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If we can use an Inverter/Converter combo unit to charge why do cars come with a separate charger?

2239 Views 22 Replies 6 Participants Last post by  gregski, 
gregski
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Newb question, in the video below Damien Maguiare demonstrates how you can charge a Prius Gen 2 battery using it's Inverter/Converter single box solution. Since this can be done, why for example does the Nissan Leaf come with a separate battery charger? Why not just rely on the Inverter/Convert in it's pancake stack?

Prius Inverter Battery Charger Part 1

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reiderM
The inverter is a 3-phase inverter (vs either single phase or split phase for chargers). Also, the voltage is different. The leaf inverter is 350v nominal. Chargers only have to be rated for 240v nominal.
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gregski
reiderM said:
The inverter is a 3-phase inverter (vs either single phase or split phase for chargers). Also, the voltage is different. The leaf inverter is 350v nominal. Chargers only have to be rated for 240v nominal.
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Thank you, I believe most or at least some Inverters are also Converters so thinking in terms of EV Conversions and using Damien's or someone elses aftermarket controller one ought to be able to command the Converter to step down the voltage, no?
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I haven't watched Damien's video, but he is in the UK as I recall... which may mean that he is feeding 3-phase power to the AC side of the inverter, to get battery-voltage DC from other side, which is what the inverter does during regenerative braking anyway.

While common AC chargers in North America get single phase 120 V (Level 1) or split-phase 240 V (Level 2), in Europe 3-phase power is commonly available to residences, and their single-phase voltage is ~240V, so their two levels are single-phase and 3-phase 240 V. That's one reason that the Type 1 (North America) and Type 2 (Europe) AC charging connectors are different.
CCS with Type 1 (J1772) ---- vs --- Type 2 (IEC 62196, Mennekes)

PE, PP, and CP control charging and are common to both, as are the DC contacts in the CCS version; note the different Line and Neutral contacts.
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Inverter and charger are two drastically different devices. An inverter doesn't do any voltage conversion, it's just PWM-ing the input voltage. A charger is a full-blown step-up/step-down converter with a dedicated transformer. I can imagine, that an inverter can be used as a charger in some limited cases, but its input/output voltage range is going to be very restricted and efficiency is going to be poor.
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gregski
Frigzy said:
Inverter and charger are two drastically different devices. An inverter doesn't do any voltage conversion, it's just PWM-ing the input voltage. A charger is a full-blown step-up/step-down converter with a dedicated transformer. I can imagine, that an inverter can be used as a charger in some limited cases, but its input/output voltage range is going to be very restricted and efficiency is going to be poor.
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Sorry let me clarify I meant an Inverter/Converter combo unit, why can't we use that, so essentially why can't we use a Converter as a Charger?
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Frigzy said:
Inverter and charger are two drastically different devices. An inverter doesn't do any voltage conversion, it's just PWM-ing the input voltage. A charger is a full-blown step-up/step-down converter with a dedicated transformer. I can imagine, that an inverter can be used as a charger in some limited cases, but its input/output voltage range is going to be very restricted and efficiency is going to be poor.
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Brian provided a more elaborate answer to this, but basically AC or BLDC inverters are typically bi-directional. During regenerative breaking they're effectively acting as rectifiers, converting 3-phase AC input from the motor to DC suitable for charging the battery. While they may not directly control the voltage, they can control the current and thus indirectly control the voltage.
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gregski said:
Sorry let me clarify I meant an Inverter/Converter combo unit, why can't we use that, so essentially why can't we use a Converter as a Charger?
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Disregard his response. His answer applies to controllers intended for brushed motors, but not AC or BLDC controllers.
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gregski
cricketo said:
Disregard his response. His answer applies to controllers intended for brushed motors, but not AC or BLDC controllers.
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I'm sorry I'm confused, disregard who's response?
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gregski said:
I'm sorry I'm confused, disregard who's response?
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what Frigzy said about "simple PWM" doesn't apply to AC/BLDC controllers(inverters).
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gregski
cricketo said:
what Frigzy said about "simple PWM" doesn't apply to AC/BLDC controllers(inverters).
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ah, thanks
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cricketo said:
what Frigzy said about "simple PWM" doesn't apply to AC/BLDC controllers(inverters).
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Sorry, but what is the principal difference (electrically-wise) between brushed and brushless inverter except for the 3-rd half bridge?
As it gets to the charging, there are 2 main problems:
1) You get 240V in the outlet (345V DC). How on Earth are you going to step up that voltage to 420V in order to charge a 400V battery pack using, basically, 3 half-bridges? What to do with 120V (level 1) charging?
2) Since you cannot really regulate the voltage, only the duty cycle of the PWM. You have to skip a part of a sine wave in order to bring voltage down, just like a dimmer switch. The power factor of such system is going to be a disaster, no regulation authority ever would approve that for customer use. There is a reason why there is a switching transformer inside your phone charger and not just a PWM-ing transistor bridge.
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Frigzy said:
Sorry, but what is the principal difference (electrically-wise) between brushed and brushless inverter except for the 3-rd half bridge?
As it gets to the charging, there are 2 main problems:
1) You get 240V in the outlet (345V DC). How on Earth are you going to step up that voltage to 420V in order to charge a 400V battery pack using, basically, 3 half-bridges? What to do with 120V (level 1) charging?
2) Since you cannot really regulate the voltage, only the duty cycle of the PWM. You have to skip a part of a sine wave in order to bring voltage down, just like a dimmer switch. The power factor of such system is going to be a disaster, no regulation authority ever would approve that for customer use. There is a reason why there is a switching transformer inside your phone charger and not just a PWM-ing transistor bridge.
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I agree with you that stepping up voltage is probably one of the main issues here, when the charging AC input is significantly lower than what the battery pack requires. At the same time, here is what a trivial boost converter looks like :
and the inverter already has the MOSFETs or IGBTs for controlling the phases and current.
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cricketo said:
I agree with you that stepping up voltage is probably one of the main issues here, when the charging AC input is significantly lower than what the battery pack requires. At the same time, here is what a trivial boost converter looks like :
and the inverter already has the MOSFETs or IGBTs for controlling the phases and current.
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Thank you for the boost converter animation - that's a good one. The inverter is still missing the main component - an inductor or a transformer. If we somehow add an inductor to the inverter, then yes - maybe it can work as a poor-man charger. Modern chargers are based on resonant topologies. It would take a quite severe modification to the inverter to enable such topology. A proper charger would have a PFC/boost stage. That can be made out of another inverter. I'm not sure if the result can still be called an inverter.
Again, I'm not saying, that it cannot be done - it totally can. But the result is going to be much inferior to a proper charger. Also, I don't know anything about the Prius inverter/converter module. However, I have a decent knowledge of Tesla components.
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gregski
so here is an ignorant question, explain to me how the Prius Inverter/Converter is working then in the video above?
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gregski said:
so here is an ignorant question, explain to me how the Prius Inverter/Converter is working then in the video above?
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My understanding of it is: when the voltage is too high, it's skipping part of the sine wave that's coming from the motor to keep the voltage low. When the voltage is too low, it's boosting the voltage using motor windings as inductors. The efficiency of that process is poor (60-70%) and the power factor is garbage, but no one cares about the power factor within the powertrain. I'm not an expert on Prius though, maybe they put some marvel of electrical engineering in there, who knows.
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gregski said:
Newb question, in the video below Damien Maguiare demonstrates how you can charge a Prius Gen 2 battery using it's Inverter/Converter single box solution. Since this can be done, why for example does the Nissan Leaf come with a separate battery charger? Why not just rely on the Inverter/Convert in it's pancake stack?

Prius Inverter Battery Charger Part 1
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Frigzy said:
Sorry, but what is the principal difference (electrically-wise) between brushed and brushless inverter except for the 3-rd half bridge?
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A brushed DC motor controller doesn't have two half-bridges... it has none, right?. It's just a single-channel PWM device, or a very big DC light dimmer. ;) The PWM output varies according to the driver's demand via the pedal.

An inverter for a three-phase motor is three coordinated half-bridges, each operating as a PWM controller, and varying (sinusoidally unless you have some "brushless" toy motor for a bike or something) through a full cycle for each passing pole pair. So it's six dimmers, all being tweaked through a full cycle (or multiple cycles) with each motor rotation, in a coordinated manner. ;)

But yes... in both cases the peak-to-peak output voltage is less than the input voltage, so if using 120 VRMS or 240 VRMS to charge a 360 Vnominal battery I assume that there would need to be a voltage boost conversion between the controller and the battery.
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cricketo said:
... here is what a trivial boost converter looks like :
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Very cool simulation! (y) :)
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Let's think about this. The standard currently is to have a costly EVSE that interfaces an on-board ac charger in the car with the AC power line, usually in a garage. And, the standard includes as an option a quick charge port that connects directly to the battery to allow DC charging directly from an external DC charger at a quick charge station.
It's time to rethink these processes. Why carry an on-board ac charger around as an extra cost and extra weight in the car when you have external DC chargers available? Why not remove the AC Charger and install it to the AC line in the garage so it will charge directly to the quick charge port?
It's time to shift gears and think making the current processes more efficient,less convoluted and less costly, i.e., removing the ac charger to the garage, dumping the lead acid battery for a LFP replacement and requiring all U.S. EVs to standardize on the CCS standard instead of the Japanese or Teslarese standard.
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