Resonant Converter Harmonic Current Control for Load-Invariant Gain
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Solution Overview
Problem
Resonant power converters exhibit load-dependent voltage gain and inefficiencies due to conduction losses, with existing methods failing to provide repeatable behavior across a wide range of regulation and load levels.
Innovation Solution
A bi-directional resonant power converter employing synchronous average harmonic current control, utilizing a non-resonant bridge current sensor, switched capacitor filter, and pulse width modulation stage to minimize synchronous average harmonic current, allowing voltage gain to be controlled solely by commanded duty cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If voltage regulation is achieved by varying the primary bridge excitation frequency, then voltage control is possible, but the voltage gain becomes highly load dependent and repeatable behavior across wide load ranges cannot be achieved
Solution Approach 1:
The patent changes the control parameter from excitation frequency to synchronous average harmonic current. By controlling the fundamental harmonic component of the bridge current in synchronism with the resonant frequency, the system achieves load-invariant voltage gain while maintaining voltage control capability through duty cycle adjustment of the full-bridge converters.
Solution Approach 2:
The patent implements feedback control by sensing the bridge current and extracting its fundamental harmonic component using a switched-capacitor filter. This feedback signal is then used to adjust the converter operation, ensuring the synchronous average harmonic current meets the desired reference, thereby achieving stable and repeatable voltage regulation across varying load conditions.
2Device complexity
If conventional control methods are used, then simple control implementation is possible, but conduction losses increase and efficiency decreases
Solution Approach 1:
The patent uses feedback control with current sensing and fundamental harmonic extraction to optimize the converter operation. The feedback mechanism adjusts the duty cycles of both full-bridge converters to minimize synchronous average harmonic current, thereby reducing conduction losses and improving efficiency while maintaining relatively simple control implementation through standard PWM techniques.
3Ease of operation
If duty cycle variation is used for regulation, then voltage control is achieved, but load and impedance dependent behavior occurs
Solution Approach 1:
The patent implements feedback control that senses the bridge current and adjusts the duty cycles based on the synchronous average harmonic current magnitude. This feedback mechanism compensates for load and impedance variations, enabling the converter to maintain load-independent behavior while achieving voltage control through duty cycle adjustment of both full-bridge converters.
Solution Approach 2:
The patent changes the control approach from direct duty cycle variation to synchronous average harmonic current control. By controlling the fundamental harmonic component of the bridge current in synchronism with the resonant frequency, the system achieves load-invariant operation while maintaining voltage control capability through coordinated duty cycle adjustment of both full-bridge converters.
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
The solution achieves load-invariant voltage gain with reduced conduction losses, enabling efficient buck-boost regulation and flexible power transfer across a wide range of load levels, while maintaining low RMS current and soft switching behavior.
Implementation Method 1
The switched capacitor filter synchronously averages and compensates the bridge current signal over each half of the fundamental harmonic switching period
Implementation Method 2
The synchronous average harmonic current controller is comprised of the non-resonant bridge current sensor (307), switched capacitor filter (308), and pulse width modulation stage (309)
Implementation Method 3
Resonant power converters are used to efficiently convert DC input power to isolated DC output power with favorable magnetic integration
Implementation Method 4
Resonant power converters can be implemented using relatively small transformers whose inherent inductance forms part of the resonant filter (105)
Implementation Method 5
The phase of the rectified secondary bridge (102) current relative to the voltage of the primary bridge results in highly efficient soft switching behavior
Data Source
AI summary
A synchronous average harmonic current controller for a bidirectional resonant power converter provides efficient load invariant voltage gain. The controller includes a switched capacitor filter which averages and compensates a current signal over each half of the synchronous switching period. The control signal encodes an independent modulated phase and non-modulated differential duty cycle error response. The error response signals provide negative feedback to a pulse width modulation stage which results in reduction of the synchronous average harmonic current. At this operating point, the harmonic voltage gain is related closely to the commanded bridge duty cycles.