LLC DC-DC Converter Input Voltage Control by Gain-Inverted Frequency
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Solution Overview
Problem
Existing solutions for controlling the DC input voltage of LLC DC-to-DC converters in electrical accumulator chargers, particularly for electric vehicles, are complex, costly, and lack a satisfactory method for quick and reliable frequency control, especially when the output voltage varies over a wide range.
Innovation Solution
A method involving a preliminary step of defining a setpoint voltage, calculating a control frequency through mathematical inversion of the converter's gain expression based on output battery voltage and input power, and applying this frequency using a feedback control mechanism with threshold values to adjust the frequency incrementally, ensuring robust and simple frequency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transfer function methods are used to control output voltage, then control accuracy is improved, but device complexity and computational cost increase
Solution Approach 1:
The patent changes the control parameter from duty cycle to frequency. By controlling the frequency of the LLC resonant converter, the method achieves accurate voltage regulation without requiring complex transfer function calculations or identification procedures. This parameter change simplifies the control system while maintaining control accuracy.
2Measurement precision
If transfer function identification methods are used, then control precision is improved, but loss of time increases due to recalculation requirements
Solution Approach 1:
The patent pre-establishes the relationship between frequency and gain for the LLC resonant converter. Instead of performing time-consuming identification procedures or recalculating transfer functions when operating points change, the method uses pre-determined frequency settings that correspond to desired output voltages, eliminating the need for real-time complex computations.
3Measurement precision
If feedback-linearized control operations are used, then control accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and utilizes the natural resonant characteristics of the LLC converter circuit. By controlling the operating frequency relative to the resonant frequency, the method leverages the inherent voltage gain properties of the resonant circuit, eliminating the need for complex feedback-linearization algorithms and reducing both hardware and software requirements.
4Adaptability or versatility
If frequency control is implemented to adjust gain, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical or electronic control mechanisms with frequency-based control. By adjusting the switching frequency of the MOSFET bridge, the method achieves wide voltage adjustment range and adaptability to different operating conditions without requiring complex control circuitry or multiple control loops.
Data Source
AI summary
A method for controlling the input voltage frequency of a DC-DC converter includes defining a setpoint voltage value, computing a control frequency value of the DC-DC converter as a function of the battery voltage, a power setpoint, and the setpoint input voltage, and applying the control frequency to the converter.