SVM Current Estimation Using Temporal Averaging and Correction
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Solution Overview
Problem
Existing methods for estimating currents in two windings of a poly-phase electrical load using a single current measuring device introduce measurement errors due to time lag and harmonic interference, making it challenging to achieve accurate simultaneous measurements.
Innovation Solution
The method involves measuring one current at the desired instant and the other current twice before and after, with the estimated value calculated as an arithmetic mean, and optionally correcting for errors using a correction term, effectively reducing errors caused by time lag and harmonic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single multiplexed A/D converter is used to measure currents in two windings, then cost is reduced and device complexity is lowered, but measurement precision deteriorates due to time lag between measurements
Solution Approach 1:
The patent applies preliminary action by measuring one current (i.b) at a specific instant before the desired measurement instant, then using this preliminary measurement combined with a correction term to estimate the current value at the desired instant. This allows the system to compensate for the time lag effect in advance, maintaining measurement precision while using a single multiplexed A/D converter.
Solution Approach 2:
The patent changes the measurement parameters by introducing a correction term that depends on the rate of variation of the current and the time lag. This parameter adjustment allows the system to correct the measurement error caused by sequential measurement, effectively maintaining measurement precision despite the time delay inherent in using a single multiplexed converter.
2Device complexity
If current measurements are taken at different instants using a single converter, then device complexity is reduced, but measurement precision deteriorates due to harmonic interference
Solution Approach 1:
The patent uses feedback by calculating a correction term based on the measured current value and its rate of variation, then applying this correction to obtain the accurate current value at the desired instant. This feedback mechanism compensates for harmonic interference effects that would otherwise degrade measurement precision when using sequential measurements with a single converter.
3Measurement precision
If repeated current measurements are performed during the same period, then measurement precision can be improved through averaging, but measurement time increases and productivity decreases
Solution Approach 1:
The patent applies partial action by performing only one measurement of each current (i.a and i.b) during the modulation period, rather than multiple repeated measurements. The correction term compensates for the single measurement approach, achieving sufficient precision without the time penalty of repeated measurements, thus maintaining productivity.
Data Source
AI summary
A method for estimating values assumed at a certain instant of each period by currents flowing respectively in two distinct windings of a poly-phase load controlled in a space vector modulation (SVM) mode, using a same measuring device, may include coupling the measuring device to the first winding and measuring a current flowing therethrough with an anticipation from the certain instant smaller than or equal to an SVM half-period. The method may also include coupling the measuring device to the second winding, measuring a current flowing therethrough at the certain instant, coupling the measuring device to the first winding, and measuring a current flowing therethrough with a delay equal to the anticipation. The method may also include estimating a value assumed at the certain instant by the current flowing through the first winding based upon the two measured values with the anticipation and with the delay respectively.