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Talking about both three-phase AC as well as DC fast charging (wherein 3 phase AC is converted to DC) in EVs, I think that the 3-phase rectifier represents a balanced 'load'. Therefore I want to know why is then a neutral required? I ask this because I think that doing away with neutral would mean getting rid of the triple-n harmonics. Is my thinking correct?

Here is a type 2 connector pinout for reference:

Type 2 connector

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  • \$\begingroup\$ Would it be used for single-phase charging? \$\endgroup\$ – Transistor Jun 26 '18 at 7:17
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    \$\begingroup\$ You could absolutley design an EV charger for three phase delta with no neutral. But what you are looking at is a nearly universal plug which needs to adapt to several countries and several different scenarios, including three phase Y as well as single phase (with neutral). \$\endgroup\$ – winny Jun 26 '18 at 7:37
  • \$\begingroup\$ @Transistor Yes, with single phase its L1+N and with three phases its L1+L2+L3+N \$\endgroup\$ – Pikachu Jun 26 '18 at 7:51
  • \$\begingroup\$ Am I correct in thinking that utilities won't have to bother about 3rd harmonic if threre was no neutral \$\endgroup\$ – Pikachu Jun 26 '18 at 7:53
  • \$\begingroup\$ @winny What about 3-phase star with no neutral? Would that work? \$\endgroup\$ – Pikachu Jun 26 '18 at 8:08
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Who says a Neutral 'is required'?

What you've drawn is a standard 3 phase connector. The standard connector always includes a neutral, because then it can be used for single phase and unbalanced loads, as well as balanced 3 phase loads. The cost of an extra pin and extra wire for the neutral is far outweighed by the improvement in flexibility for use of the connector.

It's easy enough to design any specific rectified load, whether charger, motor, whatever, to use only 3 phase with no neutral. It's a waste of time to insist that it can only be plugged into sockets without a neutral, as this would severely limit where it could be used.

It's quite possible, and this may be my first cut at a fast charger, to run the power DC from a full bridge rectifier on the 3 phases, but the control electronics from a small transformer running from a single phase and neutral. It's possible to list all sorts of practical advantages to such a split.

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  • \$\begingroup\$ In Ireland, which broadly follows the UK standards, we would use a 3P+E with no neutral connector if no neutral is available (as on a delta secondary, for example). This may be important as it prevents insertion of the 3P+N+E plugs which may be relying on N for correct operation. \$\endgroup\$ – Transistor Jun 26 '18 at 11:19
  • \$\begingroup\$ Been bitten by the TP+N+E plug on an extension cable that turned out to be wired with 4 core cable (No neutral), quite the nasty surprise with an unbalanced lighting load. \$\endgroup\$ – Dan Mills Jun 26 '18 at 11:24
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The easy, familiar, can build with jellybean switchmode parts approach to a charger is to build three single phase isolated converters and wire them star. This is because a 230V switchmode supply is a very standard thing and there are a LOT of off the shelf and high volume parts designed for such use.

Going delta increases the PFC output bus voltage (because you now have 400V RMS, so you need a PFC output north of 565V) which is out of reach for the common 400 or 450V caps and probably too high for the common mosfet choices (And you still need to build three of the things). Yea the primary current in each converter is a little lower, but the need for more expensive switching and bus caps probably trumps that consideration.

Now if you are going for a star connection, then you either need to ensure you have perfect balance and no triplen, or you need a neutral. You can of course use a synthetic neutral but that is quite a bit bit of iron, and you really don't need that weight on the vehicle, better to do that (if it is even required) on the shore side of the cable where its weight is not hurting range and acceleration.

Seriously, in the scheme of things a few amps or even a few tens of amps of triplen and imbalance is just not that big a deal, and is far easier to fix in the land side transformers then it is in a weight and size constrained mobile environment.

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