Resonant Converter Control Using Voltage and Time Variables
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Solution Overview
Problem
Existing solutions for controlling resonant power converters in fluorescent lighting face challenges with stability, especially during dimming, due to non-uniform impedance characteristics, and require efficient power factor correction, which complicates control and can lead to capacitive mode operation that may damage components.
Innovation Solution
A method and controller for a resonant power converter that uses two independent variables - a voltage level and a time period - to control the conduction interval, allowing for stable operation and matching power factor correction and resonant stage performance, especially at low power levels, and preventing capacitive mode by managing switch operation based on capacitor voltage and timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If frequency control is used to regulate power delivered to the lamp, then power delivery can be controlled, but stability deteriorates during dimming due to non-uniform impedance characteristics
Solution Approach 1:
The patent changes the control parameter from frequency to voltage level. By controlling the voltage across the resonant capacitor and using time period as a second independent variable, the system achieves stable power delivery control without the instability issues associated with frequency control during dimming operations.
Solution Approach 2:
The patent introduces a second control dimension by using both voltage level and time period as independent variables. This dual-parameter control approach provides more precise and stable power delivery control compared to single-parameter frequency control, especially during dimming when impedance characteristics vary non-uniformly.
2Reliability
If frequency is swept to higher value to avoid capacitive mode, then component destruction is prevented, but power delivery drops causing lamp shutdown
Solution Approach 1:
The patent applies preliminary action by monitoring capacitor voltage and timing to detect approaching capacitive mode conditions before they occur. By using time period control alongside voltage level control, the system can prevent capacitive mode entry through proper switch timing rather than reactive frequency sweeping, thus maintaining both component safety and continuous power delivery.
3Device complexity
If single stage PFC resonant topology is used, then component count and size are reduced, but control complexity increases due to different effects on PFC and resonant stages
Solution Approach 1:
The patent applies universality by using the same half-bridge switching circuit to perform both power factor correction and resonant power delivery functions. The dual-parameter control method (voltage level and time period) provides a unified control approach that simultaneously manages both the PFC stage and resonant stage, simplifying the control architecture despite the multi-functional requirements.
4Duration of action of stationary object
If asymmetric switching is used to prevent ion migration, then lamp lifetime is extended, but control complexity and power loss increase
Solution Approach 1:
The patent uses periodic action by implementing symmetric switching with equal on-times for both switches during each full cycle. This symmetric periodic operation prevents ion migration to electrodes while maintaining control simplicity and reducing power losses associated with asymmetric switching schemes. The symmetry is maintained while still achieving the lamp lifetime extension goal.
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 provides improved control over output power, maintains stability during deep dimming, prevents ion migration in lamps, and ensures soft switching performance, while maintaining a high power factor and efficient operation over a wide range of power levels.
Implementation Method 1
a resonant circuit connected to a node between the first and second switches and to an output connectable to an output electrical load, the resonant circuit comprising an inductor and a capacitor
Data Source
AI summary
The invention relates to methods of controlling operation of a resonant power converter and to controllers configured to operate according to such methods. Embodiments disclosed include a method of controlling a power output of a resonant power converter comprising first and second switches (S1, S2) connected in series between a pair of supply voltage lines, a resonant circuit connected to a node between the first and second switches and to an output connectable to an output electrical load, the resonant circuit comprising an inductor and a capacitor, the method comprising: closing the first switch (S1) to start a first conduction interval; setting a first voltage level (902); setting a first time period; and opening the first switch (S1) to end the first conduction interval when a voltage (901) across the capacitor crosses the first voltage level (902) and when a time period from closing the first switch exceeds the first time period (904).