LLC Converter Zero-Current Rectifier Turn-Off Control
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Solution Overview
Problem
Existing methods for controlling the turn-off operation of rectifying switching elements in LLC voltage converters result in switching losses due to premature turn-off before the secondary current reaches zero, and introduce delays that affect efficiency.
Innovation Solution
A LLC voltage converter system that includes a controller and a current sensor to measure the primary current through the input winding of the transformer. The controller determines when the secondary current is substantially zero based on the primary current measurement and its maximum value, allowing for accurate zero-current switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If existing methods are used to control the turn-off operation of rectifying switching elements, then the switching elements can be turned off, but switching losses occur due to premature turn-off before secondary current reaches zero
Solution Approach 1:
The patent uses the primary current as an intermediary parameter to indirectly determine the secondary current status. By measuring the primary current through the input winding and comparing it with its maximum value, the system can accurately determine when the secondary current reaches zero without directly measuring the secondary current, thus avoiding premature turn-off and reducing switching losses
Solution Approach 2:
The system implements feedback by continuously monitoring the primary current and using it to control the turn-off timing of the rectifying switching elements. The controller adjusts the switching timing based on the feedback from primary current measurements, ensuring that turn-off occurs at the optimal moment when secondary current reaches zero, thereby minimizing switching losses
2Productivity
If existing methods are used to control rectifying switching elements, then switching can be performed, but delays are introduced that affect efficiency
Solution Approach 1:
The system performs preliminary action by measuring the primary current in advance and using this measurement to predict when the secondary current will reach zero. This allows the controller to prepare for the optimal turn-off moment without introducing delays, as the primary current measurement is available before the secondary current actually reaches zero, enabling timely switching actions
Solution Approach 2:
The patent replaces direct secondary current measurement (which would require additional sensors and introduce delays) with primary current measurement and calculation. This substitution of measurement methodology eliminates the need for direct secondary current sensing, reducing measurement delays and improving switching response time
3Measurement precision
If direct secondary current measurement is used, then accurate zero-current detection could be achieved, but the number of components increases and associated power losses occur
Solution Approach 1:
The patent extracts only the necessary measurement (primary current) and uses it to derive the required information (secondary current status) through calculation. By taking out only the essential measurement from the transformer primary side and using the known relationship between primary and secondary currents, the system avoids the need for additional secondary current sensors, reducing component count while maintaining measurement accuracy
Solution Approach 2:
The primary current measurement serves multiple functions: it is used to determine when the secondary current reaches zero, and it can also be used for other control purposes in the converter. This multi-functionality of the primary current measurement eliminates the need for separate measurement systems, reducing overall device complexity while maintaining the ability to accurately detect zero-current conditions
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 reduces switching losses and improves efficiency by ensuring accurate zero-current switching, even under varying load conditions, while also minimizing the number of components and associated power losses.
Implementation Method 1
The magnetising inductance LM 1201 of the input winding of the transformer 1300 is magnetically coupled to an output winding 1301 of the transformer 1300. Therefore, a voltage across the magnetising inductance LM 1201 of the input winding of the transformer 1300 induces a voltage across the output winding 1301 of the transformer 1300, as defined by the ratio of turns between the input winding and the output winding 1301.
Implementation Method 2
The resonant capacitance CR 1202 and the resonant inductance LR 1203 resonate at approximately the switching frequency of the alternating voltage so as to apply a voltage across the magnetising inductance LM 1201 of the input winding of the transformer 1300.
Data Source
AI summary
A LLC voltage converter for converting a DC input voltage to a DC output voltage. The LLC voltage converter includes: a transformer having an input winding and an output winding, a controller and a current sensor. The current sensor measures a primary current through the input winding of the transformer and provides a measurement of the primary current to the controller. The controller determines when a secondary current, through the output winding of the transformer, is substantially zero based on the measurement of the primary current and a maximum value of the primary current.