LLC Converter Ripple Compensation via Feedforward Control
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Solution Overview
Problem
The output performance of on-board chargers (OBC) for environmentally-friendly vehicles decreases due to the ripple component of the input voltage in LLC converters, leading to reduced battery lifetime and increased charging time and costs.
Innovation Solution
An apparatus that adjusts the output current of the LLC converter by determining a switching frequency control value to compensate for the ripple component of the input voltage, using a current controller and a feedforward controller to ensure the output current follows the output current command, thereby improving the output performance of the OBC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PI controllers are used in the LLC converter stage, then the voltage and current of the output-end capacitor can be adjusted, but the output current follows the ripple component of the input voltage causing rapid decrease in output performance
Solution Approach 1:
The patent employs a feedback mechanism where the output current detection value is continuously monitored and compared against the output current command value. The PI controller adjusts the switching frequency control value based on the deviation between actual and desired output current, creating a closed-loop control system that actively compensates for ripple components and maintains precise output current following.
Solution Approach 2:
The patent dynamically changes the switching frequency parameter of the LLC converter based on the detected output current deviation. By adjusting the switching frequency control value in response to ripple components in the input voltage, the system adapts its operating parameters to maintain optimal output performance and prevent the output current from following the input voltage ripple.
2Device complexity
If the output current follows the ripple component of input voltage, then the LLC converter operates with simple control, but the output performance of the OBC rapidly decreases
Solution Approach 1:
A feedback control loop is implemented that monitors the output current detection value and compares it with the output current command value. The PI controller processes this feedback information and generates appropriate switching frequency control adjustments, creating a closed-loop system that actively suppresses ripple transmission while maintaining reasonable control complexity.
Solution Approach 2:
The patent introduces an intermediary control mechanism - the PI controller with switching frequency adjustment - that acts as a mediator between the input voltage ripple and the output current. This intermediary actively processes the control signal to prevent direct transmission of ripple components from input to output, thereby protecting output performance without requiring complete system redesign.
3Device complexity
If no ripple compensation is applied, then the OBC structure remains simple, but the lifetime of battery is reduced and charging time increases
Solution Approach 1:
The feedback control system continuously monitors output current and adjusts switching frequency to prevent ripple components from reaching the battery. This active compensation protects the battery from voltage stress and thermal effects caused by ripple, thereby extending battery lifetime without requiring additional protective hardware.
Solution Approach 2:
The control system performs preliminary action by proactively adjusting the switching frequency before ripple components can significantly impact the battery. The PI controller anticipates and compensates for ripple effects in real-time, preventing harmful conditions from developing and thus protecting battery longevity.
Data Source
AI summary
An apparatus for controlling an LLC converter is provided. The apparatus includes a current controller that determines a first switching frequency control value of a switching element in the LLC converter to cause an output current detection value of the LLC converter to correspond to a predetermined output current command value. Additionally, a feedforward controller determines a second switching frequency control value for operating the switching element by applying a feedforward control value that corresponds to a ripple component included in an input voltage of the LLC converter to the first switching frequency control value.