DC/DC Converter Phase Switching for AC Impedance Measurement
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Solution Overview
Problem
The existing fuel cell systems face challenges in accurately measuring AC impedance of a fuel cell stack due to the lowered response capability region of DC/DC converters, which results in reduced measurement accuracy when the operating point is within this region.
Innovation Solution
The system includes a DC/DC converter with a multiphase configuration that switches the number of drive phases, shifts passing power, or changes the carrier frequency to bring the operating point out of the lowered response capability region, thereby enhancing the measurement accuracy of AC impedance when it is requested.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC impedance measurement is performed using a DC/DC converter in the lowered response capability region, then the measurement can be conducted, but the measurement accuracy considerably lowers
Solution Approach 1:
The patent applies dynamics by making the DC/DC converter's operating mode adjustable between continuous conduction mode (CCM) and discontinuous conduction mode (DCM). This dynamic switching allows the system to adapt to different operating conditions and avoid the lowered response capability region where measurement accuracy deteriorates, thereby resolving the contradiction between enabling measurement and maintaining accuracy.
Solution Approach 2:
The patent changes the conduction mode parameter of the DC/DC converter to resolve the measurement accuracy issue. By switching between CCM and DCM based on operating conditions, the system can avoid the problematic lowered response capability region while still performing AC impedance measurements, thus maintaining both measurement capability and accuracy.
2Adaptability or versatility
If the DC/DC converter operates in the lowered response capability region, then the converter can handle varying power conditions, but the dead time compensation value largely changes and response capability lowers
Solution Approach 1:
The system dynamically switches between CCM and DCM based on the operating power level. This dynamic adaptation allows the DC/DC converter to maintain stable dead time compensation values across varying power conditions, avoiding the lowered response capability region while preserving versatility in handling different power loads.
Solution Approach 2:
By changing the conduction mode parameter (CCM/DCM) according to operating conditions, the system maintains stable response capability across a wide power handling range, preventing the large variations in dead time compensation values that occur in the lowered response capability region.
3Measurement precision
If the operating point is kept outside the lowered response capability region for accurate measurement, then measurement accuracy is maintained, but the operational flexibility is reduced
Solution Approach 1:
The system dynamically adapts its conduction mode (CCM/DCM) based on the desired measurement accuracy and operational requirements. This dynamic flexibility allows the system to maintain high measurement accuracy when needed while still operating across a wide range of power conditions, thus resolving the contradiction between precision and versatility.
Solution Approach 2:
By changing the conduction mode parameter to suit different measurement and operational needs, the system maintains measurement accuracy across a broad operational range, avoiding the need to restrict operations to a narrow safe zone while preserving measurement precision.
Data Source
AI summary
When the operation point of a DC/DC converter, which steps up/down the output voltage of a fuel cell stack, is in a range of reduction in response capability and further there is issued a request of determining an AC impedance, a controller switches numbers of the drive phases of the DC/DC converter to determine an AC impedance of the fuel cell stack. If the operation point of the DC/DC converter is in the range of reduction in response capability and further the precision of determining the AC impedance is reduced, then the determination of AC impedance in the range of reduction in response capability is inhibited and the switching of the phases of the DC/DC converter is implemented, thereby causing the operation point of the DC/DC converter to be out of the range of reduction in response capability, with the result that the precision of determining the AC impedance can be raised.