Symmetric Time Shift Control for LLC Resonant Converters
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Solution Overview
Problem
The Time Shift Control (TSC) method for LLC resonant converters suffers from unbalanced or asymmetric operation in detecting zero current crossings, leading to inefficiencies and stress on components due to unequal detection times for different types of zero-current crossings, complicating analysis and control.
Innovation Solution
The implementation of Symmetric Time Shift Control (STSC) addresses this by using the same zero-current detection time for both power switches, eliminating unbalances and reducing component stress through symmetric operation, allowing for a smaller and less expensive zero-current detection comparator with less stringent trimming requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Time Shift Control (TSC) method is used to control LLC resonant converter, then bandwidth compensation and input voltage ripple rejection are improved, but unbalanced operation occurs in detecting zero current crossings leading to component stress and control complexity
Solution Approach 1:
The patent applies asymmetry principle by intentionally introducing opposite asymmetric delays to compensate for the inherent asymmetric detection times. The first asymmetric delay compensates for the first zero-current detection time, and the second asymmetric delay compensates for the second zero-current detection time, thereby achieving symmetric overall operation despite asymmetric individual components
Solution Approach 2:
The patent changes the timing parameters by introducing adjustable asymmetric delay periods that can be tuned to match the specific detection times of the zero-current detection circuit. This allows the system to adapt to different operating conditions and maintain symmetric operation across varying loads and input voltages
2Speed
If conventional TSC method is used, then control bandwidth is improved, but analysis and control complexity increases due to multiple poles with frequency-dependent characteristics
Solution Approach 1:
The patent uses a simplified small-signal model that copies the essential dynamics of the full system without requiring analysis of all multiple frequency-dependent poles. This simplified model captures the dominant behavior needed for control design, reducing analytical complexity while maintaining accuracy for controller synthesis
3Measurement precision
If asymmetric zero-current detection times are used in TSC, then component stress increases and operation efficiency decreases, but detection precision may be improved
Solution Approach 1:
The patent implements feedback by using the detected zero-current crossing times to dynamically adjust the asymmetric delay periods. The control circuit measures the actual detection times and compensates for their asymmetry by applying opposite delays, ensuring that the overall switching timing remains symmetric and efficient
Solution Approach 2:
The patent applies preliminary action by pre-calculating and pre-applying the asymmetric delay compensation before the actual switching occurs. The opposite asymmetric delays are configured in advance based on the detected zero-current times, preventing the efficiency loss from asymmetric operation before it can occur
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
STSC improves the efficiency of LLC resonant converters by ensuring balanced operation, reducing component stress, and maintaining high bandwidth compensation and input voltage ripple rejection, while maintaining similar loop gain and phase shift characteristics as conventional TSC.
Implementation Method 1
the resonant circuit mainly responds to this fundamental frequency component of the voltage square wave while responding negligibly to higher-order frequency components or harmonics of the voltage square wave
Implementation Method 2
These sinusoidal voltages and currents are then rectified and filtered to provide direct current (DC) output power
Data Source
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AI summary
A control circuit (102) controls a switching circuit (106) of a resonant converter (100), where the switching circuit includes first and second power switches (Q1, Q2). A first on time of the first power switch (Q1) and a second on time of the second power switch (Q2) are controlled to generate a square wave signal (VHB) to drive a resonant circuit (108). The control circuit (102) controls the first on time based on a zero current detection time indicating detection of a zero current crossing of a resonant current (ITANK) generated in the resonant circuit (108) in response to the square wave signal and on a time shift delay time based on an output voltage (Vout) of the resonant converter. The second on time of the second power switch control is based on the zero current detection time detected for the first power switch (Q1) and on the time shift delay time.