Adaptive Rectifier Turn-Off Timing for Zero-Current Switching
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Solution Overview
Problem
Existing rectifier control methods in wireless power transfer systems suffer from delays in switching times due to comparator delays, leading to rectifier instability, reverse currents, and reduced efficiency, particularly at higher frequencies.
Innovation Solution
Implementing digital timers to control FET switching, which compensate for comparator delays by adjusting turn-off times over multiple cycles to achieve zero current turn-off, and are periodically or continuously readjusted based on previous cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing control methods are used to drive FETs, then the rectifier can operate, but switching delays occur due to comparator delays, causing rectifier instability, reverse currents, and reduced efficiency
Solution Approach 1:
The patent applies preliminary action by measuring the input voltage and current waveforms in advance, calculating their derivatives to predict future waveform conditions, and using these predictions to determine the optimal turn-off time before the actual switching event occurs. This allows the system to compensate for comparator delays and achieve timely FET switching, resolving the technical contradiction between reliability and switching delay.
2Loss of time
If predictive derivative waveform measurement is used to control turn-off time, then switching can be started early, but the method becomes computationally intensive and imprecise
Solution Approach 1:
The patent implements feedback by continuously monitoring the actual turn-off performance and using this information to adjust the turn-off time control parameters. The system measures the input waveforms, calculates derivatives, predicts waveform conditions, executes switching, and then uses the results to refine future predictions. This closed-loop feedback mechanism improves measurement precision while maintaining the ability to start switching early, resolving the contradiction between reducing switching delay and improving prediction accuracy.
3Measurement precision
If phase-locked loop circuitry is used to control turn-off time, then precise phase shift prediction can be achieved, but the circuitry becomes complicated and expensive
Solution Approach 1:
The patent replaces the mechanical/electronic phase-locked loop circuitry with a digital signal processing approach. Instead of using analog components and dedicated PLL hardware, the system uses digital measurements of input waveforms, computational calculation of derivatives, and digital processing to achieve phase shift prediction. This substitution maintains measurement precision while significantly reducing device complexity and cost, resolving the technical contradiction between precision and complexity.
4Loss of time
If analog comparator thresholds are adjusted dynamically to control turn-off time, then turn-off time control can be achieved, but the control becomes sensitive to load variations
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the turn-off time control parameters based on real-time measurements of input voltage and current waveforms. Instead of using fixed analog comparator thresholds, the system calculates optimal turn-off times based on measured waveform characteristics and their derivatives. This allows the system to adapt to load variations while maintaining accurate turn-off time control, resolving the contradiction between turn-off time control and load variation sensitivity.
Data Source
AI summary
A rectifier includes digital timers to control FET switching rather than direct measurement of current and/or voltage. The digital timers control turn-off time to compensate for a delay produced by comparators in the rectifier. The digital timers are adjusted over multiple cycles to arrive at a turn-off time that produces zero current turn-off. The digital timers may be periodically or continuously readjusted based on a preceding set of cycles. Adaptive turn-off via digital timers is useful for discontinuous conduction mode suppression.