Modular Multilevel Converter Overcharging Protection
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Solution Overview
Problem
In modular multilevel converters, improper closure of bypass switches can lead to overcharging of DC capacitors, potentially damaging components due to excessive voltage application.
Innovation Solution
A power conversion device with a control system that monitors the voltage of each unit converter and activates the bypass switch only when necessary, ensuring that capacitors are charged from an AC power supply and prioritizing the activation of voltage sensors and interface circuits to detect and prevent overcharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bypass switch is closed improperly during initial charging, then the DC capacitor of that unit converter is not charged, but the DC capacitor of proper unit converters connected in series may be overcharged causing component damage
Solution Approach 1:
The patent applies preliminary action by activating voltage sensors and interface circuits before the drive circuit during initial charging. This allows the system to detect capacitor voltages and identify improperly closed bypass switches before overcharging can occur. The control device monitors these voltage detections and can prevent damage by detecting abnormal conditions in advance.
Solution Approach 2:
The patent implements feedback by using voltage sensors to continuously monitor DC capacitor voltages and feed this information back to the control device. The control device uses this feedback to detect if a bypass switch is improperly closed (when voltage doesn't rise as expected) and prevents overcharging of other capacitors by controlling the charging process based on this feedback information.
2Productivity
If the power supply activates all circuits simultaneously during initial charging, then the system is simpler to control, but voltage sensors and interface circuits may not detect overcharging conditions in time
Solution Approach 1:
The patent applies preliminary action by establishing a specific activation sequence where voltage sensors and interface circuits are activated before the drive circuit. This ensures that detection circuits are ready and operational before charging begins, enabling immediate detection of overcharging conditions without delaying protection functionality.
Solution Approach 2:
The patent implements dynamics by making the circuit activation dynamic and staged rather than simultaneous. The control device activates different circuits in a predetermined sequence based on their functional requirements, creating a flexible startup process that prioritizes detection capabilities before power conversion operations begin.
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 solution effectively suppresses damage to unit converters by promptly detecting and preventing overcharging during initial charging, minimizing the risk of component damage from excessive voltage.
Implementation Method 1
The voltage sensor is configured to detect the voltage of the capacitor
Implementation Method 2
The power supply is configured to step down the voltage of the capacitor to generate a power supply voltage that is to be supplied to the control circuit
Implementation Method 3
The main circuit includes a plurality of switching elements and a capacitor, and is configured to convert a voltage of the capacitor into AC power by controlling the plurality of switching elements
Implementation Method 4
The bypass switch is configured to establish a short circuit between the pair of output terminals when the bypass switch is turned on
Data Source
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AI summary
A power converter is electrically connected with an AC power supply via a switch, and is configured with a plurality of unit converters (5) connected in series. A drive circuit (40, 42) drives a plurality of switching elements (11 to 14) of a main circuit (30). An interface circuit (48) outputs a detection value of a voltage sensor (46) to a control device (4). If a bypass switch (7) is turned off when the power converter is activated, each of the plurality of unit converters (5) charges a capacitor (15) using power supplied from the AC power supply. When the power converter is activated, a power supply (50) supplies a power supply voltage to the voltage sensor (46) and the interface circuit (48), prior to the drive circuit (40, 42). The control device (4) turns off the switch when the detection value of the voltage sensor (46) of at least one of the plurality of unit converters (5) is more than or equal to a predetermined value.