Intermediate Circuit Current Determination in Power Converters
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Solution Overview
Problem
Existing methods for determining the intermediate circuit current of a power converter, particularly in the context of functional safety for electric vehicles, are inaccurate and costly, as they rely on costly sensors and do not adequately account for non-ideal properties of power semiconductors such as switch-on and switch-off delays and dead times.
Innovation Solution
A method that measures output currents and voltages of individual phases of a power converter, corrects switching functions based on potential changes, and determines the intermediate circuit current using these corrected functions, thereby accounting for non-ideal properties of power semiconductors, which can be implemented using delta-sigma analog-to-digital converters for efficient and accurate calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the intermediate circuit current is determined using conventional methods based on phase currents and switching functions, then the cost of current sensors is reduced, but the measurement precision and accuracy are insufficient for functional safety requirements
Solution Approach 1:
The patent introduces an intermediary approach by using phase voltage measurements combined with switching function analysis to indirectly determine the intermediate circuit current. Instead of directly measuring the intermediate circuit current or relying solely on phase currents, the method uses phase voltages as an intermediary parameter to calculate the current through mathematical relationships, achieving both cost reduction and improved accuracy
Solution Approach 2:
The patent changes the measurement parameters from relying exclusively on phase currents to using phase voltages combined with switching functions. By measuring phase voltages at specific points in the switching cycle and combining these measurements with knowledge of the switching states, the method transforms the approach to achieving accurate current determination without requiring expensive intermediate circuit current sensors
2Device complexity
If the switching functions are not corrected for non-ideal properties, then the device complexity is reduced, but the measurement precision deteriorates due to switch-on and switch-off delays and dead times
Solution Approach 1:
The patent applies preliminary correction to the switching functions by pre-determining the actual switching moments that account for switch-on delays, switch-off delays, and dead times. These corrected switching functions are prepared in advance and stored, so that during operation, the accurate switching states are already available without requiring real-time complex calculations, thus maintaining low device complexity while achieving high measurement precision
Data Source
AI summary
An intermediate circuit current of a power converter is determined as precisely as possible in a simple and inexpensive manner. The intermediate circuit current is determined as a function of a detection of the measured output voltages and output currents of the individual phases.