MMC Capacitor Degradation Detection via Charging Time Analysis
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Solution Overview
Problem
Existing power conversion devices with modular multilevel converters face increased complexity and cost due to the need to measure branch current and capacitor voltage to determine capacitor degradation, making it difficult to easily assess the degraded state of submodules.
Innovation Solution
A power conversion device that determines capacitor degradation by measuring the charging and discharging times and voltage change rates of capacitors, allowing for easier identification of degraded capacitors without directly calculating capacitance or requiring additional current sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitor degradation is determined by measuring branch current and capacitor voltage with integration processing, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the necessary measurement elements (capacitor voltage and time) from the conventional method, eliminating the need for branch current measurement and integration processing. This reduces the measurement system to essential components while maintaining degradation detection capability through direct voltage-based capacitance calculation.
Solution Approach 2:
Instead of measuring current and integrating to find capacitance change, the patent inverts the approach by measuring voltage directly and using time-based calculations to determine capacitance. This reversal simplifies the measurement system while achieving the same diagnostic objective.
2Measurement precision
If capacitor degradation is determined by measuring branch current and capacitor voltage, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent removes the current sensor and integration circuitry from the measurement system, keeping only voltage measurement capabilities. This extraction of essential elements reduces component costs and simplifies manufacturing while maintaining the ability to detect capacitor degradation accurately.
3Ease of operation
If capacitor degradation is determined by measuring voltage change rates during charging and discharging, then ease of operation is improved, but measurement precision may be reduced
Solution Approach 1:
The patent performs degradation assessment continuously during normal charging and discharging operations without requiring separate measurement phases. By utilizing voltage change rates during routine operations, the system maintains continuous monitoring capability while simplifying operation and reducing additional measurement overhead.
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 approach simplifies the process of determining capacitor degradation, reducing the processing load and cost of the device while enabling timely replacement of degraded capacitors for stable operation.
Implementation Method 1
the capacitance of capacitors provided in the MMC decreases due to degradation over time
Data Source
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AI summary
A power conversion device (1) configured to perform power conversion between a DC circuit (14) and an AC circuit (12) includes power conversion circuitry (2) including a plurality of submodules (7) connected in series to each other. The power conversion device (1) further includes: a signal reception unit (110) configured to receive a signal representing a voltage of a capacitor (24) in each of the submodules (7); a time calculation unit (130) configured to calculate at least one of a charging time of the capacitor (24) and a discharging time of the capacitor (24) based on the signal; and a determination unit (160) configured to determine whether the capacitor (24) has degraded or not based on at least one of a first result of comparison of the charging time with a reference charging time serving as a reference for determining degradation of the capacitor (24), and a second result of comparison of the discharging time with a reference discharging time serving as a reference for determining degradation of the capacitor (24).