MMC DC-Line Voltage Suppression During Short-Circuit Gate Blocking
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Solution Overview
Problem
Existing power conversion systems, such as modular multilevel converters, face challenges in suppressing oscillatory voltages generated in the DC line during a short-circuiting fault, which can lead to unstable operation and energy accumulation.
Innovation Solution
The power conversion system incorporates a voltage suppression circuit connected to the DC line, which includes a diode and a current limiting element. This configuration is designed to absorb current energy and suppress oscillatory voltages when submodules are deactivated due to a short-circuiting fault.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate blocking of converter cells is performed to suppress fault current in the event of a DC short-circuiting fault, then the fault current is suppressed, but an oscillatory voltage is generated in the DC line due to current energy accumulated in the DC line
Solution Approach 1:
A voltage suppression circuit is introduced as an intermediary component between the DC line and ground. This circuit includes a switching element connected in series with a smoothing reactor and smoothing capacitor, which work together to suppress the oscillatory voltage generated in the DC line during fault conditions without interfering with the fault current suppression function of the converter cells
Solution Approach 2:
The voltage suppression circuit is pre-configured and activated when a short-circuiting fault is detected. The smoothing reactor and capacitor are designed to absorb and dampen the oscillatory voltage energy before it can cause harmful effects, providing cushioning protection to the DC line and connected equipment
2Adaptability or versatility
If the number of unit converters is increased to adapt to higher voltage, then the voltage adaptation capability is improved, but the system complexity and energy accumulation risk increase
Solution Approach 1:
The power conversion system is divided into multiple independent unit converters (sub-modules) connected in series. Each unit converter can be independently controlled and managed, allowing the system to adapt to higher voltages by simply adding more units without proportionally increasing overall system complexity. The voltage suppression circuit is also segmented and can be applied to individual units or groups of units
Solution Approach 2:
The voltage suppression circuit with switching element, smoothing reactor, and capacitor is designed as a universal module that can be applied to any unit converter in the system regardless of the total number of units. This multi-functional design allows the same circuit topology to handle voltage suppression, energy damping, and protection functions across the entire system, preventing complexity from scaling linearly with the number of units
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 proposed solution effectively suppresses voltages in the DC line during a short-circuiting fault, preventing energy accumulation and ensuring stable operation by quickly attenuating the short-circuiting current.
Implementation Method 1
the control device stops a switching operation of the plurality of sub modules included in each of the leg circuits. The voltage suppression circuit is configured to suppress a voltage generated in the DC line when the switching operation of the plurality of sub modules is stopped
Data Source
AI summary
A voltage generated in a DC line at the time when a sub module is deactivated in the event of a short-circuiting fault in the DC line is suppressed. A power conversion system includes a power converter including a leg circuit, a control device, and a voltage suppression circuit connected to a DC line. The leg circuit includes a plurality of sub modules connected in series, and at least one of them is a first sub module implemented by a sub module in a full-bridge configuration or a 1.5 half-bridge configuration. When the control device detects a short-circuiting fault in the DC line, it stops a switching operation of the plurality of sub modules. The voltage suppression circuit is configured to suppress a voltage generated in the DC line when the switching operation is stopped.