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Diffstat (limited to 'ma/safety_reset.tex')
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1 files changed, 51 insertions, 1 deletions
diff --git a/ma/safety_reset.tex b/ma/safety_reset.tex index a292458..f8c97f6 100644 --- a/ma/safety_reset.tex +++ b/ma/safety_reset.tex @@ -889,7 +889,7 @@ despite numerous distortions. \begin{figure} \centering \includegraphics{../lab-windows/fig_out/mains_voltage_spectrum} - \caption{Fourier transform of an 8 hour capture of mains voltage. Data was captured using our frequency measurement + \caption{Fourier transform of a 24 hour capture of mains voltage. Data was captured using our frequency measurement sensor described in section \ref{sec-fsensor} and FFT'ed after applying a blackman window. Vertical lines indicate $50 \text{Hz}$ and odd harmonics.} \label{mains_voltage_spectrum} @@ -1055,6 +1055,44 @@ interface and its good tolerance of system resets due to unexpected power loss. \subsection{Frequency sensor measurement results} +\begin{figure} + \centering + \includegraphics{../lab-windows/fig_out/freq_meas_trace_24h} + \caption{Trace of grid frequency over a 24 hour window. One clearly visible feature are large positive and negative + transients at full hours. Times shown are UTC. Note that the european continental synchronous area that this + sensor is placed in covers several time zones which may result in images of daily load peaks appearing in 1 hour + intervals. Fig.\ \ref{freq_meas_trace_mag} contains two magnified intervals from this plot.} + \label{freq_meas_trace} +\end{figure} +\begin{figure} + \begin{subfigure}{\textwidth} + \centering + \includegraphics{../lab-windows/fig_out/freq_meas_trace_2h_1} + \caption{A 2 hour window around 00:00 UTC.} + \end{subfigure} + \begin{subfigure}{\textwidth} + \centering + \includegraphics{../lab-windows/fig_out/freq_meas_trace_2h_2} + \caption{A 2 hour window around 18:30 UTC.} + \end{subfigure} + \caption{Two magnified 2 hour windows of the trace from fig.\ \ref{freq_meas_trace}.} + \label{freq_meas_trace_mag} +\end{figure} + +\begin{figure} + \centering + \includegraphics{../lab-windows/fig_out/freq_meas_spectrum} + \caption{Fourier transform of the 24 hour grid frequency trace in fig. \ref{freq_meas_trace} with some notable peaks + annotated with the corresponding period in seconds. The $\frac{1}{f}$ line indicates a pink noise spectrum. We can + clearly see the noise spectrum flattens below some frequency around $\frac{1}{120 \text{s}}$. This effect is due to + primary control actively regulating grid frequency over such time intervals. Beyond the $\frac{1}{f}$ slope starting + at around $1 \text{Hz}$ we can make out a white noise floor in the order of $\frac{\mu\text{Hz}}{\text{Hz}}$. + % TODO: where does this noise floor come from? Is it a fundamental property of the grid? Is it due to limitations of + % our measurement setup (such as ocxo stability/phase noise) ??? + } + \label{freq_meas_spectrum} +\end{figure} + Captured raw waveform data is processed in the Jupyter Lab environment\cite{kluyver01} and grid frequency estimates are extracted as described in sec. \ref{frequency_estimation} using the \textcite{gasior01} technique. Appendix \ref{grid_freq_estimation_notebook} contains the Jupyter notebook we used for frequency measurement. @@ -1063,6 +1101,16 @@ extracted as described in sec. \ref{frequency_estimation} using the \textcite{ga \section{Channel simulation and parameter validation} +To validate all layers of our communication stack from modulation scheme to cryptography we built a prototype +implementation in python. Implementing all components in a high-level language builds up familiartiy with the concepts +while taking away much of the implementation complexity. For our demonstrator we will not be able to use python since +our target platform is a cheap low-end microcontroller. Our demonstrator firmware will have to be written in a low-level +language such as C or rust. For prototyping these languages lack flexibility compared to python. +% FIXME introduce project outline, specs -> proto -> demo above! + +To validate our modulation scheme we performed a series of simulations. We produced modulated frequency data that we +superimposed with either of simulated pink noise or an actual grid frequency measurement series. +% FIXME do test series with simulated noise emulating measured noise spectrum \section{Implementation of a demonstrator unit} @@ -1070,6 +1118,8 @@ extracted as described in sec. \ref{frequency_estimation} using the \textcite{ga \section{Lessons learned} + + \chapter{Future work} \section{Technical standardization} The description of a safety reset system provided in this work could be translated into a formalized technical standard |