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Ability of EV Charger to withstand frequency deviations

ReddyLeaf

Vision without execution is hallucination
Mar 19, 2014
2,035
4,497
WA State
Here is a query from a friend of mine studying for a PhD in the smart grid area. Does anyone have any references or information on this topic? Others who might know more? As a preface, I don't really understand this stuff, so please feel free to reply with technical or dumbed down information. I will pass along verbatim. However, as I read the quote, the question is about EV CHARGERS (emphasis mine) and NOT EVSEs. I'm assuming that the person knows the difference between the two and is asking specifically about the CHARGER's ability to withstand frequency deviations. Thanks in advance.
I was looking for some information about the ability of EV chargers to withstand frequency deviations from their supply. I thought this would be a straightforward Google query, but I can't seem to turn up anything that answers what I'm looking for. The closest sources discuss the ability of smart chargers to use frequency as a signal to determine when to charge (e.g. smart grid applications). That's actually the reverse of what I want. I just want to confirm my assumption that EV chargers are relatively insensitive to frequency variations in the AC source, much like other power electronic interfaces.
 
According to the definition you mention, the EV Charger is the device in the car that takes AC (from the 110v or 220v fed into it), and rectifies it to DC for charging the battery. There are some additional electronics to deal with the different voltages, and the negotiation between the charger and the EVSE; however, I can't see any reason why any of that would be affected by the frequency of the AC being fed into it. In the US, this should be almost exactly 60 Hz, and in Europe, 50 Hz. (If someone else knows more, I'm anxious to learn...)
 
No telling what Tesla's criteria for correct frequency is. This is from the workshop manual for a Ford Energi PHEV:

P0D90:00 Battery Charger Input FrequencyIncorrect
DTC sets if frequency is less than 40 Hz or greater than 70 Hz more than 10 times during one charging cycle. Use a known good ACpower source.

Tesla might have more stringent requirements based on charger type, near 60Hz for single phase chargers, near 50Hz for three phase chargers.
 
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ReddyLeaf

Vision without execution is hallucination
Mar 19, 2014
2,035
4,497
WA State
Thanks everyone for the responses! Here is more info from my friend that may illuminate the question further:
My question is not so much about the potential for frequency-dependent charging, but rather how sensitive the equipment is to grid frequency conditions. For example, during the system collapse in the 2003 blackout, there were large frequency deviations (+/- 3 Hz) before the over- and under-frequency protection functions tripped the generators. Is there such as thing as over- or under-frequency protection for EV chargers? I know that variations in frequency will affect the performance of the converter and/or the inverter (if a system is allowed to provide energy to the power system). But, I'm trying to see if there is any literature addressing when frequency deviation becomes a problem, if there is such a point for these types of power electronics. For generators, it's usually about 3 Hz from nominal. I'd like to know approximately what the value is for these types of power electronic technologies. It doesn't need to be exact, but I would like a justifiable assumption for it in my simulations.

Again, I don't really understand this stuff, but I think the research relates to future grid stabilization with V2G. Yes, the grid is normally held to 60 Hz +/- a very small number, but under stress the grid can get out of sync and the frequency goes pppzzzzzttt. As I read the quote above, if the EV chargers are able to handle "extreme" frequency changes, then they should be able to help stabilize the grid. If EV chargers cannot handle "extreme" frequency changes, then they drop out and the grid loses another buffer to failure. I have no idea at what level such frequency changes would be considered "extreme," (e.g., 0.01, 0.1, 1 Hz) but that may be another part of the research project. It sounds like this research is some type of computerized grid simulation. I don't know if this type of information would be included in standard technical specifications, but that would be ideal. Hmmm, maybe somebody at http://www.manzanitamicro.com/ would know. I'll let my friend know about them.

jdbob: Thanks! Wow, that is quite a wide frequency range for the Ford Energi. I'll pass all of this information along.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,028
1,025
I haven't experimented, but I do know that the Tesla chargers sometimes get heartburn when you use cheap, non-inverter generators, which usually feature a lot of frequency deviation. They then stop charging. I don't know the thresholds, but my guess is that they're more sensitive than the Ford's. Technically, they don't have to be - but then again, you don't really expect to see frequency deviation in the power grid.
 

miimura

Well-Known Member
Aug 21, 2013
7,210
7,164
Los Altos, CA
I haven't experimented, but I do know that the Tesla chargers sometimes get heartburn when you use cheap, non-inverter generators, which usually feature a lot of frequency deviation. They then stop charging. I don't know the thresholds, but my guess is that they're more sensitive than the Ford's. Technically, they don't have to be - but then again, you don't really expect to see frequency deviation in the power grid.
I would expect that the Tesla charger sensitivity you're talking about is how sinusoidal the waveform is. In other words, the frequency purity, since a good sine wave is a single frequency while a stepped sine or square wave has many many harmonics. Without any detailed basis for this opinion, I would suspect that the Tesla charger is more sensitive to frequency purity and stability than absolute center frequency point (ie. deviation from 60Hz). However, I would also think that a good on-board charger would abort when the frequency dips too much, just to be a good grid citizen because low frequency is a signal that the grid is overloaded.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,028
1,025
I would expect that the Tesla charger sensitivity you're talking about is how sinusoidal the waveform is. In other words, the frequency purity, since a good sine wave is a single frequency while a stepped sine or square wave has many many harmonics. Without any detailed basis for this opinion, I would suspect that the Tesla charger is more sensitive to frequency purity and stability than absolute center frequency point (ie. deviation from 60Hz). However, I would also think that a good on-board charger would abort when the frequency dips too much, just to be a good grid citizen because low frequency is a signal that the grid is overloaded.

*nods*

I don't know where its specific thresholds are.

I recall this waveform from a cheap generator:
alton-noload.jpg


Although it's a bit better when put under load:
alton-load.jpg


(From an interesting collection of waveforms here: Power quality from various backup devices )
 

wdolson

Well-Known Member
Supporting Member
Jul 24, 2015
8,486
14,898
Clark Co, WA
Utilities in developed countries try extremely hard to keep the frequency of the power they are delivering to be right on the desired frequency with very low tolerances. It only varies in very extreme conditions.

However, electricity lines can pick up noise both from devices connected to the system and from the air (power lines are essentially antennas). What gets picked up from the air tends to be radio frequencies, the lower the frequency, the longer the antenna has to be to pick it up. Various things that can generate noise in a power system are switching power supplies (used by most desktop and laptop computers), inverters used by solar and wind generating systems, pulse width modulated motors which are used on some high end HVAC systems as well as some water well systems, microwave ovens, and the radio from smart meters (which broadcast in the microwave spectrum, but can be seen on house wiring too). The base frequency for the power coming down the power line from the power utility could be a pure sine wave, but by the time it gets to the plug, it could be very dirty with all the induced noise.

I wouldn't expect an EV's charger to be all that sensitive to frequency, to charge the batteries, the AC power is converted to some form of DC which will get rid of most of the noise. Though a simple DC power supply has varying voltage levels, it either just chops off half the sinusoid coming in, or flips the bottom half of the sinusoid over. Most DC power supplies have circuitry that smooths out the voltage further to where it's a constant voltage with no variation. EV chargers may vary in how much they clean up the DC and in some cases some AC could end up getting induced on top of the DC signal, but that would be a problem with insufficient filtering (bad design).
 

Cyberax

Member
Supporting Member
Jul 28, 2015
453
366
Seattle, WA
Again, I don't really understand this stuff, but I think the research relates to future grid stabilization with V2G. Yes, the grid is normally held to 60 Hz +/- a very small number, but under stress the grid can get out of sync and the frequency goes pppzzzzzttt. As I read the quote above, if the EV chargers are able to handle "extreme" frequency changes, then they should be able to help stabilize the grid.
There's no reason why EV chargers can't handle extreme variations. It's quite likely that the current chargers simply play safe and turn off the power if frequency is totally out of whack.

This makes total sense, since frequency variations mean that the grid is severely malfunctioning and it's probably a good idea to shed some load.
 

wdolson

Well-Known Member
Supporting Member
Jul 24, 2015
8,486
14,898
Clark Co, WA
We've been monitoring frequency at ~100 locations in CA, and fortunately or unfortunately, it is very close to 60Hz. I don't have any hard evidence, but I would also assume EV chargers are not that sensitive to frequency.

My (now ex) brother-in-law worked for Southern Cal Edison for many years. He was a geologist primarily looking for geothermal sites, but he knew quite a bit about the business. He told me that the electric utilities go to quite an effort to make sure the line frequency is 60 Hz with almost no deviation. For one thing electric clocks used to rely on the power coming in being exactly 60Hz to keep accurate time. Most use other means to keep accurate time today, but they still make sure the line is 60Hz.
 

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