Resonant Converter Current Estimation via Cycle Averaging
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Solution Overview
Problem
Resonant and semi-resonant DC-DC converters with variable switching frequency and sinusoidal-like output current pose challenges in accurately obtaining the cycle average value of output current, as conventional low pass filtering techniques introduce latency and inaccuracy, especially at higher load frequency transients.
Innovation Solution
A voltage converter with a variable switching frequency power stage and a control circuit that samples current between the switching node and output node, calculates the average current for the preceding cycle, and estimates the average current for the present cycle based on this information, minimizing latency and improving accuracy without requiring low pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If very low bandwidth filters are used to obtain the cycle average value of output current, then the average value can be obtained, but latency is added to the control loop and transient performance is degraded
Solution Approach 1:
The patent performs preliminary integration of the sinusoidal current waveform during the off-time period of the resonant switch. By accumulating the area under the current curve in advance during the known off-time interval, the system obtains the cycle average current value before the switching cycle completes, thereby eliminating the need for post-processing low-pass filtering that would introduce latency.
2Measurement precision
If very low bandwidth filters are used to obtain the cycle average value of output current, then the average value can be obtained, but measurement accuracy is degraded at higher load frequency transients
Solution Approach 1:
The patent dynamically adapts the integration window to match the actual off-time period of the resonant switch, which varies with switching frequency and load conditions. By adjusting the integration duration according to real-time switching parameters, the system maintains accurate cycle average current measurement across varying operating conditions, including high-frequency transients, without relying on fixed-bandwidth filters.
3Measurement precision
If conventional low pass filtering techniques are used, then the cycle average value can be obtained, but the filtered values yield an inaccurate total current when summed in multi-phase systems
Solution Approach 1:
The patent uses the measured off-time duration and switching frequency as feedback parameters to dynamically adjust the integration window for each phase. This ensures that the cycle average current calculation for each phase is synchronized and accurately reflects the actual current waveform characteristics, enabling correct summation of total current in multi-phase systems without the information loss introduced by conventional filtering.
Data Source
AI summary
A voltage converter includes a variable switching frequency power stage, a passive circuit and a control circuit. The power stage includes a high-side switch and a first low-side switch coupled to the high-side switch at a switching node of the power stage. The passive circuit couples the switching node to an output node of the voltage converter. The control circuit is operable to control cycle-by-cycle switching of the power stage and sample current at a point between the switching node and the output node, the sampled current having a half cycle sinusodial-like shape each switching cycle. For the present switching cycle, the control circuit is operable to calculate an average of the sampled current for the immediately preceding switching cycle and estimate the average sampled current for the present switching cycle based on the average sampled current calculated for the immediately preceding switching cycle.