Field Notes.
Engineering writing and research from the Arpuro team.
Instrument validation, calibration methodology, deployment notes, and signal-processing research. Papers and theses going back to 2016.
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Real-time passive control of wave energy converters using the Hilbert–Huang transform
A passive-control strategy for wave-energy converters that adapts damping to instantaneous wave frequency rather than using static tuning. HHT supplies the frequency at every sample; the adaptive controller improves energy absorption over fixed-gain in irregular seas.
Paula B. Garcia-Rosa, Geir Kulia, John V. Ringwood, Marta Molinas. IFAC-PapersOnLine (Elsevier). 2017.
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Understanding instantaneous frequency detection: a discussion of Hilbert–Huang Transform versus Wavelet Transform
A head-to-head between the Hilbert–Huang transform and discrete wavelet decomposition for instantaneous frequency in non-stationary signals. Tests on synthetic data and real EEG recordings show HHT yielding more interpretable oscillatory components.
Maximiliano Bueno-López, Marta Molinas, Geir Kulia. ITISE 2017. 2017.
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Simple model for understanding harmonics propagation in single-phase microgrids
How harmonics cycle between the AC and DC sides of a single-phase PV inverter in islanded operation: feed-forward injects even harmonics on the DC bus; feedback re-injects them as odd AC harmonics. The paper isolates and predicts the self-sustaining pattern.
Geir Kulia, Marta Molinas, Lars M. Lundheim, Olav B. Fosso. IEEE ICCEP 2017. 2017.
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Impact of time-varying angular frequency on the separation of instantaneous power components
When grid frequency drifts, the textbook active/reactive split of instantaneous power misattributes oscillatory terms. Keeps the decomposition coherent under a time-varying angular frequency, with stand-alone power-system field data as the validation case.
Benedikt Hillenbrand, Geir Kulia, Marta Molinas. IEEE ICCEP 2017. 2017.
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Towards a Real-Time Measurement Platform for Microgrids in Isolated Communities
A real-time measurement framework that uses empirical-mode decomposition to extract instantaneous frequency and amplitude from microgrid voltage and current. The grid-connected vs standalone comparison confirms isolated systems are fundamentally more non-stationary.
Geir Kulia, Marta Molinas, Lars Lundheim, Bjørn B. Larsen. Procedia Engineering (Elsevier). 2016.
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Investigation of distortions in microgrids
The MSc thesis Signal Analysis Lab (now Arpuro Labs) was built on. Examines how harmonic distortion, inverter switching artefacts, and load nonlinearities propagate in standalone microgrids — and where Hilbert–Huang reveals time-varying content Fourier flattens out.
Geir Kulia. MSc Thesis, NTNU. 2016.
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Tool for detecting waveform distortions in inverter-based microgrids: a validation study
Validation of an HHT diagnostic tool against measurements from a standalone PV microgrid in Bhutan. Time-varying frequencies and amplitude-modulation patterns invisible to Fourier show up clearly in the empirical-mode decomposition.
Geir Kulia, Marta Molinas, Lars Lundheim. IEEE GHTC 2016. 2016.
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Instantaneous Frequency in Electric Power Systems
A short technical case for treating instantaneous frequency as a fundamental observable, not a derived quantity. Surveys where Fourier and wavelet break down in microgrids and under time-varying loads, and argues for Hilbert–Huang as the right primitive.
Marta Molinas, Geir Kulia, Olav B. Fosso. Poster, NTNU 2016. 2016.
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On wind turbine failure detection from measurements of phase currents: a permutation entropy approach
Permutation entropy on phase-current measurements as a wind-turbine fault indicator. Where Fourier spectra could not separate healthy from faulty operation, the entropy of ordinal patterns did — a single scalar that tracked degradation without per-fault tuning.
Sumit Kumar Ram, Geir Kulia, Marta Molinas. arXiv 2016. 2016.