Offline 3kw EV charger is not properly PFC'd

[treez]

Hello,

Do you think the designer of our 3kw, offline battery charger has deliberately avoided full Power factor correction?


We have a 3kW EV charger which keeps stopping working so we took it apart.
Spec is:-
Vout = 250-420VDC
Vin = 85-265vac
The datasheet says PFC >0.99

Its two boost PFC stages operating alternately (each 10ms on/off) followed by a 100khz LLC resonant converter.

I noticed a PFC output ripple voltage of just 20V pk-to-pk (obviously at 100hz) , in spite of the output capacitance of the PFC stage being only 810uF.
This simply isn’t possible with a proper PFC of >0.99 at 3kw output.

I scoped the drain of one of the boost PFC FETs, and you could clearly see that it wasn’t actually switching continuously over the 10ms half sine “hump”. There were wide intervals (well above the mains zero crossing), where it had completely stopped switching altogether.
The two PFC stages are controlled by a microcontroller.

The equation for output ripple voltage (pk-to-pk) of a PFC stage is…

P(out)/ [2.pi.f(line).Co.Vo]

By this, the ripple voltage would be 29.5V, but we saw only 20V.

Therefore, do you believe that they have deliberately “cheated” on the PFC regulation? After all, EN61000-3-2 has no requirement for PFC for equipments above 1kW. Maybe they thought they’d “cheat” on the PFC just so they could use less output capacitance on the “PFC” stage.?

 

[treez]

Please advise if you know that offline EV chargers of power level >1kW need to be Power factor corrected? (in any country)

 

[treez]

Basically, we want to cheat and use our boost PFC stage as a straightforward boost converter, and not a slow bandwidth pfc stage. This is because we want to reduce the ripple voltage on the pfc output bus, because it will make regulation of the following LLC converter easier. So we want our boost pfc to not need to be fully PFC'ing the supply.

Typically , I believe domestic SMPS power supplies above 1kw do not come under power factor laws. This is because there just aren't any. But when EV chargers become extremely common, laws may change. Industry has SMPS's above 1kw, but they pay for their poor power factor, so nobody minds them not being power factor corrected. I have searched everywhere but can find nothing. I have emailed other companies who make ev chargers, but the replies come back from members of staff who obviously don't have a clue what power factor is. I had one reply which was hilarious.

Four years ago I worked for a guitar amp company, and we couldn't find out if guitar amps needed to be pfc'd, (there were posts on this and loads of other forums) I think the same "greyness" exists over EV chargers, its just not possible to find out.

 

[D.A.(Tony)Stewart]

It's not cheating to disable active PFC < %V of the Vpk or < %T of the 20ms period near zero crossing.

It's only a matter of physics and Fourier transforms

What are those values for %T & %V ? 36%? 20%?

- - - Updated - - -

Commercial equipment seems to be unregulated at present but regulations for temp rise press utilities to raise power costs or owner's with DT's onsite to pay more for DT class 1 to handle poor THD and PF from arc furnaces etc.

- - - Updated - - -

This (36%T or 20%Vpp ) is my estimate of the best case permitted deadband for 99% PF or DPF in PFC . which drops the Real power at fundamental just below 99% and HD is at -25dB ( not total)



The choice of Cap is ideal when Series Resonance Frequency (SRF) is near 100kHz . ~2mOhm Also that the ESR is < 1mOhm for 15 A to create low ripple.

 

[treez]

Sorr y I don't have access to the power supply now. But I believe that western countries are importing huge numbers of cheap non-pfc'd PSU's and these will seriously adversely affect the power system of the country when there are millions of them out there.
At the moment manufacturers are keeping well schtum about their non-PFC , as they don't want the expense of it, and want to get as far as poss without PFC.

 

[BradtheRad]

Although I don't have hands-on experience in this area...

I've experimented with simulations to explore what happens in regard to power factor.



(1) The first schematic has a resistive load, 3kW.

Waveforms of supply V and A are in sync (optimal condition).

(2) Load is resistor and inductor in series. Values adjusted to receive same Ampere level.

Supply V waveform is out of sync with supply A waveform. Notice the load calls for high Amperes at a time when supply V is low. This is not optimal. Performance may suffer.

(3) PFC capacitor added. It performs 'give and take' action in the power loop.

This restores synchronization of the supply V waveform to supply A waveform.

----------------------------

There may be a glitch in the simulation, in the sense that supply C only produces 9A, yet the load receives 18A. I'm not sure I can make sense of this. Although it may throw off the numerical figures, nevertheless the concept itself should still be valid.

 

[Easy peasy]

This sounds like a case of you get exactly what you pay for...

 

[treez]

My boss told me this 3kw battery charger cost £1000, but I saw it on the web for $1100.
Either way, these non-PFC'd offline EV chargers, at several kw, are on sale now, the Government (and lets face it its them that ultimately decide it), are not doing anything about it.
This should have been stopped now, it has not been stopped, and will likely not be stopped. This is the same governments that told us to "stand by" for the disaster of the Y2K bug. The same governments that let anybody borrow enormous amounts of money, allowing an enormous meltdown of the global banking system.

 

[Easy peasy]

it is a complaint driven system, until some-one files a complaint with the relevant authorities with attached evidence, no action will be taken....

 

[treez]

the evidence is surely already accepted?, I mean, PFC is already a requirement for all offline SMPS of 75W and upwards, 25w and upwards for lighting.
As you know, a 3kw battery charger, being used for just 12 minutes, uses as much energy as a 25w lightbulb being on for a whole day.
..and yet currently, EV Battery chargers do not have to have PFC

 

[Easy peasy]

Above 16A per phase there is no requirement for PFC... of course 7.5kW is below this, most EV chargers are PFC for the obvious reason of being able to draw max real power form a given socket...