From 503f80992d574103fbfcc661a7521b09f18986c3 Mon Sep 17 00:00:00 2001 From: jaseg Date: Tue, 29 Apr 2025 12:01:56 +0200 Subject: [PATCH] SMPC chapter work on WPT foo --- chapter-smpc/chapter.tex | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/chapter-smpc/chapter.tex b/chapter-smpc/chapter.tex index 1977f5f..2b57b2e 100644 --- a/chapter-smpc/chapter.tex +++ b/chapter-smpc/chapter.tex @@ -278,6 +278,41 @@ of our design. \subsection{Rotation-Invariant Envelope Power Supply} % Twisted Inductor paper +A central engineering challenge in inertial HSMs is transferring power and data between the payload and the rotating +mesh cage. Industrially, power and data transfer through rotating joints is usually done using slip ring assemblies. A +slip ring consists of one or more contacts that wipe on a rotating circular surface. Industrially, metal spring contacts +plated with hard gold or other common surface coatings are used for transferring small currents and data signals, and +carbon brushes are used for higher currents. Slip rings are widely used in motors and other rotating machinery. + +For use in IHSMs, slip rings have several limitations. First, they are complex precision-machined components and thus +are rather expensive. Beyond cost, they also have performance limitations. Generally, slip rings are most well-suited to +slow rotation, as high rotation increases the wear of the contacts. The design target of \qty{1000}{rpm} we use in IHSMs +are at the upper end of what commercial slip rings usually support. A third disadvantage is that they are sensitive, and +any misalignment or contamination by dust can increase wear and cause intermittant contact. + +An IHSM's data link can easily be realized using optical communication. Although power transfer using light is also +possible---and we have in fact demonstrated it in our first prototype IHSM---it comes at the disadvantage of a heavy +rotating assembly since large solar cells are needed, and it has poor end-to-end efficiency. For the large-scale meshes +needed in a high-performance IHSM tailored to SMPC applications, we engineered a better solution: A rotation-invariant +inductive Wireless Power Transfer link. + +While Wireless Power Transfer (WPT) can be implemented in many different ways, the vast majority are variants of +Inductive WPT, where the primary and secondary side are linked primarily through the magnetic component of the +electromagnetic field, and coils are used as the transmitting and receiving antenna. Inductive WPT uses low frequency, +which reduces circuit complexity, and it is well-suited for transferring high power across short distances. The +electronic realization of a WPT link is usually similar to that of a DC/DC converter, except that in place of the +inductor or flyback transformer, the pair of transceiver coils is used. Compared to a flyback transformer, the WPT +link's transceiver coil pair has a lower coupling coefficient that varies with distance. + +A challenge in WPT links is the strong dependency between link inductor coupling coefficient and distance. In a naïve +implementation that uses the link coils as a simple transformer, link efficiency would drop sharply with distance. To +decrease the impact of this distance dependency, almost all WPT implementations combine the transceiver coils with +capacitors to form a pair of tuned tank circuits that are driven like they would be in a resonant converter. Like in +resonant converters, a variety of topologies such as series, parallel, or series-parallel LC are used for these tuning +circuits. + + + \subsection{Software Considerations} \subsection{Fast Zeroization of Non-Customizable Memories}