the capacitor; a first resistor connected in parallel to the capacitor; a second resistor having a lower resistance value and a larger heat capacity than the first resistor so as to rapidly discharge the capacitor storing the voltage therein; a first switching contact connecting and disconnecting the capacitor and the second resistor; a switching unit operating switching of the first switching contact by the operating power supplied from the power supply unit; a second switching contact connecting and disconnecting the power supply unit and the switching unit; and a control unit operating switching of the second switching contact.