Thank you sir may I have another. Yes I've read several opinions. Apparently I missed the clear summary of the HF/LF basics in this thread, my apologies.
You said HF and LF both use PWM at 10+ kHz, and the difference is that what you call HF does PWM directly on the output terminals. But
@HaldorEE says all PWM is HF, which seems to conflict with that.
@BiduleOhm says HF = small light ferrite working at HF (a bit recursive) and LF uses big heavy transformer working at line frequency.
I asked about the Victron topology, which does PWM switching on input not output, has a big heavy iron transformer, but does not switch at line frequency. So it is not an "HF" or "HF Direct" topology by your definition.
@HaldorEE says it is HF because it uses PWM. It does not fit into either of
@BiduleOhm's two boxes.
Lacking any other references other than conflicting opinions, I fall back to the the reference
@Dzl usefully provided, following are some excerpts. Based on this, I would call the Victron unit an LF transformer-based topology using an H-bridge and PWM for pure sine generation.
"Low Frequency Transformer Based Inverters
"The following topologies are based on low frequency switching of the low voltage DC side, applying
the resulting DC pulses to a step-up transformer. Two common topologies are the push-pull, and
the H-Bridge. The push-pull topology is suitable for production of square and modified square output
waveforms, while the H-Bridge is useful for producing modified square wave and sine wave outputs."
... (later in the part on H-Bridge topology)
"After a period of time (variable according to pulse width modulation for voltage regulation) the
switches that were closed open, and the bottom two transistor switches close providing off-time
shorting (Figure 9B). The length of the on and off-time is determined according to the PWM
controller."
"High Frequency Inverters
"High frequency inverters are another approach to creating higher power AC from low voltage DC.
The name, high frequency, refers to the speed at which the transistors switch on and off. This type of
inverter creates low voltage AC from battery power, and applies it to a high frequency transformer,
which creates high voltage AC. The high voltage AC is then rectified (changed back to DC) to high
voltage DC and then a low frequency switcher (an H-Bridge) creates utility power AC."
...
"The main advantage behind high frequency switchers is the very lightweight and physical size. Most
HF inverters are low cost for the smaller sized units (less than about 300W).
Disadvantages of HF inverters are poor surge ability due to the characteristics of the switching power
section supplying the bridge (limits their usage to motor loads). Lack of isolation between the
transistors and AC loads makes them very vulnerable to transients caused by reactive loads since
there is no transformer to isolate and act as a “flywheel” to oppose fast changes in output current. HF
inverters exhibit high idle current because the high voltage switcher runs constantly, and this also
often causes interference with TV’s, radios, etc."