DC Link Capacitance Measurement Using Three-Point Voltage Decay
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Solution Overview
Problem
Existing power conversion systems face challenges in accurately measuring the capacitance of DC link capacitors, which is crucial for maintaining system efficiency and preventing failures due to capacitance degradation.
Innovation Solution
A component and method for measuring DC link capacitance in power conversion systems, which includes a power suspension module, a bleeding resistor, an auxiliary power supply, and a measurement module. The system suspends power flow between the DC source and the DC link capacitor, measures voltages at specific times, and calculates the current capacitance using the resistance of the bleeding resistor and the measured voltages and times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex circuitry or sensors are used to determine capacitance degradation, then measurement capability is provided, but device complexity increases and accuracy decreases due to auxiliary load conditions
Solution Approach 1:
The patent extracts the auxiliary power supply load from the capacitance measurement equation by measuring voltage at three distinct time points during the discharge phase. This allows the measurement to be performed without requiring knowledge of the auxiliary power consumption, thereby simplifying the measurement circuitry while maintaining accuracy despite the presence of auxiliary loads.
Solution Approach 2:
The patent introduces a bleeding resistor as an intermediary element that provides a known discharge path for the DC link capacitor. By controlling the discharge process through this resistor and measuring voltage at specific time intervals, the system can calculate capacitance without direct interaction with the auxiliary power supply, thus avoiding the complexity of monitoring auxiliary load conditions.
2Measurement precision
If auxiliary power supply load is considered in capacitance measurement, then measurement accuracy may improve, but device complexity and difficulty of measurement increase
Solution Approach 1:
The patent enables the DC link capacitor to serve itself by using its own discharge characteristics through the bleeding resistor to reveal its capacitance value. The auxiliary power supply, while present, does not interfere with this self-measurement process because the voltage decay curve captured at three time points mathematically separates the capacitor's contribution from the auxiliary load's consumption.
Solution Approach 2:
The patent employs periodic voltage measurements at three distinct time points during the capacitor discharge process. This periodic sampling of the voltage decay curve allows the system to extract capacitance information without requiring continuous monitoring or knowledge of auxiliary power consumption, thereby simplifying the measurement implementation while maintaining accuracy.
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 allows for accurate measurement of DC link capacitance without requiring knowledge of the auxiliary power supply's power draw, enabling timely detection of capacitance degradation and preventing system failures.
Implementation Method 1
measuring direct current ('DC') link capacitance in a power conversion system
Implementation Method 2
A bleeding resistor is connected in parallel with the DC link capacitor
Implementation Method 3
a measurement module configured to measure, using a voltage sensing circuit to measure voltage across the DC link capacitor, a first voltage at a first time, a second voltage at a second time, and a third voltage at a third time
Data Source
AI summary
A component includes a power suspension module that suspends providing power from a DC source to a DC link capacitor and from the capacitor to a load. A bleeding resistor is connected in parallel with the capacitor and an auxiliary power supply draws power from the capacitor. The component includes a measurement module that measures a first, second and third capacitor voltage at a first, second, time, and third time in response suspending power between the DC source and the load. The component includes a capacitance module that uses bleeding resistor resistance, the voltages and the times to determine a current capacitance of the capacitor, a capacitance comparison module that compares the current capacitance with an initial capacitance of the capacitor, and an alert module that sends an alert in response to determining that a difference between the current capacitance and the initial capacitance is above a capacitance degradation threshold.