AC Input Voltage Sensing in Power Converters Using DC Bus Reconstruction
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Solution Overview
Problem
Conventional boost power converters face challenges in achieving high switching frequencies and effective over-current protection while maintaining Critical Conduction Mode (CrCM) operation, leading to inefficiencies and limitations in power factor correction.
Innovation Solution
The development of a power factor correction circuit that senses high-bandwidth bidirectional inductor current using current-sense resistors, compares it against programmable thresholds, and adjusts synchronous rectifier conduction time based on pulse counting, enabling CrCM control and over-current protection, while allowing for higher switching frequencies and efficient current sharing between phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensing methods are used in boost power converters, then the device complexity is reduced, but the measurement precision of inductor current is insufficient to enable high switching frequencies and effective CrCM control
Solution Approach 1:
The current sensing function is segmented into two independent paths: one path senses current during the switch on-time for CrCM control, and another path senses current during off-time for over-current protection. This segmentation allows each sensing path to be optimized for its specific function, achieving high measurement precision without requiring a single complex sensing circuit to handle all functions.
Solution Approach 2:
The patent introduces an intermediary current sensing circuit that measures inductor current and provides signals to both the CrCM control logic and over-current protection logic. This intermediary sensing mechanism enables high-frequency operation by providing precise current measurement data to the control system without directly complicating the main power conversion circuitry.
2Productivity
If higher switching frequencies are implemented, then the productivity of the power converter is improved, but over-current conditions and loss of CrCM operation occur
Solution Approach 1:
The patent implements feedback control by continuously monitoring inductor current through sensing circuits and using this information to regulate the switch timing. The sensed current feedback enables the control system to maintain CrCM operation at high switching frequencies by adjusting the switch on-time based on actual current conditions, preventing loss of CrCM mode and ensuring reliable operation.
Solution Approach 2:
The over-current protection circuit performs preliminary detection of current conditions before dangerous over-current states develop. By sensing current in advance and triggering protection actions proactively, the system prevents over-current conditions that would otherwise occur at high switching frequencies, thereby maintaining reliability while enabling higher productivity.
3Reliability
If over-current protection is added to CrCM control, then the reliability of the power converter is improved, but the device complexity increases
Solution Approach 1:
The current sensing circuit is designed with multi-functionality, serving both CrCM control and over-current protection functions through a single sensing infrastructure. This universal sensing approach allows the system to achieve improved reliability through both protection mechanisms without proportionally increasing device complexity, as the same sensing hardware supports multiple critical functions.
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 prevents over-current conditions, enables higher switching frequencies, and ensures efficient power factor correction by effectively regulating inductor current and voltage, thereby improving the performance of boost power converters.
Implementation Method 1
sensing high bandwidth bidirectional inductor current using current-sense resistor based per-switch current-sensing
Data Source
AI summary
A method of measuring an AC input voltage at an input of a power converter includes measuring a DC bus voltage corresponding to the power converter. During a positive half-cycle of the AC input voltage, the method includes measuring a first voltage at the input of the power converter. During a negative half-cycle of the AC input voltage, the method includes turning on a high-side switch, measuring a second voltage at the input of the power converter, and computing a third voltage equal to the second voltage minus the DC bus voltage. The method further includes providing the AC input voltage as the first voltage during the positive AC half-cycle and the third voltage during the negative AC half-cycle.