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| What kind of variable load does an EV car present to the EVSE? |
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| 741:
What kind of frequency content & phase shifts does the current draw from an EV car have? For the purposes of power calculation is some kind of DSP indicated, or does the car's charge current stay pretty constant (slowly smoothly varying)? I'd like to make a semi-realistic LTSpice model of what one might realistically see during the charge process on an EV car. |
| fcb:
--- Quote from: 741 on January 06, 2020, 02:22:51 pm ---What kind of frequency content & phase shifts does the current draw from an EV car have? For the purposes of power calculation is some kind of DSP indicated, or does the car's charge current stay pretty constant (slowly smoothly varying)? I'd like to make a semi-realistic LTSpice model of what one might realistically see during the charge process on an EV car. --- End quote --- Let's assume you have are talking about single phase, 32A (7kW) - probably covers most of the EV's on the market at present. 1. The charger circuits built into the cars are actually fairly good when it comes to harmonic content and PF (power factor) - PFC mandatory at those levels. I won't mention the name, but there is one EV i've come across that breaks all these rules when it came to market. 2. Charge current can vary hugely, and somewhat arbitarily. The EVSE (charge point on the wall) can also request the car sticks to a maximum limit as well - and the car will ramp down pretty quickly to the requested levels. Power calculation can be done with a DSP easily, or you can roll your own single/three phase meter. 3. Bear-in-mind that the typical EVSE is effectively a posh relay and more or less just connects the car to the domestic supply. So modelling this is fairly pointless IMO. If you are talking about DC (rapid charging) then that is a whole heap more complex. All the procedures/protocols are defined in a series of EN documents. 4. The most contentious bit now is grounding protection mechanisms and the interpretation of EU rules around them. |
| richard.cs:
Harmonics are definitely controlled, but at least on a Zoe there is substantial ripple current at the switching frequency (a few kHz). Numerous other devices on the same supply can be heard "singing" with the same tone the car makes during charging, presumably ones with piezoelectric filtering capacitors or un-potted chokes. |
| 741:
OK Many thanks. Re --- Quote ---more or less just connects the car to the domestic supply --- End quote --- Sure: But it is "what happens then" - after the relay turns on - I was concerned about. Judging from the reply can I assume a model of a simple pure resistance, hence no need to look at harmonics?... But then I see --- Quote ---there is substantial ripple current at the switching frequency (a few kHz) --- End quote --- so if this is a significant contribution to power consumption I have to care about it. |
| fcb:
Had a few Zoe’s - the car does sing on charge - but never experienced any secondary effects. If you want to meter the power, then you should definitely build a proper power meter (there are some quite nice signal chip parts if you don’t want to roll your own). The last charger I designed used 3 rowgowski coils for current pickup and we rolled our own energy meter in the main processor, is probably just use a single chip solution if I did it again. What accuracy class do you need to hit?? The sequencing for charging and all the voltages/resistances/timings are explained in the EN standards - there is a Wikipedia entry on charging that explains CP/PP and the different connectors etc pretty well. |
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