Resonant Current Measurement Using a State-Space Observer ADC
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Solution Overview
Problem
Conventional power converter control systems face latency issues due to high frequency switching, leading to phase delay and instability, which is exacerbated by the need for increased control bandwidth with the adoption of GaN HEMT devices, requiring a reduction in iTank ADC latency by a factor of 10× to maintain stability.
Innovation Solution
The implementation of a state space observer and a hybrid ADC that uses a comparator and counter to iteratively refine current approximations, eliminating the need for successive approximation methods and reducing latency to 10 ns, allowing GaN HEMT devices to operate at increased switching frequencies with improved stability and enabling a 3× reduction in transformer size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency is increased to improve power conversion efficiency, then productivity increases, but phase delay increases causing control instability
Solution Approach 1:
The system performs preliminary actions by predicting future current values using a state-space model before the actual measurement is available. The predictor uses the system model and previous measurements to estimate the current at the next sampling instant, effectively compensating for the measurement delay and maintaining control stability at high switching frequencies.
Solution Approach 2:
A state-space predictor acts as an intermediary between the delayed current measurement and the control loop. Instead of directly using the delayed measurement, the predictor generates an intermediate estimated value that reflects the current state, bridging the gap caused by measurement latency and enabling stable high-frequency operation.
2Speed
If the control bandwidth is increased to improve responsiveness, then speed increases, but phase delay causes negative feedback to become positive feedback
Solution Approach 1:
The predictor performs preliminary calculation of the current value before it is actually measured, allowing the control loop to operate with future-predicted values rather than delayed past values. This eliminates the phase delay that would otherwise cause feedback instability at high bandwidths.
3Measurement precision
If a 12-bit SAR ADC is used to achieve high measurement precision, then measurement precision improves, but latency increases by requiring up to 12 successive approximations
Solution Approach 1:
The state-space predictor performs preliminary estimation of the current value using the system model and previous measurements. This predicted value is available immediately without requiring the full 12-bit SAR ADC conversion process, providing low-latency current information for the control loop while maintaining sufficient precision through the predictive algorithm.
Data Source
AI summary
An apparatus for measuring current in a power converter is provided. The apparatus comprises a state space observer configured to provide a statistically most probable state of the power converter and an analog digital converter comprising a comparator configured to compare a first state space observer current approximation to a real time current input signal to determine if the first state space observer current approximation is too high or too low and a counter configured to be incremented or decremented based on a result of a comparison at the comparator, wherein an output of the counter is input to the state space observer and added to the first state space observer current approximation to calculate a second state space observer current approximation that will be one count closer to a final correct value.