Until recent news such as this, I didn't know it was the "conceptually simple" but practically difficult ability to switch (interrupt) a GW or so of DC energy flow preventing the implementation of better than point-to-point HVDC (i.e. multiple access point) power grids.<p>Evidently interruption's easier with AC because of the zero-crossings of current every half-cycle.<p>Three alternate solutions to HVDC circuit interruption are described in this article. Two are electronically integrated with the output circuitry of the bidirectional AC-DC converters (bidirectional energy flow AC-DC converters being an interesting, but off-topic subject in their own right).<p>I find it an ingenious use of an IGBT bridge surrounding a capacitor to throw the cap's charge into reversed polarity so as to stop the current flow -- effectively opening the circuit. This tells me the cap would seem to be in series with the DC side somehow. Were it in parallel, well, it wouldn't make much sense to reverse the cap's polarity as you'd only get to do it once.<p>I also find it fascinating that the mathematics it takes to describe AC circuits is far more complex than for DC -- one has to accept that there genuinely exists a square root of negative one, "imaginary" though we may call it.<p>As in programming, good nomenclature is often late to the table. I wouldn't try (and I'm certainly not qualified) to "refactor" centuries, maybe millennia [1] of mathematical terminology.<p>-----<p>[1] <a href="https://en.wikipedia.org/wiki/Imaginary_number" rel="nofollow">https://en.wikipedia.org/wiki/Imaginary_number</a>
Germany also stores some energy by pumping water uphill for storage behind dams, but there's only so much capacity (only so many dams). That will change if other low-cost grid-level energy storage systems become available.<p><a href="https://en.wikipedia.org/wiki/Grid_energy_storage" rel="nofollow">https://en.wikipedia.org/wiki/Grid_energy_storage</a>
Germany has a problem. It has a desire to increase renewables (mostly from wind), which is found in the north. The primary consumers of the energy (manufacturing) are not in the north, in fact many are in the south. They need to master the transmission of that energy from north to south.