In another thread the point was raised that at least for high voltage or high current levels, solid state switching can only be done at AC zero crossing points. I am doubtful of some of the information posted, but more so because the information seems incomplete or inconsistent, rather than technical correctness.
Switching at other than zero crossing certainly must be taking place in various devices. Lighting dimmers are one example where the AC cycle is itself chopped at various points other than the zero-crossing. Merely acting on incoming DC is a general example, since DC has no zero-crossing.
The discussion that raised the point involved high voltage DC or back to back AC frequency conversion at high voltage. Voltages in excess of 100kV would be involved. High currents would involved as well. The examples of contradiction are low voltage (under 600 volts) cases. However, there is the possibility of high currents even in the low voltage cases.
What I would like to know is, specifically for controlled switching (e.g. not for ordinary rectifiers), what is the current state-of-the-art of available products, and actually used products, in terms of what is the maximum levels of voltage and/or current that can be switched. This might need to be answered separately for a single solid state component and for a stacked arrangement of components to increase voltage and.or current.
Do DC-to-AC inverters actually use pulse width modulation or pulse density modulation technology to produce sine wave approximations from a single DC voltage? Or is the state of the are in inverter technology still based on "analog amplifier" or other technologies?
I've reviewed a wide range of inverters of interest and beyond interest. One thing I have found in the technical descriptions of these devices is that no one reveals the type of technology used to achieve the claimed performance in terms of sine wave quality. They don't even say if they are using pulse width modulation or pulse density modulation. Maybe they are not using any of these methods at all.
I would like to know what frequencies are being used to generate the sine waves in these devices to evaluate particular issues, such as RFI or even health hazards.
For the simplest and/or most efficient design, what is the optimal ratio of voltage between incoming DC voltage and direct (before any transformer) outgoing AC (RMS) voltage?
Is it feasible to do pulse width/density modulation on 480 volts DC to produce a waveform than can be filtered easily (with a minimum of LC components) to 240 volts AC at 50 Hz or 60 Hz (before any voltage changing transformer stage)?