Fuel Cell Converter Phase Control for AC Impedance Measurement
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Solution Overview
Problem
The accuracy of AC impedance measurement in fuel cell systems is compromised due to the 'dead zone' phenomenon in magnetically coupled converters, where current interruption occurs, making it difficult to measure AC impedance effectively, especially when the fuel cell operates in discontinuous mode and the switches face challenges in switching from ON to OFF, leading to suboptimal control of the fuel cell's operating state.
Innovation Solution
A fuel cell system with a controller that operates magnetically coupled coils at the same phase and duty ratio, avoiding the dead zone by switching the coils when a condition is met, ensuring continuous current measurement and optimal impedance assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If magnetically coupled coils are operated at different phases to reduce output current ripple, then power conversion efficiency is improved, but dead zone phenomenon occurs causing inaccurate AC impedance measurement
Solution Approach 1:
The patent dynamically adjusts the phase difference between magnetically coupled coils based on operating conditions. When output current is high, coils operate at different phases (e.g., 180°) to minimize ripple. When output current is low, coils switch to same-phase operation to avoid dead zone and enable accurate AC impedance measurement. This dynamic phase adjustment resolves the contradiction between ripple reduction and measurement accuracy.
Solution Approach 2:
The controller changes the phase difference parameter between coils based on output current magnitude. At high current levels, a large phase difference (e.g., 180°) is applied to reduce ripple. At low current levels, the phase difference is reduced to 0° (same phase) to eliminate dead zone occurrence, thereby enabling accurate AC impedance measurement while maintaining acceptable ripple performance.
2Measurement precision
If duty ratio is changed to measure AC impedance, then measurement capability is improved, but output current value cannot be changed in dead zone region
Solution Approach 1:
The system dynamically switches between different coil phase relationships based on operating conditions. When AC impedance measurement is required and output current is low, the controller transitions to same-phase operation, allowing duty ratio changes to effectively control output current and enable accurate measurement. This dynamic adaptation resolves the contradiction between measurement capability and current controllability.
3Loss of energy
If switches are operated at different phases to improve power conversion, then energy efficiency is improved, but switches cannot be smoothly switched from ON to OFF
Solution Approach 1:
The patent implements dynamic phase adjustment of switch operation. At high power levels, switches operate at different phases (e.g., 180° phase difference) to maximize power conversion efficiency. At low power levels, switches operate at the same phase to prevent dead zone occurrence and ensure smooth switching transitions. This dynamic control resolves the contradiction between efficiency and switching reliability.
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 allows for accurate AC impedance measurement and optimal control of the fuel cell's operating state by minimizing the occurrence of the dead zone, thereby improving the system's response performance and efficiency.
Implementation Method 1
a magnetically coupled converter including a magnetically coupled reactor in which several coils are magnetically coupled on the same core
Implementation Method 2
to relax the magnetic saturation of the core of the reactor and reduce output current ripple
Data Source
Figure 1~2
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Figure 5~7
AI summary
To provide a fuel cell system configured to appropriately measure the AC impedance of a fuel cell. A fuel cell system wherein the controller controls ON and OFF of the switches of n phases; wherein the controller operates the switches of the n phases at different phases, and the controller operates the switches of the n phases at the same duty ratio; wherein the controller operates the switches of the n phases at the same phase, when the controller determines that a specific condition is met; and wherein the controller measures the AC impedance of the fuel cell from the current waveform and voltage waveform of the fuel cell.